U.S.
JGOFS Synthesis & Modeling Project U.S.
JGOFS Synthesis & Modeling Project
Preprints
Preprint Access: submitted in press 2003 2002 2001 2000 1999
1st SMP
Special Issue in DSR II
Links to Existing Preprint
Servers
Abstracts
Bob
Key's list of Data Reports and References from the WOCE Radiocarbon Program,
which includes:
Chai F; Jiang M; Barber RT; Dugdale RC; Chao Y (in press) Interdecadal variation in the transition zone chlorophyll front, a physical-biological model simulation between 1960 and 1990 Journal of Oceanography 59(4): 461-475. :
ABSTRACT:
The North Pacific Transition Zone (NPTZ) is bounded by two oceanographic fronts at approximately 30-32$deg;N (Subtropical Front) and 42-45°N (SubarcticFront) in the central Pacific. The Transition Zone Chlorophyll Front (TZCF) is a biological front within the NPTZ that separates the low chlorophyll subtropicalgyres and the high chlorophyll subarctic gyres in the central Pacific Ocean. The interdecadal climate variability affects marine ecosystems in both the subtropicaland subarctic gyres, consequently the position of the TZCF. A three-dimensional physical-biological model has been used to study interdecadal variation of theTZCF using a retrospective analysis of a 30-year (1960-1990) model simulation. The physical-biological model is forced with the monthly mean heat flux andsurface wind stress from the Comprehensive Ocean Atmosphere Data Set (COADS). The modeled TZCF, operationally defined as the isopleth of 0.2 mg/m3 surface chlorophyll, is located between 26°N and 27°N in the central North Pacific duringthe winter and between 34°N and 35°N during the summer, which agrees with the seasonal migration patterns of the TZCF detected with the SeaWiFS surfacechlorophyll. The modeled winter mixed layer depth (MLD) shows the largest increase between 30°N and 40°N in the central North Pacific (150°E to 180°), with avalue of 40-60% higher (deeper mixed layer) during 1979-90 relative to 1964-75 values. In the subarctic gyre in both the northeast (Ocean Station Papa) andnorthwest Pacific (Oyashio region), the modeled winter MLD decreases by about 20% during the period of 1979-90 relative to 1964-75 levels. The winter Ekmanpumping velocity difference between 1979-90 and 1964-75 shows the largest increase located between 30°N and 45°N in the central and eastern North Pacific(180°to 150°W). In the subarctic northeast Pacific region including the Gulf of Alaska, The winter Ekman pumping velocity decreases during the period of1979-90, but its value increases in the northwest Pacific (Oyashio region) after the 1976-77 climatic shift. The modeled winter surface nitrate difference between1979-90 and 1964-75 shows increase in the latitudinal band between 30°N and 45°N from the west to the east (135°E-135°W), the modeled nitrateconcentration is about 10 to 50% higher in general during the period of 1979-90 relative to 1964-75 values depending upon locations. The increase in thewinter surface nitrate concentration during 1979-90 is caused by a combination of the winter MLD increase and the winter Ekman pumping enhancement afterthe 1976-77 climatic shift. The modeled nitrate concentration increase after 1976-77 lead to the primary productivity increase in the central North Pacific(30°N-40°N and 180°-140°W). Enhanced primary productivity after the 1976-77 climatic shift contributes higher phytoplankton biomass and therefore elevateschlorophyll level in the central North Pacific. Increase in the modeled chlorophyll expand the chlorophyll transitional zone and push the TZCF equatorward.Historical fishery catch data near the TZCF might yield some information to confirm the interdecadal migration patterns of the TZCF in the central North Pacific. :
Doney SC; Lindsay K; Moore JK. (in press) Global Ocean Carbon Cycling, in: M.J.R. Fasham, J. Field, T. Platt, and B. Zeitzschel (eds.), Ocean Biogeochemistry: A JGOFS Synthesis, Springer Verlag, , vol. , pp. .
ABSTRACT:
One of the central objectives of the Joint Global Ocean Flux Study (JGOFS) is to use data from the extensive field effort to improve and evaluate numericalocean carbon cycle models, models that will subsequently be used to better understand the present ocean state and predict past and potential future responsesto anthropogenic perturbations and climate change. Historically, ocean biological and chemical modelling has evolved along three related, though often distinct,paths: anthropogenic CO2 transient tracer uptake; biogeochemical cycles; and ecosystem dynamics. An important trend is the unification of these threeapproaches, leading ultimately to a coherent modeling framework linking ocean physics, biology and chemistry over a range of time and space scales. Substantialimprovements are underway on the current suite of numerical models to incorporate the major shifts in biogeochemical paradigms resulting from recent fieldstudies. Marine biogeochemical modeling is inherently data driven, and the JGOFS field data sets (time-series, process studies, and global survey) together withthe emerging satellite products are invaluable in two ways: the basis for new and improved, mechanistically based parameterizations of specific biogeochemicalprocesses; and the resource for testing the overall skill of integrated system models through detailed model-data comparisons. Here we present a selectiveoverview of the current state, future directions and major challenges for basin to global ocean carbon cycle modelling, drawing on examples primarily from theNCAR program. Several themes are highlighted including multi-element cycling and community structure, large-scale physical circulation, mesoscale space andtime variability, mass exchange between the open ocean and the atmosphere, land and coastal ocean, climate variability, and model-data evaluation and dataassimilation.:
Doney SC; Glover DM; McCue SJ; Fuentes M (2003) Mesoscale variability of SeaWiFS Satellite Ocean Color. Global patterns and spatial scales. J. Geophys. Res. 108(C2): 3024, doi:10.1029/2001JC000843.
ABSTRACT:
Using the semivariogram approach from geostatistics, we characterize for the first time the global patters of mesoscale (approx. 10-200 km and days to a fewweeks) ocean biological variability. The magnitude of the variability and length scale fields are reported for a full year of SeaWiFS ocean color data. The analysisshows a number of coherent geographical patters across a wide range of biological and physical environments. When normalized to the mean chlorophyll as acoefficient of variation, the resolved mesoscale variance (relative sill) is approximately uniform in the tropics and subtropics (0.1-0.2), increasing to 0.3-1.0 inupwelling (Equatorial Pacific, coastal) and subpolar/polar regions, approximately scaling with the mean chlorophyll concentration. The unresolved variance(nugget), which includes submesoscale geophysical variability as well as instrument/algorithm noise, is inversely correlated with mean chlorophyll concentrationin the oligotrophic subtropics (an indication of instrument/algorithm noise) reducing to a low background value (0.1) elsewhere. Mesoscale variance dominatesocean color with strong seasonality. The mesoscale spatial scale (range) is approximately zonal, with values of 200-350 km near the Equator to less than 50 kmclose to the poles similar to the physical deformation radius. Our results demonstrate the global gernerality of previous local and regional findings that physicalmesoscale turbulence governs biological spatial scales both directly (e.g. stirring) and indirectly (e.g. nutrient injection). The same is not true, at least directly, forthe (normalized) magnitude of the biological variability, which is not well correlated with mesoscale eddy kinetic energy and in particular does not show thecharacteristic west-east asymmetry associated with the western boundary currents. Regional deviations from these large-scale variance and spatiallength-scales trends, for example lower range and higher resolved variance in coastal upwelling regimes, are explicable by the characteristics of thebiological-physical interaction in those environments. :
McGillicuddy DJ; Kosnyrev VK (2001) Dynamical interpolation of mesoscale flows in the Topex/Poseidon diamond surrounding the U.S. JGOFS Bermuda Atlantic Time-series Site. J. Geophys. Res. 106(C8): 16,641-16,656. :
ABSTRACT:
An open boundary ocean model is configured in a domain bounded by the four Topex/Poseidon (T/P) ground tracks surrounding the U.S. JGOFS Bermuda AtlanticTimes-series (BATS) site. This implementation facilitates prescription of model boundary conditions directly from altimetric measurements (both T/P and EuropeanResource Satellite ERS-2). The expected error characteristics for a domain of this size with periodically updated boundary conditions are established withidealized numerical experiments using simulated data. A hindcast simulation is then constructed using actual altimetric observations during the period October1992 through September 1998. Quantitative evaluation of the simulation suggests significant skill. The correlation coefficient between predicted sea levelanomaly and ERS observations in the model interior is 0.89; that for predicted versus observed dynamic height anomaly based on hydrography at the BATS siteis 0.73. Comparison with the idealized experiments suggest that the main source of error in the hindcast is temporal undersampling of the boundary conditions. The hindcast simulation described herein provides a basis for retrospective analysis of BATS observations in the context of the mesoscale eddy field.:
Chai F; Dugdale RC; Peng T-H; Wilkerson FP; Barber RT (2002) One Dimensional Ecosystem Model of the Equatorial Pacific Upwelling System, PartI: Model Development and Silicon and Nitrogen Cycle. Deep-Sea Res. II 49: 2713-2745.
