back to Agenda

Temporal variability in global inorganic carbon distributions

1 Bermuda Biological Station For Research, Inc., 17 Biological Station Lane, Ferry Reach, GEO1, BERMUDA, nick@bbsr.edu
2 NOAA/PMEL, 7600 Sandpoint Way NE, Seattle, WA 98115

ABSTRACT:

Bauer, J.E. (1); P.G. Verity (2); D.J. Repeta (3) and D.J. DeMaster (4)

Budgets of biogenic elements in the NW Atlantic ocean margin

1 School of Marine Science, College of William & Mary, Gloucester Point, VA, bauer@vims.edu

1 School of Marine Science, College of William & Mary, Gloucester Point, VA, 23062, bauer@vims.edu
2 Skidaway Institute of Oceanography, Savannah, GA 31411, peter@skio.peachnet.edu
3 Dept Marine Chemistry and Geochemistry, WHOI 02543, drepeta@whoi.edi
4 Dept Marine, Earth and Atmospheric Sciences, Box 8208, North Carolina State Univ., Raleigh, NC 27695, dave_demaster@ncsu.edu

ABSTRACT:
The cycling of carbon and other biogenic elements in ocean margins is predicted to be impacted significantly by global environmental change, owing to the proximity of margins to the continents and population centers. To reduce major uncertainties in predicting future environmental change in ocean margins, and to help establish the dominant factors regulating the cycling of biogenic elements there, the Ocean Margins Program (OMP), initially funded by the U.S. Department of Energy, was undertaken in the Mid-Atlantic Bight region of the NW Atlantic continental margin. The central objectives of OMP are 1) to quantify the processes and mechanisms affecting the cycling of biogenic elements, especially C, in the NW Atlantic; 2) to define ocean margin sources and sinks and place them in the context of global biogeochemical cycles; and 3) to determine whether margins, especially shelf and slope systems, are quantitatively important in CO₂ sequestration, and/or carbon export to the interior ocean and sediments. This presentation will give the major highlights and findings of the NSF-funded synthesis and modeling phase of OMP, including that NW Atlantic margin waters 1) are a net annual CO₂ sink, with inner, mid- and outer shelf regions taking up ~0.1, 0.7 and 0.2 Mt C/yr, respectively; 2) contain significant amounts of both marine and terrestrial DOC and POC in shelf and shallow slope waters, and very old (older than from open North Atlantic waters) DOC and POC in slope waters; and 3) export ~18-20 Mt C/yr in the form of DOC to the open ocean. These DOC fluxes are up to four times greater than the corresponding POC fluxes. The synthesis and modeling phase of OMP will culminate in a forthcoming special volume of Deep-Sea Research-II, "Carbon Cycling and Fluxes in the Northwest Atlantic Continental Margin: Findings of the Ocean Margins Program".

Bishop, J.K.B. (1); C.K. Guay (1); J.T. Sherman (2); C. Moore (3) and R.E. Davis (2)

Magnitude, variability and controls of particulate export in the upper ocean.

1 Lawrence Berkely National Laboratory, Berkeley, CA
2 Scripps Inst. of Oceanography, La Jolla, CA
3 WET Labs, Inc., Philomath, OR

ABSTRACT:
Approximately 1 Pg (10¹⁵ g) of marine plant carbon biomass photosynthetically fixes ~50 Pg of carbon per year. The very fast turnover times for ocean carbon biomass coupled with slow traditional observing systems means that a major 'space-time' gap exists for ocean carbon cycle observations in all but a few locations. The international project Argo will deploy several thousand autonomous profiling floats over the next few years to measure mid-depth ocean circulation, temperature, and salinity to provide an improved view of the climate state of the ocean. The recent 20-fold plus improvement of rates of ocean to satellite data telemetry permits augmentation of the long-lived Argo-style floats with low-power sensors for carbon system components. This paper describes the development of a prototype autonomous carbon observer capable of performing high frequency observations of the upper kilometer for seasons to years. The aim is to enable improved exploration of the ocean biological carbon pump processes and how the pump responds to day-to-day variations of physical forcing. We have developed and tested in the laboratory and at sea optical methods to ovserve particulate organic carbon (POC) and particulate inorganic carbon (PIC); we are continuing to explore the use of other optical properties to characterize additional particulate matter properties. Integration of POC and PIC sensors onto the Sounding Oceanographic Lagrangian Observer (SOLO) is underway with the goal of deploying pairs of SOLO-carbon observers to explore the carbon biomass variability in the subarctic north Pacific and north Atlantic oceans. A fully implemented "C-Argo" observer requires addition of sensors for dissolved carbon species and related nutrient substrates but additional effort is needed to reduce size and power requirements of the existing suite of sensors. Possible operational modes for a "C-Argo" observer are described.

Buesseler, K. (1)

Magnitude, variability and controls of particulate export in the upper ocean.

1 WHOI, kbuesseler@whoi.edu

ABSTRACT:
We propose to examine, within existing JGOFS and related international data sets, the relationships between export and production and the special role that food web processes may have in controlling upper ocean export. The results thus far indicate that the relative rates of C fixation and C removal via sinking particles vary widely as a function of local food web dynamics (Buesseler, 1998). Given the large number of studies which now use ²³⁴Th as a proxy for POC export, we can start to compile global maps of POC export from the upper ocean. We will look directly at the full range of ²³⁴Th export data to assess trends between seasonal, episodic, or regional flux variability and a suite of physical and biological parameters. Because a significant portion of export may occur during short pulses or events, our goal is to help explain export variability in order to better model long-term mean export over larger time or space scales.

If common mechanisms can be found for the variations of production and export, these could then be incorporated into more reliable models of the global carbon cycle. While much of the ocean is characterized by low relative POC export, sites of high export are most often characterized by food webs dominated by large phytoplankton, in particular diatoms. If this result holds, models that attempt to predict new and export production from surface chlorophyll or production alone will not resolve the local carbon balance or allow one to model export controls. A mechanistic understanding of the underlying export processes is crucial to being able to incorporate this understanding into models, particularly if we desire to predict fluxes in future climate states.

We are closing in on the rate of exchange of CO₂ between the ocean and atmosphere, a crucial flux for JGOFS. The partial pressure of CO₂ at the surface is determined by thermodynamic effects on partial pressure and the balance of carbon fluxes into and away from the surface ocean. Determining the removal terms for carbon is one of the most challenging tasks; however, without measuring them correctly, our global models and global synthesis will always be tenuous. This is why understanding export is one of the highest priorities for SMP. We have to know what leaves the surface to balance against what is mixed into the surface or added by nitrogen fixation or atmospheric deposition. We also have to understand how this changes with time, ecosystem structure and physical regime. This proposal results in a global synthesis of the thorium derived export data. This will lead to a better understanding of underlying export processes is crucial to being able to incorporate this understanding into models, particularly if we desire to predict fluxes in future climate states.

We are closing in on the rate of exchange of CO₂ between the ocean and atmosphere, a crucial flux for JGOFS. The partial pressure of CO₂ at the surface is determined by thermodynamic effects on partial pressure and the balance of carbon fluxes into and away from the surface ocean. Determining the removal terms for carbon is one of the most challenging tasks; however, without measuring them correctly, our global models and global synthesis will always be tenuous. This is why understanding export is one of the highest priorities for SMP. We have to know what leaves the surface to balance against what is mixed into the surface or added by nitrogen fixation or atmospheric deposition. We also have to understand how this changes with time, ecosystem structure and physical regime. This proposal results in a global synthesis of the thorium derived export data. This will lead to a better understanding of carbon fluxes and parameterization of export that can be inserted into other models.

Burd, A. (1) and G. Jackson (1)

A model for the distribution of particle flux in the mid-water column controlled by subsurface biotic interactions.

1 Dept of Oceanography, Texas A&M Univ., College Station, Texas 77843-3146, aburd@ocean.tamu.edu

ABSTRACT:
The mid-water zone, between 100 and 1000 m, is important in controlling the downward transport of material from the surface waters. Existing descriptions of the change of particle flux with depth rely upon empirical relationships that ignore the biological processes that control the flux. We examine a series of simple predator-prey models incorporating particle flux. Steady state predictions vary between the models, with one model showing an exponential decrease in particle flux and predator concentration; the other model shows an inverse relationship between flux and depth. Perturbations from steady state indicate that changes in animal concentrations can lead to large changes in particle flux that are not synchronous with variations in the surface flux.

Carlson, Craig (1); Stephen Giovanonni (2) and Dennis Hansell (3)

Determining the response of surface and deep bacterioplankton communities to DOM which accumulates at the Bermuda Atlantic Time-series Study Station (BATS)

1 University of California at Santa Barbara
2 University of Oregon
3 University of Miami

ABSTRACT:
DOC dynamics at BATS demonstrate an annual pattern where DOC stocks accumulate rapidly within the surface 100m after spring restratification and stay elevated until the next deep mixing event. As a result of mixing, a portion of this seasonally accumulated DOC is mixed to depth (>200m) and subsequently removed after restratification. It is hypothesized that microbial remineralization is responsible for deep DOC removal. If true then DOC, which accumulates in the surface, is resistant to rapid microbial degradation by surface bacterioplankton communities but is available to deeper communities.

The objective of our work was to simulate a deep mixing event in which deep bacterioplankton populations were mixed with surface water DOM. Experiments consisted of controls and several treatments of organic and inorganic amendments in which 0.2 µm filtrate, collected from 10m, was inoculated with natural bacterioplankton communities collected from 10m and 250m and incubated at respective in situ temperatures. Bacterioplankton abundances from 10m inoculum (control and inorganic amendments) increased 14% over 3 days while abundances from 250m inoculum (initially lower than 10 m treatments) increased 185% and reached similar abundance levels as 10m inoculum. The experimental and field observations suggest the possibility that specialized microbial communities may affect a portion of the DOC drawdown observed at depth in the Sargasso Sea.

Carlson, Craig (1); Stephen Giovanonni (2) and Dennis Hansell (3)

Amendment on DOC availability and community structure of bacterioplankton in the northwestern Sargasso Sea

1 University of California at Santa Barbara
2 University of Oregon
3 University of Miami

ABSTRACT:
DOC dynamics in the Sargasso Sea (at BATS) demonstrate an annual pattern which includes a rapid build up of DOC in the upper 40 m in the late spring following stratification of the water column. Integrated DOC stocks then level off, in this depth layer, or slowly decrease throughout the summer and into fall. During winter mixing a portion of this accumulated DOC is mixed to depth and mineralized. The objective of our work was to determine if microbial utilization of the DOC pool, present in the surface mixed layer would be stimulated upon the removal of grazers or with the amendment of organic or inorganic nutrients. Seawater cultures were performed with naturally occurring bacterioplankton populations and levels of DOC collected from the surface 20 m during several U.S. JGOFS BATS cruises. Each experiment consisted of several treatments and combinations of NH₄, PO₄ and labile organic nutrient amendments and were monitored over the course of a week to months. DOC measurements were made by high temperature combustion, bacterial abundance was determined via epifluorescence microscopy and bacterial species composition was monitored with LH-PCR.

Results show that in grazer free unamended control where DOC concentrations were same as the BATS mixed layer (i.e. 68 µM C) there was little increase in bacterial abundances and no significant removal of DOC over the course of the culture. Addition of NH₄ and PO₄ alone or in combination showed no significant difference in bacterial response or DOC removal from the unamended control. The addition of glucose alone stimulated bacterial growth, however, DOC levels in the culture were not drawn below initial BATS mixed layer concentrations over a duration of a month. A cocktail of glucose, NH₄ and PO₄, too, greatly stimulated bacterial growth in surface seawater cultures, with eventual removal of all the amended DOC plus an additional 5 µM from the original surface mixed layer concentrations. The addition of labile carbon source resulted in a clear shifts in bacterioplankton community structure relative to control or inorganic nutrient ammendments. These observations point to possibility that a combination of nutrient will create conditions where a species composition will evolve that is able to utilize more recalcitrant DOM.

Carr, Mary-Elena (1) and Wendy Tang (2)

A comparison of the CO₂ exchange coefficient estimated with space-borne measurements of wind speed: SSM/I versus QuikSCAT for 2000

1 NASA, JPL, Pasadena CA. mec@pacific.jpl.nasa.gov
2 California Institute of Technology

ABSTRACT:
We aim to construct a 13-year time series of monthly global K, the exchange coefficient for CO₂ with SSM/I data using the Wanninkhof (1992) parameterization. The data quality of SSM/I is inferior to that of scatterometers, which additionally provide the wind direction. However the 13 year time series of daily global maps allows the opportunity to address interannual variability and the concurrent sensors the chance to tackle sub-diurnal changes. To address the quality of SSM/I for our purposes we compare the exchange coefficient and flux derived with SSM/I and with QuikScat for monthly mean wind speed values for the year of 2000. Hereafter we assume that the QuikScat is "correct".

The exchange coefficients estimated from the two wind sensors present the same patterns in space and in time, although those estimated from SSM/I are generally larger. For both sensors, most values (>67%) fall between 2.5 and 10 x10² mol m^-2 y^-1 µatm^-1. The consistent seasonal changes are not reflected in the global mean value, which is maximum in July. The global mean K_SSM/I is approximately 1x10² mol m^-2 y^-1 µatm^-1 larger than K_QSCAT for all months, with larger differences the second half of the year. For the comparison year, the zonal mean K_SSM/I are consistently larger, except between 40°S and 50°S and within 20° of the equator. Generally zonal K maxima are overestimated by SSM/I. High northern latitude zonal means of K_SSM/I are are always larger than those of K_QSCAT.

The global mean flux estimated with the Delta pCO₂ field of Takahashi (1999) and K estimated from SSM/I is between 3.01 and 4.11 GtC y^-1, while the QSCAT estimate ranges between 1.39 and 2.86GtC y^-1: boreal summer presents minimum values. Differences in flux estimated from the two sensors are around 1 GtC, but were greater than 1.5 GtC from May to August 2000. SSM/I overestimates K more in areas of negative Delta pCO₂, thus overestimating the oceanic sink term.

