Atmospheric depositional fluxes of trace elements, 210Pb, and 7Be to the Sargasso Sea

Abstract

Atmospheric wet and bulk depositional fluxes of trace elements (Fe, Al, Mn, Zn, Pb, Cu, Cd, Ni, and Cr), 210Pb, and 7Be (bulk only) to the Sargasso Sea were measured at Bermuda from September 1996 to September 1997. Wet deposition was the dominant process of trace element deposition over most of the sampling seasons, based on the measured bulk versus wet depositional fluxes. Although about half of the Mn in Bermuda precipitation was calculated to originate from noncrustal sources, its seasonal trend is similar to the Fe and Al, suggesting primary sources from continental crustal materials. On the other hand, Cd, Zn, Pb, Cu, Ni, and Cr in Bermuda precipitation originate mainly from noncrustal sources (presumably anthropogenic) based on enrichment factor analyses. The noncrustal sources were highest during the fall‐winter due to more frequent intrusion of U.S. continental air as the Bermuda High weakens. Atmospheric depositional fluxes of 210Pb showed a good correlation with the 7Be fluxes (r2=0.84) at Bermuda, indicating major transport of 210Pb via the upper troposphere from continents, along with other trace elements. Annual depositional fluxes of noncrustal elements (Cd, Zn, Pb, Cu, Ni, and Cr) at Bermuda were a factor of 2 to 3 lower than those at the mid‐Atlantic Bight and were about 2–20 fold lower during the sampling year than those during the early 1980s. This confirms the rapid evolution of trace element inputs to the upper Sargasso Sea during the last few decades resulting from industrial emission controls in the surrounding continents.