USING TH-234 DISEQUILIBRIA TO ESTIMATE THE VERTICAL REMOVAL RATES OF POLYCYCLIC AROMATIC-HYDROCARBONS FROM THE SURFACE OCEAN

A novel Th-234-Coupled approach was employed to deduce the vertical fl uxes of polycyclic aromatic hydrocarbons (PAHs) through surface waters of harbor, coastal, shelf, and pelagic regimes. We found reasonable a greement between these surface ocean fluxes, based on direct measureme nts of mixed-layer properties, and fluxes deduced from underlying sedi ments. Fluxes decreased exponentially away from the northeastern U.S.A . Source-diagnostic molecular ratios indicate that atmospheric fall-ou t of combustion-derived PAHs from the continents is the dominant sourc e. Despite higher unit area fluxes inshore, the open ocean represents a large integral sink for PAHs. For example, of the 60 metric tonnes o f pyrene that we estimate to annually become sequestered in the wester n North Atlantic, only similar to 10% is deposited in coastal waters w hile the remaining 90% is exported farther offshore on the continental shelf and to pelagic regimes. (C) 1997 Elsevier Science B.V. All righ ts reserved.