Attempts are being made to correct for the bias in the SSM/I estimates which is correlated to temperature, atmospheric water vapor, and wind speed.

Chai, F. (1); R.T. Barber (2); M.S. Jiang; R.C. Dugdale (3); T.-H. Peng (4)

Modeling the ecosystem responses and carbon cycle to iron enrichments in the equatorial Pacific Ocean

1 School of Marine Sciences, 5741 Libby Hall, Univ. of Maine, Orono, ME 04469-5741, fchai@maine.edu
2 Duke Univ. Marine Lab., 135 Duke Marine Lab Road, Beaufort, NC 28516-9751
3 Romberg Tiburon Center for Environmental Studies, San Francisco State Univ., PO Box 855, 3150 Paradise Dr., Tiburon, CA 94920-0855
4 Ocean Chemistry Division, NOAA/AOML, 4301 Rickenbacker Causeway, Miami, FL 33149-1026

ABSTRACT:
In situ iron-enrichment experiments in the equatorial Pacific Ocean and the Southern Ocean have shown that additional iron to high-nitrate, low-chlorophyll (HNLC) waters triggers a series of changes in the productivity and growth of phytoplankton. The logistic constraints on the length of observation have prevented these otherwise successful efforts from resolving the full temporal pattern of responses. The use of an ocean ecosystem model developed for the equatorial Pacific Ocean should contribute to the understanding of detailed ecosystem responses and potential effects to the carbon cycle to the iron enrichment experiments. The model consists of ten compartments describing two size classes of phytoplankton and zooplankton, detrital nitrogen and detrital silicon, silicate, total CO₂ and two forms of dissolved inorganic nitrogen: nitrate (NO₃) and ammonium (NH₄), which are treated separately, thus enabling division of primary production into new production and regenerated production. This ten-component biogeochemical model is embedded into a three-dimensional ocean circulation model based on the Modular Ocean Model (MOM), and forced with COADS monthly wind and heat flux. In the eastern equatorial Pacific, multiple iron-enrichment experiments in an area of 360,000 km² are simulated by changing the photosynthetic efficiency and nutrient uptake kinetics in a given spatial domain. With this ecosystem model it is possible to investigate the biological and geochemical consequences of iron enrichment experiments in the equatorial Pacific Ocean.

Christian, J. (1)

Modeling at station ALOHA

1 Earth System Science Interdisciplinary Ctr, Univ. of Maryland, 2207 Computer + Space Sciences Bldg, Univ. Maryland, College Park, MD 20742, jrc@essic.umd.edu

ABSTRACT:
The data collected during 12 years of observations at the US-JGOFS time series station ALOHA show an ecosystem that is quite different from the ones for which most biogeochemical models now in use were developed. Particularly important are the major role of nitrogen fixation in new N supply, the key role of dissolved organic matter in elemental cycling, and the variable C:N:P stoichiometry associated with these processes. The ecosystem at ALOHA is highly regenerative and the mechanisms responsible for decoupling production and regeneration are not clear. We will show results of model experiments that demonstrate the importance of variable C:N:P stoichiometry in modelling the C cycle at Station ALOHA and ways in which these processes can be addressed in biogeochemical models.

Deutsch, C. (1) and J. Sarmiento (1)

Diagnosing nitrogen fixation and denitrification in a GCM

1 Program in Atmospheric and Oceanic Sciences, Princeton Univ., Princeton, NJ, USA, 08544

ABSTRACT:
We make a first attempt to diagnose nitrogen fixation and denitrification in the Princeton OGCM. We begin with the phosphate-based OCMIP model framework, in which export production is represented by restoring phosphate to observed values at the surface. To this we add a simple nitrogen cycle, with parameterizations for the biogenic sources and sinks of fixed nitrogen.

Previous OCMIP models have ignored oxygen limitation on remineralization in oxygen minimum zones (O₂ < 4 µM). We simply convert the excess oxygen demand to a constant stoichiometric nitrate consumption in denitrification. Export production in previous models ignored the possibility of nitrogen limitation. We restore both N and P at the surface, and assume that nitrogen fixation supplies any nitrate export deficits that result.

The "warm thermocline" from model physics results in oxygen minima that are too large, and hence a total water column denitrification rate (~300 TgN/yr) that is twice observational estimates. Nitrate export deficits (relative to N:P = 16 stoichiometry) implied by nutrient damping, arise in tropical regions and in the southern ocean. The nitrogen fixation inferred in the southern ocean is inconsistent with the temperature range at which the dominant nitrogen fixing organisms, Trichodesmium, have been observed. In addition, hot spots of nitrogen fixation are indicated overlying denitrification zones, where N:P ratios are low, but surface nutrients are not depleted. Thus, further controls on nitrogen fixation parameterizations are required to represent its observed distribution.
(poster)

Dickson A. (1)

Synthesis of a global surface pCO₂ data set

1 Marine Physical Laboratory, Scripps Institution of Oceanography, Univ. of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0902, adickson@ucsd.edu

ABSTRACT:

Dinniman, M.S. (1); E.E. Hofmann (1); J.M. Klinck (1); W.O. Smith (2) and B.B. Prezelin (3)

Development of regional physical-biological models for the Ross Sea and west Antarctic Peninsula

1 Ctr for Coastal Physical Oceanography, Old Dominion Univ., Norfolk, VA 23529, msd@ccpo.odu.edu
2 Virginia Institute of Marine Science, College of William and Mary, Gloucester Pt, VA 23062
3 Biological Sciences, Ecology, Evolution and Marine Biology, UCSB, Santa Barbara, CA 93106

ABSTRACT:
Our SMP project is focused on development of a suite of physical and biological models that incorporate data sets collected in the Ross Sea as part of the U.S. Southern Ocean Joint Global Ocean Flux Study (JGOFS) and historical data sets from the west Antarctic Peninsula (WAP) region. The intent of the data analyses and modeling activities is to provide syntheses that allow comparison of similarities and differences in the two systems and thereby allowing fundamental questions on the controls of phytoplankton productivity and growth in these two systems to be addressed. During the past year our primary effort has been on the development, testing, and implementation of regional numerical circulation models for the Ross Sea and the WAP. Comparisons of the patterns in the simulated circulation fields show good correspondence to observed circulation features. Our effort is now focused on refining the circulation models so that they can be coupled with models for lower trophic level processes. A second effort uses a one-dimensional, time- and depth-dependent model of the descent-ascent cycle of the eggs and larvae of Antarctic krill (Euphausia superba) to investigate the circum-Antarctic distribution of this dominant herbivore. Simulations with this model show that regions of the Antarctic continental shelf that are favorable to successful hatching of krill embryos are irregularly scattered around the Antarctic, but with the highest concentration along the Antarctic Peninsula. The simulations also suggest that hatching success is largely determined by the environmental structure in these regions. Some areas, such as portions of the Ross Sea, lack the necessary environmental structure for successful hatching, which may underlie the lack of Antarctic krill in these areas. This has implications for differences in material cycling and export in the Ross Sea and WAP regions. A third effort has been on the development of nutrient fields for input to the circulation models. This has resulted in considerable analyses of nutrient and primary production measurements in the two regions. Preliminary results of these analyses will be presented.

Doney, S.C. (1) and M. Hecht (1)

Antarctic Bottom Water formation and deep water chlorofluorocarbon distributions in a global ocean climate model

1 NCAR, Boulder, CO, doney@ucar.edu

ABSTRACT:
The ocean distributions of chlorofluorocarbons (CFCs) have been measured extensively in order to determine the mechanisms, rates, and pathways associated with thermohaline deep water formation.  Here we compare model temperature, salinity and CFC-11 fields from the NCAR global ocean climate model against observations with emphasis on the patterns of Antarctic Bottom Water (AABW) production, properties, and circulation in the Southern Ocean.  The model control simulation forms deep water as observed in both the Weddell and Ross Seas, though not along other sectors of the Antarctic coast.  Examination of the deep water CFC-11 distribution, total inventory, and profiles along individual observational sections demonstrate that the decadal-scale deep water ventilation in the model Southern Ocean is both too weak and too restricted to the Ross and Weddell Sea source regions.  A series of sensitivity experiments is conducted to determine the factors contributing to these deficiencies.  The incorporation of a simple bottom boundary layer (BBL) scheme leads to only minor reductions in overall model-data error.  The limited impact of the BBL may reflect in part other model large-scale circulation problems, for example the lack of saline Circumpolar Deep Water along the Antarctic slope, and the coarse vertical resolution of the model.  The surface boundary conditions in the permanent sea ice covered regions are a more major factor, leading to inadequate formation of dense, cold and relatively saline shelf waters, the precursors of AABW.  Improved model-data agreement is found by combining the BBL parameterization with reasonably small adjustments in the surface restoring salinities along the coast, justified by undersampling of winter conditions in standard climatologies.  The resulting changes in deepwater properties and circulation are somewhat similar to the effect of coupling with an active sea ice model.

Doney, S.C. (1); S. Yeager (1); G. Danabasoglu (1); W.G. Large (1); J.C. McWilliams (1)

Modeling global oceanic interannual variability (1958--1997): Simulation design and model--data evaluation

1 NCAR, P.O. Box 3000, Boulder, CO 80307-3000, doney@ucar.edu

ABSTRACT:
The ocean exhibits significant low frequency variability across a range of spatial scales from regional to global, with much of the signal associated with atmosphere--ocean climate modes. Here we explore and evaluate the simulated interannual variability from the oceanic component of the global NCAR Community Climate System Model (CCSM) forced with historical (1958--1997) surface atmospheric reanalysis estimates and assorted satellite data products. The simulations are conducted in a fully prognostic mode, reserving the oceanic observational data sets as independent measures of model skill. A new anisotropic, horizonal viscosity scheme is introduced that, atypical for coarse resolution models, results in the separation of the Gulf Stream off Cape Hatteras and the southward penetration of the sub-polar gyre along the east coast of North America. The framework for the forced historical simulations is discussed, and the model long-term subsurface drift and initial condition sensitivity are characterized. Overall, the model shows considerable skill in replicating observed interannual variability. Satellite data records of sea surface temperature and height, while of limited total duration, are key evaluation data sets because of their relatively high temporal frequency (monthly) and complete spatial coverage, and the model--data agreement is generally very good both in magnitude and phase. The comparison with in-situ surface temperature, integrated heat content, and surface salinity data is also favorable. The largest disagreements between the simulated and observed subsurface temperature and integrated heat content fields are in the Southern Ocean, Arctic, and western boundary currents and can be attributed to limited observational sampling density, the model under-ice forcing parameterization, and the model gyre structure. The historical subsurface oceanic data record is often sparse and incomplete, and in many regions the model simulations may provide equally valid, alternative estimates of oceanic low frequency variability.

Ducklow, H. (1); M. Roman (2) and G. Jackson (3)

Ecosystem structure, biogeochemical fluxes and vulnerability to climate change perturbations

1 School of Marine Sciences, College of William & Mary, Box 1346, Rte 1208 Greate Rd, Gloucester Point, VA 23062-1346, duck@vims.edu
2 Horn Point Environmental Lab, Univ. of Maryland, Box 775, Cambridge, MD 21613
3 Dept of Oceanography, Texas A&M Univ., College Station, Texas 77843-3146

ABSTRACT:

Dunne J. (1); A. Gnanadesikan (1); P. Swathi (1); J. Sarmiento (1) and R. Armstrong (2)

Calibration and application of a size-based ecosystem model with a prognostic e-ratio

1 Program in Atmospheric and Oceanic Sciences, Princeton Univ., Princeton, NJ, USA, 08544
2 SUNY Marine Science Research Center, Stony Brook, NY, 11794

ABSTRACT:
We have developed an ecosystem model to simulate the dynamics of small and large phytoplankton as they relate to regenerated production, particle export and transport of dissolved organic matter. This model has been calibrated using euphotic zone data on temperature, chlorophyll biomass, primary production and new production and/or particle export from 78 sites. Where available, we have also utilized data on size-fractionated primary production, size-fractionated phytoplankton biomass and the carbon:chlorophyll ratio of phytoplankton. The data was used for three temperature-dependent parameterizations: 1) the relationship between primary production and phytoplankton size structure 2) rates of phytoplankton loss (sum of grazing, sinking, mortality, etc.) and 3) particle export associated with production by small and large phytoplankton. The data is consistent with almost exclusive control of particle export by large phytoplankton.

