Abstracts
(listed alphabetically by first author)
TALK
Bacterial control of DOM cycling in the open sea and marginal seas.
I. Steady state flow analysis
Tom Anderson 1 and Hugh Ducklow 2
1 Southampton Oceanography Centre, Southampton UNITED KINGDOM
2 School of Marine Sciences, College of William & Mary, Gloucester
Point, VA
Bacteria are pivotal in the cycling of dissolved organic matter in marine
systems. Comparison of various ocean provinces reveals a wide range in
stocks of DOC, yet surprisingly little variability in bacterial biomass.
There is a need to uncover the causes and mechanisms of such variability
in the microbial loop if we are to better understand its importance in
marine biogeochemical cycles. Topics which require study include the origin
of DOM and efficiency with which it is utilized by bacteria, and the question
of whether bacteria are regulated top-down (by predators and viruses) or
bottom-up (by resources). We are using data collected in JGOFS to study:
(1) the efficiency of utilization of DOC by bacteria from observed bacterial
production to primary production ratios (BP:PP); (2) causes of variability
in observed DOC standing stocks, and (3) the factors which control bacterial
biomass. The results of steady-state flow analyses to address these issues,
and applied to contrasting ocean provinces, suggest that recent lower estimates
for conversion efficiencies (ca 15-30%) can only be accommodated by foodweb
models if the ratio of BP/PP is also low. We suggest that most of the open
sea is characterized by BP/PP around 10-15%. Higher values might occur
during larger departures from the quasi- steady state, e.g., the decline
of the phytoplankton bloom in the N. Atlantic and even the Ross Sea. Higher
ratios in the Arabian Sea coastal zone are driven by transient responses
to monsoonal forcing or perhaps terrestrial inputs of organic matter.
TALK
A bottom (of the ocean) up approach to ecosystem modeling for global
biogeochemistry
Rob Armstrong 1, et al.
1 Marine Sciences Research Center, State University of New York, Stony Brook, NY
Here I report on progress in three areas supported by two SMP grants,
one to Jorge Sarmiento and me (ending soon), and one to Mike Landry and
me (about to begin). In both efforts, a key ingredient is to model ecosystem
structure in a manner that supports global studies of the redistribution
of carbon and related biogenic elements throughout the water column. My
working hypothesis is that this goal cannot be accomplished by creating
an exquisite ecosystem model, no matter how detailed, and then appending
to it a model of remineralization and export, as in the Martin curve. Instead,
considerations of redistribution must be paramount, and the requirements
of redistribution will determine the structure of the ecosystem model.
I start by describing the new remineralization model of Armstrong et al.
(Nature, in review), which posits an intimate dependence of deep-water
organic carbon remineralization on the quantity and type of mineral ballasts
(carbonate, silicate, and dust). Next I describe ongoing efforts in the
Sarmiento group to develop and calibrate an ecosystem model that can supply
(in an average sense) the organic carbon and ballast fluxes needed to drive
the remineralization model. Finally I indicate how the food-web work with
Mike Landry will contribute a more detailed look at how ecosystem processes
influence export and redistribution, leading to more detailed predictions
and to greater confidence in their accuracy.
POSTER
Seasonal Variability of Dissolved Inorganic Carbon and Comparative
Estimates of Anthropogenic CO2 in the Indian Ocean
Nicholas R. Bates 1, Christopher L. Sabine 2, and A. Christine Pequignet 1
1 Bermuda Biological Station For Research, Inc., Ferry Reach, GEO1,
BERMUDA
2 Joint Institute for the Study of Atmosphere and Ocean, University
of Washington, c/o NOAA/PMEL
We have examined the seasonal variability of dissolved inorganic carbon
(DIC) and total alkalinity (TA) in the surface layer of the Indian Ocean.
Multiple linear regression (MLR) analyses were conducted using data from
the WOCE CO2 survey, NOAA OACES and JGOFS Arabian Sea programs. These data
cover a range of seasons as well as hydrographic and biogeochemical regimes
in the Indian Ocean. A better understanding of the seasonal variability
of DIC and TA are necessary for validation of global and regional biogeochemical
models. We also examined the entire water column in order to compare different
methods for estimating the oceanic distribution of anthropogenic CO2 .
We compare the approaches presented by Sabine et al. (1999) with the approach
used by Peng et al., (2000) with particular emphasis on the effect that
seasonal and interannual variability might have on these estimates.
POSTER
The carbon cycle in the upper North Atlantic: A simplistic view.
Goran Brostrom 1
1 Massachusetts Institute of Technology, Cambridge, MA
An analysis of data from the northern North Atlantic shows that there
is a clear relation between the total inorganic carbonate concentration
and the temperature in the winter mixed layer. In this study, I investigate
how this simple relation can be used to compare model results from a general
circulation model with data, and whether the relation can be described
by a simple model. A theoretical framework that focuses on the relation
between variables and the temperature of the winter mixed layer is presented
and analyzed in some detail using results from a general circulation model.
An important theoretical quantity highlighted in this study is the dynamical
equilibrium concentration of the system; that is, the total inorganic carbonate
concentration of the winter mixed layer that would give zero annual flux
of CO2. It is shown that it is necessary to consider the integrated effect
of the annual cycles in sea surface temperature and biological production
to describe the system quantitatively. The difference in dynamical equilibrium
concentration between the southern and northern North Atlantic is of the
order of 250 mmol/kg; of this, the net effect of the annual cycles is 50
mmol/kg, which is not negligible. Further, the higher equilibrium concentration
in the Nordic seas implies that the concentration of the winter mixed layer
is about 200 mmol/kg higher in the Nordic seas as compared to the Sargasso
Sea. Of this, it is shown that about 90 mmol/kg is the result of entrainment
of carbon rich deep-water and about 110 mmol/kg is due to air-sea flux
of CO2.
POSTER
Advection of plankton in GCM's, is there a potential problem?
Goran Brostrom 1
1 Massachusetts Institute of Technology, Cambridge, MA
There is a widespread use of general circulation models (GCM) to study
the importance of various physical and biological processes for the primary
production, and to understand the structure of the food web. In this study,
I investigate one of the caveats that may arise when there is potentially
high phytoplankton growth rate (but lack of plankton) in low horizontal
resolution models. Under the prescribed situation, the advection and diffusion
may act to initiate an exponential growth of plankton in a large grid cell;
further, when a certain concentration is reached, it may seed the surrounding
grid cells with phytoplankton. Accordingly, the phytoplankton bloom can
travel faster in the model than the ocean currents that carries them. According
to some numerical experiments, the resolution of the model needs to be
on the order of Dx~U/gP to describe the advection of plankton in an adequate
way,. Here, U is the typical horizontal advection velocity and gP represents
the growth rate of phytoplankton. With U=0.1m/s and gP=1 day-1,
it follows that a resolution of about 8 km is crucial to describe the phytoplankton
dynamics in a correct way. Most GCM experiments uses coarser resolution;
accordingly, the results regarding the advection of plankton in these models
should thus be viewed with some caution.
TALK
A Comparison Of Potential Productivity In The California And Benguela
Currents
M-E Carr 1 and E. J. Kearns 2
1 Jet Propulsion Laboratory, Pasadena, CA
2 Rosenstiel School of Marine and Atmospheric Science, University of
Miami
The regions associated with the Atlantic and Pacific equatorward flowing
eastern boundary currents (EBC), i.e. the Canary, Benguela, California,
and Peru-Humboldt Currents, have long been recognized for their high productivity.
Although their area makes up a fraction of 1% of the world ocean, they
account for 5% of global primary production and 17% of global fish catch.
Here we compare the potential productivity of the two EBCs for which we
have most comprehensive in situ data: the California Current system (CCS)
and Benguela Current System (BCS). These two areas are the two end-members
in potential productivity as estimated from satellite-derived chlorophyll.
According to the first two years of SeaWiFS data, the BCS is the most productive
EBC, with an average of 2.45 gC/m2/d, and the CCS is the least,
with an average of 0.8 gC/m2/d. This reflects three major processes:
forcing due to light and upwelling favorable winds, the nutrient regime
in the upwelled water, and circulation patterns which enable or hinder
accumulation of cells or nutrients. We examine these processes using historical
hydrographic data and satellite measurements to quantify the controlling
factors of primary production in these two regions.
