A high resolution study of surface layer hydrographic and biogeochemical properties between Chesapeake Bay and Bermuda

Surface hydrographic and biogeochemical properties were measured contemporaneously at high spatial density during a w x transit from Chesapeake Bay, across the Middle Atlantic Bight MAB and Gulf Stream to the Sargasso Sea near Bermuda w x from 28 September–2 October 1996. Discrete samples were collected for total organic carbon TOC , dissolved organic w x w x w x w x carbon DOC , total organic nitrogen TON , dissolved organic nitrogen DON , total carbon dioxide TCO and alkalinity 2 w x TA . Continuous measurements of temperature, salinity, fluorescence, seawater pCO and atmospheric pCO were also 2 2 Ž . Ž . Ž . collected. Estuarine waters of Chesapeake Bay salinity)20 had high pCO )600 matm and high TOC )200 mM , 2 Ž . Ž . DOC )190 mM and TON )20 mM concentrations reflecting the riverine input of terrestrial organic matter. Low Ž . Ž . seawater pCO concentrations ;350 matm , compared to MAB waters ;370–430 matm , were observed in the offshore 2 plume of the Chesapeake. High TOC, TON, TCO and alkalinity concentrations were observed within a filament of low 2 salinity shelf water abutting the western wall of the Gulf Stream. These filaments are apparently advected off the shelf near Cape Hatteras and subducted beneath the Gulf Stream. We estimate that this process will export shelf organic carbon into the North Atlantic basin at a rate ;3–31=10 g C year, depending on the amount of water advected off the shelf. q 1999 Elsevier Science B.V. All rights reserved.