The resulting model has been incorporated into the Princeton Ocean Biogeochemical Model to diagnose new production, particle export and dissolved organic carbon transport through nutrient restoring of the MOM3 general circulation model. These simulations provide new insight on both the potential role of regenerated production and production of dissolved organic matter in modulating export of particles and dissolved organic material into the ocean's interior. In the future, these simulations will be used to provide a baseline comparison with the fully prognostic version of this ecosystem model currently under development.
(poster)

Follows, M. (1)

Meteorological modulation of the North Atlantic spring bloom

1 Dept of Earth, Atmosphere and Planetary Sciences, MIT, mick@plume.mit.edu

ABSTRACT:
Using ocean time-series observations and remote chlorophyll estimates derived from SeaWiFS ocean color observations we examine and illustrate the relationships between changes in the intensity of the spring bloom and changes in weather patterns, mediated by upper ocean mixing.  A simplified two-layer model provides the conceptual framework, predicting regional regimes of differing biological response to vertical mixing anomalies in the ocean surface boundary layer.  The mixing anomalies may be derived from re-analyzed meteorological data. We examine two regimes of regional and interannual sensitivity to meteorological forcing, defined by the ratio of the spring critical layer depth and the winter mixed layer depth.  The subtropics are characterized by an enhanced bloom in response to enhanced mixing, both across the region and from year to year.  There are consistent, interannual changes which are coordinated over large regions.  These are comparable in magnitude to the regional variations in each bloom. In the subpolar regime regional variations reflect retardation of the bloom by enhanced mixing.  Local interannual changes in the subpolar region, however, are small relative to the regional variations and do not show a clear and consistent response to interannual variability in the local meteorological forcing.  We infer that other factors, including changes in insolation, local mesoscale variability, and grazing exert a stronger influence on local interannual variability of the subpolar bloom. We discuss the implications of decadal climate changes for the bloom in the light of these relationships.
poster

Follows, M. (1)

The oceans' subtropical gyres and atmospheric pCO₂

1 Dept of Earth, Atmosphere and Planetary Sciences, MIT, mick@plume.mit.edu

ABSTRACT:
Using simplified models, we examine the role of the wind-driven subtropical gyres in modulating atmospheric pCO₂. The ventilated thermocline of the subtropical oceans, formed by the action of wind-stress on the ocean surface, represents a significant fraction of the total ocean volume.  Subtropical thermocline waters are ventilated at mid-latitudes by relatively warm surface waters.  The global budget of dissolved inorganic carbon in these waters is sensitive to the properties of the subtropical, subduction regions.  Using a three-dimensional, single-basin, ocean circulation and biogeochemistry model, coupled to a simple representation of the atmosphere, we illustrate the role of the wind-driven gyre circulation in setting atmospheric pCO₂.  In particular we examine the sensitivity of pCO₂ to changes in the properties of the warm (subtropical) and cold (subpolar) surface waters.  We demonstrate that the resolved, wind-driven, subtropical gyres enhance the sensitivity of atmospheric pCO₂ to warm surface water properties in three-dimensional, global carbon cycle models, relative to highly idealized box models.

Friedrichs, M. (1)

Regional ecosystem model testbeds. A JGOFS synthesis and modeling project.

1 Center for Coastal Physical Oceanography, Old Dominion Univ., marjy@ccpo.odu.edu

ABSTRACT:
An important legacy of the JGOFS SMP will be the formulation of a broad suite of models designed to simulate biogeochemical cycling at the various process study sites.  Although this set of models and modeling studies has already substantially advanced our understanding of these systems, few quantitative intercomparisons of these models have been made.  The recently funded Regional Ecosystem Model Testbed Project proposes to conduct these intercomparisons to critically examine which ecosystem structures and formulations are most robust, to investigate and explore the reasons for their success, and ultimately add to the mechanistic understanding of how and why euphotic zone production, and the associated export of carbon, vary among diverse oceanographic regions.  To accomplish these goals and provide a forum for testing and comparing various ecosystem models, we propose to develop a series of "regional testbeds," based on the high quality and large quantity of observations available from various JGOFS study sites. Websites will be constructed for all testbeds and will include access to the physical fields required to force the models, as well as time-series of biogeochemical data that will be used for either evaluation or optimization/assimilation.  These websites will be available as a community resource, and, in this study, will be used to facilitate both intra-site and inter-site model comparisons.  This proposed research will capitalize on work previously accomplished under the JGOFS SMP: the twelve co-investigators involved in this project will freely provide their regional expertise, model code, forcing fields, and biogeochemical data sets to this project.  To further promote model intercomparisons, this project will involve annual hands-on workshops in which scientists (including but not limited to the co-investigators of this proposal) will work together to quantitatively assess different biogeochemical models and modeling approaches.

Gao, Yuan (1); Song-Miao Fan (1) and Jorge L. Sarmiento (1)

Aeolian iron input to the ocean through precipitation scavenging: A modeling perspective

1 Program in Atmospheric and Oceanic Sciences, Princeton Univ., Princeton, NJ, USA, 08544

ABSTRACT:
Aeolian dust input may be a critical source of iron to phytoplankton growth in certain oceanic regions. We used a GFDL SKYHI atmospheric general circulation model (GCM) to simulate dust transport and removal by dry and wet deposition to the ocean. Model results reveal extremely low dust concentrations over the equatorial Pacific and Southern Ocean. After partitioning the two deposition processes, we find that wet deposition through precipitation accounts for ~40% of the total deposition over the coastal sea and ~60% over the open ocean. This GCM result is supported by data analysis with simple model calculations. The finding suggests that large silt particles are removed more rapidly than small clay particles, which dominate in concentration over the ocean far from the continents and are more sensitive to precipitation scavenging. Air-to-sea deposition of aeolian iron is thus influenced by precipitation distributions as well as atmospheric transport. We speculate that episodic precipitation events may serve as natural Fe fertilization experiments, promoting phytoplankton response.
(poster)

Gao, Yuan (1); Jorge L. Sarmiento (1); Paul Falkowski (2) and Yoram J. Kaufman (3)

The atmosphere-oceanic biosphere interaction: Characterization of aeolian iron deposition and its linkage to oceanic biogeochemical cycles

1 Program in Atmospheric and Oceanic Sciences, Princeton Univ., Princeton, NJ, USA, 08544
2 Institute of Marine and Coastal Sciences, Rutgers Univ., New Brunswick, NJ, USA, 08901
3 Laboratory for Atmospheres, NASA Goddard Space Flight Center, Greenbelt, MD, 20771

ABSTRACT:
We present our preliminary results and an interdisciplinary approach to characterize aeolian iron deposition and its impact on oceanic nutrient and carbon cycles. Our recent data analysis based on in situ measurements from a variety of marine locations demonstrated strong seasonal variations in the total aeolian Fe fluxes in different oceanic basins. We found that the predominant fraction of the Fe inputs entering the oceans in the Northern Hemisphere, with the summer flux rates being ca. twice those of winter. In addition, individual-particle analyses reveal that dust particles are modified significantly by interactions with other acidic species during the long-range transport, which may alter the chemical forms of Fe in dust affecting its solubility and thus bioavailability in the surface ocean. With the recognition that the relationship between phytoplankton biomass, photosynthetic rate and aeolian iron may be non-liner on a global scale, our current modeling efforts aims to examine the relationships using a global ocean GCM model. With the launch of Terre satellite, a preliminary analysis of MODIS data demonstrates the potential of satellite retrievals to improve the quantification of aeolian Fe fluxes and then its impacts on ocean biogeochemical cycles.
(poster)

Gardner, W. (1); M.J. Richardson (1) and A.V. Mishonov (1)

The use of beam attenuation to predict POC: bottle or pump data?

1 Dept. Oceanography, Texas A&M Univ., College Station, TX, 77843, wgardner@ocean.tamu.edu ,

ABSTRACT:
One of the goals of the JGOFS program is to reduce the uncertainties in carbon budgets for the ocean. Particulate organic carbon is a small portion of the total carbon in the ocean, but it is the fraction that can move independently of the surrounding water, i.e. it can sink. There are two primary ways to sample and measure particulate organic carbon (POC) from water samples in the ocean, but the results can differ by than a factor of 5-10. The oldest and most common method is to collect water samples (up to a few liters), filter the water and analyze the filter for POC. The other method uses in-situ pumps to filter thousands of liters of water to obtain large samples of particulate matter. A fraction of the filter is then analyzed for POC. The problem is that POC concentrations measured from bottle samples are often 5-10 times the concentrations measured using in-situ pumps. A mechanism which we could use to determine which of the above POC sampling methods is more accurate comes from DOC measurements (dissolved organic carbon). DOC is measured by filtering a small water sample (10-200 mls) and measuring the total organic carbon (TOC) in the water, not carbon on a filter. In areas where POC concentrations are high, one can take two small volumes of water, and analyze one filtered and one unfiltered for total organic carbon (TOC). The difference between the two samples should be POC. The bottle POC data yields somewhat higher values than the TOC method, but the in-situ pump POC values are much lower than either of the other methods. At low POC concentrations (<2 µM/l) bottle POC values may be elevated due to adsorption of DOC on filters, but at concentrations >2 µM/l the contribution of adsorption is negligible. There are few studies where any two of these methods have been tested simultaneously, but optical data (using beam transmissometers) have been collected simultaneously with the different POC sampling methods and POC/beam Cp ratios can be used to compare results from different sites. We will present some of these comparisons and discuss reasons why the in-situ pump values are most likely too low. The primary reason seems to be the difference in filtration pressures with in-situ pumps (~1 atm) versus bottle samples (~ 0.25 atm) and secondarily the nominal pore size of quartz filters used with in-situ pumps (~1 µm quartz) versus filters used with bottle samples (0.7 µm GFF). It is crucial to understand which of the above methods is correct when making carbon budgets, especially as we employ more optical methods to quantify carbon pools more rapidly.

Glover, David (1) and Maureen Conte (1)

A coupled epipelagic-meso/bathypelagic particle flux model for the BATS/OFP site

1 Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Mail Stop #25, Woods Hole, MA 02543-1541, dglover@whoi.edu

ABSTRACT:
This proposal to the NSF U.S. JGOFS Synthesis and Modeling Program (SMP) will combine the observations of deep-water sediment traps (21+ years) at the Oceanic Flux Program (OFP), euphotic zone measurements (10+ years) at the Bermuda Atlantic Time-series Site (BATS), and historical meso/bathypelagic zooplankton data with an ecosystem-based biogeochemical model of particle flux from the epipelagic to meso/bathypelagic zone. Of fundamental concern is how changes in ocean remineralization will affect the magnitude of material fluxes through the water column.

Our overarching goal is to mechanistically connect euphotic zone processes with meso- and bathypelagic zone processes by means of a prognostic model that can be used to further our understanding of this unparalleled time-series and test hypotheses constrained by a battery of in situ data. In order to realize this goal we will derive a meso/bathypelagic ecosystem structure and use it to model the flux of biogeochemically active constituents (carbon, nitrogen and silica). The meso/bathypelagic portion of the model will be driven by a well established epipelagic model that couples an intermediately complex, yet robust, ecosystem model with a state-of-the-art physical upper ocean mixing model. The choice of driver is guided by our underlying hypothesis that the meso/bathypelagic activity inferred from the sediment trap data is a response to time-varying responses of the upper ocean ecosystem to events of meteorological scale.

There is a remarkably strong covariance between the upper ocean particle flux at BATS and the deep particle flux measured by the OFP traps, as well as intense modification and strong convergence of the composition of the particle flux with depth to a invariant composition with respect to the magnitude of mass flux. These are the primary impetuses for development of a new model coupling recent physical-biological models of the surface ocean with particle flux and zooplankton reprocessing activities in the meso- and bathypelagic ocean. Numerical simulation of the biologically mediated repackaging of downward moving detritus will provide new insights into the mechanisms and rates of mid- to deep-water particle flux and remineralization. A combination of oceanographic and meteorological conditions spanning many space and time scales generally contributes to the observed signals. By mechanistically linking the upper and deep ocean with a model of the long-term Bermuda sediment trap records we can begin to deconvolve the multiple contributors (e.g. interannual variability associated with ENSO, NAO) to the deep flux patterns we observe.

Gnanadesikan, A. (1); P. Swathi (1); R. Slater (1) and R. Key (1)

Radiocarbon in the Pacific Ocean: Comparisons of models and data

1 Program in Atmospheric and Oceanic Sciences, Princeton Univ., Princeton, NJ, USA, 08544

ABSTRACT:
We examine the sensitivity of the radiocarbon distribution in a suite of general circulation models to changes in the boundary conditions and internal mixing. Achieving a reasonable distribution of radiocarbon within the Pacific seems to require a high rate of vertical exchange within the Southern Ocean. However, it is not clear how to reconcile this with the observed temperature and salinity structure. The extreme sensitivity of the radiocarbon distribution to boundary conditions is demonstrated. The most realistic solution for radiocarbon appears to be achieved with a somewhat higher vertical diffusivity within the pycnocline than supported by direct measurements.
(poster)

Green, Sara E. (1); Raymond N. Sambrotto and Lloyd H. Burckle

Nutrient consumption and export estimates in the Indian and Pacific regions of the Antarctic Polar Front (APF)

1 Lamont-Doherty Earth Observatory, Columbia Univ., Palisades, NY 10964, sgreen@ldeo.columbia.edu

ABSTRACT:
We compared nutrient uptake in the region south of the Antarctic Polar Front (APF) along 62°E in the Indian, 0° in the Atlantic, and 88°W, 126°W, and 170°W in the Pacific Ocean to compare surface productivity with sediment opal accumulation patterns. In each region we computed the nutrient consumption of silicic acid and nitrate just south of the polar front. Net consumption varied with the latitude of the APF. Silicic acid and nitrate uptake increased northward by 13% and 15%/degrees latitude, respectively. This reflects the longer growing season at lower latitudes and suggests that the circumpolar seasonal production that occurs south of the APF is, in part, dependent on light availability. However, less of the variation in silicic acid uptake was predicted by latitude as it was for nitrate. Extrapolation from net Si:C and C:N uptake ratios along 170°W, predicts a range in surface carbon export of 2 to 9 mol C m^-2 yr^-1 (24-108 gC m^-2 yr^-1) along the APF. However the opal accumulation in surface sediments varies zonally along the APF. We use these accumulations to refine our estimates of circumpolar carbon export in the APF region.
(poster)

Gregg, Watson W. (1); Nancy Casey-McCabe (2) and Richard A. Scheper (3)

Direct radiative effects of clouds on ocean phytoplankton: Simulations with a coupled, three-dimensional general circulation/biogeochemical/radiative model

1 NASA/Goddard Space Flight Center, Laboratory for Hydrospheric Processes, Greenbelt, MD 20771, gregg@cabin.gsfc.nasa.gov
2 Science Systems and Applications, Inc., 5900 Princess Garden Parkway, Suite 300, Lanham, MD 20706
3 Naval Research Laboratory, Code 5720, Washington DC, 20375