TALK
Modeling Interannual Variability of Plankton and Biogeochemistry
in the Tropical Pacific Ocean
James R. Christian 1, Mark A. Verschell 2, Raghu Murtugudde 3, Antonio J. Busalacchi 4, and Charles R. McClain 4
1 Universities Space Research Association, NASA Goddard Space Flight
Center, Greenbelt, MD
2 National Research Council, NASA Goddard Space Flight Center, Greenbelt,
MD
3 ESSIC, University of Maryland, College Park, MD, USA
4 NASA Goddard Space Flight Center, Greenbelt, MD, USA
A coupled physical-biogeochemical model of the tropical Pacific Ocean
was developed. The model incorporates both iron- and-nitrogen limited phytoplankton
growth, and succession of phytoplankton size classes in accordance with
the "ecumenical" iron hypothesis. The model shows a very strong El Niño
- Southern Oscillation component to phytoplankton variability in the central
equatorial Pacific. It is possible that this mode is more dominant in the
model than in nature, although the correlation of modeled and observed
chlorophyll in this region is strong. This is the primary interannual mode
that must be captured in order to simulate biogeochemical responses to
longer term climatic changes, and this is the first time that this has
been achieved with a prognostic biogeochemical model. The realism of the
simulation is limited primarily by lack of information about the abundance
and distribution of dissolved iron; the magnitude and distribution of the
aeolian iron flux and the assumption of constant Fe:N ratios are also important
sources of uncertainty. The sensitivity of the simulation to the way that
iron is initialized in the western Pacific thermocline emphasizes the importance
of the equatorial undercurrent throughout the tropical Pacific and the
need for iron observations in this region. Longer term (e.g., decadal)
changes in ocean biogeochemistry are difficult to verify, but are coherent
with available meteorological and oceanographic observations. The biogeochemical
model maintains realistic nutrient pools over the time scales required
for interannual simulation, and appears to respond in a realistic fashion
to changing upper ocean hydrography and circulation.
TALK
Modeling microbial processes and dissolved organic matter: a case
study at the US-JGOFS time series Station ALOHA
James R. Christian 1, and Ricardo M. Letelier 2
1 Universities Space Research Association, NASA Goddard Space Flight
Center, Greenbelt, MD
2 College of Oceanic and Atmospheric Sciences, Oregon State University,
Corvallis, OR,
The development of coupled physical-biological models of ocean biogeochemistry
is hampered by several critical knowledge gaps. Plankton models have attempted
to incorporate the "microbial loop" and dissolved organic substances, but
have done so using formulations that are highly uncertain. As these processes
play a significant role in biogeochemical cycling in the oceans, we consider
development of more realistic models of this component of the community
to be critical to development of global models that have a mechanistic
basis for predicting elemental budgets. The HOT data base provides an excellent
opportunity to develop and test such a model. Observations at HOT deviate
strongly from established paradigms of plankton ecology (seasonal convection,
nitrate-based production, metazoan zooplankton as primary consumers) that
are to some extent assumed in plankton models. The HOT data base provides
an unprecedented opportunity to validate a more realistic model, as observations
of dissolved organic substances have been made routinely throughout the
HOT project, and significant interannual variability in these has been
observed. To provide a meaningful simulation of such variability requires
a mechanistic model not only of plankton population biology, but of the
interface between biology and chemistry that is found in the decomposer
loop.
POSTER
Modeling Trichodesmium and the Impact Nitrogen Fixation in
the Atlantic Ocean
Victoria J. Coles 1 and Raleigh R. Hood 1
1 Horn Point Environmental Laboratory, Cambridge, MD
Nitrogen fixation is important because it can drive a net export of carbon from surface waters to the deep ocean, and the balance between nitrogen fixation and denitrification ultimately determines the degree to which phytoplankton in the oceans are nitrogen limited. Geochemical and direct rate estimates suggest that a large fraction of global marine N2-fixation occurs in the Altantic, and that the resulting flux of new nitrogen from the atmosphere to the ocean is significant (i.e., comparable to inputs of NO3 from the deep ocean).
The conspicuous marine cyanobacterium, Trichodesmium, is believed to be the most significant N2-fixer. We have a very poor understanding of the spatial and temporal variability in the distribution of this organism, and of the impact of the resulting N fluxes on the pelagic ecosystem. Factors which control the growth of Trichodesmium are not well understood, but are thought to include temperature, mixing/light, iron, and competition with other phytoplankton species.
In this poster we describe modeling studies which explore these issues.
It is shown that the influence of two factors, mixed layer depth
and competition with other phytoplankton species, is sufficient to
explain meridional variability in the distribution of Trichodesmium
colonies in the western tropical Atlantic. The model also predicts
high colony concentrations/N2-fixation in the eastern tropical Atlantic
which appear to be reflected in geochemical (N*) data. In addition
we show that N fluxes due to N2-fixation can have a significant impact
on the distribution of phytoplankton, and that inclusion of Trichodesmium
chlorophyll helps to explain some of the discrepancies between model-predicted
and satellite-derived chlorophyll concentrations.
POSTER
Assembly, Quality Control and Analysis of Components of the Carbon Dioxide System
Margarita Conkright 1 and Paulette Murphy 1
1 NOAA/NODC, Silver Springs, MD
Abstract pending
TALK
Iron Cycling and Nutrient Limitation Patterns in the World Ocean:
Results from A Marine Ecosystem Model
Scott C. Doney 1, J. Keith Moore 1, Joan A. Kleypas 1, David M. Glover 2, and Inez Y. Fung 3
1 National Center for Atmospheric Research, Boulder, CO 80307
2 Woods Hole Oceanographic Institution, Woods Hole, MA 02543
3 University of California Berkeley, Berkeley, CA 94720
A marine ecosystem mixed layer model is used to study iron cycling and
nutrient limitation patterns in surface waters of the world ocean. The
ecosystem model has two size classes of phytoplankton including a small
phytoplankton class whose growth rates can be limited by available nitrogen,
iron, and/or light, and a large phytoplankton class explicitly modeled
as diatoms whose growth can be limited by available nitrogen, iron, silica,
and/or light levels. Primary and export production in the model are sensitive
to variations in the atmospheric iron source over most of the world ocean.
Using an assumed solubility of 2% for the atmospheric iron inputs the model
produces realistic patterns of primary production, particulate organic
carbon export, surface chlorophyll concentrations, phytoplankton cellular
iron / carbon ratios, and surface layer dissolved iron concentrations.
During summer months the smaller phytoplankton are iron-limited over 51%
of the world ocean, with 30% of the ocean nitrogen-limited and 19% nutrient-replete.
Diatom growth rates are iron-limited over 42% of the ocean, nitrogen-limited
over 40%, silica-limited over 18%, and nutrient-replete over < 1%. Thus,
nitrogen limits phytoplankton growth rates over less than half of the world
ocean. This pattern is seen even at significantly higher solubilities for
the atmospheric iron input. These results suggest that the familiar paradigm
that nitrate inputs to the surface layer can be equated with particulate
carbon export needs to be expanded to include multiple limiting nutrients
and modes of export.
TALK & POSTER
Effect of Interannual Variability of Mixing and Light on Phytoplankton
Abundances
Stephanie Dutkiewicz 1, Mick Follows 1, John Marshall 1, Watson W. Gregg 2
1 Department of Earth, Atmospheric and Planetary Sciences, Massachusetts
Institute of Technology
2 NASA Goddard Flight Center, Laboratory for Hydrospheric Processes
In previous studies, using a combination of remote ocean color observations
and numerical models, we have predicted and found relationships between
springtime surface heat fluxes, wind forcing, boundary-layer mixing, and
the intensity of the spring phytoplankton blooms in the North Atlantic.
These relationships were robust in subtropical regions, but do not emerge
as clearly in subpolar regions indicating the added importance of other
sources of variability in that region. Here we address the importance of
the interannual variations of sea surface insolation. We perform a suite
of sensitivity experiments with a physical-biological model of the North
Atlantic to examine the response of surface chlorophyll to variability
in meteorological forcing, upper-ocean mixing, and incident surface radiation.
The physical general circulation model is forced with reanalyzed, twice-daily,
meteorological fields for 1989-1993. Surface photosynthetically active
radiation, resolved into several optical wavelength bands, is specified
from remotely sensed data over the same time period. In the subtropics,
variability in chlorophyll caused by changing light fields, is eclipsed
by variability induced by circulations and mixing. In higher, light limited
latitudes, however, variability in insolation has a more significant impact
on the chlorophyll distribution. This can account (in part) for the weaker
subpolar relationship between the SeaWiFS-derived chlorophyll variability
and surface flux variability found in our earlier studies.