ABSTRACT:
A one-dimensional ecosystem model was developed for the equatorial Pacific upwelling system,and the model was used to study nitrogen and silicon cycle inthe equatorial Pacific.The ecosystem model consisted of 10 components (nitrate, silicate, ammonium, small phytoplankton, diatom, micro-andmeso-zooplankton,detrital nitrogen and silicon, and total CO2). The ecosystem model was forced by the area-averaged (5°S-5°N. 90°W-180°, the Wyrtki Box)annual mean upwelling velocity and vertical diffusivity obtained from a three-dimensional circulation model. The model was capable of reproducing thelow-silicate, high-nitrate, and low-chlorophyll (LSHNLC)conditions in the equatorial Pacific. The linkage to carbon cycle was through the consumption ofassimilated nitrate and silicate (i.e. new productions). Model simulations demonstrated that low-silicate concentration in the equatorial Pacific limits production ofdiatoms, and it resulted in low percentage of diatoms, 16%, in the total phytoplankton biomass. In the area of 5°S-5°N and 90°W-180°, the model produced anestimated sea-to-air CO2 flux of 4.3 mol m-2 yr-1, which is consistent with the observed results ranging of 1.0-4.5 mol m-2 yr-1. The ammonium inhibition playedan important role in determining the nitrogen cycle in the model. The modeled surface nitrate concentration could increase by a factor of 10 (from 0.8 to 8.0 mmolm-3) when the strength of the ammonium inhibition increased from psi=1.0 to 10.0 (mmol m-3). The effects of both micro-and meso-zooplankton grazing weretested by varying the micro-and meso-zooplankton maximum grazing rates, G1max and G2max. The modeled results were quite sensitive to the zooplanktongrazing parameters. The current model considered the role of iron implicitly through the parameters that determine the growth rate of diatoms. Severaliron-enrichment experiments were conducted by changing the parameter alpha (the initial slope of the photosynthetic rate over irradiance at low irradiance),Ksi(OH)4 (half-saturation concentration of silicate uptake by diatom), and mu2max (the potential maximum specific diatom growth rate) in the regulation terms ofsilicate uptake by diatom. Within the first 5 days in the modeled iron-enrichment experiment,the diatom biomass increased from 0.08 to 2.5 mmol m-3, more than afactor of 30 increase. But the diatom populations crashed 2 weeks after the experiment started, due to exhaustion of available silicate and increasedmesozooplankton population. The modeled iron-enrichment experiments produced several ecological behaviors similar to these observed during the IronEx-2. :
Christian JR; Verschell MA; Murtugudde R; Busalacchi AJ; McClain CR (2002) Biogeochemical modelling of the tropical Pacific Ocean. I. Seasonal and interannual variability. Deep-Sea Res. II 49(1-3): 509-543.
ABSTRACT:
A coupled physical-biogeochemical model has been developed in order to study physical-biological interactions in the tropical Pacific Ocean onseasonal-to-interannual timescales. The model incorporates both iron- and-nitrogen limited phytoplankton growth, and succession of phytoplankton size classesin accordance with the ecumenical iron hypothesis. The model shows a strong El Niño Southern Oscillation component to phytoplankton variability in thecentral equatorial Pacific over the period 1980-1998. It is possible that this mode is more dominant in the model than in nature, although the correlation ofmodelled and observed chlorophyll in this region is strong. The model results show that interannual variability dominates over the mean seasonal cycle for bothphysical and biogeochemical fields, with the exception of undercurrent transport west of the dateline. Physical and biogeochemical fields show consistentseasonal phasing among the four El Niño events simulated, although there is variability in the magnitudes and exact timing. Nutrient concentration anomalies atconstant temperature in the thermocline of the central equatorial Pacific appear to be largely advected from the west, and the strong seasonal cycle of theequatorial undercurrent in the west introduces a significant annual component to the variability of nutrient concentrations at longitudes where the mean seasonalcycle of the local physical forcing is negligible. The biogeochemical model maintains realistic nutrient pools over the time scales required for interannualsimulation, and responds in a realistic fashion to changing upper ocean hydrography and circulation. The model is quite sensitive to the temporal resolution of thewind forcing, which introduces additional uncertainty into the validation and prediction of biogeochemical fields. :
Christian JR; Verschell MA; Murtugudde R; Busalacchi AJ; McClain CR (2002) Biogeochemical modelling of the tropical Pacific Ocean. II. Iron biogeochemistry. Deep-Sea Res. II, 49(1-3): 545-565 .
ABSTRACT:
A coupled physical-biogeochemical model of the tropical Pacific Ocean with simultaneous iron and nitrogen limitation was developed in order to study questionsof iron biogeochemistry, its effects on upper ocean production, and ultimately the biogeochemical cycles of the other elements. The model results suggest thatiron limitation is ubiquitous in the equatorial Pacific, and extends further west than is generally believed unless there are significant inputs of geothermal iron atquite shallow depths. Most model parameters (e.g., iron solubility, scavenging rates, Fe:N ratios) must be near the limit of their generally accepted range ofvalues in order to prevent elevated surface nitrate concentrations from spreading further into the warm pool than is observed. Transport of geothermal iron in theequatorial undercurrent (EUC) provides a possible mechanism for limiting surface nitrate in the warm pool, but the source must be near the upper boundary of theEUC to provide iron to the surface west of the dateline. Accumulations of ammonium in the western Pacific appear to result from the exhaustion of iron in upwelledwater before nitrogen, and are highly consistent with field observations. The realism of the simulation is limited primarily by lack of information about theabundance and distribution of dissolved iron; the magnitude and distribution of the aeolian iron flux and the assumption of constant Fe:N ratios are also importantsources of uncertainty. The sensitivity of the simulation to the way that iron is initialized in the western Pacific thermocline emphasizes the importance of theequatorial undercurrent throughout the tropical Pacific and the need for iron observations in this region. :
Doney SC; Hecht MW (2002) Antarctic bottom water formation and deep water chlorofluorocarbon distributions in a global ocean climate model. J. Phys. Oceanogr. 32: 1642-1666.
ABSTRACT:
The ocean distributions of chlorofluorocarbons (CFCs) have been measured extensively in order to determine the mechanisms, rates, and pathways associatedwith thermohaline deep water formation. Here we compare model temperature, salinity and CFC-11 fields from the NCAR global ocean climate model againstobservations with emphasis on the patterns of Antarctic Bottom Water (AABW) production, properties, and circulation in the Southern Ocean. The model controlsimulation forms deep water as observed in both the Weddell and Ross Seas, though not along other sectors of the Antarctic coast. Examination of the deepwater CFC-11 distribution, total inventory, and profiles along individual observational sections demonstrate that the decadal-scale deep water ventilation in themodel Southern Ocean is both too weak and too restricted to the Ross and Weddell Sea source regions. A series of sensitivity experiments is conducted todetermine the factors contributing to these deficiencies. The incorporation of a simple bottom boundary layer (BBL) scheme leads to only minor reductions inoverall model-data error. The limited impact of the BBL may reflect in part other model large-scale circulation problems, for example the lack of salineCircumpolar Deep Water along the Antarctic slope, and the coarse vertical resolution of the model. The surface boundary conditions in the permanent sea icecovered regions are a more major factor, leading to inadequate formation of dense, cold and relatively saline shelf waters, the precursors of AABW. Improvedmodel-data agreement is found by combining the BBL parameterization with reasonably small adjustments in the surface restoring salinities on the Weddell andRoss Shelves, justified by undersampling of winter conditions in standard climatologies. The resulting changes in deepwater properties and circulation aresomewhat similar to the effect of coupling with an active sea ice model. :
Dugdale RC; Barber RT; Chai F; Peng T-H; Wilkerson FP (2002) One Dimensional Ecosystem Model of the Equatorial Pacific Upwelling System, Part II: Sensitivity Analysis and Comparison with JGOFS EqPac Data. Deep-Sea Res. II 49: 2747-2768 .
