| PROJECT
DESCRIPTION: |
The proposed research will be the development of
a food web model that can be incorporated into a global circulation model
(GCM) to predict export production and to characterize the nature of the
carbon exported to the interior of the ocean. The model will be similar
to the food web model developed conceptually at the 1999 Synthesis and
Modeling (SMP) food web workshop in Keystone, Colorado. In the model phytoplankton
are envisioned as consisting of five functional groups, small phytoplankton
such as Synechococcus and Prochlorococcus, diatoms, coccolithophores,
Phaeocystis, and nitrogen fixers. Division of the phytoplankton
in this manner is hypothesized to be necessary to explain the dependence
of export ratios on temperature and primary production, to account for
the allocation of exported carbon between calcium carbonate, particulate
organic carbon, and dissolved organic carbon, and to take into account
various methods of ballasting (fecal pellets, calcium carbonate, and silica)
that influence the sinking and remineralisation rates of particulate carbon.
A distinguishing characteristic of the model is the assumption that open
ocean biological communities adapt to environmental conditions in a way
that tends to maximize the stability of the steady state condition toward
which the communities evolve. This same hypothesis has previously been
tested with a simpler food web model in which the phytoplankton are envisioned
as consisting of only two functional groups, small and large phytoplankton.
The success of that previous model, which was developed with funding from
the first phase of the SMP, has provided the motivation for extending this
same approach to the more complex model with five functional phytoplankton
groups. It is hypothesized that a stable coupled physical-biological model
of the ocean will require that the biological component be adaptive. With
respect to export production, specific questions to be addressed with the
model will include the following:
-
How much of the organic carbon is exported as dissolved organic carbon
(DOC) and how much as particulate carbon (PC)
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Of the PC export, how much is exported as particulate organic carbon (POC)
and how much as carbonate carbon (CC)
-
To what extent is the exported POC ballasted by silica and/or carbonate
or sequestered by incorporation into encapsulated fecal pellets
Once the adaptive parameters in the model have been determined through
steady state analysis, a time-dependent version of the model will be run
to explore model behavior when the forcing functions are time dependent.
Questions to be addressed with the time-dependent version will include
the role of DOC export and the ability of the model?s output to facilitate
description of nutrient and oxygen profiles in the interior of the ocean.
An additional issue to be explored with the time-dependent version will
be the need to allow for non-Redfield stoichiometry in processes such as
nutrient uptake and remineralisation. The food web model developed at the
Keystone meeting is sufficiently complex as to make its incorporation into
more elaborate GCMs problematic. Consequently, the final phase of the proposed
research will involve examination of the impact on model performance of
simplifications of the food web structure proposed at the Keystone meeting.
In other words, the final phase of the project will attempt to identify
the simplest possible food web model that can simulate the aspects of system
behavior necessary to explain the pattern of export production in the ocean
and the nature of exported carbon.
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| PUBLICATIONS: |
Laws, E.A., P.G. Falkowski, W.O. Smith, H. Ducklow, and J.J. McCarthy.
2000. Temperature effects on export production in the open ocean. Global
Biogeochemical Cycles, 14(4), 1231-1246.
Laws, E. A., E. Sakshaug, M. Babin, Y. Dandonneau, P. Falkowski, R. Geider,
L. Legendre, A. Morel, M. Sondergaard, M. Takahashi, and P. leB Williams.
2002. Photosynthesis and primary productivity in marine ecosystems:
Practical aspects and application of techniques. JGOFS Report No. 36.
Bergen, Norway, 93 pp.
Cassar, N., E.A. Laws, B.N. Popp, and R.R. Bidigare. 2002. Sources of
inorganic carbon for photosynthesis in marine diatoms. Limnology and
Oceanography, 47, 1192-1197.
Laws, E.A., 2003. Partitioning of microbial biomass in pelagic aquatic
communities: Maximum resiliency as a food web organizing construct. Aquatic
Microbial Ecology, 32, 1-10.
Laws, E.A. 2003. Mesozooplankton grazing and primary production: An
alternative assessment. Limnology and Oceanography, 48, 1357-1359.
Falkowski, P.G., E.A. Laws, R.T. Barber, and J. Murray. 2003.
Phytoplankton and their role in primary, new, and export production. Pages
99-121 in M. J. R. Fasham (Ed.), Ocean Biogeochemistry: The Role of the
Ocean Carbon Cycle in Global Change. Springer.
Laws, E.A., 2004. New Production in the equatorial Pacific: A Comparison of
field Data with Estimates derived from empirical and theoretical Models.
Deep-Sea Research, 51(2), 205-211.
Laws, E.A., 2004. Export Flux and Stability as Regulators of Community
Composition in Pelagic Marine Biological Communities: Implications for
Regime Shifts. Progress in Oceanography (in press).
Cassar, N., E.A. Laws, R. R. Bidigare, and B.N. Popp. 2004. Bicarbonate
uptake by Southern Ocean Phytoplankton. Global Biogeochemical Cycles.
2003GB002116 (in press).
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