Table of Contents

• Dataset Description
• Parameters
• Deployments
• Project Information
• Program Information
• Funding

Several recent studies, in systems as different from one another as the Sargasso Sea, Equatorial Pacific and Southern Ocean, have shown that diatoms are responsible for much of the new and export production in surface waters. Those observations, combined with the diatoms' absolute growth requirement for Si, suggest that the availability of dissolved Si may regulate new and export production in much of the sea. Models of carbon and nitrogen cycling in the upper ocean must therefore incorporate Si control of diatom productivity and organic-matter export if their goal is to predict the biological response of the oceans to natural and anthropogenic forcing. That task is currently impossible for most of the ocean due to the scarcity of data regarding factors regulating Si cycling (e.g. silica production rates, silica dissolution rates and Si limitation of diatom productivity).

It is now clear that the marine Si cycle is strongly bimodal in character. The Southern Ocean lies at one extreme, where a relatively high fraction (on the order of 10%) of the silica produced by diatoms in the surface waters is preserved in the sediments. At the opposite extreme are the mid-ocean gyres, where annual rates of silica production in surface waters are surprisingly close to those in the Southern Ocean but almost none of the opal produced accumulates in the sediments. The mechanisms that produce and regulate this bimodal Si cycle must be understood, as they play a major role in controlling the availability of dissolved Si in surface waters. This availability in turn regulates diatom productivity and the ability of diatoms to contribute to new and export production. Thus we must achieve a more realistic understanding of the linkages between the Si cycle and the cycles of carbon and nitrogen, both to determine when Si is - and is not - a major regulator of organic carbon export and to model carbon export accurately when it is strongly influenced by Si availability.

We propose to combine the synthesis of several large data sets obtained during the U.S. and French JGOFS programs with a new generation of physical/biogeochemical models which explicitly include Si regulation of diatom productivity, to make the first data-based determination of the factors controlling the cycling of Si in the upper 200 - 500 m of the ocean. We propose further to investigate how changes in the character of the Si cycle affect the ability of diatoms to contribute to carbon and nitrogen export from surface waters. A team of U.S. and French investigators (Dave Nelson, Mark Brzezinski, Paul Tréguer and Philippe Pondaven) will synthesize the information on Si cycling and Si regulation of diatom productivity from extensive JGOFS data sets obtained during the U.S. Bermuda Atlantic Times Series (BATS) program in the Sargasso Sea, the U.S. Antarctic Environment Southern Ocean Process Study (AESOPS) in the Pacific sector of the Southern Ocean and the French ANTARES and KERFIX programs in the Indian sector of the Southern Ocean. BATS, ANTARES and AESOPS are the only three projects yet conducted, anywhere in the open sea, where studies of Si cycling and Si limitation have been carried out in coordination with studies of primary production and nitrogen cycling, with seasonal coverage. It is a great advantage that these projects also investigated the two end members of the bimodal marine Si cycle.

While those field programs were underway, new physical/biogeochemical models were developed which explicitly include Si cycling and Si limitation terms regulating diatom growth and productivity. One of us (Pondaven) has been instrumental in developing those models, and we now propose to apply them to the BATS, ANTARES and AESOPS study areas and the large data sets on Si, C and N cycling obtained there. Through a combination of data synthesis and numerical modeling we will: 1) identify those processes that are the strongest determinants of the character of the Si cycle in the upper ocean, and 2) assess how the resulting differences in the Si cycle affect the ability of diatoms to contribute to new and export production.

The results will establish a foundation for the next generation of global biogeochemical models of marine carbon cycling, which must explicitly incorporate Si regulation of carbon and nitrogen export in systems where diatom productivity is limited by Si.

There were no cruises associated directly with the US JGOFS SMP. The SMP deployment refers to the project being deployed.

INTRODUCTION

The Joint Global Ocean Flux Study (JGOFS) was an international scientific program devoted to the study of the ocean biogeochemistry of carbon and related elements and the linkages of the ocean with the global carbon cycle. The U.S. JGOFS program involved a decade long, intensive field effort that included: two on-going time-series stations off Hawaii and Bermuda; a series of process studies in the North Atlantic, Equatorial Pacific, Arabian Sea, and Southern Ocean; and a Global Ocean CO₂ Survey in conjunction with the World Ocean Circulation Experiment (WOCE). The resulting ocean biogeochemical data sets, together with satellite ocean color data from the NASA Sea-viewing Wide Field-of-view Sensor (SeaWiFS), formed a unique, long-term resource for the ocean community. With the completion of the field phase in the late 1990s, the U.S. JGOFS initiated a final Synthesis and Modeling Project (SMP), to build on and integrate these data sets in order to address the key scientific themes of JGOFS:

• determine the processes controlling the oceanic carbon cycle and ocean-atmosphere carbon fluxes
• develop improved capabilities for predicting future changes.

Specifically, the central objective of the SMP was to synthesize knowledge gained from U.S. JGOFS and related studies into a set of models to reflect the current understanding of the ocean carbon cycle and its associated uncertainties (U.S. JGOFS, 1997). The SMP was tasked to address not only the processes that control carbon partitioning among oceanic reservoirs, but also the implications for ocean/atmosphere carbon exchange. Both data synthesis and modeling proposals were encouraged with an emphasis on coordinated interaction between the two. The major elements of the program included:

• Individual PI level projects
• Topical Working Groups
• Project management team (two co-coordinators and a project scientist)
• Data management (both distributed and centralized)
• Community activities (PI meetings, mini-workshops, special issues etc.).

