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

Abstract

Surface hydrographic and biogeochemical properties were measured contemporaneously at high spatial density during a transit from Chesapeake Bay, across the Middle Atlantic Bight [MAB] and Gulf Stream to the Sargasso Sea near Bermuda from 28 September–2 October 1996. Discrete samples were collected for total organic carbon [TOC], dissolved organic carbon [DOC], total organic nitrogen [TON], dissolved organic nitrogen [DON], total carbon dioxide [TCO2] and alkalinity [TA]. Continuous measurements of temperature, salinity, fluorescence, seawater pCO2 and atmospheric pCO2 were also collected. Estuarine waters of Chesapeake Bay (salinity>20) had high pCO2 (>600 μatm) and high TOC (>200 μM), DOC (>190 μM) and TON (>20 μM) concentrations reflecting the riverine input of terrestrial organic matter. Low seawater pCO2 concentrations (∼350 μatm), compared to MAB waters (∼370–430 μatm), were observed in the offshore plume of the Chesapeake. High TOC, TON, TCO2 and alkalinity concentrations were observed within a filament of low 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 ∼3–31×1012 g C year−1, depending on the amount of water advected off the shelf.