ABSTRACT
A coupled, three-dimensional general circulation/biogeochemical/radiative model was used to evaluate the direct effects clouds on phytoplankton distributions, abundances, and primary production in the global oceans.  Specifically, the effects of changes in cloud liquid water path (LWP) and cover were addressed.  Changes in LWP and cover affected 1) global and regional annual primary production, 2) vertical distributions of phytoplankton, and 3) timing of the spring bloom.  There were minimal effects on phytoplankton functional group compositions.  Global annual primary production changed by +10% when LWP was doubled/halved: increased LWP produced less irradiance and less primary production.  Interannual variability in LWP produced about +4% change.  Primary production effects were most pronounced in high latitudes, where fast growing, fast sinking diatoms predominated, which may represent the greatest potential for carbon sequestration.  The results have implications for climate change and the study of interannual variability on ocean phytoplankton and primary production.
(talk & poster)

Gruber, N. (1); N. Bates (2) and C.C. Keeling (3)

The influence of the North Atlantic Oscillation on the carbon cycle in the North Atlantic

1 Institute of Geophysics and Planetary Physics & Dept Atmospheric Sciences, UCLA, Los Angeles, CA, ngruber@igpp.ucla.edu
2 Nick Bates, Bermuda Biological Station for Research, Inc., Bermuda
3 Scripps Institution of Oceanography, Univ. of Calif., San Diego, La Jolla, CA

ABSTRACT:
The North Atlantic Oscillation (NAO) is the leading mode of interannual variability over the entire North Atlantic region. While the influence of NAO on sea surface temperature (SST) and mixed layer depth variations has been well studied, the influence of the meteorological forcing associated with NAO on surface ocean biogeochemical cycles is largely unknown. We investigate the connection of the NAO with the surface ocean carbon cycle near Bermuda in the northwestern Sargasso Sea on the basis of a 17 year time series of upper ocean measurements of dissolved inorganic carbon (DIC), of its stable isotopic ratio (¹³C/¹²C), and of alkalinity (Alk) made by C.D. Keeling. We will combine these observations with the inorganic carbon observations made by N. Bates at the U.S. JGOFS time series station BATS since 1993. Anomalies of DIC show significant (p < 0.05) anti-correlation with the NAO index of Hurrell [1995] [Bates, in press], while those of the ¹³C/¹²C ratio of DIC are positively correlated. Since variations in ¹³C/¹²C are mainly driven by the net balance between carbon uptake by phytoplankton and release by respiration and remineralization (net community production), these correlations indicate that interannual variability in net community production is tied to the NAO as has been shown to be the case for net primary production by Bates [in press]. This connection was further investigated with a simple diagnostic box model, which quantifies the contributions of the different governing processes - air-sea gas exchange, vertical and horizontal mixing and net community production - to the observed variability. We find that years with increased convection (negative NAO) tend to have an increased uptake of CO₂ from the atmosphere, driven mainly by the cooler SSTs, increased entrainment of DIC from below and increased net community production, likely as a result of the increased influx of nutrients by deeper convection. This is consistent with the view that phytoplankton in the subtropical gyres is primarily nutrient limited. The opposite is the case in the subpolar gyres, where increased vertical mixing tends to lead to lower productivity because of light limitation. We hypothesize that winters with weak convection in the subpolar gyres (negative NAO) have a negative DIC anomaly and hence a negative pCO₂ anomaly because of reduced entrainment of DIC from below and stronger biological drawdown during spring/summer. This likely leads to an increased uptake of CO₂ from the atmosphere. If this reasoning is correct, it appears possible that CO₂ fluxes over the entire North Atlantic are varying in phase and may contribute significantly to the observed variability in atmospheric CO₂.

Honjo, Sus; et al. (1)

Export flux of the organic/inorganic carbon and biogenetic silica particles to the ocean interior; a global model

1 Dept. Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, shonjo@whoi.edu

ABSTRACT:

Hood, Raleigh; et al. (1); Victoria J. Coles(1) and Douglas G. Capone(2)

Modeling the distribution of Trichodesmium and Nitrogren fixation in the Atlantic Ocean

1 University of Maryland Center for Environmental Science, Cambridge, MD, 21613
2 Wrigley Institute for Environmental Studies, USC, Los Angeles, CA, 90089

ABSTRACT:
In this project we use a coupled, 3-dimensional, biological-physical model, which includes an explicit, dynamic representation of Trichodesmium, to predict the distribution of Trichodesmium and rates of N₂-fixation in the tropical and subtropical Atlantic ocean. It is shown that the model reproduces the approximate observed meridional distribution of Trichodesmium in the Atlantic and elevated concentrations in specific coastal and open ocean regions where Trichodesmium is known to occur. These regions include the Gulf of Mexico, the Carribbean, the southern Sargasso Sea, the northern coast of South America, northwest Africa and equatorial waters. The model also appears to reproduce the seasonality of Trichodesmium populations in subtropical waters. High and persistent concentrations and rates of N₂-fixation are generated in the Gulf of Guinea off of Africa, but we have no observations to confirm or deny this. In general, increased Trichodesmium concentrations develop in regions where the mixed layer is relatively thin (resulting in high mean light levels) for extended periods of time, and phytoplankton concentrations are low. The model-predicted Trichodesmium distributions are therefore very sensitive to the fidelity of the physical model's representation of mixed layer depth variability, and the biological model's estimated phytoplankton concentrations. Some obvious discrepancies between the model-predicted Trichodesmium populations and observations can be attributed to over-estimation of the depth of the mixed layer. In upwelling regions the model generates a successional sequence where phytoplankton blooms first develop in response to elevated nutrient concentrations, followed by increased Trichodesmium concentrations after the phytoplankton deplete the nutrients. We also see stimulation of phytoplankton growth in regions where the rates of N₂-fixation are high. These results are consistent with observed species successions off of NW Africa (where upwelling-induced diatom blooms give way to Trichodesmium after nutrients are depleted), and in the Gulf of Mexico where N₂-fixation appears to stimulate harmful algal blooms. We believe that our model includes the primary factors which dictate when and where Trichodesmium occurs in the Atlantic. However, second order effects, such as Fe or P limitation which are not included in the model, probably constrain total biomass accumulation.

Hood, Raleigh; et al. (1)

A 3-dimensional validation of a coupled biological/chemical/physical model for the Arabian Sea

1 Horn Point Environmental Laboratory, 2020 Horns Point Rd, P.O. Box 775, Cambridge, MD 21613

ABSTRACT:

Husrevoglu, Yusuf Sinan and Eileen E. Hofmann (1)

A circumpolar modeling study of habitat control of Antarctic krill (Euphausia superba) spawning

1 Dept Ocean, Earth and Atmospheric Sciences, Center for Coastal Physical Oceanography, Old Dominion Univ., Norfolk, Virginia

ABSTRACT:
A one-dimensional, time- and temperature-dependent model is implemented to simulate the descent-ascent cycle of Antarctic krill (Euphausia superba) embryos and larvae. Physiological parameterization is based on laboratory measurements. Inputs to the model are monthly mean climatologies of ambient temperature and density fields. Model calculations are carried out on circumpolar scale, south of 60°S with 1 degree resolution and results are extrapolated to 5 min resolution in accordance with the topography data. Embryos that hit the bottom before hatching are assumed preyed upon or mechanically destroyed. Simulations of the descent-ascent cycle using environmental conditions representative of the Antarctic krill spawning season (December through March) resulted in unconstrained success in hatching over deep regions, attracting attention to areas within the 1000 m isobath where krill populations are consistently observed. Shelf regions favorable to successful hatching are irregularly scattered over the Palmer Archipelago, Biscoe Islands, Marguerite Bay, offshore Wilkes Land, and to the east and west of the Prydz Bay, but cover larger areas over Bellingshausen Sea off Alexander Island and Amundsen Sea. The seasonal signal for this set of simulations manifests itself with increasing hatching depths in time, except for regions scattered offshore Wilkes Land, Queen Maud Land and eastern shelf of the Antarctic Peninsula, suggesting that late spawning is favored over these regions. Another set of calculations, for which specific temperature profiles are used as input, resulted in successful completion of the descent-ascent cycle over the western shelf of the Antarctic Peninsula, in regions where calculations with mean monthly climatologies suggested embryos would hit the bottom prior to hatching. This may indicate that the climatologies are too smooth to be used for drawing conclusions about the success of krill spawning in specific regions. Hatching depth increased by 100 to 150 m, yielding minimum hatching depths of about 600 m, when smaller values of initial egg diameter are used in the calculations. Sensitivity of the model to initial egg diameter may indicate that spawning larger eggs is a reproductive strategy adopted by krill to decrease mortality of embryos over the continental slope and shelf regions.
(poster)

Iglesias-Rodríguez, M. Débora (1,4); Christopher W. Brown (2); Scott C. Doney (3); Joan Kleypas (3); Dorota Kolber (1); Zbigniew Kolber (1); Paul K. Hayes (4) and Paul G. Falkowski (1,5)

Representing key phytoplankton functional groups in ocean carbon cycle models: Coccolithophorids

1 Environmental Biophysics and Molecular Ecology Program, Inst. Marine and Coastal Sciences, Rutgers Univ., 71 Dudley Rd, New Brunswick, NJ 08901, iglesias@imcs.ac.uk
2 NOAA/NESDIS, 5200 AUth Rd, Camp Springs, MD 20746-4304
3 NCAR, PO Box 3000, Boulder, CO 80307-3000
4 School of Biological Sciences, Univ. Bristol, Woodland Road, Bristol BS8 1UG, m.d.iglesias-rodriguez@bristol.ac.uk
Dept Geology, Rutgers Univ.

ABSTRACT:
In this paper we address the physical and chemical processes that select for coccolithophorid blooms. Our primary goal is to develop both diagnostic and prognostic models that represent the spatial and temporal dynamics of coccolithophorid blooms in order to improve our knowledge of the action of these organisms in the fluxes of carbon between the ocean, atmosphere, and the lithosphere. Based on monthly composite satellite imagery of coccolithophorid blooms and global climatological maps of physical variables and nutrient fields, we developed a probability density analysis that accounts for the physical chemical variables that predict the spatio-temporal distribution of coccolithophorids in the world oceans. Our analysis revealed that areas with sea surface temperatures (SST) between 3 and 15°C, a critical irradiance (euphotic zone depth x irradiance/mixed layer depth) between 25 and 150 mmol quanta m^-2 s^-1, and decreasing nitrate concentrations (DN/Dt < 0) are selective for upper ocean large-scale coccolithophorid blooms. SST, critical irradiance, and DN/Dt were predicted for the years 2060-2070 using the NCAR Community Climate System Model to generate future monthly probability distributions of coccolithophorids based upon the relationships observed between the environmental variables and coccolithophorid blooms in modern oceans. Our projected probability distributions suggest that in the North Atlantic, the largest habitat for coccolithophorids on Earth, the areal extent of the coccolithophorid blooms will decrease by up to 50% by the middle of this century. We discuss how the magnitude of carbon fluxes may be affected by the evolutionary success of coccolithophorids in future climate scenarios.

Jackson, G. (1) and A. Burd (1)

Upper-ocean aggregation models for interpreting and predicting carbon fluxes

1 Dept of Oceanography, Texas A&M Univ., College Station, Texas 77843-3146, gjackson@ocean.tamu.edu

ABSTRACT:
The removal of organic matter from the surface mixed layer by falling particles can be greatly influenced by aggregate formation. We have been exploring the implications of the interactions between coagulation and food web dynamics. The result can be greatly enhanced sedimentation at certain times of the yearly cycle. We have also been working to compare the results of the models with measurements of particle flux as a function of particle size. Results to date are encouraging in that the models predict import aspects of the export.

Jahnke, Richard A. (1)

Global distribution of biological pump efficiency: Can the "Martin Curve" be universally applied?

1 Skidaway Institute of Oceanography, 10 Ocean Science Circle, Savannah, GA 31411, rick@skio.peachnet.edu

ABSTRACT:
Here I investigate the spatial variation in carbon transfer efficiency by comparing previously published global distributions of surface primary production and abyssal sea floor benthic oxygen fluxes, a surrogate for deep particulate organic carbon fluxes. The proportion of surface water primary production reaching the deep sea floor is observed to vary from as low as 0.07% to greater than 10%. This greater than 100-fold variation in transfer efficiency may be attributed to a variety of factors and must be understood to quantify the role of the biological pump in controlling atmospheric carbon dioxide and for relating sediment paleoproxies to surface productivity. Regardless of which productivity distribution is used, transfer efficiencies are significantly larger along continental margins relative to the gyre regions. Possible reasons for this increased efficiency include alternative nutrient sources that may influence ecosystem composition and proximity to lithogenic particles that may ballast sinking organic materials. Because these regions also tend to have elevated surface productivities, these environments contribute significantly to the transfer of organic carbon to the deep sea. In contrast, latitudinal variations in calculated transfer efficiency depend on the productivity distribution used. Future efforts to develop global distributions of the biological pump will need to resolve the differences among the reported global primary productivity distributions.