ABSTRACT:
A one-dimensional model ofthe equatorial Pacific upwelling ecosystem that incorporates two phytoplankton components,two grazers,and three nutrients, Si(OH)4,NO3, and NH4 (Chai et al.,Deep-Sea Research II (2002) 2713-2745), was designed to consider the effects of Si(OH)4 limitation on the diatom growth andecosystem functioning. Model output was obtained for a range of source concentrations of Si(OH)4, 3-15 mmol m-3, coinciding with the range measured at 120 mdepth during JGOFS EqPac. NO3 was held at 12 mmol m-3, reflecting the relatively greater concentrations of NO3 compared to Si(OH)4 in the JGOFS data. Themodel was shown to function as a chemostat-like system with the loss rates, provided largely from zooplankton grazing, controlling growth rates of thephytoplankton. When different source concentrations of Si(OH)4 were applied, surface concentrations of Si(OH)4 varied within a narrow range compared to NO3as would occur in a chemostat with limiting Si(OH)4 and non-limiting NO3 in the feed water. Vertical profiles of nutrients compared well with field data. Modelresults are compared with field data for new and total nitrogen production and export of N, Si, and C, and with other models, although none consider Si(OH)4specifically. The model suggests that the stability of the equatorial system with its narrow range of biological and chemical variables is conferred by the action ofdiatoms providing food for mesozooplankton whose grazing also depletes the picoplankton. Diatoms increase with source Si(OH)4 concentrations, andpicoplankton population and NO3 consumption decrease, resulting in a maximum surface TCO2 and increased CO2 flux to the atmosphere at intermediate sourceSi(OH)4 concentrations. Diatoms function in the equatorial system as a silica pump to export silica. This means that sedimented biogenic silica under theequatorial upwelling area should be viewed as an amplifier of changes in surface properties, with important consequences to paleoequatorial productivity.:
Dugdale RC; Wischmeyer AG; Wilkerson FK; Barber RT; Chai F; Jiang M; Peng T-H (2002) Source of meridional asymmetry of nutrients to the equatorial upwelling ecosystem and modeling of the impact on ocean-atmosphere CO2 flux. Deep-Sea Res. II 49: 2515-2531.
ABSTRACT:
Si(OH)4, NO3, and TCO2 are shown to be distributed asymmetrically in a north/south direction about the equatorial Pacific using data from WEPOCS III andJGOFS EqPac cruises. Equatorial Si(OH)4 concentrations are shown to be the product of both geochemical and physical interactions with chemical processes,occurring in at least three regions remote from the equatorial Pacific, and physical delivery processes from the equatorial undercurrent (EUC) to the surface layervarying over a range of time scales. The EUC was partitioned into upper and lower portions, the upper providing source water to the central upwelling area andthe lower crossing the Pacific without upwelling and thought to reenter the surface along the coast of Peru and to the eastern equatorial upwelling area. Thesource waters from the North Pacific, the north equatorial countercurrent (NECC) and from the South Pacific, the New Guinea coastal undercurrent (NGCUC) alsowere partitioned according to source for the upper and lower EUC. Mean concentrations and ranges of nutrients for each source partition were obtained fielddata. Current flow and advective data output from a 3-D physical model were used with the field nutrient data to calculate nutrient fluxes into the EUC. Althoughthe in flow ofwater from the north and south were approximately equal, the stronger asymmetric distribution of Si(OH)4 compared to NO3 resulted in identifying theSouth Pacific source as only 30% of the total supply of Si(OH)4 to the EUC and the cause ofa low Si(OH)4:NO3 condition. These results suggest a couplingbetween Southern Ocean productivity, equatorial productivity, and the efflux of CO2 to the atmosphere from the equatorial upwelling system. :
Ianson D; Allen SE (2002) A two-dimensional nitrogen and carbon flux model in a coastal upwelling region. Global Biogeochem. Cycles 16(1): 10.1029/2001GB001451..
ABSTRACT:
Coastal upwelling regions are associated with high primary production and disproportionately large fluxes of organic matter relative to the global ocean. However,coastal regions are usually homogenized in global ocean carbon models. We have developed a carbon and nitrogen flux model including all major processes bothwithin and below the euphotic zone over seasonal to decadal timescales for coastal upwelling regions. These fluxes control surface pCO2. The model is applied tothe west coast of Vancouver Island, Canada (~49N, 126W). Net annual air-sea CO2 exchange and export flux of inorganic and organic carbon and nitrogen fromthe system to the rest of the ocean are estimated for different model scenarios. Model sensitivities are discussed. Results show strong biological drawdown ofpCO2 during summer and atmospheric CO2 invasion. However, this invasion is nearly balanced by gas evasion during winter. Therefore the region is a muchsmaller sink of atmospheric CO2 (6 g C m-2 yr-1, or equivalently 200 kg C yr-1 per m coastline) than the summer season predicts. More significantly, there is alarge flux of inorganic carbon (3 x 104 kg C yr-1 per m coastline) from intermediate depth ocean water to the surface ocean via the coastal system compared to asmall export of organic carbon (all dissolved) (2 x 103 C yr-1 per m coastline) back into the lower layer of the open ocean. Thus we suggest that the dominanteffect of coastal upwelling on the global ocean is providing a conduit for inorganic carbon to the surface ocean. :
Hofmann EE; Friedrichs MAM (2002) Predictive modeling for marine ecosystems. , in: Robinson, A.R.; McCarthy, J.J.; Rothschild B.J. (eds.), The Sea, John Wiley and Sons, Inc., NY, vol. 12, pp. 537-565.
ABSTRACT:
none:
Lierheimer LJ; Banse K (2003) Seasonal and interannual variability of phytoplankton pigment in the Laccadive (Lakshadweep) Sea as observed by the Coastal Zone Color Scanner. Proc. Indian Acad. Sci. (Earth Planet. Sci.) 111(2): 163-185 .
ABSTRACT:
Based on Coastal Zone Color Scanner data from November 1978 through December 1981, the seasonal cycle of phytoplankton pigment in the upper part of theeuphotic zone is established for the offshore Laccadive Sea. Year-round, the pigment content is low and the seasonal range is small, following the pattern of thenutrient-poor Arabian Sea to the west. Apparently, indigenous phytoplankton blooms are absent. July and August, however, were poorly studied because ofcloud cover. Interannual differences during the northeast monsoon and the spring intermonsoon periods are minor. The abundant phytoplankton caused by theupwelling off India during the southwest monsoon remains essentially restricted to the shelf, but there are occasional large, zonal outbreaks into the LaccadiveSea, as well as others advected to the south of India. Visual inspection of the raw CZCS scenes for June through November 1982-1985, with almost no datauntil August or even September, shows such outbreaks of pigment-rich water to be common. Inspection of monthly SeaWiFS images for 1997 through part of2001 confirms the absence of indigenous phytoplankton blooms. :
Doney SC; Glover DM (2001) Ocean process tracers: modelling the ocean carbon system., in: Steele and K. Turekian (ed.), Encyclopedia of Ocean Sciences, Academic Press, London, UK, vol. 4, pp. 1929-1935.
ABSTRACT:
none:
Friedrichs MAM; Hofmann EE (2001) Physical control of biological processes in the central equatorial Pacific Ocean. Deep-Sea Res. I 48 : 1023-1069 .