POSTER
On the seasonal nitrate distribution and relation to air-sea oxygen
flux in the global ocean
Hernan Garcia 1 and Ralph Keeling 1
1 Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA
We report on a preliminary analysis of the seasonal nitrate distribution
in the surface ocean. We use linear least-squares regressions between nitrate
and seasonal sea-surface temperature to interpolate the nitrate data in
latitudinal bands. The results indicate good correlation coefficients between
nitrate and biologically mediated air-sea oxygen flux in latitudinal bands
poleward of about 30°. This general correlation suggests that nitrate
uptake is an important component driving the air-sea seasonal oxygen biological
flux at middle to high latitudes. Tropical nitrate values are difficult
to resolve spatially and temporally because the seasonal nitrate amplitude
is relatively small except near upwelling regions.
POSTER
Status of nutrient data calibration for the Pacific WHP, One-time
survey
L.I. Gordon 1, C.W. Mordy 2, A.A. Ross 1, J.C. Jennings, Jr. 1, J. Johnson 3
1 College of Oceanic and Atmos. Sci., Oregon State Univ., Corvallis,
OR
2 NOAA/PMEL, Seattle, WA
3
This is to report our progress in deriving corrections to the WHP nutrient data sets for individual Pacific lines to make them as internally consistent as possible. We follow two lines of attack. First is a quantitative analysis of errors inherent in any analytical protocol such as that suggested by Gordon et al., for the WHP and JGOFS nutrient work. We compare the results with actual, quality control data obtained from some of the legs. Second is a statistical analysis of the data acquired in the Pacific at stations reoccupied after varying intervals. At this writing, we are substantially done with the work necessary to decide upon the method and values of corrections to apply.
We have concluded that additive, zero-offset errors are negligible compared with factorial, or multiplicative, errors. The latter stem mainly from variance in preparation of working, calibration standards. These standards are used to calibrate the range, or sensitivity of the nutrient analysis systems. We have made estimates of accuracy and precision in preparing working standards derived by propagating errors of the steps in the preparation. We compare these results with data from replicate preparations of standards made during several legs.
Within the context of the results of the error analyses just noted we proceed to the ultimate step: From the statistical analysis of data at reoccupied stations, we are close to deciding upon a set of lines whose nutrient data may be used as ``referee'' lines for deriving quantitative correction factors. We will propagate the corrections forward as necessary through all of the reoccupations until all lines will have had correction factors assigned to them. We will close with a list of caveats to be used in using these correction factors.
At the Workshop we will meet with our Co-Pi's on the ``Redfield Ratios'' project to decide upon the integrity of our correction factors. If appropriate, we will then report within the SMP community our conclusion of which lines appear to be the most suitable as ``referee'' lines. We will also report a matrix of correction factors for each nutrient on each Pacific line and a much smaller matrix of secondary correction factors which might be used to correct to different referee lines.
TALK
Zooplankton grazing functions and ecosystem dynamics: a critical
review of the assumptions. Part II
Wendy Gentleman 1, Andrew Leising 1, Bruce Frost 1, Jim Murray 1, Suzanne Strom 2
1 University of Washington, School of Oceanography, Seattle, WA
2 Shannon Point Marine Center, Anacortes, WA
see Leising for abstract
TALK
New Production as a Constraint on Ocean Circulation
Anand Gnanadesikan 1
1 AOS Program, Princeton University, Princeton, NJ
The ocean circulation can be energized either by low-latitude diffusion
or by Southern Ocean winds. The two alternatives have very different implications
for new production. This talk compares estimates of new production from
satellites and nutrient climatologies with that predicted from four general
circulation models. Vertical diffusion is found to play an important role,
not only at low but also at high latitudes.
TALK
Net air-sea fluxes of natural and anthropogenic CO2 from an inversion
of ocean inorganic carbon observations
N. Gruber 1,2, M. Gloor 1,3, and J.L. Sarmiento 1
1 AOS Program, Princeton University, Princeton, NJ
2 now at IGPP/Department of Atmospheric Sciences, UCLA, Los Angeles,
CA
3 now at Max Planck Institute for Biogeosciences, Jena, Germany
The large number of dissolved inorganic carbon (DIC) observations obtained
by JGOFS on the WOCE hydrographic survey provide us with an outstanding
snapshot of the ocean carbon distribution. A technique has been developed
in order to separate the anthropogenic carbon component from the pre-industrial
component of the DIC (Gruber et al. [1996]) and this has been applied to
data from both the Atlantic and Indian Oceans (Gruber [1998]; Sabine [1999]).
We make use of these results together with some preliminary results from
the Pacific Ocean in order to estimate the pre-industrial and anthropogenic
air-sea flux of carbon dioxide. We use an ocean inverse model approach
to establish the relationship between interior concentrations and surface
fluxes. This relationship is obtained using an ocean circulation model
analogous to similar approaches used in analyzing atmospheric carbon dioxide
observations. The resulting pre-industrial air-sea fluxes of CO2 reveal
the expected pattern of CO2 uptake by the oceans in the high latitudes
and release back into the atmosphere in the low latitudes. By contrast,
the air-sea flux of anthropogenic CO2 is found to be into the ocean everywhere,
totalling about 1.6 Pg C/yr (preliminary estimate). The total air-sea fluxes
(i.e. pre-industrial and anthropogenic) agree very well with the flux estimates
of Takahashi et al. [1999] in regions where both techniques have good data
coverage, particularly the North Atlantic. The inversion results do not
show a large cross-equatorial southward carbon transport in the Atlantic
such as has been proposed by Keeling et al. [1989], Broecker and Peng [1992],
and Keeling and Peng [1995]; the transport obtained by the inversion is
only 0.21 Pg C/yr. Neither does it show a large efflux of carbon dioxide
from the Southern Ocean, such as would be required by Keeling et al. [1989].
TALK
Recent highlights from the Ocean Carbon-Cycle Model Intercomparison
Project (OCMIP)
N. Gruber 1,2 and OCMIP members
(1) AOS Program, Princeton University, Princeton, NJ
(2) now at IGPP/Department of Atmospheric Sciences, UCLA, Los Angeles,
CA
The Ocean Carbon-Cycle Model Intercomparison Project (OCMIP) was started
in the mid 1990s with support from IGBP/GAIM in order to identify the principal
differences between global-scale, three-dimensional, ocean carbon-cycle
models, to accelerate their development, and to improve their predictive
capacity. Four models participated in the 1st phase that ended in 1997.
In the second phase that started in 1998 this number increased to thirteen
with the participation of four modeling groups from the U.S. (MIT, NCAR,
LLNL, and PU) funded through JGOFS/SMP. Rigorous protocols were developed
during OCMIP-2 so that all modeling groups could make consistent simulations.
The focus of OCMIP-2 was to study (1) natural CO2, (2) anthropogenic CO2,
and (3) transient tracers (i.e. chlorofluorocarbons (CFC), radiocarbon
(14C)), with the latter aimed at a careful evaluation of model circulation.
All groups have finished the required simulations for OCMIP2 and analysis
of the results are underway. My presentation will focus on some of the
recent highlights of this project on the basis of the presentations that
will be made during the OCMIP2 workshop being held in the week before the
JGOFS/SMP meeting.
TALK
Dissolved Organic Carbon Export by Overturning Circulation
Dennis A. Hansell 1 and Craig A. Carlson 1
1 Bermuda Biological Station for Research, Inc., St. George's BERMUDA
Here we provide observations of DOC export with water mass formation,
evaluate the controls on DOC export, and describe the global distribution
of water mass formation sites and the associated DOC export. We conclude
with estimates for the contribution of DOC export to total export by the
biological pump. It is obvious that DOC-enriched waters involved in overturning
circulation will effect DOC export. DOC-enriched surface waters, however,
are limited in distribution to the latitudes north of the Antarctic Polar
Frontal Zone. Mode waters formed north of those latitudes effectively export
DOC. Overturning circulation south of this region (e.g., Bottom Water formation
and high latitude Antarctic Intermediate Water) do not carry significant
loads of DOC, so export is minimal. We define the term "exportable" DOC,
to distinguish those waters with DOC export capability ("exportable" DOC
present) from those without such a capability. Based on our calculations
of DOC export to intermediate and deep portions of the ocean, we estimate
that DOC meets 10% of the carbon oxidation requirement at >500 m. The contribution
of DOC to exported C oxidized at depths <500 m is elevated relative
to the deep ocean. DOC contributes 15-40% of oxygen utilization at the
BATS site in the Sargasso Sea (Hansell and Carlson, 2000) and up to 45%
in the main thermoclines of the South Pacific and Indian Oceans (Doval
and Hansell, 2000). The global contribution of DOC to export must lie between
the 10% value of the deep ocean and the 40% value of the main thermocline.
We predict that the contribution of DOC to global export in the open ocean
will fall in the range of 20-30%.