Key, Robert M. (1) and Stephany Rubin (2)

Separating natural and bomb-produced radiocarbon in the ocean: The potential alkalinity method

1 Atmospheric and Oceanic Sciences, Princeton Univ., Princeton, NJ, key@princeton.edu
2 Lamont Doherty Earth Observatory, Palisades, NY

ABSTRACT:
The oceanic radiocarbon (D¹⁴C) distribution is used to study processes ranging from large scale circulation to global climate change. In almost all instances these studies require differentiation of naturally occurring radiocarbon from that produced by the atmospheric nuclear weapons testing. The best prior separation method was based on the correlation between natural D¹⁴C and dissolved silicate. The new algorithm discussed here is based on the correlation between D¹⁴C and potential alkalinity. The potential alkalinity algorithm is more linear than the silicate function and more importantly, is applicable for all latitudes.
(poster)

Klinck, John M. (1) and Michael S. Dinniman (1)

Modeling the circulation in the Ross Sea and on the west Antarctic Peninsula: A prelude to biogeochemical modelling

1 CCPO, Old Dominion Univ., VA

ABSTRACT:
Exchange of Circumpolar Deep Water onto Antarctic Seas and continental shelves has a large influence on sea ice and biological processes. The Regional Ocean Modeling System (ROMS) model is configured for both the Ross Sea and the west Antarctic Peninsula, using grid resolutions of 5 km. The present focus in on the ice-free circulation driven by monthly wind stress climatology and monthly varying water properties at the boundary from the Levitus (1998) climatology. The ACC is included in the Antarctic Peninsula model as an imposed transport across the model boundaries. Preliminary simulations show the strong influence of bottom topography on the circulation. Mesoscale eddies occur along the Peninsula shelf break, but do not seem important along the Ross Sea shelf. The potential influence of sea-ice and surface buoyancy fluxes will be discussed.
(poster)

Landry, M.R. (1) and R.A. Armstrong (2)

Microplankton Dynamics in Tropical Open-Ocean Ecosystems

1 Dept. Oceanogr., Univ. Hawaii at Manoa, landry@iniki.soest.hawaii.edu
2 MSRC, State Univ. NY, Stony Brook

ABSTRACT:
Although JGOFS investigations have indicated strong links among physical-chemical environmental forcing, plankton community structure, and the fate of carbon production (remineralization or export), these relationships are crudely portrayed in plankton food web models. It is presently unclear how much information on size and taxonomic composition is needed for adequate model predictions and to what extent community dynamics and biogeochemical fluxes in different water masses are linked by common organizational principles and regulatory mechanisms. Based on observed similarities in the stocks and process rates in diverse tropical oceanic ecosystems (EqPac, Arabian Sea, HOT, BATS), we believe that they will lend themselves to representation in a general tropical ocean model with common structure and parameters. To investigate the minimum level of complexity required to capture essential biological realities in global models, we hope to develop and statistically examine an interrelated spectrum of models, all calibrated to common data sets but differing in structural complexity. Our specific objectives are: 1) to develop data-constrained representations of planktonic community structure and trophic interactions; 2) to construct models of temporal plankton community dynamics and associated biogeochemical fluxes at the Hawaii Ocean Time-series (HOT) site and following iron perturbation in the equatorial Pacific (IronEx II); 3) to compare and test simple parameterizations for lower trophic level interactions and export fluxes for use in 3-D coupled models; 4) to develop a general tropical ocean model that includes appropriate responses to nutrient supply (Arabian Sea) and iron-limitation (Equatorial Pacific).

As the first step in this process, we are examining the number and relative strenghts of trophic linkages in the microbial community based on experimental manipulations at Stn. ALOHA. Collected seawater was sequentially size-fractionation to truncate the food web at different organism sizes (1, 2, 5, 10 and 20 µm), and the response variable, net bacterial growth rate, was assessed from flow cytometric analyses of the changes in cell abundance. The corresponding size structure of the protistan grazer assemblage was measured microscopically. Microbial community responses varied markedly among the experiments, but 88% of the variability was explained by the size structure of heterotrophic flagellate grazers. For experiments conducted with relatively high bacterial biomass compared to Hflag, the bacteria showed little growth response to the removal of predators and may have been resource limited. When conditions were defined by relatively low bacterial biomass and high Hflag biomass, a depression of net growth in the smallest size fraction (<1 µm) compared to the <2 µm fraction suggested selection for smaller bacterivores. At intermediate conditions, where the biomass ratio of bacteria to Hflag was transitioning from higher to lower values, the growth dynamics of bacteria were marked by significant cascade influences among the different size fractions. These results may be features of a regular oscillatory pattern that regulates open-ocean microbial populations at different temporal and spatial scales. In such oscillations, the indirect influences of a protistan predatory chain can tip the balance between resource limitation and predatory control.

Laws, Ed (1)

Theory and application of adaptive food web models

1 Univ. of Hawaii, Oceanography Dept, 1000 Pope Road, Honolulu, HI 96822, laws@soest.hawaii.edu

ABSTRACT:
Interest in the evolution of biological communities stems from the time of Lotka (1922), who postulated that "Natural selection tends to make the energy flux through the system a maximum, so far as compatible with the constraints to which the system is subject." This idea was developed on a grand scale by Odum (1983), who suggested that "systems prevail that develop designs that maximize the flow of useful energy. . . They maximize power, and theories and corollaries derived from the maximum power principle explain much about the structure and processes of systems." Recently, Cropp and Gabric (2001) have shown, with the use of a simple food chain model, that application of the maximum power principle and related ecologically defined "thermodynamic imperatives" leads to a condition of maximum resilience to perturbation. Application of the maximum resilience principle to more complex food web models of open ocean pelagic communities leads to conclusions that are in remarkable agreement with observations from JGOFS and other studies.

References:
Cropp, R. and A. Gabric. 2001. Ecosystem adaptation: Do ecosystems maximize resilience? Ecology (in press).
Odum, H. T. 1983. Systems Ecology: An Introduction. Wiley, New York.
Lotka, A. J. 1922. Contribution to the energetics of evolution. Proc. Natl. Acad. Sci. 8: 147-150.

Lee, Kitack; et al. (1)

Water column dissolution rates of CaCO₃ in the Atlantic Ocean

1 NOAA/AOML/OCD, 4301 Rickenbacker Causeway Miami, FL 33149, lee@aoml.noaa.gov

ABSTRACT:

Lindsay, K. (1) and S.C. Doney (1)

Comparison of model physics relevant to the carbon cycle in OCMIP-2

1 NCAR, P.O. Box 3000,Boulder, CO 80307-3000, klindsay@ucar.edu

ABSTRACT:
The stated objective of OCMIP-2 is to improve the predictive capacity and speed the development of global-scale, three-dimensional, ocean carbon-cycle models through standardized model evaluation and model intercomparison. Each of the 13 participating modeling groups performed a suite of standardized model runs. The runs include simulations of transient tracers and an equilibrium biogeochemical run. In order to better understand the model tracer output, the modeled ocean physics are also being analyzed and compared. We present preliminary results from this intercomparison, which includes models from all of the participating groups. A variety of physical parameterizations are represented by the models, including different treatments of vertical coordinates, surface boundary layers and horizontal mixing schemes. Model aspects that are examined include: surface forcing and mixing, water column hydrography, wind-driven circulation and thermohaline circulation. Particular attention is paid to those features that figure prominently in the carbon-cycle.

Lizotte, Michael (1) and Giacomo DiTullio (2)

Phytoplankton community structure: the role of dominant taxa in determining particulate elemental composition, carbon fixation, and bio-optical properties

1 Bigelow Laboratory for Ocean Sciences, 180 McKown Point Road, West Boothbay Harbor, ME 04575, MLizotte@bigelow.org
2 Grice Marine Laboratory, Univ. Charleston, 205 Fort Johnson, Charleston, SC 29412

ABSTRACT:
Phytoplankton community structure, particularly for functional groups, has been identified as critical need as we progress from current ocean biogeochemistry models (with generic phytoplankton parameterizations) to more explicit models. High-Performance-Liquid-Chromatography (HPLC) methods for characterizing phytoplankton pigments have been used widely in the past two decades, and we will report on our success in using these data sets to make a first-order approximation of phytoplankton community structure. Our goal is to identify data sets showing dominance by single taxonomic groups to determine whether phytoplankton-related parameters vary systematically as a function of community structure. We will summarize our progress in analyzing data sets for nutrient utilization, particulate elemental composition, and photosynthetic parameters.

Macdonald, Alison M. (1) and R. Wanninkhof (2)

Meridional transport of CO₂ in the subtropical North Atlantic

1 WHOI, 360 Woods Hole Road, MS #21, Woods Hole, MA 02543, amacdonald@whoi.edu
2 NOAA/AOML, 4301 Rickenbacker Causeway, Miami, FL 33149, wanninkhof@aoml.noaa.gov

ABSTRACT:
In January and February of 1998, when an unprecedented fourth repetition of the zonal hydrographic transect at latitude 24.5°N in the Atlantic was undertaken, a full section of carbon measurements was obtained for the second time in less than a decade. The field of total carbon (TCO₂) along this section is compared to that provided by the 1992 transect which followed a similar path (albeit in a different season). Using a simple box inverse analysis to determine estimates of absolute velocity, the transport of TCO₂ across 24.5° is estimated to Be -0.86±0.99 PgC yr^-1 and -1.25±0.96 PgC yr^-1 southward (1 PgC yr^-1 = 1 GtC/yr = 2642 kmolC s^-1) in 1998 and 1992, respectively. These values are consistent with, but smaller than the previously published estimate from 1992 transect. The concentration of TCO₂ changes little compared to its mean value, so its transport closely follows that of mass. It is therefore not surprising that the large uncertainty assigned to our estimates is directly related to the uncertainty in the mass balance across the section. Of interest is that these new estimates reduce the large regional divergence in the meridional carbon transport suggested by previous studies and brings into question the idea that the tropical Atlantic is outgassing carbon, while the subpolar Atlantic is sequestering it. Seasonal effects are likely important and uncertainty in the carbon transports themselves are a hindrance to determining the "true" picture.

The flux of anthropogenic carbon (ACO₂) across the two transects has been estimated as northward at 0.12 ± 0.08 PgC yr^-1 and 0.17±0.06 PgC yr^-1 for the 1998 and 1992 sections, respectively. Concentrations of ACO₂ vary a great deal (1998 mean ACO₂ = 13±15 µmol kg^-1). They are surface intensified and previous studies suggest that surface values are higher to the south of 24.5°N than to the north. Therefore, the net transport of ACO₂ across 24.5°N is strongly affected by the difference in concentrations between the northward flowing shallow Florida Current and the mass balancing return flow dominated by the deep interior. The net northward transport of ACO₂ is opposite the net flow of total carbon and suggests, as has been found by others, that the pre-industrial southward transport of carbon within the Atlantic was stronger than it is today.

Marinov, I. (1); A. Gnanadesikan (1); R. Slater (1); J. Sarmiento (1) and N. Gruber (2)

Spatial distribution of air-sea CO₂ fluxes. An analysis of Princeton biogeochemical model simulations under different circulation scenarios.

1 Program in Atmospheric and Oceanic Sciences, Princeton Univ., Princeton, NJ, USA, 08544
2 Dept. Atmospheric Sciences, Univ. of California, Los Angeles, CA, 90024

ABSTRACT:
Despite recent work in the area (Murnane and Sarmiento, GBC '99), the magnitude and spatial distribution of the preindustrial air-sea CO₂ fluxes is not fully understood. In this study we try to asses the differential roles of the solubility pump, soft tissue, and carbonate pumps in determining the spatial distribution of air-sea CO₂ fluxes and in the large scale transport of carbon by the oceans.

Locally the solubility pump creates features such as the significant loss of CO₂ from the equatorial region due to warming of relatively cold upwelled water. This loss is offset by the gain of CO₂ in high latitudes due to cooling of the surface water. The pump is incompletely realized because of the finite gas exchange time, which allows the circulation to change the surface carbon before air-sea exchange takes place. Also, escape of excess CO₂ to the atmosphere occurs in regions where biological uptake is inefficient. In these regions biological uptake does not have time to strip out excess carbon before it is released to atmosphere.

We propose to explain the CO₂ flux and carbon transport pattern in terms of the competitions between solubility pump, gas exchange, biological pump, and circulation, as exemplified above. The influence of circulation on the biological pumps and CO₂ flux distribution will be examined in a series of five pre-anthropogenic simulations with different circulations due to different horizontal and vertical diffusivities. The model used is the Princeton GCM with carbon chemistry consistent with OCMIP 2 requirements. Preliminary results suggest that changing the circulation does not have a strong influence on the general air-sea carbon flux distribution, unlike what is expected. Finally, we attempt to understand the GCM results by comparing them to the results of a simple five box model of the ocean.
(poster)

Martin, W. (1) and F. Sayles(1)

Cycling of organic carbon and CaCO₃ in marine sediments: Parameterization for global models

1 Dept of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543-1050, wmartin@whoi.edu

ABSTRACT:

Matear, R.J. (1); B. I. McNeil (2)

A comparison of CFC 11-age derived estimates of anthropogenic CO₂ to multi-parametric linear regression estimates in the Southern Ocean

1 Program in Atmospheric and Oceanic Sciences, Princeton Univ., Princeton, NJ, USA, 08544
2 Antarctic CRC, Univ. of Tasmania, GPO Box 252-80, Hobart, 7001, Tasmania, Australia, and Program in Atmospheric and Oceanic Sciences, Princeton Univ., NJ, USA, 08544

ABSTRACT:
The change in anthropogenic CO₂ from 1968 to 1996 was estimated using a CFC-age method for three WOCE sections (P12, P14, P15) in the Southern Ocean and directly compared to values obtained using a Multi-parametric Linear Regression method over the same period. The agreement in anthropogenic CO₂ concentrations between the two independent methods was very good (8%) for waters younger than 30 years. The good agreement provides confidence that either method can estimate multi-decadal changes in anthropogenic CO₂ in the ocean. In all three sections, the greatest inventory of anthropogenic CO₂ occurs in the Sub-Antarctic Zone with detectable penetration to a depth of 1500 m. South of the Polar Front the penetration of anthropogenic CO₂ shallows and by 60S it is generally confined to the upper 200m of the ocean. The exception was along 140E, where we observed high concentrations (11-12 mmol/kg) in Antarctic Bottom Water (AABW) and along 170E where the AABW signal was detectable (6-8 mmol/kg) below 2500 m. Further east along 170W, we were unable to detect an anthropogenic CO₂ signal in AABW.
(poster)

Matsumoto, K. (1); J.L. Sarmiento (1); M.A. Brzezinski (2)

Silicate "leakage" and glacial atmospheric pCO₂

1 Program in Atmospheric and Oceanic Sciences, Princeton Univ., Princeton, NJ, USA, 08544
2 Dept. of Biological Sciences, Univ. of California, Santa Barbara, CA, USA 93106