ABSTRACT:
A five-component (phytoplankton, zooplankton, ammonium, nitrate, detritus) physical-biological model was developed to investigate the effects of physicalprocesses on daily to interannual time scales, on the lower trophic levels of the central equatorial Pacific. Many of the biological processes included in theecosystem model respond to environmental fluctuations with time scales between 1 and 10 d, which are not typically resolved by basin- to global-scalecirculation models. Therefore, the equatorial Pacific ecosystem model is forced using daily information (solar radiation, velocity, temperature) from the TropicalAtmosphere Ocean (TAO) mooring array. The ecosystem model also requires vertical velocity information which necessitated the development of a method forcomputing daily vertical velocities from the TAO array. Much of the variability in primary production, plankton and nutrient concentrations observed in 1992during the US Joint Global Ocean Flux Study Equatorial Pacific Process Study time-series cruises (TS1 and TS2), is well reproduced in the model simulations.Simulations demonstrate that lower primary productivities during TS1 as compared to TS2 result from the deeper thermocline that persisted during TS1 as a resultof El Niño conditions; however, because of the simultaneous reduction in grazing pressure, simulated chlorophyll levels are similar for these two time periods.Simulations of this single-species ecosystem model successfully reproduce data collected both during and after the El Niño, suggesting that species compositionchanges are not of first-order importance when examining the effects of the 1991-92 El Niño on the equatorial Pacific ecosystem. A 60-70% increase inchlorophyll concentration and a 400% increase in the chlorophyll contribution by diatoms was associated with the passage of a tropical instability wave (20-dperiod) across the study site during TS2. This period of high chlorophyll concentration and diatom abundance coincided temporally with strong northwardvelocities and strong downwelling velocities in the upper euphotic zone. Observations and simulations suggest that this increase in chlorophyll concentration andchange in species composition not only results from in situ diatom growth stimulated by increased iron concentrations, but also results from the advection ofdiatoms toward the convergent front located along the leading (western) edge of the instability wave. Equatorially trapped internal gravity waves can alsostimulate in situ phytoplankton growth as high-frequency vertical motions introduce limiting micronutrients, such as iron, into the euphotic zone. Because ironcan be taken up by the picoplankton on time scales much shorter than the wave period (6-8 days), these waves may provide a mechanism for effecting a largeflux of iron into the euphotic zone. Exclusion of these high-frequency motions results in an iron flux to the euphotic zone that may be underestimated by morethan 30%.:
Friedrichs MAM (2001) A data assimilative marine ecosystem model of the central equatorial Pacific: Numerical twin experiments. J. Mar. Res. 59: 859-894.
ABSTRACT:
A five-component, data assimilative marine ecosystem model is developed for the high-nutrient low-chlorophyll region of the central equatorial Pacific (ON,140W). Identical twin experiments, in which model-generated synthetic 'data' are assimilated into the model, are employed to determined the feasibility ofimproving simulation skill by assimilating in situ cruise data (plankton,nutrients, and primary production) and remotely-sensed ocean color data. Simple dataassimilative schemes such as data insertion or nudging may be insufficient for lower trophic level marine ecosystem models, since they require long time-series ofdaily to weekly plankton and nutrient data as well as adequate knowledge of the governing ecosystem parameters. In contrast, the variational adjoint technique,which minimizes model-data misfits by optimizing tunable ecosystem parameters, holds much promise for assimilating biological data into marine ecosystemmodels. Using sampling strategies typical of those employed during the U.S. Joint Global Flux Study (JGOFS) equatorial Pacific process study and theremotely-sensed ocean color data available from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), parameters that characterize processes such asgrowth, grazing, mortality, and recycling can be estimated. Simulation skill is improved even if synthetic data associated with 40% random noise are assimilated;however, the presence of biases of 10-20% proves to be more detrimental to the assimilation results. Although increasing the length of the assimilated time seriesimproves simulation skill if random errors are present in the data, simulation skill may deteriorate as more biased data are assimilated. As biological data sets,including in situ, satellite and acousitc sources, continue to grow, daa assimilative biological-physical models will play an increasingly crucial role in largeinterdisciplinary oceanographic observational programs. :
Siegel DA; Maritorena S; Nelson NB; Hansell DA; Lorenzi-Kayser M (2002) Global distribution and dynamics of colored dissolved and detrital organic materials J. Geophys. Res. 107(12) : 3228, doi:10.1029/2001JC000965.
ABSTRACT:
Colored dissolved organic matter (CDOM), also referred to as gelbstoff, gilvin or yellow matter, has long been known to be an important component of the opticalproperties of coastal and estuarine environments. However, an understanding of the processes regulating its global distribution and variability, its relationship tothe total pool of dissolved organic carbon (DOC), and its influence on light availability remain largely unexplored. Satellite imagery from the Sea-viewing WideField-of-view Sensor (SeaWiFS) are used to characterize the global distribution of light absorption due to colored detrital and dissolved materials (CDM). Thequantity CDM is considered as it is not yet possible to differentiate CDOM and detrital particulate absorption from ocean color spectra on a routine basis.Nonetheless, analysis of an extensive field data set indicates that detrital particulates make only a small contribution to CDM. A comparison of coincident fieldobservations of CDM with SeaWiFS retrievals shows good agreement indicating that the present procedures perform well. To first order, the basin-scale CDM distribution reflects patterns of wind-driven vertical circulation of the gyres modulated by a meridional trend of increasingCDM towards higher latitudes. The global CDM distribution appears regulated by a coupling of biological, photochemical and physical oceanographic processesall acting on a local-scale and greater than 50% of blue light absorption is controlled by CDM. Significant differences in both CDM concentration and itscontribution to blue light absorption are found spatially among the major ocean basins and temporally on variety of time scales. Significant impacts of riverinedischarges can be discerned although their effects are largely localized. Basin-scale distributions of CDM and DOC are largely unrelated, indicating that CDM isa small and highly variable fraction of the global DOC pool. This first view of the global CDM distribution opens many new doors for the quantification of globalmarine photoprocesses using satellite ocean color data. :
Murtugudde R; Beauchamp J; McClain CR; Lewis M; Busalacchi AJ (2002) Effects of penetrative radiation on the upper tropical ocean circulation. J. Climate 15(5): 470-486.
ABSTRACT:
The effects of penetrative radiation on the upper tropical ocean circulation have been investigated with an ocean general circulation model (OGCM) withattenuation depths derived from remotely sensed color data. The OGCM is a reduced gravity, primitive equation, sigma coordinate model coupled to an advectiveatmospheric mixed layer model. Our simulations use a single exponential profile for radiation attenuation in the water column which is quite accurate for OGCMswith fairly coarse vertical resolution. The control runs use an attenuation depth of 17 m while the simulations use spatially variable attenuation depths. When avariable depth oceanic mixed layer is explicitly represented with interactive surface heat fluxes, the results can be counterintuitive. In the eastern equatorialPacific, a tropical ocean region with one of the strongest biological activity, the realistic attenuation depths result in increased loss of radiation to thesubsurface, but increased sea surface temperatures (SSTs) compared to the control run. Enhanced subsurface heating leads to weaker stratification, deepermixed layers, reduced surface divergence and hence less upwelling and entrainment. Thus, some of the systematic deficiencies in the present day climatemodels, such as the colder than observed cold-tongue in the equatorial Pacific may simply be related to inaccurate representation of the penetrative radiationand can be improved by the formulation presented here. The differences in ecosystems in each of the tropical oceans are clearly manifested in the manner inwhich biological heat trapping affects the upper ocean. While the tropical Atlantic has many similarities to the Pacific, the Amazon, Congo and Niger riverdischarges dominate the attenuation of radiation. In the Indian Ocean, elevated biological activity and heat trapping are away from the equator in the ArabianSea and the southern tropics. For climate models, in view of their sensitivity to the zonal distribution of SST, using a basin mean of the ocean color derivedattenuation depth reduces the SST errors significantly in the Pacific although they occur in regions of high mean SST and may have potential feedbacks incoupled climate models. On the other hand, the spatial variations of attenuation depths in the Atlantic arc crucial since using the basin mean producessignificant errors. Thus the simplest and the most economic formulation is to simply employ the annual mean spatially variable attenuation depths derived fromocean color.:
Lima ID; Doney SC (submitted) A three-dimensional, multi-nutrient, size-structured ecosystem model
for the North Atlantic. Global Biogeochemical Cycles
ABSTRACT: In this study, we incorporate a relatively complex ecosystem model into a three-dimensional, general ocean circulation model for the North Atlantic basin and compare model results with field data from in situ measurements (BATS, NABE and OWSI) and satellite ocean color (SeaWiFS) imagery. In addition to multi-element nutrient limitation, the ecosystem model includes distinct phytoplankton functional groups as well as size structure in the phytoplankton and detritus compartments and incorporates a more realistic, mechanistic based phytoplankton growth and photoadaptation model. Model skill is evaluated quantitatively against satellite estimates of chlorophyll and primary productivity using a Taylor diagram. The model reproduces the magnitude and the general spatial and temporal patterns in nutrients, chlorophyll and primary production seen in in situ and satellite data and shows substantial improvements over prior basin-scale simulations of the North Atlantic. Model-data correlation for the overall time-space distribution of satellite chlorophyll fields is ~0.6 and the magnitude of the model time-space variability for is comparable to the observed value. The model generally overestimates the temporal and spatial amplitude of variation of the satellite estimates of primary productivity by 20%--50%, and the modeled and satellite fields are less well correlated (0.4--0.6). In the model, diatoms are generally nitrogen limited in the subtropical gyre and silica limited at higher latitudes and in upwelling regions along the equator and the west coast of Africa. In the BATS region, diatoms are nitrogen limited during late winter and early spring and silica limited during the rest of the year. The model also reproduces observed characteristics of the ecosystem dynamics, e.g., the dominance of the picophytoplankton and episodic diatom blooms in the subtropics, the silica-controlled shift in the phytoplankton community towards smaller size classes in the summer at higher latitudes and the associated decrease in new production and export of particulate carbon. The main discrepancy between model results and observations is the overestimation of chlorophyll concentrations and primary production along the northern edge of the subtropical gyre, due to excessive convective mixing in winter from the physical model, and the underestimation of chlorophyll concentrations and primary production along the coastal areas. Model results suggest that the episodic diatom blooms observed at BATS are related to interannual variations in the advective/meridional transport of nutrients and cells from higher latitudes. Sensitivity experiments and comparison with previous similar modeling studies show that the explicit inclusion of size structure in the phytoplankton and detritus compartments and silica limitation for diatoms result in an improvement in model skill. Removal of silica limitation has a significant impact on ecosystem dynamics, by increasing diatom relative abundance and export of particulate carbon and reducing regenerated production in the euphotic zone.