TALK
Evaluation of marine primary productivity in the tropical Pacific
and Atlantic Oceans using satellite ocean color and numerical models
E. Hofmann 1, M. Friedrichs 1, C. McClain 2, A. Busalacchi 2, R. Murtugudde 2, J. Christian 2, T. Clayton 1, M. Verschell 2, J. Koziana
1 Center for Coastal Phys. Oceanogr., Old Domininion Univ., Norfolk,
VA
2 NASA/GSFC, Greenbelt, MD
In order to gain further insight into biological-physical interactions
in the tropical Pacific surface layer, we have undertaken a multi-faceted
approach in which we have (i) examined the importance of phytoplankton-induced
turbidity on the vertical structure and heat content of the upper ocean
by means of a coupled bio-optical and mixed layer model, (ii) investigated
the formation of Trichodesmium blooms and implications for their
remote detection through the use of a Trichodesmium buoyancy-regulation
model and radiative transfer modeling and (iii) demonstrated the feasibility
of assimilating SeaWiFS ocean color measurements in order to improve the
simulation skill of a one-dimensional ecosystem model. The one-dimensional
model results highlighted the importance of phytoplankton-induced turbidity
in heating of the upper ocean, the potential mechanisms that may underlie
Trichodesmium
blooms and the importance of multiple size classes of phytoplankton and
zooplankton, as well as the potential for limitation by both macro- and
micronutrients in the equatorial Pacific marine ecosystem. The results
of these studies are now being combined as we proceed to the next stage
of developing a basin scale that includes data assimilation capability.
TALK
Comparative modeling and data analysis studies for the Ross Sea
and West Antarctic Peninsula Regions: a JGOFS synthesis and modeling project
Eileen Hofmann 1, John Klinck 1, Walker Smith 2, Barbara Prézelin 3
1 Center for Coastal Phys. Oceanogr., Old Domininion Univ., Norfolk,
VA
2 Virginia Inst. Mar. Sci., Gloucester Point, VA
3 Biological Sciences, Univ. Calif. Santa Barbara, Santa Barbara, CA
Our recently funded 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 data sets from the west Antarctic Peninsula region collected
during the Palmer Long-Term Ecological Research program. The modeling effort
will be in conjunction with analyses of these data sets as well as analyses
of historical data sets from the two regions. 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. Our general focus is on understanding the
role of light, macro- and micronutrient limitation, and circulation in
producing the observed horizontal and vertical gradients in phytoplankton
distribution and production. Thus, the data analyses and model simulations
will be used to test specific hypotheses concerning the regulation of phytoplankton
growth, production, and species composition in the two regions. As a start
towards addressing our project objectives we have undertaken a modeling
study that is designed to investigate the circum-Antarctic distribution
of Antarctic krill (Euphausia superba) and preliminary results from this
study will be presented. Also, preliminary work on the development of circulation
models for the Ross Sea and Antarctic Peninsula regions will be presented.
TALK
Global Export and Recycling of Biogenic Material into the Ocean Interior;
Strategy and Initial Results towards a Synthesis
S. Honjo 1, R. Francois 1, and S. Manganini 1
1 Woods Hole Oceanographic Institution
A large numbers of moored, longer term, time-series deep-sea sediment traps have been deployed by our group and others in the world ocean over the past 2 decades, and more are being deployed every year. We have started compiling published and unpublished sediment trap flux data into an integrated and consistent data set. Our goal is to refine our present estimates of global and regional fluxes and remineralization of biogenic material (organic C, calcite, aragonite, opal, N, and P) and lithogenic particle input in the ocean interior. More specifically, we plan to:
TALK
Part 1: Remote Estimation of Nitrogen Fixation by Trichodesmium
Raleigh R. Hood 1, Ajit Subramaniam 2, Linda R. May , Edward J. Carpenter 3, and Douglas G. Capone 4
1 Horn Point Environmental Laboratory, Cambridge, MD
2 University of Southern California, Los Angeles, CA
3 State University of New York, Stony Brook, NY
4 Department of Biological Sciences & Wrigley Institute for Environmental Studies, University of Southern California, Los Angeles, CA
In this paper a non-spectral model is described that can be used to calculate N2-fixation rate from remote estimates of Trichodesmium biomass. This model, which is similar to formulations that have been developed for estimating primary production from satellite-derived phytoplankton chlorophyll concentrations, is parameterized using measured Trichodesmium N2-fixation vs. irradiance data and observed subsurface Trichodesmium biomass profiles from the Tropical Atlantic Ocean. These data reveal that the N2-fixation vs. irradiance responses and subsurface distributions of Trichodesmium vary substantially in tropical waters. Sensitivity analyses show that the calculated rates are sensitive to only one of three forcing variables: the remotely sensed Trichodesmium chlorophyll concentration, BT(sat), and two of the model parameters: the maximum N2-fixation rate, Pmax (BT ), and the depth of the subsurface Trichodesmium biomass maximum, Zm. The model is particularly sensitive to the latter. The results from a series of correlation analyses are presented which reveal statistically significant correlations between the diffuse attenuation coefficient, Kpar, and , Pmax (BT ), and between wind speed and Zm. These relationships are suggested as potential means of accounting for natural variability in Pmax (BT ) and Zm. An example remote sensing-based rate calculation is made using SeaWiFS-derived Trichodesmium chlorophyll concentration in the South Atlantic Bight. Although the optical conditions in the Bight were not all within the range used to derive the model parameters, the model gives rates that are consistent with direct rate measurements in Trichodesmium blooms.
Part 2: Detecting Trichodesmium Blooms in SeaWiFS Imagery
Ajit Subramaniam 1, Raleigh R. Hood 2, Christopher W. Brown 2, Edward J. Carpenter 3, and Douglas G. Capone 4
1 University of Southern California, Los Angeles, CA
2 Horn Point Environmental Laboratory, Cambridge, MD
3 State University of New York, Stony Brook, NY
4 Department of Biological Sciences & Wrigley Institute for Environmental Studies, University of Southern California, Los Angeles, CA
An optical model for calculating remote sensing reflectance is was
parameterized for Trichodesmium and other phytoplankton. The normalized
water-leaving radiance thus derived
is was compared to that determined from a SeaWiFS scene of a Trichodesmium
bloom in the Capricorn Channel in the Great Barrier Reef. The comparison
showsed that, while the optical model predictsed the absolute magnitude
of the 490 nm channel reasonably well, the magnitude of the other
channels and hence the spectral shape predicted by the model for Trichodesmium
blooms doesid not match that determined by SeaWiFS. The model iwas
then run for varying proportions of Trichodesmium and other phytoplankton.
A proportion of 40% Trichodesmium and 60% other phytoplankton fits
the spectrum of a SeaWiFS pixel from the middle of a Trichodesmium
bloom very well. The SeaWiFS data from the Capricorn Channel are
were used to construct a classification scheme for Trichodesmium based
on the magnitude of the 490-channel reflectance and the spectral shape
of reflectance at 443, 490 and 555 channels. This scheme, which A
Trichodesmium classification scheme was is derived for moderate chlorophyll
concentrations between 0.8 and 1.5 mg/m3, and is tested against other
known highly reflective phenomena in the water such as sediments plumes
and coccolithophore blooms. The classification is also applied to
a Trichodesmium bloom encountered in the South Atlantic Bight during
a cruise in the fall of 1998 when various optical in-situ measurements
and Trichodesmium cell counts were made. We conclude that it is possible
to map and track Trichodesmium blooms of moderate concentrations over
time, even in waters as optically complex as the South Atlantic Bight.
However, ancillary data such as wind speeds and water temperature
will be required as additional constraints to minimize false positive
retrievals.
POSTER
Modeling sub-euphotic zone zooplankton dynamics and its impact on
falling organic matter
George A. Jackson 1 and Adrian B. Burd 1
1 Texas A&M University, College Station, TX
abstract pending
TALK
Global Synthesis of Deep Ocean Carbon, Carbonate, Opal and Nutrient
Particle Fluxes, Benthic Fluxes and Sediment Accumulation
Richard A. Jahnke 1
1 Skidaway Inst.Oceanography, Savannah, GA
The goal of this project is to synthesize sea floor measurements into a global description of particulate fluxes of carbon and nutrients in the deep ocean. The strategy for constructing this description will be to build upon previously published compilations of sediment accumulation and benthic fluxes (i.e. Jahnke, 1996) by 1) Improving the fundamental data sets from which the estimated flux distributions and patterns are derived. This will include the incorporation of recent results (sedimentary organic C, CaCO3 , opal, accumulation rates, and benthic fluxes of O2, TIC, nutrients, and selected tracers such as Ba and Ge) into the primary data sets; re-examination of the methods used to establish the mean sedimentary property fields; and expansion of the regions considered to include continental margins and high latitudes. 2) Assimilating the individual measurements into a general organic C-CaCO3-Opal diagenetic model to provide a mechanistically more meaningful method for establishing basin-wide flux patterns and rates. This model will expand upon the use of time-normalized master variables for extending model applicability throughout the ocean basins.