ABSTRACT:
Using a simple box model, we investigate the effects of reducing the Si:N uptake ratio by Antarctic diatoms on the marine silicate cycle and atmospheric pCO₂. Recent incubation experiments demonstrate such a phenomena when Fe is added [Hutchins and Bruland, Nature, 393, 561-564, 1998; Takeda, Nature, 393, 774-777, 1998; Frank et al., DSR II, 47, 3315-3338], which suggests that a reduced Si:N uptake ratio might have occurred in the Southern Ocean during glacial times, when the dust content in Antarctic ice cores was much higher. A similar reduction in the uptake ratio may be realized with an increased production of non-diatoms such as Phaeocystis. Our model shows that a reduced Si:N export ratios in the Southern Ocean allows more silicic acid to "leak" out into the low latitude surface waters, which are presently low in silicic acid relative to nitrate. The extra silicic acid in low latitudes may enhance the growth of diatoms at the expense of other phytoplankton, which would diminish the rain ratio of CaCO₃ to organic carbon and weaken the carbonate pump. The atmospheric pCO₂ drawdown depends critically on the initial, modern rain ratio, which has generally been assumed to be 0.2~0.3, but our recent analysis shows that the ratio could be 0.1 or lower. We show that the typical pCO₂ response to this forcing in box models is insufficient to account for the full glacial atmospheric pCO₂ drawdown. However, GCMs have as much as a four-fold larger response than box models and would be able to account for the full glacial pCO₂ reduction if the initial CaCO₃ to organic carbon rain ratio were about 0.15.
(poster)

Matsumoto, K. (1); J.L. Sarmiento (1); R. Key (1); R.D. Slater (1); C. Sabine (2)

Bomb radiocarbon versus anthropogenic CO₂ in GCMs

1 Program in Atmospheric and Oceanic Sciences, Princeton Univ., Princeton, NJ, USA, 08544
2 NOAA Pacific Marine Environmental Laboratory, Seattle, WA, 98115

ABSTRACT:
We examine the distributions of bomb-derived radiocarbon (¹⁴C) and anthropogenic CO₂ as simulated by a suite of GCMs participating in the Ocean Carbon Model Intercomparison Project (OCMIP). Because of the time scale differences in their introduction into the atmosphere and in their gas exchange equilibration, the two tracers are distributed in a dissimilar manner in the ocean. OCMIP mandates the use of a standardized marine biogeochemistry model, so differences in the simulated distribution of bomb ¹⁴C and anthropogenic CO₂ in OCMIP models can be attributed to differences in the model physics. Of particular importance are the relative strengths of parameterized vertical and horizontal mixing. Preliminary analysis indicates that mixing in the Southern Ocean and the advective pathways of the North Atlantic Deep Water play important roles. We expect these differences to provide useful insights into the strengths and weaknesses of the GCMs, which will aid our ongoing efforts to improve these models and their predictive capabilities with regard to anthropogenic CO₂ uptake by the ocean.
(poster)

McGillicuddy, D.J. (1); S.C. Doney (2); L.A. Anderson (1); M.E. Maltrud (3); and F.O. Bryan (2)

The role of mesoscale eddies in basin-scale biogeochemical budgets of the North Atlantic: results from a high resolution (0.1 degree) simulation

1 AOPE, WHOI, dmcgillicuddy@whoi.edu
2 National Center for Atmospheric Research, Boulder, CO.
3 Los Alamos National Laboratory, Los Alamos, NM.

ABSTRACT:
Several different lines of evidence have emerged which suggest that mesoscale eddies are an important mode of nutrient transport to surface waters of the oligotrophic open ocean.  These include: (1) regional eddy resolving numerical calculations, (2) mesoscale biogeochemical surveys, (3) high temporal resolution moored time series, (4) ocean color imagery, and (5) satellite-based statistical models.  Nutrient flux calculations from (1) and (5) suggest that eddy-induced nutrient transport is sufficient to balance geochemical estimates of new production for the western subtropical North Atlantic.  Until very recently, mesoscale phenomenology was not accessible in large-scale ocean models -- eddy resolving simulations were only possible in regional contexts. Increased computational capability, together with progress in ocean modeling, have facilitated some of the first truly eddy resolving basin-scale simulations.  We will report on our initial results of a nutrient transport calculation based on a 0.1 degree resolution simulation of the North Atlantic, using the Los Alamos Parallel Ocean Program (POP).  Diagnosis of the model solutions suggests that, except for the wintertime period of deep convection, the dominant mechanism of nutrient input to the euphotic zone is vertical advection by eddies.  Annual fluxes in the Sargasso Sea are of the same order as the regional estimates mentioned above.
(talk and poster)

McGillicuddy, D.J., Jr. (1); V.K. Kosnyrev (1); E.N. Sweeney; and K.O. Buesseler

Modeling mesoscale biogeochemical processes in a Topex/Poseidon diamond surrounding the U.S. JGOFS Bermuda Atlantic Time-series Study

1 AOPE, WHOI, dmcgillicuddy@whoi.edu

ABSTRACT:
An interdisciplinary modeling system has been configured in the Topex/Poseidon (T/P) "diamond" surrounding the Bermuda Atlantic Time-series (BATS) site.  After extensive experimentation with the treatment of the open boundary conditions, a realistic hindcast of sea level variations in the interior of the domain has been achieved by prescribing information only along the boundaries.  The time series of RMS difference between simulated and observed SLA fields for the entire altimetric record available to date shows hindcast skill that is in most cases the same order as the altimetric measurement error (3-5cm).  The T/P diamond model is being used to diagnose mesoscale biogeochemical processes in a retrospective analysis of BATS data.  This activity was begun with an attempt to interpret a three-year time series record of particle flux based on thorium-234 measurements made by K.O. Buesseler.  During this time period, there were three anomalously high flux events.  Analysis of contemporaneous results from the T/P diamond model reveals that each of the three events took place when eddy features were present.  The first two (June 1993 and August 1994) were associated with cyclonic features (negative sea level anomalies), while the last one (July 1995) was associated with with a positive sea level anomaly.  Concurrent hydrographic measurements reveal the latter to be associated with a so-called ``Mode water eddy,'' a thick bolus of 18-degree water which depresses the main thermocline and lifts the seasonal thermocline.  Previous work has shown that both cyclones and Mode water eddies can inject nutrients into the euphotic zone, causing the accumulation of phytoplankton biomass in their interiors.  Thus the high particulate flux events inferred from the thorium-234 flux measurements are consistent with these eddy-driven mechanisms.

McNichol, Ann P. (1) and Paul D. Quay (2)

Oceanic CO₂ uptake rates derived from an ocean-wide ¹³C/¹²C-DIC data set

1 National Ocean Sciences AMS Facility, Woods Hole Oceanographic Institution, McLean Laboratory, Mail Stop #8, 360 Woods Hole Road, Woods Hole, MA 02543-1539, amcnicnol@whoi.edu
2 School of Oceanography, Univ. of Washington, P.O. Box 357940, Seattle, WA 98195

ABSTRACT:
Significant progress has been made on all the goals identified in this project. We have deposited all of the Pacific data measured during the WOCE and OACES programs by our laboratories in both the WOCE and GLODAP databases and will deposit the Indian and Atlantic data by the end of the project. We have used inter-laboratory measurements on a variety of samples as well as compared 11 Indian Ocean stations that were measured by both laboratories to convince ourselves that there is not a significant offset between the two labs. The data indicate that the UW measurements are more precise than the NOSAMS measurements. A comparison of the WOCE data with historical data indicates that some of the older data may be less reliable that originally assumed (Lerperger et al. 2000). This finding emphasizes the need to develop models that do not rely on comparisons with older data in order to increase confidence in our calculations. This new ocean-wide d13C data set substantially improves the usefulness of d13C as a tracer of the anthropogenic CO₂ perturbation. The global surface ocean average d13C change is estimated at 0.16±0.02 permil decade^-1 between the 1970s and 1990s with the greatest changes observed in the subtropics and the smallest changes in the polar and southern oceans. The global average air-sea d13C disequilibrium in 1995 is estimated at 0.60±0.10 permil with the disequilibrium being significantly lower in the Indian Ocean (0.23 permil) versus either the Atlantic (0.63 permil) or the Pacific (0.73 permil) oceans. The global average depth-integrated anthropogenic change in d13C-DIC was estimated at 67±30 permil m decade^-1. We will compare the CO₂ uptake rates calculated from these values and an atmospheric budget approach as well as a box diffusion model (Quay et al., in preparation)

Mishonov, A. V. (1); W. Gardner (1); & M.J. Richardson (1)

Global POC assessment based on transmissometer data

1 Dept. Oceanography, Texas A&M Univ., avm@ocean.tamu.edu ,

ABSTRACT:
During the first year of this project all transmissometer data available from WOCE, JGOFS, S.A.V.E., and some other sources were collected, quality controlled, edited, and format transformed.  All transmissometer data are loaded into an intermediate data base and sections of Beam Attenuation Coefficient (Beam Cp) have been constructed for all WOCE, S.A.V.E., and others lines in the Atlantic, Pacific, Indian, and Southern Oceans.  Relationship between Beam Cp and Particulate Organic Carbon (POC) was evaluated based on jointly acquired data sets in the Atlantic.  These data sets for the Atlantic were obtained during the JGOFS NABE expedition and at the Bermuda Atlantic Time Series.  These two data sets contain about 800 data pairs and yield a high correlation (>0.9) between these two variables.  This correlation allows us to calculate the POC values based on transmissometer data and build the sections and maps of the POC distribution for the Atlantic Ocean.  Data for the Pacific Ocean will be our next target.  Correlation between Beam Cp and POC will be assessed based on Ross Sea, Antarctic Polar Front Zone and Hawaii Oceanographic Time (HOT) Series data sets.  Preliminary evaluation of the HOT Series shows that the transmissometer data need some attention before they could be used for joint analysis.  The web-site of the "Global Synthesis of POC Using Satellite Data calibrated with Transmissometer and POC Data from JGOFS/WOCE" project (http://www-ocean.tamu.edu/~pdgroup/TAMU-SMP.html) was launched, which provides access to all sections and maps created.

Mishonov, A.V. (1); W. Gardner (1); & M.J. Richardson (1)

Assessment of upper beam attenuation data collected during the South Atlantic Ventilation Experiment

1 Dept. Oceanography, Texas A&M Univ., avm@ocean.tamu.edu ,

ABSTRACT:
Transmissometer data were collected during six South Atlantic Ventilation Experiment (SAVE) hydrographic expeditions conducted from November 1987 to March 1989 from R/V Knorr and Melville. A total of 361 beam attenuation profiles were made with a SeaTech transmissometer interfaced with a CTD/rosette. These data were processed and examined as vertical sections of the surface 500 m. Although the data were not synoptic, we also mapped the data in plan view for presentation. Data were integrated for the upper 30 m for comparison with the distribution obtained from satellite color data. No synchronous satellite data are available for those years, but we have compared our data with ocean color data from other years for comparable seasons. In general, values are high in the Argentine basin and along the upwelling areas of the western coast of Africa. Values were low in the central gyre region between 5° and 35°S. This marches the chlorophyll distribution based on 30-month compilation of CZCS data for the South Atlantic, reaffirming that most particulate matter in surface waters of the open ocean is of recent biological origin. Comparison will also be made with the hydrology and currents to interpret the observed distribution.
(poster)

Murphy, Paulette P.(1) and Margarita Conkright (1)

Progress in the development of a database for carbon dioxide parameters in seawater

1 Ocean Climate Laboratory, NODC/NOAA, Room 4240, 1315 East-West Highway, Silver Spring, MD 20910-3282, pmurphy@nodc.noaa.gov

ABSTRACT:
A wealth of recent CO₂ data has only now made it possible to develop a canonical database for the carbon dioxide parameters dissolved in seawater. A comprehensive database would be useful for a variety of purposes, e.g., to determine long-term changes in dissolved carbon concentrations, to assess the to predict future atmosphere, and to develop a better understanding of the carbon cycle on a basin-wide scale. We report progress on building a database for the parameters which, with temperature and salinity, completely describe the chemical state of CO₂ in seawater: CT (sum of dissolved inorganic carbon species), partial pressure of CO₂ (pCO₂), total alkalinity (AT), and pH). The focus to date has been on historical data (pre-1990), and we outline plans to rescue important historical datasets, as well as add modern data.

Murtugudde, Raghu (1)

The dynamics of the 1998 La Niña phytoplankton bloom in the equatorial Pacific

1 Univ. of Maryland, College Park, MD 20742, ragu@vinsanto.essic.umd.edu

ABSTRACT:
The strongest El Niño of the century occurred during 1997-1998 which was closely followed by the most intense La Niña during the summer of 1998. During mid-June 1998, the thermocline surfaced in the central equatorial Pacific with a drop in SST of over 10C producing an equally dramatic ecosystem response with the greatest ever surface chlorophyll-a concentrations observed in the central equatorial Pacific. The surface bloom appeared between 2°N and 5°N during May 1998, shifted equatorward by early June and expanded westward during mid-June 1998. During July and August 1998, the bloom intensified and migrated eastward, with highest concentrations with apparent eastward propagation. Our analyses of ocean color show that a Yanai wave generated by the sudden collapse of the northerly wind anomalies at the end of April 1998 was responsible for the wave pattern in the surface chlorophyll. The eastward propagation of the bloom was caused by an eastward increase of mixed layer entrainment combined with an anomalously shallow thermocline accompanying the eastward establishment of the trades and the seasonal upwelling. We combine TAO data with several remotely sensed observations to demonstrate the details of this physical-biological interaction.