Lima ID; Olson DB; Doney SC (2002) Intrinsic Dynamics and Stability Properties of Size-Structured Pelagic Ecosystem Models. J. Plankton Res. 24: 533-556.
ABSTRACT:
Although pelagic ecosystem models, coupled with ocean circulation models, are being widely used to quantify fluxes of nutrients and carbon in the ocean atregional and basin scales, relatively little work has been done on understanding their intrinsic dynamics independently of physical forcing. In this study, thedynamics of three common formulations for the NPZD class of models (nutrient, phytoplankton, zooplankton and detritus) using two different types of predationfunctional response are analyzed and compared. Our goal is to characterize the stability properties of this class of models with respect to variations in light andtotal nutrient concentrations. Despite important structural differences, the different model formulations all show asymptotic stable equilibria at low total nutrientconcentrations and high to moderate light intensities and limit cycle oscillations at low light intensities and high total nitrogen concentrations. Limit cycles areformed through a Hopf bifurcation, as a phase lag develops between predator (Zi) and prey (Pi or Zi-1) due to a relatively sharp increase in the growth rate of theprey in relation to that of the predator. The use of variable preferences in the functional response provides a density-dependent mechanism that allows thesystem to self-regulate, increasing system stability considerably, but do not eliminate the instabilities completely. Instabilities occur at light and nutrient levelsthat correspond to those observed on the bottom of the euphotic zone near the nutricline, where the deep chlorophyll maximum is usually located. This suggeststhat the deep chlorophyll maximum might be dynamically unstable. This dynamical disequilibrium in species composition and the characteristically long transienttimes would allow species persistence in the presence of seasonal and mesoscale variations and provide a mechanism for species coexistence in the relativelyhomogeneous open ocean environment, thereby providing a potential solution for the "paradox of plankton". In the multi-species models, the higher diversity ofspecies (wider range of values for the biological parameters) allows biological activity (photosynthesis, grazing and predation) to occur under a wider range oflight and nutrient conditions resulting in higher primary and secondary production and lower nutrient concentrations at light intensities equivalent to those in theupper part of the euphotic zone, than in the single-species model. :
Lima ID; Olson DB; Doney SC (2002) Biological response to frontal dynamics and mesoscale variability in oligotrophic environments: biological production and community structure. J. Geophys. Res. 107(C8): 10.1029/2000JC000393.
ABSTRACT:
Two food web models, a single-species and a multi-species formulation, are incorporated into a three-dimensional eddy-resolving model of an unstable frontaljet to investigate the effects of mesoscale instabilities on biological production and community structure in oligotrophic ocean environments. The growinginstability wave triggers the formation of divergence and convergence and consequently upwelling and downwelling zones along the jet. Most of the biologicalproduction takes place near the surface on the cyclonic (northern) side of the front and on the upstream region of meander crests in response to nutrientupwelling. However, strong advection downstream and downward in the convergence regions (downstream side of meander crests) result in accumulation ofbiomass at depth on the anticyclonic (southern) side of the front, leading to spatial separation between regions of biological growth and regions of biomassaccumulation. The large domain and long duration of the runs allow for investigation of diverse phenomena including eddy-eddy, eddy-front interactions for bothcyclonic and anticyclonic features. In addition to the traditional cyclonic eddy pumping mechanism, we observe enhanced primary production and biomassaccumulation on the edges of anticyclonic eddies due to eddy-eddy interactions and biomass filaments trailing behind detached cyclonic eddies propagatingaway from the front. In the multi-species formulation, the mesoscale dynamics drives a sustained shift in the phytoplankton community towards the large sizeclasses that is consistent with observations and that has not been observed in previous similar process modeling studies. Because of the higher speciesdiversity, nutrients are used more efficiently in the multi-species system, resulting in higher total plankton biomass for the same amount of total nitrogen in thedomain. The fractional increase in total biomass is less pronounced inside the unstable front and eddies where species diversity is lower (large size classesdominate).:
McClain CR; Christian JR; Signorini SR; Lewis MR; Asanuma I; Turk D; Dupouy-Douchement C (2002) Satellite ocean-color observations of the tropical Pacific Ocean. Deep-Sea Res. II 49: 2533-2560.
ABSTRACT:
The Coastal Zone Color Scanner (CZCS) data set provided some insights into biological processes in the equatorial Pacific, but the sampling was too sparse toaddress questions on temporal and spatial variability. Since late 1996, the Ocean Color¯Temperature Sensor (OCTS), the Polarization Detection EnvironmentalRadiometer (POLDER), the Sea-viewing Wide Field-of-View Sensor (SeaWiFS), and the Moderate-Resolution Imaging Spectroradiometer (MODIS) haveprovided a nearly continuous record of biological processes in this region for the first time. This study summarizes the SeaWiFS observations of the tropicalPacific from September 1997 through March 2000, with particular emphasis on equatorial and mesoscale variability, the influence of biological processes onpenetrating irradiance, and the performance of primary production algorithms in this region. Specific mesoscale phenomena described are the phytoplanktonblooms along the west coast of Central America, in the vicinity of the Costa Rica dome, and south of the equator. The coastal Central American and Costa Ricadome blooms result from orographically steered coastal winds and Ekman divergence, respectively. An unusual bloom event occurred south of the equator andpersisted for several months in 1999; specific mechanisms that would have sustained the bloom could not be identified. Also, the time-evolution of the equatorialbloom during the May¯August 1998 transition from El Niño to La Niña is discussed. Again, no concise and broadly accepted explanation of the bloom's genesisand migration has yet emerged. During this transition, the monthly mean diffuse attenuation coefficient decreased by a factor of 3 at some locations along theequator. This change in water transparency, coupled with large changes in mixed-layer depth, resulted in significant changes in surface layer heating rates thatwere substantiated with field observations. Finally, certain primary production algorithms designed to use remotely sensed chlorophyll-a concentrations areevaluated. None of the algorithms capture the observed variability in primary production, and all appear to underestimate the total primary production of thetropical Pacific.:
Moore JK; Doney SC; Kleypas JA; Glover DM; Fung I (2002) An intermediate complexity marine ecosystem model for the global domain. Deep-Sea Res. II 49(1-3): 403-462.
