Collaborative Research: Seasonal Biogeochemical Processes in the Ross Sea: A Modeling Approach

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The Ross Sea is an oceanographic system with several unusual characteristics, including being the mostbiologically productive in the Antarctic, having elevated bird and mammal stocks, having relatively simplephytoplankton composition, having annually consistent sea ice changes dominated by polynyas, havingseasonally low iron concentrations, and being perturbed by large icebergs calved from the Ross Ice Shelf atvarious intervals. A number of research programs have studied various oceanographic processes in the RossSea, but a comprehensive synthesis of circulation and biogeochemical processes remains lacking. Theoverall goal of this project is to develop coupled circulation and biological models that will allow us tounderstand nutrient and carbon cycling in the Ross Sea, as well as to assess the interaction of circulationand biological processes on biogeochemical fluxes and distributions in space and time. This effort builds onour existing fine resolution circulation model (with nutrients) and our analysis of historical nutrient data for the Ross Sea.The interdisciplinary research team will address six research questions: (1) What are the conversion pathways and rates of exchange of heat, salt, macronutrients and iron?, (2) What are the effects of icebergs B19 and C15 on local circulation in the southwest corner of the Ross Sea, and does the presence of these icebergs (and those that might form in the future) affect circulation underneath the Ross Ice Shelf and the formation of High Salinity Shelf Water?, (3) What is the contribution of warm oceanic water to polynya formation?, (4) Why does the Ross Sea polynya phytoplankton bloom begin at the end of October, which issignificantly before other blooms at the same latitude?, (5) Are there regional differences in the fate of primary production within the Ross Sea and if so, what causes these differences?, and (6) What regulates the seasonal transition, from a light- to iron-limited system? To address these questions, observations of water properties, water movement, ocean color,nutrient concentrations and other biogeochemical variables to test the results of the models will be gathered. Specific products will be developed from these data (e.g., T/S volumetric census, volumetric fluxes of heat and nutrients, total primary production and others) to compare to the model solutions. The research team will modify the circulation model to include the cavity beneath the Ross Ice shelf, dynamic sea ice, better atmospheric forcing, tides and iron; furthermore, an existing bio-optical model will be included as well, with multiple phytoplankton classes and their iron dependence. A vertical and time (z,t) dependent model will be used to adjust both physical and biological parameters. An adjoint-based data assimilation model will be developed to obtain an optimal set of parameters based on previous observations in the Ross Sea. The 1-D model will be included in the a regional ecosystem test bed activity along with appropriate model code, forcingand observations. As a result of this study, the investigators will be able to extend the limited observations to understand the biogeochemical linkages in the Ross Sea, and will specifically address the effect of large icebergs on circulation and biological processes and the effect of iron on primary production and phytoplankton taxonomic composition. This project will contribute to graduate education at the College of William and Mary and Old Dominion University through support of a graduate student and the use of these results in graduate classes. A Postdoctoral scholar will receive get expanded training in biological physical interaction in ocean models. Computer animations which will illustrate basic processes in the Ross Sea will be made available on a web page and will be used for public presentations at the Virginia Science Museum in Richmond, VA.