1. U.S. Eastern Continental Shelf Carbon Budget: Modeling, Data Assimilation, and Analysis U.S. ECoS Science Team* ABSTRACT. The U.S. Eastern Continental Shelf Carbon Budget (U.S. ECoS) Program, which began in summer 2004, is funded as part of the NASA Interdisciplinary Science Program. The overall goal of this project is to develop carbon budgets for the Mid-Atlantic Bight (MAB) and South Atlantic Bight (SAB) along the eastern U.S. coast. The U.S. ECoS program is structured around five themes which are focused on: 1) development and implementation of circulation, biogeochemistry, and carbon cycling models for the east coast of the U.S.; 2) analyses of historical in situ measurements and satellite- derived data; 3) a limited field measurement effort designed to provide measurements for input to the biogeochemistry and carbon cycling models; 4) development and implementation of data assimilative biogeochemical and carbon cycling models; and 5) interfacing the circulation, biogeochemistry and carbon cycling models with climate models. Our research is particularly germane to NASA’s carbon cycle research focus topic and coastal research initiative and the U.S. Climate Change Research Program, all of which emphasize the North American Carbon Program. RESEARCH QUESTIONS 1) What are the relative carbon inputs to the MAB and SAB from terrestrial sources and in situ biological processes? 2) What is the fate of DOC input to the continental shelf from estuarine and riverine systems? 3) What are the dominant food web pathways that control carbon cycling and flux in this region? 4) Are there fundamental differences in the manner in which carbon is cycled on the MAB and SAB continental shelf? 5) Is the carbon cycle of the MAB and SAB sensitive to climate change? Longitude (West) Latitude (North) *U.S. ECoS Science Team Eileen Hofmann (ODU)Project oversight, 1D modeling Marjorie Friedrichs (ODU)1D modeling, data assimilation Chuck McClain (GSFC) Project oversight, satellite data Sergio Signorini (GSFC) Satellite data analyses Antonio Mannino (GSFC) Carbon cycling Cindy Lee (SUNY-SB)Carbon cycling Jay O’Reilly (NOAA)Satellite data analyses Dale Haidvogel (Rutgers)Circulation modeling John Wilkin (Rutgers)Circulation modeling Katja Fennel (Rutgers)Biogeochemical modeling Sybil Seitzinger (Rutgers)Food web and nutrient dynamics Jim Yoder (URI)Food web and nutrient dynamics Ray Najjar (Penn State)Oxygen data, climate modeling David Pollard (Penn State)Climate modeling The biogeochemical model used in this project (Figure 1) is designed to investigate nutrient cycling of the lower trophic levels of the MAB and SAB. This model is coupled to a circulation model that is based on the Regional Ocean Modeling System (ROMS v.2) that has been implemented for the continental shelf and adjacent deep ocean of the U.S. east coast (Northeast North American (NENA) Shelf Model). Comparisons of simulated chlorophyll distributions obtained with the coupled circulation-biogeochemical model show features that are similar to those seen in chlorophyll distributions obtained from SeaWiFS measurements (Figures 2, 3). The biogeochemical model is currently being modified to include data assimilation capability. Figure 1 Figure 2 Simulated Chlorophyll Figure 2 SeaWiFS Chlorophyll Figure 5 Figure 4 Comparisons of simulated monthly-averaged chlorophyll concentrations with measured in situ and SeaWiFS-derived chlorophyll values at different sites in the MAB (Figure 4) show that the biogeochemical model captures the chlorophyll annual cycle. The biogeochemical model is coupled to a carbon cycling model. The simulated annual air-sea CO 2 flux shows that the MAB and SAB provide a net sink for carbon (Figure 5). Additional simulations are ongoing to investigate the processes that underlie this result. Sink Source Figure 3 Satellite data analyses are an integral part of the project and provide inputs and verifications for the simulated distributions obtained from the coupled model. One such example is the Western North Atlantic POC composite (mg C L-1, log scale is 0.01 to 5.0) for April 1998 (Figure 6) derived from SeaWiFS normalized water leaving radiances and the Clark empirical algorithm (D. Clark, unpublished). Note the nearshore sources (yellow-red high values) originating from rivers and estuaries. The lowest values are in the Sargasso Sea. The patchiness south of the Gulf Stream may be due to POC advection by cold core eddies. Figure 6 Satellite-derived data sets also provide an approach for assessing seasonal and interannual variability in primary production (Figures 7, 8), and for comparing estimates of primary production derived from different algorithms (Figure 7). In situ data sets, such as the MARMAP data, provide calibration for the satellite-derived values (Figure 7). Figure 7 Figure 8 The field sampling component of the U.S. ECoS project is focused on Chesapeake Bay (Figure 9) and includes measurements of DOC, POC, CDOM and other nutrient and chlorophyll-related parameters. results show that DOC is variable and is lower in summer- fall than in winter-spring (Figure 9). Measurements from Delaware Bay show summer-fall differences in CDOM absorption coefficients (Figure 10). The field sampling program is providing measurements that are critical to the biogeochemical and carbon cycling models. Figure 10 Figure 9