ABSTRACT:
A new marine ecosystem model designed for the global domain is presented, and model output is compared with field data from nine different locations. Field datawere collected as part of the international JGOFS (Joint Global Ocean Flux Study) program, and from historical time series stations. The field data include a widevariety of marine ecosystem types, including nitrogen- and iron-limited systems, and different physical environments from high latitudes to the mid-ocean gyres.Model output is generally in good agreement with field data from these diverse ecosystems. These results imply that the ecosystem model presented here can bereliably applied over the global domain. The model includes multiple potentially limiting nutrients that regulate phytoplankton growth rates. There are threephytoplankton classes, diatoms, diazotrophs, and a generic small phytoplankton class. Growth rates can be limited by available nitrogen, phosphorus, iron,and/or light levels. The diatoms can also be limited by silicon. The diazotrophs are capable of nitrogen fixation of N2 gas and cannot be nitrogen limited.Calcification by phytoplankton is parameterized as a variable fraction of primary production by the small phytoplankton group. There is one zooplankton classwhich grazes the three phytoplankton groups and a large detrital pool. The large detrital pool sinks out of the mixed layer, while a smaller detrital poolrepresenting dissolved organic matter and very small particulates does not sink. Remineralization of the detrital pools is parameterized with a temperaturedependent function. We explicitly model the dissolved iron cycle in marine surface waters including inputs of iron from subsurface sources and from atmosphericdust deposition.:
Moore JK; Doney SC; Glover DM; Fung I (2002) Iron cycling and nutrient limitation patters in surface waters of the world ocean. Deep-Sea Res. II 49(1-3): 463-507.
ABSTRACT:
A global marine ecosystem mixed layer model is used to study iron cycling and nutrient limitation patterns in surface waters of the world ocean. The ecosystemmodel has a small phytoplankton size class whose growth can be limited by N, P, Fe, and/or light, a diatom class which can also be Si limited and a diazotrophphytoplankton class whose growth rates can be limited by P, Fe, and/or light levels. The model also includes a parameterization of calcification by phytoplanktonand is described in detail by Moore et al. (this issue). The model reproduces the observed high nitrate, low chlorophyll (HNLC) conditions in the Southern Ocean,subarctic Northeast Pacific, and equatorial Pacific, and realistic global patterns of primary production, biogenic silica production, nitrogen fixation, particulateorganic carbon export, calcium carbonate export, and surface chlorophyll concentrations. Phytoplankton cellular Fe/C ratios and surface layer dissolved ironconcentrations are also in general agreement with the limited field data. Primary production, community structure, and the sinking carbon flux are quite sensitiveto large variations in the atmospheric iron source, particularly in the HNLC regions. This supports the Iron Hypothesis of Martin (1990). Nitrogen fixation is alsostrongly influenced by atmospheric iron deposition. Nitrogen limits phytoplankton growth rates over less than half of the world ocean during summer months.Export of biogenic carbon is dominated by the sinking particulate flux, but detrainment and turbulent mixing account for 30 % of global carbon export. Our resultsin conjunction with other recent studies suggest the familiar paradigm that nitrate inputs to the surface layer can be equated with particulate carbon export needsto be expanded to include multiple limiting nutrients and modes of export. :
Dutkiewicz S; Follows M; Marshall J; Gregg WW (2001) Interannual variability of phytoplankton abundances in the North Atlantic. Deep-Sea Res. II 48(10): 2323-2344 .
ABSTRACT:
A framework is developed for examining spatial patterns of interannual variability in springtime chlorophyll concentrations as a response to physical changes. Asimplified, two-layer bio-physical model reveals regional responses to interannual variability of convective mixing. Vertical mixing can promote productivity inthe surface waters through enhanced nutrient supply, but can also retard productivity due to the transport of phytoplankton below Sverdrup's critical layer duringspring and the end of winter mixed layer, hc/hm. The responses predicted by the simplified model are found in a more sophisticated four-compartment, nitrogenbased ecosystem model, driven by a general circulation model of the North Atlantic. Anomalously strong convective mixing leads to enhanced chlorophyllconcentrations in regions of shallow mixed layers (hc/hm ~ 1), such as the subtropics. In contrast, in the subpolar regions where mixed layers are deeper (hc/hm<< 1), the sensitivity to convective mixing is weaker, and increased mixing can lead to lower phytoplankton abundances. The numerical model also revealsregions of more complex behaviour, such as the inter-gyre boundary, where advective supply of nutrients plays a significant role on interannual timescales. Preliminary analyses of in situ and remote observations from the Bermuda Atlantic Time-Series, Ocean Weather Station "India" and the Coastal Zone ColorScanner also show qualitative agreement. The conceptual framework provides a tool for the analysis of ongoing remote ocean color observations.:
Hood RR; Bates NR; Capone DG; Olson DB (2001) Modeling the effect of nitrogen fixation on carbon and nitrogen fluxes at BATS. Deep-Sea Res. II 48(8-9): 1609-1648.
ABSTRACT:
Recent geochemical estimates of N2-fixation in the North Atlantic ocean indicate rates that are significantly higher than those derived from direct observations. In this paper different N2-fixation rate scenarios are explored using a 1-dimensional, biogeochemical model which includes an explicit representation ofTrichodesmium. This model reproduces most of the observed interannual variability in phytoplankton production and generates seasonal Trichodesmium biomassand N2-fixation cycles similar to those observed at BATS. Two solutions are presented, one where the N2-fixation rate is increased enough to reproduce theobserved summertime draw down of DIC and a second where it is tuned to reproduce the observed sediment trap fluxes. The high N2-fixation solution reproducesthe seasonal and interannual variability in DIC concentrations quite accurately and generates N2-fixation rates that agree with direct rate measurements from1990 and recent geochemical estimates. However, this solution generates export fluxes that are more than 4 times higher than observed, and predicts thedevelopment of DON and DOC anomalies in late summer/early fall that have not been observed. In contrast, the low N2-fixation solution generates trap fluxesthat are approximately correct, but overestimates the summertime DIC concentrations by 20-30 umole/kg. Both solutions indicate that there is significantinterannual variability in N2-fixation at BATS and that the rates were much lower in 1995-1996 than in the previous six years. It is suggested that this variabilityis linked to decadal-scale fluctuations in the North Atlantic climate. :
Jackson GA (2001) Effect of coagulation on a model planktonic food web. Deep-Sea Res. I 48(1): 95-123.
ABSTRACT:
Observations have shown that aggregates ("marine snow") are an important fraction of the vertical flux of organic matter in the ocean. There has been separationbetween coagulation models, which have focused on phytoplankton blooms in which particle concentrations are high and grazing is low and neglectable, andplankton models which have focused on food web interactions but that have ignored coagulation dynamics. This separation has partly resulted from the difficultyin describing the interactions among the multiple particle sources using a coagulation model for a food web. New approaches for describing particle dynamicsnow make it possible to do so. The present study examines the effect of combining the food web model of Fasham et al. (1990) with a particle dynamics model andapplying the combined model to describe the annual cycle of an oligotrophic plankton system. Results show that coagulation can have an important effect onparticle flux even in such a low particle concentration environment by increasing average particle settling speed and by increasing the ratio of maximum tominimum daily vertical flux over the coarse of a yearly cycle. In addition, coagulation forms large, rapidly sinking particles. Grazing and the accompanyingformation of fecal pellets can compete for particles, but the fecal pellets can also participate in the formation of large aggregates. Among the variables that caninfluence export rates are phytoplankton size and concentration as well as depth of the surface mixed layer. The results provide evidence for the importance ofcoagulation processes in enhancing particle export even in central ocean regions.:
Johnson GC; Robbins PE; Hufford GE (2001) Systematic Adjustments of Hydrographic Sections for Internal Consistency. Journal of Atmospheric and Oceanic Technology 18(7) : 1234-1244 .
ABSTRACT:
A significant legacy of the World Ocean Circulation Experiment (WOCE) is the large number of high-quality, high-resolution,full-depth, transoceanic hydrographic sections occupied starting in the mid-1980's. The data from these sections provide historically unprecedented sampling ofWorld Ocean water properties. Data used here include pressure, temperature, salinity, dissolved oxygen, and nutrients (nitrate, phosphate, and silicic acid).While the WOCE Hydrographic Programme (WHP) made unprecedented efforts to employ standardized measurement techniques on all sections, small butsignificant systematic differences among sections are found. A simple method for adjusting these measurements to maximize internal consistency is presented andapplied to all available data in the Pacific Basin. First, all the sections are broken into distinct cruise legs, each consisting of the stations between port stops.Then, crossovers are identified where two different cruise legs cross or approach each other. Using hydrographic data from each cruise leg near each crossover,linear fits are made of properties on potential temperature surfaces against distance along cruise-track. These fits are then used to evaluate property ratios ordifferences and their standard deviations at crossovers. A set of least-squares models are used to generate a set of adjustments, with related uncertainties, forall the properties of each cruise leg. These adjustments minimize differences among cruise legs at the crossovers in a least-squares sense. The adjustments canbe weighted by difference uncertainties, and damped by a priori estimates of the expected differences. The adjustments generally bring data from different cruiselegs to agreement within WHP target accuracies.:
McGillicuddy DJ; Kosnyrev VK; Ryan JP; Yoder JA (2001) Covariation of mesoscale ocean color and sea surface temperature patterns in the Sargasso Sea. Deep-Sea Res. II 48(8-9): 1823-1836.