Murtugudde, Raghu (1)

Ecosystem-climate feedbacks in a coupled physical-biological model

1 Univ. of Maryland, College Park, MD 20742, ragu@vinsanto.essic.umd.edu

ABSTRACT:
It is evident that ocean circulation affects marine ecosystems considerably. The feedback from the marine ecosystems to the upper ocean circulation are quantified here. The traditional approaches for representing penetrative radiation in ocean GCMs is to ignore it or to assume a constant attenuation depth and coefficient. An OGCM coupled to a nine-component ecosystem model and a simple coupled ocean-atmosphere model are employed here to quantify the effects of surface chlorophyll distribution on upper ocean dynamics and thermodynamics. Contrasting the simulations with constant and variable attenuation of surface radiation shows significant effects not only on mixed layer quantities such as SST and currents, but also large scale thermocline depth distribution, Equatorial Undercurrent, and so on. For example, the eastern equatorial cold tongue is warmer by nearly 0.8°C when CZCS derived attenuation depths are used. The change in SST gradient associated with the phytoplankton bloom may thus have significant feedback on winds in the coupled climate system. The fully coupled OGCM-ecosystem model is used with the feedbacks from the biological model to the physical model turned on and off. It is shown that the interactive ecosystem simulations confirm the findings with the simple formulations above. The results are also reproduced in a simple coupled ocean-atmosphere model. Detailed analyses of the dynamical and thermodynamical affects for all three oceans indicate that climate models must account for penetrative radiation effects even if in a simple formulation with ocean color derived attenuation coefficients and depths.

Najjar, R. (1)

Simulation of export production by models participating in OCMIP (Ocean Carbon-cycle Model Intercomparison Project)

1 Dept of Meteorology, Pennsylvania State Univ., 522 Walker Building, University Park, PA 16802-5013, najjar@essc.psu.edu

ABSTRACT:
The main goal of the Ocean Carbon-cycle Model Intercomparison Project (OCMIP) is to improve global marine carbon cycle models through rigorous evaluation and comparison of a controlled set of simulations by a wide variety models. A secondary goal of the project is to make estimates of poorly known but important fluxes in the global carbon cycle, such as export production and the uptake of anthropogenic carbon dioxide. Currently 13 modeling groups are participating in OCMIP. The OCMIP suite of simulations includes natural and bomb radiocarbon, anthropogenic carbon dioxide, chlorofluorocarbons, abiotic preindustrial carbon dioxide and a simple biotic carbon cycle. Here we discuss the results of the biotic simulations, which are based on a simple "nutrient-restoring" approach in which surface phosphate is nudged towards the observed mean annual cycle. The organic phosphorus produced as a result of this nudging is partitioned into rapidly sinking particles that follow sediment-trap depth scaling and a dissolved phase that decays with a time scale of about 2 months. Results are available for more than half of the 13 models. Despite the similar surface nutrient field imposed on all of the models, predicted export production varies by more than a factor of two (from 8.3 to 19.9 Gt C per year), presumably reflecting the different rates of upper ocean circulation among the models. The mean export production, 14.4 Gt C per year, is similar to a previous estimate derived from satellite-based primary productivity and the f-ratio model of Laws et al. (2000). The spatial and temporal structure of the predicted export production also varies considerably among the models. Reasons for the differences and tracer-based approaches for constraining the export production distribution will be discussed.

Robbins, P.; et al. (1)

Where is the "Carbon Equator"?

1 Physical Oceanography Res. Div., Scripps Institution of Oceanography, Univ.of California, San Diego, 9500 Gilman Drive, Mailcode 0230, La Jolla, CA 92093-0230, probbins@ucsd.edu

ABSTRACT:
The postulated interhemispheric transport of carbon is a fundamental feature of the global carbon cycle and a primary motivation and benchmark for studies of meridional transport in both the atmosphere and ocean. There is, however, a fundamental dynamical mismatch between the ocean and the atmosphere regarding the effective equator for each system. In the atmosphere, the Intertropical Convergence Zone (ITCZ) marks the boundary between the atmosphere of the Northern and Southern Hemisphere. The ITZC is located where the upward lifting limbs of the northern and southern Hadley circulations meet and form an effective barrier limiting exchange of air between the hemispheres. Because a primary forcing mechanism of the Hadley Circulation is solar heating the ITZC migrates with season. Owing to the greater landmass in the northern hemisphere the annual mean position of the ITCZ is about 7 degrees N. In contrast, the dynamics of the tropical ocean circulation are strongly controlled by adiabatic vorticity dynamics, resulting in a circulation tightly locked to the true equator. The difference between the location of the effective equator in atmosphere and ocean complicates interpretation of the interhemispheric transport of carbon and may partially explain discrepancies in different estimates. Estimating the extent to which carbon "feels" the difference in the oceanic and atmospheric equator challenges current understanding of the mechanisms of interhemispheric transport in the atmosphere.

Roman, M. (1)

Why are there more mesozooplankton at HOT as compared to BATS?

1 roman@hpl.umces.edu

ABSTRACT:
Mesozooplankton growth rates were estimated for the Hawaiian (HOT) and Bermuda (BATS) ocean time-series stations using the empirical model of Hirst and Lampitt (1998) which predicts copepod growth rate from temperature and body size. Using this approach we derived seasonal and annual estimates of mesozooplankton production as well as rates of mesozooplankton ingestion and egestion using assumed growth and assimilation efficiencies for the period 1994 - 1997. Annual mesozooplankton production estimates at HOT (average 0.79 mol C m^-2 y^-1) were higher than production estimates at BATS (average 0.33 mol C m^-2 y^-1) due to both higher mesozooplankton biomass and higher estimated mesozooplankton individual growth rates. Annual primary production at the two sites was similar (average 14.92 mol C m^-2 y^-1 at HOT and 13.43 mol C m^-2 y^-1 at BATS). Thus, mesozooplankton production was a greater fraction of primary production at HOT (0.05) as compared to BATS (0.02). Mesozooplankton potentially contributed more to the gravitational flux of carbon at HOT, where the ratio of the average annual estimate of mesozooplankton fecal pellet carbon production / annual estimate of carbon flux at the base of the euphotic zone was 1.03 compared to the same ratio of 0.39 at BATS. Mortality estimates were similar to estimates ofomesozooplankton production when compared over the entire study period. The higher mesozooplankton biomass and derived rate parameters at HOT compared to BATS may be due to the more episodic nature of nutrient inputs at BATS which could result in mis-matches between increases in phytoplankton production and the grazing/production response by mesozooplankton. In addition, there is evidence to suggest that there are periodic blooms of gelatinous herbivorous macrozooplankton (salps) at BATS which may not be captured sufficiently by the monthly sampling program. Thus the gelatinous zooplankton would add to the overall grazing impact on the phytoplankton at BATS as well as the contribution of zooplankton to the gravitational flux of biogenic material via fecal pellet production.

Ryabchenko, V.A.; M.J.R. Fasham; V.A. Gorchakov; T.R. Anderson; & H.W. Ducklow

Results from a 3-D ecosystem model of the Arabian Sea

ABSTRACT:
The 3D Indian Ocean model of Ryabchenko et al. (1998) has been developed to include DOM cycling, photoadaptation of phytoplankton cells, nitrification and denitrification processes. Seasonal cycles of phytoplankton and nutrients in the euphotic zone are simulated well in the coastal upwelling areas of Somalia and Oman. In the central Arabian Sea the model works well during the inter-monsoon periods and the SW monsoon, but there are discrepancies between model and data during the NE monsoon that are presently unexplained. Comparison is made with predicted DOM and bacterial production and JGOFS data. The annual averages of semi-labile DOC agree well with recent compilations and reflect in the intensive mixing in the Arabian Sea due to the two monsoonal seasons.

Sabine, Christopher L. (1); R.A. Feely (2); R. Wanninkhof (3); R.M. Key (4); G.C. Johnson (2); F.J. Millero (5); K. Lee (3); Tsung-Hung Peng (3); A. Kozyr (6); J.L. Bullister (2); M.F. Lamb (2); and D. Greeley (2)

Global CO₂ synthesis

1 Joint Inst. for the Study of Atmosphere and Ocean, Univ. Wash., c/o NOAA/PMEL, 7600 Sand Point Way NE, Seattle, WA 98115, sabine@pmel.noaa.gov
2 NOAA/PMEL, 7600 Sandpoint Way NE, Seattle, WA 98115
3 NOAA/AOML, 4301 Rickenbacker Causeway, Miami, FL 33149
4 AOS Program, Princeton Univ., Forrestal Campus/Sayre Hall, Princeton, NJ 08544
5 Univ. Miami/ RSMAS, 4600 Rickenbacker Causeway, Miami, FL 33149
6 Carbon Dioxide Information Analysis Center, ORNL, Oak Ridge, TN 37831

ABSTRACT:
Between 1991 and 1996, carbon measurements were made on twenty-four WOCE/JGOFS/OACES cruises in the Pacific Ocean. Investigators from 15 different laboratories and 4 countries have analyzed at least two of the four measurable ocean carbon parameters (DIC, TAlk, fCO2, and pH).  Several different lines of evidence were used to examine the consistency of the Pacific data including comparison of calibration techniques, results from certified reference material analyses, precision of at-sea replicate analyses, agreement between shipboard analyses and replicate shore-based analyses, comparison of deep water values at locations where two or more cruises overlapped or crossed, consistency with other hydrographic parameters, and internal consistency with multiple carbon parameter measurements.  With the adjustments proposed here, the data were combined to generate a Pacific Ocean data set with over 36,000 unique sample locations analyzed for at least two carbon parameters.  The best data coverage was for DIC, which has an estimated overall accuracy of ~3 mmol kg^-1 after the proposed adjustments.  TAlk, the second most common carbon parameter, has an estimated overall accuracy of ~5 mmol kg^-1.  These data have been used to estimate the distribution of anthropogenic CO₂in the Pacific using the C* technique.  These distributions will be discussed and compared with 3-D global carbon model estimates.  Preliminary investigations suggest that the model- and data-based estimates of anthropogenic CO₂ agree reasonably well.  The data-based estimate of the total anthropogenic CO₂ inventory for the Pacific (45 Pg C), for example, is encompassed by the range of model-based estimates (45-60 Pg C).  A more detailed examination of the various estimates reveals interesting differences in the distribution of anthropogenic CO₂ in the oceans.  With the completion of the Pacific synthesis, we are now focusing on a synthesis of Atlantic data from the 1990s.  Preliminary results from this work will be presented along with a discussion of the significance of the new Atlantic synthesis.

Sambrotto, R.N. (1); G. Broström (2) and M.-L. Dickson (3)

Nitrogen uptake and net community production using JGOFS data and 1-D modeling

1 Lamont-Doherty Earth Observatory, 61 Rt. 9W / Palisades, NY 10964, sambrott@ldeo.columbia.edu
2 Göteborg Univ., Earth Science Centre, Dept of Oceanography Box 460, S-405 30 Göteborg, Sweden
3 Marine and Atmospheric Chemistry, Univ. of Rhode Island, Graduate School of Oceanography, Bay Campus, Narragansett, RI 02882

ABSTRACT:
Surface water budgets have been shown to exhibit variable ratios of carbon to nitrogen consumption and ratios both below and above those typical of particulate organic material have been recorded during different stages of bloom development. Elevated ratios of carbon to nitrogen consumption can increase the sink for atmospheric carbon by extending the period of surface water carbon dioxide deficits. We suggest that changes in carbon and nitrogen uptake ratios could be the result of a lag between the uptake and reduction of nitrate by eukaryotic algae early in the bloom sequence and the somewhat later development of a diverse and efficient recycling community. Here, we use a 1-D model to investigate how the hypothesized recycling offset can effect the observed changes in carbon and nitrogen consumption during bloom development. We use a simple PZN model with the addition of a minimum number of new pools to explicitly account for dissolved organic matter and bacterial growth. Model results in several biogeochemical domains of the North Atlantic will be discussed.

Sarmiento, J. (1); et al.

A new estimate of the CaCO₃ to organic carbon export ratio

1 Program in Atmospheric and Oceanic Sciences, Princeton Univ., Princeton, NJ, USA, 08544, jls@splash.princeton.edu

ABSTRACT:

Sarmiento, J. (1); R. Barber (2), L. Bopp (3); S. Doney (4); A.C. Hirst (5); J. Kleypas (4); R. Matear (1); U. Mikolajewica (); P. Monfray (1); J. Orr (); S. Spall (); R. Slater (1); and R. Stouffer ()

Inferred response of ocean ecosystems to climate warming

1 Program in Atmospheric and Oceanic Sciences, Princeton Univ., Princeton, NJ, USA, 08544, jls@splash.princeton.edu
2 Duke Univ. Marine Lab., 135 Duke Marine Lab Road, Beaufort, NC 28516-9751
3 Max Planck Inst. Biogeochemistry, Kahlaische Strasse 10., D-07745 Jena, GERMANY
4 National Center for Atmospheric Research, Boulder, CO.
5 DAR, CSIRO, AUSTRALIA

ABSTRACT:
We examine six different coupled climate model simulations of future climate change to determine the range of behavior of those aspects of global warming simulations that are relevant to the ocean biological response. The overall response we infer from examining the physical response of the ocean to global warming is decreased biological production in low latitude upwelling regions and the poleward half of the subtropical gyres, and increased production in the polar regions. Wind-driven upwelling is the dominant mechanism of nutrient supply along the highly productive western margins of the continents and in the equatorial regions. Models predict widely varying results, but the general tendency is towards a reduction of upwelling in these regions, from which we would infer that biological production would decrease. The dominant mechanism for nutrient supply in the subtropical gyres poleward of the subtropical convergence zone is wintertime convection. These regions tend to become more stratified with future climate change, which reduces the depth of wintertime mixing. The expectation, supported by model predictions, is that this would result in reduced biological production. The polar regions generally have a high supply of nutrients due to upwelling and convection, but can suffer from low productivity due to low light supply in deep mixed layers. Increased stratification, which occurs in most models, though with a complex pattern, would thus tend to increase biological production. Exceptions to this would be where low levels of micronutrient supply by dust limit the production, such as is thought to be the case in the Southern Ocean and North Pacific, or where the decreased mixing reduced the nutrient supply to less than the potential biological uptake. The mechanism of nutrient supply to regions between the equatorial upwelling bands and subtropical convergence is poorly understood and poorly simulated in most models. It is difficult to determine how these regions will respond to future climate change. The changes that we have described will also very likely lead to changes in ocean ecology as the major phytoplankton groups such as diatoms, coccolithophorids, flagellates, Phaeocystis, and nitrogen fixers, are sensitive to water column stratification as well as nutrient content.

