Analysis of Trace Metals in Bottom Sediments in Support of Deepwater Biological Processes Studies on the U.S. South Atlantic Continental Slope and Rise

摘要

The study is part of a multidisciplinary program conducted along the entire continental slope and rise off the Atlantic states to characterize the biology, chemistry, and geology of the sea floor prior to exploratory drilling for petroleum. The distribution of sediment types and associated trace metals from natural sources will be used to help predict the fate of sediment reactive contaminants introduced to the water column by future development activities. Sediment samples collected on three cruises to the continental slope and rise off the South Atlantic states were analyzed for 12 metals (Al, Ba, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, V, and Zn). The metal concentrations are lower than those reported for world average shales, indicating an absence of major contamination. At some locations, Pb is enriched in the surface sediments by about a factor of 2 higher than deeper sections of sediment cores. The maximum concentration of Pb is only 17 ppm. This enrichment is probably related to onshore burning of gasoline containing lead additives. The potential biological effects of this enrichment cannot yet be evaluated. There is a positive correlation between the concentration of metals and the concentration of silt and clay. Lead inventories at stations at the northern limit of the study area are 5-10 times higher than predicted from the estimated atmospheric flux over the last century. Biological, chemical and physical processes which enhance metal scavanging from seawater must be relatively intense to account for the high inventories.