The SMP became a full fledged program with the funding of the first SMP awards in early 1998. Funding for SMP grants was provided by the National Science Foundation (NSF), the National Aeronautical and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA), and Department of Energy (DOE).

PROGRAM SCOPE

Specific projects within the SMP fell into two broad categories: data synthesis and extrapolation, and modeling. There was considerable (and necessary) overlap between the two, and the overview of the projects provided below is certainly a simplification of the collective efforts of the individual researchers (details on individual SMP grants can be found at http://usjgofs.whoi.edu/mzweb/syn-mod.htm). The scope and balance of the SMP was based on geographic region of study and investigation of biogeochemical processes.

Synthesis and Modeling Projects

The U.S. JGOFS SMP continued through the 2003-2004 time frame. As the program matured and specific initial projects were completed, the foci for the program was refined to emphasize both emerging new scientific directions and remaining unfinished elements of the original implementation plan. The SMP together with the U.S. JGOFS Steering Committee periodically assessed the program with regard to future priorities. During the active research phase, these are some of the topics identified as filling critical gaps for SMP science:

1. synthesis of primary production, new production and export production (both particulate and dissolved)
2. the mechanisms and rates of mid to deep water particle flux and remineralization as well as sediment diagenesis
3. controls and distributions of calcium carbonate and silica production, transport and remineralization
4. biogeochemical effects of trace metal cycling
5. spatial and temporal extrapolation of biogeochemical flux estimates (e.g. export production) from local to basin and global scales
6. development, evaluation and incorporation of mechanistically based, biological models for global carbon cycle simulations
7. synthesis and modeling studies of the Arabian Sea, Southern Ocean, North Atlantic, ocean margins (with respect to the role of each in basin to global-scale carbon cycle), and the set of U.S. and international time-series stations data.

At the local to regional scale, a series of data synthesis and food web modeling investigations explored aspects of euphotic zone production, recycling, export, transport and remineralization, and sediment cycling using the JGOFS process and time-series data base and related data sets. Individual projects concentrated, for example, on subsets of the overall JGOFS data (e.g. bacteria, mesozooplankton, HPLC pigments). Related projects focused on the distribution and dynamics of planktonic functional groups (e.g. N₂ fixers, diatoms, calcifiers). The eventual aim of many of these food web related studies was to extrapolate the findings to basin and global scale and/or to develop improved process-based parameterizations that could be incorporated into regional and global models.

One or more regional ecosystem modeling studies were undertaken for each of the following U.S. process/time-series study locations: Equatorial Pacific and Atlantic, Arabian Sea, Ross Sea, Bermuda, and North Atlantic. Additionally, there were four projects which concentrated on data synthesis and/or modeling for various continental margins: NW Atlantic margin, southern Caribbean, Cariaco Basin, and several coastal upwelling regions. The regional synthesis and modeling studies as well as some of the food web projects relied heavily on satellite data. Many SMP projects utilized satellite data, in particular SeaWiFS ocean color, as an integral part of both model evaluation and time/space extrapolation.

On the global perspective, over a dozen synthesis groups worked on the JGOFS/WOCE global CO₂ survey data with good coverage for all of the carbon related parameters (DIC, alkalinity, ¹³C, ¹⁴C, nutrients, oxygen, pCO₂, etc.). A coordinated global biogeochemical modeling effort was initiated as part of the international Ocean Carbon Model Intercomparison Project (OCMIP, http://www.ipsl.jussieu.fr/OCMIP/). As the name implies, this was an observation-based evaluation of some thirteen global ocean biogeochemical models of the natural and anthropogenic inorganic carbon system, biogeochemical fields (nutrients, oxygen), and related passive chemical tracers (e.g. CFCs, ¹⁴C, ³He).

Links to Related Programs Subsequent to US JGOFS SMP:

Ocean Carbon & Biogeochemistry (OCB)
North American Carbon Program (NACP) Coastal Synthesis
 

The United States Joint Global Ocean Flux Study was a national component of international JGOFS and an integral part of global climate change research.

The U.S. launched the Joint Global Ocean Flux Study (JGOFS) in the late 1980s to study the ocean carbon cycle. An ambitious goal was set to understand the controls on the concentrations and fluxes of carbon and associated nutrients in the ocean. A new field of ocean biogeochemistry emerged with an emphasis on quality measurements of carbon system parameters and interdisciplinary field studies of the biological, chemical and physical process which control the ocean carbon cycle. As we studied ocean biogeochemistry, we learned that our simple views of carbon uptake and transport were severely limited, and a new "wave" of ocean science was born. U.S. JGOFS has been supported primarily by the U.S. National Science Foundation in collaboration with the National Oceanic and Atmospheric Administration, the National Aeronautics and Space Administration, the Department of Energy and the Office of Naval Research. U.S. JGOFS, ended in 2005 with the conclusion of the Synthesis and Modeling Project (SMP).