| The atmospheric depositional fluxes of trace elements (Al, Fe, Mn, Pb, Cd, Cr, Zn, Cu, and Ni), 7Be, and 210Pb and seawater profiles of 210Pb, 210Po, and 234Th were measured in the Sargasso Sea (during 1996–1997, seasonally), and equatorial and South Atlantic ocean (during summer 1996) to determine the upper ocean biogeochemistry of trace elements in association with local meteorology and atmospheric chemistry. Also, atmospheric deposition of trace elements in the main source region, mid-Atlantic Bight, was determined to compare with the remote oceanic results.; In the Sargasso Sea, the seasonal variation in atmospheric deposition of crustal elements is primarily controlled by the spring-fall incursions of Saharan dust, while anthropogenic elements are associated with the winter incursions of industrialized continental air sources. The anthropogenic trace element fluxes from the atmosphere decrease significantly in the order: mid-Atlantic coast > Sargasso Sea equatorial Atlantic Ocean > South Atlantic Ocean. In the upper ocean (0–150 m), improved 234Th and 210 Po box models yield the total residence times of Po and Th to be less than a year with distinct seasonal variations. Based on the particulate residence times of Po and Th, seasonal and annual export of POC was successfully estimated. The higher export of POC and radionuclides during the summer 1997 in the Sargasso Sea was unusual and seems to be due to nitrogen fixation following increased wet-deposition of Saharan dust Fe. Relative to the Sargasso Sea, the equatorial ocean shows higher export of radionuclides and POC at 100 m, but lower export at 150 m due to efficient re-mineralization below the mixed layer. |