The development of a global description of deep particulate fluxes and burial rates will permit a variety of issues to be assessed. For example, the role of continental margins in the transfer of organic matter to the deep sea can be directly evaluated by quantitatively comparing the fluxes associated with margins to that of the global total flux. The role of siliceous organisms in controlling deep fluxes can be assessed by determining what proportion of the total flux is associated with opal input. Additionally, because the ratio of benthic flux to accumulation rate defines the relationship between the rain rate and preserved sedimentary record, these studies will provide fundamental calibration information for paleoceanographic proxies and tracers.
Reference:
Jahnke, R. A. (1996) The global ocean flux of particulate organic carbon:
Areal distribution and magnitude. Global Biogeochem. Cycles 10: 71-88.
POSTER
Physical-Biogeochemical Modelling Modulation of Decadal Variability on ENSO events in the Equatorial Pacific
M.S. Jiang 1, F. Chai 1, R.T. Barber 2, R. Dugdale 3, F. Wilkerson 3, T-H Peng 4, Y. Chao 5
1 University of Maine, Orono, ME
2 Duke University Marine Lab, Beaufort NC
3 Romberg Tiburon Center for Environmental Studies, San Francisco State
University, Tiburon, CA
4 AOML/NOAA
5 JPL/NASA
Although decadal scale physical changes have been observed at several locations in the Pacific ocean, how these subtle but pervasive variations have altered ecosystem processes and biogeochemical fluxes remains largely unclear. To improve our understanding of physical variability and the ecosystem response in the Pacific Ocean, a coupled physical-biogeochemical model has been developed. A 10-component biogeochemical model has been embedded in Modular Ocean Model(MOM) with modifications and configurations for the Pacific Ocean by Chao et al. at the JPL. The model is used to simulate both physical and biogeochemail conditions between 1955-1993. Based on this long-term model simulation, we present the results focused on the role of decadal variations on the ENSO events occurring before/after the climatic regime shift in 1976/77.
It is generally agreed that the signals of Pacific Decadal Oscillation(PDO)
primarily originate from Northwest Pacific and affect Equatorial Pacific
through intergyre exchanges. The detailed nature of ENSO events may be
modulated by this persistent process. As a consequence, the ecosystem
behaviors in the Equatorial Pacific should be affected by the modulated ENSO,
primarily through the depth of nutricline and upwelling variability. With
preliminary modeled results, we examine the evolution of ENSO before and after
climatic shift. The nutrient fluxes and phytoplanton responses are studied as
well. Furthermore, the difference in nitrogen and silicon cycle for the water
columns is addressed in order to investigate the factors that determine
vertical structure of nitrate and silicate for the top 2000m.
POSTER:
Decadal scale trends in North Pacific nutrient and oxygen concentrations:
Biological or physical explanation?
Klaus Keller 1, R. D. Slater 2, M. Bender 1, and R. M. Key 1
1 Dept. Geosciences, Princeton Univ., Princeton, NJ
2 AOS Program, Princeton Univ., Princeton, NJ
We analyze North Pacific GEOSECS (1970's) and WOCE (1990's) observations
to examine potential oceanic carbon uptake resulting from decadal trends
of the marine biological carbon pump. Nitrate concentrations and apparent
oxygen utilization decreased significantly in deep waters (between approximately
1000 and 1600 m), and increased, though not significantly, in shallow waters
(above roughly 750 m). A sensitivity study of an ocean general circulation
model indicates that reasonable perturbations of the biological carbon
pump due to changes in export production or remineralization efficiency
are insufficient to account for the deep water tracer trends. However,
changes in deep water ventilation rates could explain the deep water tracer
trends and would be consistent with radiocarbon derived water age trends.
Trends in oxygen and nitrate concentrations provide relatively poor constraints
on decadal scale trends in the marine biological carbon pump for two reasons.
First, most of the expected changes due to decadal scale perturbations
of the marine biota occur in shallow waters, where the available data is
typically too sparse to account for the strong spatial and temporal variability.
Second, alternative explanations for the observed tracer trends (e.g.,
changes in the water ventilation rates) cannot be firmly rejected. As a
result, estimates of oceanic carbon uptake due to decadal trends in the
marine biological carbon pump are rather uncertain.
POSTER
Nutrients and primary production in the mixed layer - A compilation
of data collected at eight JGOFS sites
J. Kleypas 1, Scott Doney 1, and Keith Moore 1
1 National Center for Atmospheric Research, Boulder, CO
Field measurements of nutrients, primary production and other parameters
were compiled for eight JGOFS time-series and process study sites. Daily
mixed layer depths were determined for each site, and then used to calculate
average mixed layer concentrations for each available parameter. These
resulting data sets should facilitate regional and global ecosystem model
development by providing a consistent, quality controlled set of observations
for key JGOFS sites. So far, data are available for eight locations: BATS,
HOT, EqPAC, Kerfix, Station P, Arabian Sea, NABE, and Southern Ocean. These
data will be made available soon along with a technical report describing
data sources, methodologies, and results.
TALK
Global Fields of Carbonate Ion Concentration Using the Recently
Collected WOCE/JGOFS Global Carbon Data
Kitack Lee 1,2, R. A. Feely 3 , F.J. Millero 4, C. Sabine 3, and T.-H. Peng 1
1 Atlantic Oceanographic and Meteorological Laboratory/NOAA, Miami, FL
2 RSMAS/CIMAS, University of Miami, Miami, FL
3 Pacific Marine Environmental Laboratory, NOAA, Seattle, WA
4 Rosenstiel School of Marine and Atmospheric Science/MAC, University
of Miami, Miami, FL
Previous studies by Feely et al., (1988); Sabine et al. (1995); and
Archer (1996) have demonstrated that carbonate ion concentrations in seawater
plays a major role in controlling seawater saturation with respect to calcite
and aragonite, and subsequently the carbonate lysocline depth in the major
ocean basins. Over the past eight years (1990-1998), the WOCE/JGOFS multi-national
CO2 survey of the global ocean has generated a high quality global database,
which is an order of magnitude more measurements than the previous GEOSECS
survey. A multi-investigator analysis of these data has resulted in a unified
database for the Pacific and Indian Oceans (Johnson et al., 1998; Millero
et al., 1998; Sabine et al., 1999; Lamb et al., 2000). We have calculated
seawater carbonate ion concentration using this globally coherent total
inorganic carbon and total alkalinity data along with a set of thermodynamic
constants, which is most internally consistent using laboratory-calibrated
measurement protocols (Lee et al., 2000). We will show how the use of the
new carbo
n data has changed the calculated carbonate ion distributions in the
oceans as compared with the previous studies.
References:
Archer, D. E., 1996. An atlas of the distribution of calcium carbonate in sediments of the deep sea. Global Biogeochem. Cycles, 10, 159-174.
Feely, R.A., R.H. Byrne, J.G. Acker, P.R. Betzer, C.-T.A. Chen, J.F. Gendron, and M.F. Lamb.`, 1988. Winter-summer variations of calcite and aragonite saturation in the northeast Pacific. Mar. Chem., 25, 227241.
Johnson et al., 1998. Coulometric total carbon dioxide analysis for marine studies: Assessment of the quality of total inorganic carbon measurements made during the US Indian Ocean CO2 Survey 1994-1996. Mar. Chem., 63, 21-37.
Lamb et al., 2000. Internal consistency and synthesis of Pacific Ocean CO2 survey data, Deep-Sea Res. II, submitted.
Lee, K., Millero, F.J., Byrne, R.H., Feely, R.A., and Wanninkhof, R., 2000. The recommended dissociation constants of carbonic acid in seawater, Geophys. Res. Lett., 27, 229-232.
Millero et al., 1998. Assessment of the quality of the shipboard measurements of total alkalinity on the WOCE hydrographic program Indian Ocean CO2 survey cruises 1994-1996, Mar. Chem., 63, 9-20.
Sabine, C. L., F. T. Mackenzie, C. Winn, D. M. Karl, 1995. Geochemistry of carbon dioxide in seawater at the Hawaii Ocean time series station, ALOHA, Global Biogeochem. Cycles, 9: 637-651.