Siegel, Dave (1); Jim Yoder (2); Scott Doney (3); and Maureen Kennelly (2)

Satellite views of the North Atlantic spring bloom

1 UCSB, davey@bren.ucsb.edu
2 URI
3 NCAR

ABSTRACT:
The North Atlantic Ocean has long been recognized to be one of the most productive regions of the world ocean.  Large seasonal changes in upper ocean mixing brings new nutrients into the upper layers during the winter.  The rapid biological incorporation of these nutrients leads to the spring bloom and it thought to be an important contributor to export flux in the North Atlantic basin.  Here, we use satellite ocean color imagery, regional circulation model output and available field data sets to diagnose the characteristics of the spring bloom for the North Atlantic Ocean.  A primary goal of this work is to assess the applicability of Sverdrup's [1953] spring bloom hypothesis to explaining seasonal changes in basin scale chlorophyll biomass.

Takahashi, Taro (1)

Global sea-air CO₂ flux based on climatological surface ocean pCO₂, and biological utilization of CO₂ in surface ocean waters

1 Lamont Doherty Earth Observatory of Columbia University, Palisades, NY 10964
in collaboration with:
Stewart C. Sutherland and Colm Sweeney, LDEO, Palisades, NY
Alain Poisson and Nicolas Metzl, Laboratoire de Biogeochimie et Chimie Marines, Universite Pierre et Marie Curie, Paris, FRANCE
Bronte Tilbrook, Antarctic CRC and CSIRO Mar. Res., Hobart, AUSTRALIA
Nicolas Bates, Bermuda Biol. Station for Res., BERMUDA
Rik Wanninkhof, AOML/NOAA, Miami, FL
Richard A. Feely and Christopher Sabine, PMEL/NOAA, Seattle, WA
Jon Olafsson, Univ. Iceland and Mar. Res. Inst., Reykjavik, ICELAND
Yukihiro Nojiri, Global Warming Mechanism Lab., Nat. Inst. Environ, Studies, Tsukuba, JAPAN

ABSTRACT:
Based on about 940,000 measurements of surface water pCO₂ obtained since the International Geophysical Year of 1956-59, the climatological, monthly distribution of pCO₂ in the global surface waters representing mean non-ElNino conditions has been obtained with a spatial resolution of 4° x 5° for a reference year 1995. The monthly and annual net sea-air CO₂ flux has been computed using the NCEP/NCAR 41-year mean monthly wind speeds. An annual net uptake flux of CO₂ by the global oceans has been estimated to be 2.2 (+22% or -19%) PgC yr^-1 using the (wind speed)² dependence of the CO₂ gas transfer velocity of Wanninkhof (1992). The errors associated with the wind speed variation have been estimated using one standard deviation (about ± 2 m sec^-1) from the mean monthly wind speed observed over each 4° x 5° pixel area of the global oceans. The new global uptake flux obtained with the Wanninkhof (wind speed)² dependence is compared with those obtained previously using a smaller number of measurements, about 250,000 and 550,000 respectively, and are found to be consisten within ± 0.2 PgC yr^-1. This estimate for the global ocean uptake flux is consistent with atmospheric CO₂ and oxygen concentrations during the 1990s (Keeling et al., 1996; Battle et al., 2000). However, if the (wind speed)³ dependence of Wanninkhof and McGillis (1999) is used instead, the annual ocean uptake as well as the sensitivity to wind speed variability is increased by about 70%.

A zone between 40° and 60° latitudes in both the northern and southern hemispheres is found to be a major sink for atmospheric CO₂.  In these areas, poleward flowing warm waters meet and mix with the cold subpolar waters rich in nutrients.  The pCO₂ in the surface water is decreased by the cooling effect on warm waters and by the biological drawdown of pCO₂ in subpolar waters.  High wind speeds over these low pCO₂ waters increase the CO₂ uptake rate fo the ocean waters.

The pCO₂ in surface waters of the global oceans varies seasonally over a wide range about 60% above and below the current atmospheric pCO₂ level of about 360 uatm.  A global map showing the seasonal amplitude of surface water pCO₂ is presented.  The effect of biological utilization of CO₂ is differentiated from that of seasonal termperature changes using seasonal temperature data.  The seasonal amplitude of surface water pCO₂ in high latitude waters located poleward of about 40° latitude and in the equatorial zone is dominated by the biology effect, whereas that in the temperate gyre regions is dominated by the temperature effect.  These effects are about 6 months out of phase.  Accordingly, along the boundaries between these two regimes, they tend to cancel each other, forming a zone of small pCO₂ amplitude.  Small areas such as the northwestern Arabian Sea and the eastern equatorial Pacific, where seasonal upwelling occur, exhibit intense seasonal changes in pCO₂ due to the biological drawdown of CO₂ .

The net biological CO₂ utilization within the mixed layer has been estimated using the seasonal amplitude of surface water pCO₂ (normalized to the mean annual temperature in each pixel area), the Revelle factor (evaluated for each pixel area), the seasonal mean mixed layer depth, and the sea-air CO₂ flux.  This method is valid when the vertical mixing of deep waters is negligibly small during early half of phytoplankton growth period, and accordingly is not applicable for the wind-driven upwelling areas such as the Arabian Sea and eastern equatorial Pacific.  The CO₂ utilization rates thus estimated are broadly consistent with the export flux estimated by Laws et al. (2000) using the SeaWiFS ocean color data and food web models.

Thompson, L. (1)

Mechanisms controlling the biological pump and CO₂ uptake rates in the North Pacific.

1 School of Oceanogr., Univ. Washington, Box 357940, Seattle, WA 98195, luanne@ocean.washington.edu

ABSTRACT:
The goal of this proposal is to quantify the physical mechanisms controlling the rates of biological carbon export and the uptake of anthropogenic CO₂ in the North Pacific Ocean.  We propose to use a basin-wide, isopycnal general-circulation model (GCM) as the basis of our analysis.  The model is operational and has been used to evaluate mechanisms of subduction and water mass formation in the North Pacific and is currently being tested using CFCs.

Our strategy is to first, incorporate bomb ¹⁴C into the model to validate its advective and diffusive fields. By adding this carbon-based tracer we will have verified the model with both CFCs and ¹⁴C-two tracers with different boundary conditions and time histories. Next, the three-dimensional distribution of biological carbon export and remineralization rates will be determined by using the observed distributions of several biological productivity tracers, specifically NO₃, PO₄, (and their dissolved organic counterparts DON and DOP), O₂/Ar/N₂ and the 1¹³C/¹²C of the dissolved inorganic carbon (DIC). We will then simulate the anthropogenic CO₂ perturbation and utilize independent reconstructions of the anthropogenic DIC and ¹³C/¹²C changes in the North Pacific to validate the model's predictions. Finally, we will examine the model response to decadal variability in forcing.

There are several important reasons to choose the North Pacific Ocean as the site for a basin-scale modeling study. There are three JGOFS time-series sites that yield observed carbon fluxes and anthropogenic CO2 signals to compare to model predictions. The lack of deep-water formation at its poleward boundary simplifies the meridional circulation compared to the North Atlantic and southern oceans and justifies shorter model runs.  Finally, the North Pacific has been the site of intensive chemical tracer measurements, specifically CFCs, ¹⁴C and ¹³C/¹²C, over the last 10 years.

We will focus our modeling efforts on quantifying physical processes that likely control tracer, nutrient and CO₂ fluxes in the upper ocean: 1) equatorial-subtropical and subtropical-subpolar exchange, 2) thermocline ventilation and isopycnal transport both with and without eddies, and 3) diapycnal mixing and the influence of eddies in the upper thermocline, and 4) the impact of decadal variability on biological carbon export.

Paul Tréguer (1); Philippe Pondaven (1); David M. Nelson (2); Mark A. Brzezinski (3); Stéphane Blain (1); and Rudolph Corvaisier (1)

The sub-surface chlorophyll maximum in the seasonal ice zone (Southern Ocean): its importance for the production of carbon and biogenic silica

1 Université de Bretagne Occidentale, Institut Universitaire Européen de la Mer, UMR 6539, Brest-France, Paul.Treguer@univ-brest.fr
2 Oregon State Univ., College of Ocean Atmospheric and Earth Sciences, Corvallis, Oregon, USA
3 Univ. California at Santa Barbara, Santa Barbara, California, USA

ABSTRACT:
The inability of satellite sensors to detect frequently occuring sub-surface chlorophyll patches has been recently inferred to explain the discrepency between the annual estimates of export production in the Southern Ocean (SO), derived from satellite based productivity estimates and from outputs of inverse models.

The presence of a sub-surface maximum (SCM) is a common feature to the oligotrophic systems (as shown for instance at the Bermuda Atlantic Time Series Station). Chronic nutrient limitation during the productive season usually explains the build up of this SCM below the well mixed layer, i.e. within the nutricline - where sufficient light still permits photosynthesis. During summer numerous French and Australian cruises have detected SCMs extending to the whole seasonal ice zone (SIZ) of the Indian sector of the SO. In January-February 1994 a SCM has been observed in the temperature minimum layer of the SIZ (62°E transect: 66°S-58°S and station M3: 63°S 71°E). The specific uptake rates of carbon and of silicic acid were generally suboptimal and not significantly different in the SCM layer (range: 0.02-0.11 d^-1 and 0.02-0.06 d^-1, respectively) and in the mixed layer (range: 0.07 - 0.16 d^-1 and 0.04-0.09 d^-1, respectively). Non-limiting amounts of major nutrients (N, P, Si) suggest that the growth of phytoplankton is limited by other factors, including top-down and/or bottom-up control. In this SCM diatoms were significant contributors to the biomass and the primary production. The SCM accounted for between 30-60% of both the primary production and the biogenic silica production. Here we use SO-JGOFS data and a 1-D coupled biological-physical model to : (1) investigate the different scenarios that may account for the formation of SCMs, and (2) infer the contribution of SCMs to the annual production of organic carbon and biogenic silica within the SIZ of the SO.

Wiggert, Jerry(1)

Processes controlling interannual variations in wintertime primary productivity in the central Arabian Sea

1 ESSIC, Univ. Maryland, College Park, MD 20742-2465, jwiggert@essic.umd.edu

ABSTRACT:
Three years of ocean color observations obtained by SeaWiFS reveal significant interannual variation in surface chlorophyll concentrations in the central Arabian Sea during the Northeast (winter) monsoon (NEM). Consistent with previous findings in the literature, no obvious relation to sea surface temperature is apparent. A strong relation with interannual variability in thermocline depth has been established using an interannually forced ocean general circulation model (OGCM). This relation consists of reduced chlorophyll concentration associated with a deeper thermocline. Deeper winter convection is generally associated with higher nutrient concentrations and therefore higher phytoplankton biomass. Both in-situ observations from the U. S. JGOFS Arabian Sea Expedition and net wintertime nutrient entrainment estimated with the OGCM simulation indicate that mixed layer concentrations are always sufficiently high to be non-limiting. This raises two questions. What process(es) check phytoplankton growth? What leads to the noted relationship between deeper thermocline and reduced chlorophyll concentration? A prominent feature of the NEM is the large-amplitude diurnal cycle of the mixed layer that is evident in moored temperature time series. We hypothesize that the nighttime penetration of this diurnal mixing, which is defined by the interannually varying thermocline depth, determines the magnitude of phytoplankton biomass that will be retained in the euphotic zone for the following photoperiod. This daily dilution acts to check the accumulation of phytoplankton biomass and prevents a full phytoplankton bloom. A simple 1-D model has been developed to quantify this process. An excellent correspondence exists between model-predicted mixed layer chlorophyll concentration as it varies with thermocline depth and the coincident SeaWiFS observations. The results presented here summarize the body of research documented in Wiggert et al., 2001.
(poster)

Yoder, James A. (1) and Maureen A. Kennelly (1)

Interannual variability of global satellite chlorophyll patterns

1 Graduate School of Oceanography, URI, So. Ferry Rd., Narragansett, RI 02882,

ABSTRACT:
Satellite remote sensing of ocean color, which began in 1978 with the launch of CZCS, provides basin scale measurements of chlorophyll concentration, an index of phytoplankton biomass.  Our goal is to use data from the four ocean color sensors (CZCS, OCTS, POLDER and SeaWiFS) to assess inter-annual variability and determine its causes. In this presentation, we will discuss results of the first three years of global SeaWiFS imagery. Our analyses are based on global imagery from 1998-2000 that are binned, averaged and smoothed on a 1 deg. X 1 deg. global grid and at a nominal 8-day resolution.  Results, which include the year (1998) of transition from El Niño to La Niña conditions, are presented in different ways to emphasize inter-annual variability by basin and region.

Zhang, Jia-Zhong (1)

The use of pH and buffer intensity to estimate the Redfield ratios in the ocean

1 Coop. Inst. Mar. Atmos. Studies, RSMAS, Univ. Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, zhang@aoml.noaa.gov

ABSTRACT:
pH of seawater is governed by the content of total carbon dioxide and ionic equilibria between hydrogen ion and various inorganic carbon species in seawater. Buffer intensity is defined as a measure of ability of seawater to accommodate addition of acid or base without appreciable pH change.  It can be calculated from pH and total carbon dioxide of seawater.  pH data in conjunction with buffer intensity can be used to quantify the carbon cycle in the ocean.  The total amount of acid that has been released or consumed by any biogeochemical processes can be calculated from the change in pH multiplied by buffer intensity of seawater, dC_H = d(ßpH).  This approach has been used to estimate the Redfield ratio in remineralization process in the Antarctic Intermediate Water in the South Pacific.  Based on the observational data (pH, total carbon dioxide, O₂ and nutrient measurements on P18 cruise), calculated elemental remineralization ratios are 173, 107 and 14.3 for O/P, C/P and N/P, respectively.  The dissolution of calcium carbonate accounts for 21.5% of carbon increased from the remineralization in the Antarctic Intermediate Water.