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MARI/CCPO Seminar Series

USECoS: Seasonal and Interannual Variability of Nitrogen Fluxes Along the Mid-Atlantic Bight

Eileen E. Hofmann, Center for Coastal Physical Oceanography, Old Dominion University

Our understanding of nitrogen cycling on continental shelves, a critical component of global nutrient cycling, is often hampered by limited observations compared to the strong variability apparent on relatively small time and space scales. Numerical models are able to partially alleviate this issue by filling temporal and spatial data gaps and hence resolving annual area-integrated nutrient fluxes. As part of a NASA-funded Interdisciplinary Science project, a land-ocean-biogeochemical modeling system was implemented to simulate the nitrogen budget during 2004-2007 on the Mid-Atlantic Bight (MAB) shelf. Quantitative model skill assessment was conducted via extensive comparisons to satellite observations and in situ data where available. Model simulations demonstrate that denitrification and burial fluxes have pronounced seasonal variation but change little from year to year. In contrast, annual net community production (NCP) varies significantly between years, but overall is positive indicating a net autotrophic system. Whereas the advective influx of nitrogen from the bays and rivers on the western boundary of the MAB changes only slightly among the four years examined. the advective fluxes across the eastern and northern boundaries change dramatically. These changes are associated with changes in the position of the relatively high-nutrient Labrador Sea waters advecting into the MAB from the north and the relatively low-nutrient Gulf Stream waters advecting into the MAB from the southeast.