ABSTRACT:
During the lifetime of the Coastal Zone color Scanner, there were 21 instances in which both satellite-derived ocean color and sea surface temperature aresimultaneously available over large areas of the Sargasso Sea. These images reveal close correspondence between mesoscale structures observed intemperature and pigment fields. In general, higher (lower) pigment biomass occurs in mesoscale features consisting of cold (warm) temperature anomalies. Thisrelationship is consistent with the idea that upward displacement of isopycnals at the base of the euphotic zone by mesoscale eddies is an important mechanismof nutrient supply in the region. :
Ono S; Ennyu A; Najjar RG; Bates N (2001) Shallow remineralization in the Sargasso Sea estimated from seasonal variations in oxygen, dissolved inorganic carbon and nitrate. Deep-Sea Res. II 48(8-9): 1567-1582.
ABSTRACT:
A diagnostic model of the mean annual cycles of oxygen, dissolved inorganic carbon (DIC) and nitrate below the mixed layer at the Bermuda Atlantic Time-seriesStudy (BATS) site is presented and used to estimate organic matter remineralization in the seasonal thermocline. The model includes lateral and verticaladvection as well as vertical diffusion, which are found to be significant components of the seasonal budgets of oxygen, DIC and nitrate. The vertical andseasonal variation of the remineralization rates deduced from the oxygen and DIC distributions are very similar. Both locate the spring-summer communitycompensation depth at ~85 m and the remineralization rate maximum at ~120 m; nitrate-based estimates of these depths are about 40 m greater. Remineralizationrates based on oxygen, DIC and nitrate all show the seasonal maximum to occur in the late spring, presumably reflecting the decomposition of organic matterformed during the spring bloom. The remineralization rate integrated between 100 and 250 m and between mid-April and mid-December is estimated to be 2.08 ±0.38 mol O2 m-2, 1.53 ± 0.35 mol C m-2 and 0.080 ± 0.046 mol N m-2. These imply remineralization ratios of O2:C = 1.4 ± 0.40 and C:N = 19 ± 12. The formeragrees well with the canonical Redfield ratio and the latter is significantly larger. The analysis is consistent with the export and remineralization of nitrogen-poororganic matter from surface waters. :
Siegel DA; et al. (2001) Bio-optical modeling of primary production on regional scales: The Bermuda BioOptics Project Deep-Sea Res. II 48(8-9): 1865-1896 .
ABSTRACT:
Regional to global scale estimates of primary production must rely on remotely sensed quantities. Here, we characterize in situ light-primary productionrelationships and assess the predictive capability of several global primary production models using a 6-year time series collected as part of the U.S. JGOFSBermuda Atlantic Time Series (BATS). The consistency and longevity of this data set provides an excellent opportunity to evaluate bio-optical modelingmethodologies and their predictive capabilities for estimating rates of water column integrated primary production, integralPP, for use with satellite ocean colorobservations. We find that existing and regionally tuned parameterizations for vertically integrated chlorophyll content and euphotic zone depth do not explainmuch of the observed variability at this site. Fortunately, the use of these parameterizations for light availability and harvesting capacity has little influence uponmodeled rates of integralPP. Site-specific and previously published global models of primary production both perform poorly and account for less than 40% of thevariance in integralPP. A sensitivity analysis is performed to demonstrate the importance of light saturated rates of primary production, P*sat , compared with otherphotophysiological parameters. This is because nearly one-half of integralPP occurs under light-saturated conditions. Unfortunately, we were unable to derive asimple parameterization for P*sat that significantly improves prediction of integralPP. The failure of global integralPP models to encapsulate a major portion of theobserved variance is due in part to the restricted range of integralPP observations for this site. A similar result is found comparing global chlorophyll-reflectancealgorithms to the present observations. More importantly, we demonstrate that there exists a time-scale (roughly 200 days) above which the modeleddistributions of integralPP are consistent with the observational data. By low-pass filtering the observed and modeled integralPP time series, the model'spredictive skill levels increase substantially. We believe that the assumptions of steady state and balanced growth used in bio-optical models of integralPP areinconsistent with observational data. Most of the observed variance in integralPP is driven by a variety of ecosystem disturbance processes that are simply notaccounted for in bio-optical models. This puts important bounds on how integralPP models should be developed, validated and applied.:
Signorini SR; McClain CR; Christian JR; Wong CS (2001) Seasonal and interannual variability of phytoplankton, nutrients, TCO2, pCO2, and O2 in the esthern subarctic Pacific (ocean weather station Papa) J. Geophys. Res.J. Geophys. Res.J. Geophys. Res. 106(C12): 31,197-31,215 .
ABSTRACT:
A coupled, one-dimensional ecosystem/carbon flux model is used to simulate the seasonal and interannual variability of phytoplankton, nutrients, TCO2, O2, andpCO2 at ocean weather station Papa (OWS P at 50°N, 145°W). The 23-year interannual simulation (1958-1980) is validated with available data and analyzed toextend seasonal and interannual variations beyond the limited observational records. The seasonal cycles of pCO2 and sea-air CO2 flux are controlled by acombination of thermodynamics, winds, and biological uptake. There is ingassing of CO2 during the fall-winter months when SSTs are colder and wind forcing isvigorous, while there is a much smaller ingassing of CO2 during the summer when sea surface temperatures are warmer and wind speeds are reduced. Biologicalproduction plays a major role in maintaining the air-sea equilibrium. An abiotic simulation showed that OWS P would be a source of atmospheric CO2 (1.41 mol Cm-2 yr-2) if the biological sink of CO2 were removed. The peak net community production in summer compensates for the increased temperature effect on pCO2,which prevents large outgassing in summer. Oxygen anomalies relative to the temperature-determined saturation value show that there is a seasonal cycle ofair-sea flux, with ingassing in winter and outgassing in summer. The net surface oxygen flux is positive (0.8 mol m-2 yr-2), indicating that OWS P is a source ofoxygen to the atmosphere. The average primary production is 167 g C m-2 yr-2. The 1960-1980 (1958 and 1959 spin-up years removed) mean carbon flux is-1.8 mol C m-2 yr-2, indicating that the ocean at OWS P is a sink of atmospheric carbon. The sea-air CO2 flux ranges from -1.2 to -2.3 mol C m-2 yr-2 during the21-year simulation period. This finding emphasizes the need for long-term observations to accurately determine carbon flux budgets. A series of sensitivityexperiments indicate that the seasonal variability and overall (21 years) mean of TCO2, pCO2, delta-pCO2, and air-sea CO2 flux are strongly dependent on thegas transfer formulation adopted, the total alkalinity near the surface, and the bottom (350 m) value adopted for TCO2. The secular atmospheric pCO2 upwardtrend is manifested in the TCO2 concentration within the upper 100 m by an increase of 15 mmol m-3 in 20 years, consistent with observations at other locations[Winn et al., 1998; Bates, 2001]. :
Caldeira K; Duffy PB (2000) The role of the Southern Ocean in uptake and storage of anthropogenic carbon dioxide. Science 287(5453): 620-622.
ABSTRACT:
An ocean-climate model that shows high fluxes of anthropogenic carbon dioxide into the Southern Ocean, but very low storage of anthropogenic carbon there,agrees with observation-based estimates of ocean storage of anthropogenic carbon dioxide. This low simulated storage indicates a subordinate role for deepconvection in the present-day Southern Ocean. The primary mechanism transporting anthropogenic carbon out of the Southern Ocean is isopycnal transport.These results imply that if global climate change reduces the density of surface waters in the Southern Ocean, isopycnal surfaces that now outcrop may becomeisolated from the atmosphere, tending to diminish Southern Ocean carbon uptake. :
Lee K; Millero FJ; Byrne RH; Feely RA; Wanninkhof R (2000) The recommended dissociation constants of carbonic acid in seawater. Geophys. Res. Lett. 27: 229-232.