TALK
Zooplankton grazing functions and ecosystem dynamics: a critical
review of the assumptions. Part I
Andrew Leising 1, Wendy Gentleman 1, Bruce Frost 1, Jim Murray 1, Suzanne Strom 2
1 University of Washington, School of Oceanography, Seattle, WA
2 Shannon Point Marine Center, Anacortes, WA
The equatorial and subarctic Pacific ecosystems are HNLC (High Nitrate Low Chlorophyll) regions. The importance of microzooplankton grazing to the maintenance of this HNLC condition is well known, and is a major process in ecosystem models used to study mechanistic controls and to predict carbon export. We show, however, that the formulations used to characterize the grazer response entail assumptions that can
significantly impact the model results. Current models rely upon a lower
feeding threshold for the microzooplankton in order to achieve the HNLC
condition. However, the assumption that the specific microzooplankton living
within these HNLC regions have a lower feeding threshold has not been rigorously
tested, and so the parameters characterizing their functional response
are ill-constrained. Here, we present a simple model of the HNLC system
without a lower threshold, which can capture the HNLC dynamics under current
climatological forcing, but which displays different dynamics when subjected
to larger environmental perturbations. Examination of the mathematical
functions commonly used to characterize the response of a grazer to multiple
prey items reveals that they can behave in ways that are contrary to our
conceptual model of these processes. In particular, prey selection formulas
that represent prey preference and prey switching imply unrealistic grazing
dynamics at low prey concentrations. These assumptions, implicit in the
mathematics, can affect model predictions of ecosystem dynamics. Both explicit
and implicit assumptions relating to grazing are critical to the model
results; different formulations imply different mechanistic controls, and/or
yield different results when extrapolated to other regions or perturbed
beyond currently observed forcing. This suggests future studies need to
concentrate on experimental determination and proper mathematical characterization
of the functional responses of microzooplankton.
TALK
Preliminary results from an ecosystem model for the North Atlantic
Ivan Lima 1, Scott Doney 1, David Glover 2, Frank Bryan 1, Dennis McGillicuddy 3, Larry Anderson 3 and Mathew Maltrud 4
1 National Center for Atmospheric Research, Boulder, CO
2 Woods Hole Oceanographic Institution, Woods Hole, MA
3 Woods Hole Oceanographic Institution, Woods Hole, MA
4 Los Alamos National Laboratory, Los Alamos, NM
The episodic upwelling of nutrients into the euphotic zone by mesoscale
eddies is thought to significantly increase the net community production
and export of organic carbon both in seasonally and permanently oligotrophic
regions of the ocean. Biological--physical coupling due to eddies (nutrient
injection, turbulent stirring etc.) also modulates the observed time and
space scales for biological variability such as that recorded by moorings,
field studies and satellite remote sensing. In this study, an NPZD ecosystem
model is incorporated into a high resolution 3-D physical model for the
North Atlantic based on the Los Alamos Parallel Ocean Program (POP). Model
experiments at varying spatial resolution from non-eddy resolving through
eddy permitting are used to investigate the impact of mesoscale eddies
on biological production across a range of marine environments. Preliminary
results will be presented and discussed focusing on the time and space
scales of primary production and phytoplankton biomass and the impact of
mesoscale variability on export production.
TALK
The role of mesoscale eddies in basin-scale biogeochemical budgets
of the North Atlantic: results from a high resolution (0.1 degree) simulation
D.J. McGillicuddy 1, S.C. Doney 2, L.A. Anderson 1, M.E. Maltrud 3, and F.O. Bryan 2.
1 Dept of Applied Ocean Physics and Engineering, Woods Hole Oceanographic
Inst., Woods Hole, MA
2 National Center for Atmospheric Research, Boulder, CO
3 Los Alamos National Laboratory, Los Alamos, NM
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
Modeling Mesoscale Biogeochemical Processesin a Topex/Poseidon Diamond
Surrounding the U.S. JGOFS Bermuda Atlantic Time-series Study
D.J. McGillicuddy 1, Jr., V.K. Kosnyrev 1, E.N. Sweeney 1 and K.O. Buesseler 2
1 Dept of Applied Ocean Physics and Engineering, Woods Hole Oceanographic
Inst., Woods Hole, MA
2 Dept of Marine Chemistry and Geochemistry, Woods Hole Oceanographic
Inst., Woods Hole, MA
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.
POSTER
DI13C in the world's oceans
A.P. McNichol 1 and P.D. Quay 2
1 NOSAMS, Woods Hole Oceanographic Institution, Woods Hole, MA, 02543
2 University of Washington, Seattle, WA, 98195
Over the past decade, almost 25000 samples have been collected for the measurement of d13C in dissolved inorganic carbon (DI13C) at either UW or NOSAMS. Data from these cruises represent the first high quality, ocean-wide DI13C data set. The measured distributions of DI13C in the oceans will provide useful feedback to global ocean models trying to reproduce the observations. Data from the surface ocean can provide estimates of the rate of uptake of anthropogenic CO2 while the deeper data will allow a re-examination of basic ocean processes.
In two papers, (Sonnerup et al. 1999, Sonnerup et al., in press) two different approaches, one using pre-formed DI13C and the other a multiple linear regression, are used to assess the uptake of anthropogenic CO2 over time without relying on historic measurements of DI13C. This is critical because of the problems observed in older data sets (Kroopnik 1985, Lerperger et al., in review). Using the new data set with existing published calculations, it is possible to refine an estimate of anthropogenic CO2 uptake to 1.7 ± 0.8 Gt C/yr (Quay, in prep.). This estimate is consistent with previous ones but has a greatly reduced error.
Impressive as this data set and the work that can be accomplished with
it are, important areas of the ocean lack data. More samples need
to be collected in the southern Atlantic Ocean, particularly in the east,
to have truly global coverage.
TALK (and poster?)
Global POC synthesis from beam attenuation data collected during
JGOFS, WOCE and other programs
A.V. Mishonov 1, W.D. Gardner 1, M.J. Richardson 1
1 Department of Oceanography, Texas A & M University, College Station, TX
The objective of this project is to convert extensive beam attenuation
data to POC to obtain a global synthesis of POC. By interfacing transmissometers
with CTDs we have collected beam attenuation data over the last decade
during 17 WOCE cruises and other hydrographic programs. We are using beam
cp:POC relationships to convert the beam attenuation data to POC. These
relationships have been derived by our group during JGOFS Process studies
beginning in 1989 and during other programs. These beam attenuation data
include basin-wide transects in the North and South Atlantic, North and
South Pacific, Indian, and Southern Oceans. The raw data reside in our
laboratory. We are beginning to extract the data, convert them to POC and
compile a data inventory for this global data set. The data are in several
different formats from the many different programs. The raw transmissometer
data and the corresponding CTD data are will be put into a standard format
and entered into a data base along with the appropriate metadata (station
location, time, etc.). We presently have preliminary assessed 27 data sets
consisting of more than 2300 transmissometer casts to add to the 19 cruises
worth of data obtained during JGOFS. Considerable work is needed in quality
control and processing the new data to make them compatible with JGOFS
data sets. These data sets are particularly useful because spatial coverage
of the new data sets is much greater than was available from JGOFS.
TALK
Synoptic Analysis of Factors Influencing Carbon Fluxes at the CARIACO
Continental Margin Time Series
Frank Muller-Karger 1, Ramon Varela 2, Robert Thunell 3, and Denis Nadeau 4
1 University of South Florida
2 Fundacion La Salle, Venezuela
3 University of South Carolina, Columbia, SC
4 Raytheon
Monthly hydrographic, primary production, and settling particulate carbon
flux observations have been since November 1995 at 10.5° N, 64.67°
W within the Cariaco Basin, off Venezuela. Upwelling of Subtropical Underwater
(SUW) starts around October and lasted through approximately May of the
following year. The upwelling seasonal cycle seems to be slightly out of
phase with that of the Trade Winds by 1-3 months. The upwelling cycle is
also punctuated by transient extremes associated with subsurface ventilation
events and this has substantial impact on annual primary production values.
Settling carbon flux measured with sediment traps was about 5.6% of integrated
primary production at 275 m and about 1.7% at 1,225 m with no seasonality
in the proportion of vertical flux to primary production. In total, between
10-11 gC m-2 y-1 were delivered to the
bottom sediment of Cariaco, which suggests that between 4x105
and 1x106 metric Tons of C y-1 were delivered to
sediments within the upwelling area of the Cariaco Basin. We propose that
this represents permanent sequestration of carbon previously entrained
in the North Atlantic gyre in the area of formation of SUW. Results suggests
that upwelled inorganic nitrogen with an N* signature acquired in transit
to the Caribbean Sea, rather than nitrogen fixation, is responsible for
the large productivity and particulate carbon settling flux in the Cariaco
Basin.
