Dissolved organic carbon in the Mid-Atlantic Bight

The Mid-Atlantic Bight (MAB) is a highly productive continental shelf region on the eastern North American coast and a potential sight for the export of organic carbon to the open ocean. The dynamics of dissolved organic carbon (DOC) in the MAB were studied during three cruises in April 1994, March 1996 and August 1996 in order to characterize DOC distributions on the shelf, estimate inventories of DOC on the shelf and quantify DOC transport. There were clear spatial and temporal trends in DOC distributions. Concentrations of DOC were greater inshore than offshore and increased southward along the shelf. The total DOC inventory on the shelf during the March and April cruises was estimated at ∼5.88×1012 g C and this increased by 0.4×1012 g C (7%) in August. A simple mass balance of DOC input and export in the MAB resulted in total export of 18.7–19.6×1012g C yr−1. Up to 67% of this carbon is recycled oceanic DOC that is refractory with respect to MAB seawater residence times, ∼4% is introduced through estuaries, sediments and rainwater and at least 29% of the exported shelf DOC (4.1–7.4×1012 g C yr−1) is produced on the shelf. Net ecosystem production of DOC in the MAB is estimated to be between 10% and 18% of MAB primary productivity estimates. Our data supports the hypothesis that the MAB as a whole is net autotrophic for the periods of study and that DOC is an important component in ocean margin carbon budgets.