ABSTRACT:
A coherent representation of carbonate dissociation constants and measured inorganic carbon species is essential for a wide range of environmentally importantissues such as oceanic uptake of anthropogenic CO2 and carbon cycle depictions in ocean circulation models. Previous studies have shown varying degrees ofdiscordance between calculated and measured CO2-system parameters. It is unclear if this is due to errors in thermodynamic models or in measurements. In thiswork, we address this issue using a large field dataset (15,300 water samples) covering all ocean basins. Our field data, obtained using laboratory-calibratedmeasurement protocols, are most consistent with calculated parameters using the dissociation constants of Mehrbach et al. [1973] as refit by Dickson and Millero[1987]. Thus, these constants are recommended for use in the synthesis of the inorganic carbon data collected during the global CO2 survey during the 1990sand for characterization of the carbonate system in seawater. :
Lee K; Wanninkhof RH; Feely RA; Millero FJ; Peng T-H (2000) Global relationships of total inorganic carbon with temperature and nitrate in surface water. Global Biogeochem. Cycles 14(30) : 979-994.
ABSTRACT:
High quality total inorganic carbon (CT) measurements made in the major ocean basins as part of the Joint Global Ocean Flux Study (JGOFS), the NationalOceanic and Atmospheric Administration/Ocean Atmosphere Carbon Exchange Study (NOAA/OACES), and the Department of Energy/World Ocean CirculationExperiment (DOE/WOCE) programs are related to sea surface temperature (SST) and nitrate (NO3-). A simple two-parameter function with SST and NO3- of theform NCT = a + b SST + c SST2 + d NO3- fits salinity (S)-normalized surface CT (NCT = CT x 35/S) data for different parts of the oceans within an area-weightederror of ±7 mmol kg-1 (1sigma). Estimated values of NCT using the derived algorithms with NO3- and SST are compared with values calculated from the surfacepartial pressure of CO2 (pCO2SW) [Takahashi et al., 1997] and total alkalinity (AT) [Millero et al., 1998] fields using thermodynamic models. Comparisons of theestimated values of NCT with measurements not used to derive the same algorithms, and comparisons with the values calculated from global AT and pCO2SWfields, give a realistic uncertainty of ±15 mmol kg-1 in estimated CT. The derived correlations of NCT with SST and NO3- presented here make it possible toestimate surface CT over the ocean from climatological SST, S, and NO3- fields. :
Loukos H; Vivier F; Murphy PP; Harrison DE; Le Quéré C (2000) Interannual Variability of Equatorial Pacific CO2 Fluxes Estimated from Temperature and Salinity Data. Geophys. Res. Lett. 27: 1735-1738.
ABSTRACT:
Based on atmospheric data and models, the tropical CO2 source anomaly reaches up to 2 GtC yr-1gp, but the respective contributions of the terrestrial biosphereand the oceans to this flux are difficult to quantify. Here we present a new method for estimating CO2 fluxes from oceanic observations based on the surprisinglygood predictive skill of temperature and salinity for surface dissolved inorganic carbon. Using historical temperature and salinity data, we reconstruct the basinscale CO2 flux to the atmosphere in the equatorial Pacific from 1982 to 1993. We find that interannual anomalies do not exceed 0.4 ± 0.2 GtC yr-1gp whichsuggests that up to 80% of the tropical CO2 source anomaly is due to the terrestrial biosphere. :
Doney SC (1999) Major challenges confronting marine biogeochemical modeling. Global Biogeochem. Cycles 13: 705-714.
ABSTRACT:
Substantial improvements are required in the current suite of numerical models if we are to better understand the present ocean biogeochemical state and predictpotential future responses to anthropogenic perturbations. At present, major impediments to marine biogeochemical modeling include the inadequaterepresentation of: multi-element cycling and community structure; large-scale physical circulation; mesoscale space and time variability; and mass exchangebetween the open ocean, and the atmosphere, land and coastal ocean. Marine biogeochemical modeling is inherently data driven, and significant progress onany of these topics will require close collaboration between the observational and modeling communities. Two main thrusts should be to develop improved,mechanistically based parameterizations of specific biogeochemical processes and to test the overall skill of integrated system models through detailedmodel-data comparison of both the mean state and seasonal to inter-decadal variability. :
Gnanadesikan A; Toggweiler JR (1999) Constraints placed by silicon cycling on vertical exchange in general circulation models. Geophys. Res. Lett. 26: 1865-1868.
ABSTRACT:
The flux of biogenic silica out of the oceanic mixed layer (the export flux) must balance the import of high-silicate deep waters associated with mass exchangebetween the surface and deep ocean. Recent regional estimates of the export flux limit it to 50-80 Tmol yr-1gp. In order to reproduce such low export fluxes,coarse-resolution general circulation models must have low pycnocline diffusivity and a lateral exchange scheme which involves advection of tracers byunresolved mesoscale eddies. Failure to capture low rates of vertical exchange will result in climate models which overpredict the uptake of anthropogeniccarbon dioxide and fail to capture the proper locations and rates of density transformation. :
Lee K; Karl DM; Wanninkhof R; Zhang J-Z (2002) Global estimates of net carbon production in the nitrate-depleted tropical and subtropical oceans. Geophysical Research Letters 29: 10.1029/2001GL014198.
ABSTRACT:
Nitrate availability is generally considered to be thelimiting factor for oceanic new production and this concept iscentral in our observational and modeling efforts. However,recent time-series observations off Bermuda and Hawaiiindicate a significant removal of total dissolved inorganiccarbon CT in the absence of measurable nitrate. Here weestimate net carbon production in nitrate-depleted tropicaland subtropical waters with temperatures higher than 20oCfrom the decrease in the salinity normalized CT inventorywithin the surface mixed layer. This method yields a globalvalue of 0.8 ± 0.3 petagrams of carbon per year (Pg C/yr, Pg= 1015 grams), which equates to a significant fraction (20–40%) of the recent estimates of total new production in thetropical and subtropical oceans. The remainder is presumablysupported by upward flux of nutrients into the euphotic zonevia eddy diffusion and turbulent mixing processes or lateralexchange. Our calculation provides the first global-scaleestimate of net carbon production in the absence ofmeasurable nitrate. We hypothesize that it is attributable todinitrogen (N2) fixing microorganisms, which can utilize theinexhaustible dissolved N2 pool and thereby bypass nitrate limitation.:
Lee K. (2001) Global Net Community Production Estimated from the Annual Cycle of Surface Water Total Dissolved Inorganic Carbon Limnology and Oceanogrphy 46 : 1287-1297.
ABSTRACT:
Global net community production is determined, for the first time, from the decrease in salinity (S)-normalized total dissolved inorganic carbon (NCT = CT x 35/S) inventory in the surface mixed layer corrected for changes due to net air-sea CO2 exchange and diffusive carbon flux from the upper thermocline. Changes in the mixed layer NCT inventory are estimated using a derived annual cycle of NCT and global records of the mixed layer depth. The annual NCT cycle is deduced from regional algorithms relating NCT to sea surface temperature (SST) and nitrate (NO3-), along with global records of seasonal mean SST and NO3-, and from the monthly mean surface partial pressure of CO2 and total alkalinity fields using thermodynamic models. The two methods show similar regional trends and yield global net community production estimates of 6.7 and 8.0 Gt C (1 Gt C = 1 x 10^12 kg Carbon), respectively. The two global estimates are not significantly different and represent an 8-month! period of 1990 (warming period) during which the mixed layer NCT concentration decreases. However, the estimates do not account for net community production during a 4-month cooling period. Ratios of net community production during the warming and cooling periods are estimated from multi-year sediment trap data at the Hawaiian Ocean Time-series (22oN, 158oW) and Ocean Weather Station P (50oN, 145oW) sites. Global extrapolation of these ratios yields annual rates of net community production of 9.1 ± 2.7 and 10.8 ± 2.7 Gt C yr-1.:
Links
to Existing Preprint Servers (of
relevance to SMP)
(1) list of publications and reports
(2) direct access to text of final data reports for various WOCE legs
(3) copies of grey literature reports.