POSTER
Distribution of Bomb-produced Radiocarbon in a Physical-Biogeochemical
Model of the Pacific Ocean
T-H Peng 1, F Chai 2, M S Jiang 2, and Y Chao 3
1 NOAA/AOML, Miami, FL
2 University of Maine, Orono, ME
3 JPL/NASA, Pasadena, CA
A coupled physical-biogeochemical model has been developed to improve
our understanding of physical variability and the ecosystem response in
the Pacific Ocean. A 10-component biogeochemical model, developed initially
for the equatorial Pacific, has been embedded in Modular Ocean Model (MOM)
with modifications and configurations for the Pacific Ocean by Chao et
al. at the JPL. The model is used to simulate both physical and biogeochemical
conditions between 1950-1993. Before this model can be used confidently
to study the ecosystem structure changes on seasonal to decadal time scales
in the Pacific Ocean, we need to evaluate how well the model could simulate
the distribution of bomb radiocarbon as observed during the GEOSECS and
in recent WOCE expeditions. We have introduced bomb radiocarbon into the
model beginning in 1950 and let it run through 1993. The preliminary results
show that the integrated water column inventory of bomb C14 is in good
agreement with that published by Broecker et al. (1995). The pattern of
the latitudinal zoning distribution for the surface bomb C14 is also consistent
with the observations and other modeling studies. In some locations, the
discrepancies between the modeled bomb C14 and the observations indicate
the vertical mixing and upwelling (downwelling) need to be improved in
the model.
TALK
Ocean Margins Program: Overview of Mooring Array
Leonard Pietrafesa 1
1 North Carolina State University, Raleigh, NC
Abstract
TALK
Budgets of Biogenic Elements in the NW Atlantic Ocean Margin: A
Synthesis and Modeling Project - An Update of the First Year
Donald Redalje 1, Peter Verity 2, Daniel Repeta 3, Leonard Pietrafesa 4, and Richard Jahnke 2
1 The University of Southern Mississippi, Stennis Space Center, MS
2 Skidaway Institute of Oceanography, Savannah, GA
3 Woods Hole Oceanographic Institution, Woods Hole, MA
4 North Carolina State University, Raleigh, NC
The Ocean Margins Program consisted of an integrated multidisciplinary field research program to quantify the physics and biogeochemical processes affecting carbon fluxes, nutrient cycles, and ecological dynamics in shelf and slope waters off of Cape Hatteras, where carbon burial in sediments and carbon export to the interior ocean were expected to be maximal. This field program was conducted from 1993 through 1996. The Synthesis and Modeling portions of this study were begun in 1999 with funding from the U.S. JGOFS Synthesis and Modeling Program (SMP). Our goal was to address the major goals of the SMP with a focus placed upon examining cycles of inorganic and organic carbon and nutrients, and the physical and biogeochemical processes that impact the export of these materials from coastal waters to the interior ocean.
In order to accomplish these tasks, a series of workshops were held
so that members of each study group could assess the state of data analysis
and plan for publication of results. The study groups include: the mooring
data group, the water column process study group, the benthic process study
group, and the shelfwide survey group. Each study group has developed a
plan for completing analyses and developing a series of manuscripts for
submission to the literature, both as individual or group authored research
papers and as special issues of various journals. There was also an effort
made to make the OMP database accessible to the oceanographic community
through links with the U.S. JGOFS SMP web page.
TALK
Oxygen and Carbon fluxes in the Pacific Ocean Determined the WOCE/JGOFS
Hydrographic Survey
Paul E. Robbins 1, Lynne Talley 1, Gregory Johnson 2 and Richard Feeley 2
1 Scripps Inst. of Oceanography, La Jolla, CA
2 NOAA/Pacific Mar. Environ. Lab., Seattle, WA
The large-scale circulation of the Pacific Ocean is diagnosed from hydrographic station data collected ad part of the WOCE field program. Transport fields calculated from geostrophic shear and wind-driven Ekman velocities are adjusted using a box inverse model to insure selected net property constraints within geographic regions and non-outcropping density layers. Heat and oxygen flux divergence are combined to estimate the large-scale effects of the solubility and biological pumps on the air/sea exchange of oxygen.
The south Pacific basin is characterized by heat loss in the east and
gain in the west but with little net gain or loss over the entire basin.
In contrast, the ocean appears to be gaining large amounts of oxygen from
the atmosphere in this region with the largest gains in the vicinity of
the circumpolar front. The primary cause of this large uptake appears to
be the ventilation of low oxygen Pacific and Indian Deep waters. The large-scale
heat and oxygen balances are combined to estimate the pre-anthropogenic
air/sea exchange of carbon.
TALK
A revised method for estimating anthropogenic carbon inventories
in the ocean
Paul E. Robbins 1, and Andrew Dickson 2
1 Physical Oceanography Research Division, Scripps Institution of Oceanography,
La Jolla, CA
2 Marine Physical Lab, Scripps Institution of Oceanography, La Jolla,
CA
Current estimates of anthropogenic carbon in the ocean, e.g. Gruber
et al. (1996), rely on CFC measurements to "date" the water age. An assumption
in this methodology is that once a parcel of water subducts from the surface
mixed layer, no subsequent mixing takes place. Previous work has demonstrated
that isopycnal mixing rates typical of the ocean thermocline can significantly
skew interpretations of ventilation age based on transient tracers (Robbins
et al., 2000). A new methodology is developed to estimate anthropogenic
carbon inventories based on observed inventories of CFCs. The method explicitly
recognizes that mixing does occur in the ocean interior: fluid parcels
are treated as containing a distribution of ages rather then a single discrete
age. Idealized numerical simulations demonstrate that the new method has
greater accuracy for estimating anthropogenic carbon inventories. The greatest
improvements are for water masses characterized by mean ventilation ages
older then the characteristic time scale of CFC input.
POSTER
Consistency and Synthesis of Pacific Ocean CO2 Survey Data
Christopher L. Sabine 1, M.F. Lamb 2, 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, and D. Greeley 2
1 Joint Institute for the Study of Atmosphere and Ocean, University
of Washington, c/o NOAA/PMEL, Seattle, WA
2 NOAA/Pacific Marine Environmental Laboratory, Seattle, WA
3 NOAA/Atlantic Oceanographic and Meteorological Laboratory, Miami,
FL
4 Department of Geosciences, Princeton University/Guyot Hall, Princeton,
NJ
5 University of Miami/ RSMAS, 4600 Rickenbacker
Causeway, Miami, FL
6 Carbon Dioxide Information Analysis Center, ORNL, Oak Ridge, TN
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). The goal of this work is to assess the quality of the Pacific carbon survey data and to make recommendations for generating a unified data set that is consistent between cruises. Several different lines of evidence were used to examine the consistency 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 can be 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 umol kg-1 after the
proposed adjustments. TAlk, the second most common carbon parameter, has
an estimated overall accuracy of ~5 umol kg-1.
TALK
Estimate of new (nitrate) uptake and net community production in
the Antarctic Polar Front region
Raymond Sambrotto 1, Mary-Lynn Dickson 2 and Goran Brostrom 3
1 Lamont-Doherty Earth Observatory, Palisades, NY
2 Univ. of Rhode Island, Grad. School of Oceanography,,Narragansett,
RI
3 Massachusetts Institute of Technology, Cambridge, MA
A consistent series of fronts partition the Southern Ocean into physically
distinct regions surrounding the Antarctic continent. These regions are
associated with characteristic physical mixing, community structure and
production. Data from German, U.S. and French field work in Atlantic, Pacific
and Indian sectors were synthesized in an attempt to characterize the new
production regimes in each hydrographic domain. Both instantaneous rate
measurements and water column nutrient budgets were used to estimate yearly
new production that ranged from 300 to over 600 mmoles of nitrate m-2
y-1. Thus, the APF region does not appear to fit the general
conception of a high nitratelow chlorophyll region. Data are available
in the Pacific sector to compare Net Community Production (NCP) and new
production. On a depth by depth basis, the ratio of NCP to new (nitrate)
production varied widely. Values both well above and below that expected
from the conversion of new production first to carbon (by the Redfield
C/N ratio of 6.6) and then to oxygen (by the photosynthetic quotient (PQ)
of 1.4) were measured. Low ratios of NCP to new production were measured
at high light levels and may be due, in part, to light inhibition of NCP
during the on-deck incubations. At lower light levels, more oxygen accumulated
than expected from nitrate uptake. Therefore, because the PQ is physiologically
limited to a fairly narrow range, the C/N production ratio may exceed ~10
for the productive month of December. These comparisons will be used to
estimate circumpolar rates of new production and oxygen production.
TALK
Sensitivity of air-sea CO2 balance to surface nutrients and ocean
circulation
J. L. Sarmiento 1, A. Gnanadesikan 1 and R. Slater 1
1 AOS Program, Princeton Univ., Princeton, NJ
I will describe some new model simulations examining the issue of how
nutrient depletion affects the air-sea balance of carbon dioxide in a general
circulation model.
TALK
Global Ocean Distribution of Colored Organic Materials
David A. Siegel 1, Stéphane Maritorena 1, Norman B. Nelson 1,2 and Manuela Lorenzi-Kaiser 1
1 Inst. for Computational Earth System Sci., Univ. of California, Santa
Barbara, Santa Barbara, CA
2 Bermuda Biological Station for Research, Ferry Reach, BERMUDA
It is often presumed that the dominant fraction of dissolved chromophoric
yellow matter found in the oceans is of terrestrial origin and that these
materials have a minor role in regulating light availability for open ocean
photoprocesses. Yellow matter, also referred to as gelbstoff, gilvin, or
colored dissolved organic matter, is an important intermediary for photochemical
reactions affecting the upper ocean carbon budget as well as air-sea exchanges
of several atmospheric trace gases which influence the Earth's radiation
budget. However, the global distribution of yellow matter and its temporal
variability remain largely unknown. Here, we use global satellite imagery
from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and recent advances
in ocean color algorithms to describe the time-space variability in the
global distribution of colored detrital material (CDM) concentrations.
Determinations of CDM represent the combined influence of dissolved organic
matter and detrital particulates on light absorption, as it is not yet
possible to routinely separate these similar optical signals from an ocean
color spectrum. Field observations and an analysis of published bio-optical
relationships indicate that dissolved chromophoric materials dominate the
CDM signal. To first order, CDM distributions resemble basin scale patterns
for chlorophyll pigment concentrations and net primary production although
locations of riverine inputs can be discerned. Nearly two-thirds of the
non-water absorption of blue light is due to CDM. Significant differences
in both CDM concentration and its contribution to the total non-water absorption
are found spatially among the major ocean basins and temporally on intraseasonal
to interannual time scales. These satellite-based observations demonstrate
that the assumption of an exclusive terrestrial source for CDM is incorrect
and that local biological and biogeochemical processes must regulate CDM
dynamics. This first view of the global CDM distribution opens new doors
for quantifying marine photoprocesses and vertical water mass exchanges
on a global scale.
TALK
Basin Scale Estimates of New production during 1997-1999 El Niño
and La Niña Events in the tropical Pacific; a multi-sensor approach
Daniela Turk 1, M.J. McPhaden 2, M.R. Lewis 1, and A.J. Busalacchi 3
1 Dept. of Oceanography, Dalhousie University, Halifax, NS, CANADA
2 NOAA/PMEL, Seattle, WA
3 Laboratory for Hydrospheric Processes, NASA/Goddard Space Flight
Center, Greenbelt, MD
The significance of interannual variability in biological production
in the equatorial Pacific for the global carbon cycle has been suggested,
but only recently available satellite and buoy observations provide a mean
to monitor the magnitude of this variability over the large area of the
tropical Pacific. Direct measurements of new production along the equator
have suggested that interannual variation in new production in the western
and central equatorial Pacific correlate well with the changes in thermocline/nitricline
depth during the eastward expansion of the Western Pacific Warm, by changing
the supply of nutrients into the upper well-lit surface layer. Frequently,
as a results of nutricline shoaling, a large variations of new production
appear at depth below the upper surface mixed layer, and do not have a
surface signature in SeaWiFS pigment. Here, we present a study of the variation
in new production during 1997-1999 El Niño and La Niña conditions
in the equatorial Pacific basin. A combination of ship observations, TOGA-Tao
buoy array data, TOPEX/Poseidon dynamic height, and SeaWiFS ocean color,
are used to provide an analysis, and to explore the consequences for interannual
variability in the planetary carbon cycle.
TALK
Primary productivity during the winter monsoon in the northern Arabian
Sea: Processes controlling diurnal cycling and interannual variability
Jerry Wiggert 1
1 Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD
During the boreal winter, cool, dry air originating over the Tibetan
Plateau propagates across the northern Arabian Sea. This atmospheric phenomenon
has been termed the Northeast Monsoon (NEM). During the US/JGOFS Arabian
Sea expedition, a meteorological buoy, located approximately 1200 km from
where the prevailing winds go offshore, observed mean atmospheric temperatures
that were 1°C lower than mean SST and a mean relative humidity of 70.3%
over the winter monsoon period. These atmospheric conditions result in
significant long wave and latent heat fluxes out of the surface ocean which,
along with the observed mean wind stress of 0.07 N/m2, result
in deep wintertime convection. Over the course of the winter, these fluxes
of heat and momentum deepen the surface mixed layer and transport nutrients
into the euphotic zone. Coincident with these processes, relatively high
rates of primary productivity (1.64 gC/m2/d and 1.06 gC/m2/d)
were observed during US/JGOFS process cruises conducted during two successive
winter monsoons. Additionally, three successive years of SeaWiFS imagery
reveals a consistent increase in surface chlorophyll over the course of
the winter monsoon as well as significant interannual variation in chlorophyll.
In situ observations from the US/JGOFS expedition, moored time series,
satellite observations, results of a 1-D bio-physical model and results
from an interannually forced ocean general circulation model are presented.
These observations and model results are used to illustrate how the combination
of diurnal mixed layer dynamics and thermocline depth lead to the winter
phytoplankton bloom and interannual variation in surface chlorophyll and
areal primary productivity.
POSTER
Meridional assymetric nutrient distribution in the equatorial Pacific
upwelling system: its role in the variability of CO2 efflux to the atmosphere
Wischmeyer 1, R. Dugdale 1, R. Barber 2, F. Chai 3, T.Peng 4, F. Wilkerson 1
1 Romberg Tiburon Center for Environmental Studies, San Francisco State
University, Tiburon, CA
2 Duke University Marine Lab, Beaufort NC
3 School of Marine Sciences, University of Maine, Orono, ME
4 Ocean Chemistry Division, NOAA/AOML, Miami, FL
The equatorial Pacific ocean has received growing attention as the main
area in producing climate variations. Looking at both, decadal and glacial/interglacial
timescales the El Nino-La Nina mechanism may play a central role in changing
weather conditions at distant locations. However, during modern El Niño
events atmospheric CO2 tends to decrease whereas on interglacial timescales
it increases. We suggest the meridional assymetric distribution in dissolved
inorganic carbon and silicon in the equatorial Pacific may be the cause
for this as it controls CO2 efflux from the equatorial upwelling zone (EUZ).
TALK
Interannual variability in satellite ocean color imagery
James Yoder 1
1 Graduate School of Oceanography, URI, Narragansett, RI
As part of the U.S. JGOFS Synthesis and Modeling Program (SMP), imagery from Coastal Zone Color Scanner (CZCS), Ocean Color and Temperature Scanner (OCTS), POLDER (Polarization and Directionality of the Earth's Reflectances) and Sea Wide Field Sensor (SeaWiFS) are used to study seasonal to interannual changes in phytoplankton chlorophyll a concentrations in the global ocean. The ultimate objective is to use the results from five years of CZCS, almost 1 year of OCTS/POLDER and 3 years of SeaWiFS imagery to assess year-to-year variability and determine its causes.
To accomplish the objectives, imagery at 4-18 km spatial resolution are first mapped to a common global grid at 0.25 degree resolution and at monthly, and for some years, weekly temporal resolution. Chlorophyll frequency distributions from each sensor are compared to evaluate systematic algorithm biases and other artifacts. Chlorophyll imagery are then compared in absolute terms and using a relative index which tries to correct for bio-optical and other algorithm differences between sensor processing. Measures of variability are also calculated taking into account that coverage, and thus the number of observations at each pixel, are not always the same.
The initial results show that the most striking large-scale differences are associated with the 1997/1998 El Niño, but other more subtle interannual differences in pattern are also observed in the North Atlantic. These results are discussed in relation to modeling and other studies that relate phytoplankton productivity and biomass to seasonal to interannual changes in large-scale ocean physical processes. Our tentative conclusions are that currently available data products from the four sensors cannot yet be used for quantitative comparisons of chlorophyll concentration (absolute units) in many areas of the ocean, but that the global patterns observed by all the sensors are robust and interpretable.