Trace metal distributions off the Antarctic Peninsula in the Weddell Sea

Abstract

Dissolved trace metals (Ag, Al, Cd, Co, Cu, Fe, Ni, Pb, and Zn), inorganic nutrients (PO4, H4SiO4), and chlorophyll a were measured at 19 stations along a surface water transect from the Antarctic Peninsula into the Weddell Sea. The range of concentrations of metals and nutrients measured along the western rim of the Weddell Sea were consistent with previous results from the Southern Ocean. Metal levels measured in the Weddell Sea showed two distinct patterns: (1) metals (Al, Co, and Pb) that generally had lower levels in the Weddell Sea; and (2) dissolved constituents (Ag, Cd, Cu, Fe, Ni, Zn, PO4, H4SiO4) that showed an enrichment in the Weddell Sea, as compared to other ocean basins. While this dichotomy suggested that high metal concentrations may result from natural processes, the impact of anthropogenic processes on metal levels in Antarctic waters is also evident. A comparison of the stable lead isotopic composition reported for surface waters of the Weddell Sea and our Southern Hemisphere aerosol samples suggested that the cycling of Pb in those waters has been influenced by industrial Pb from South America. The importance of biological activity on the cycling of bioactive metals in the Weddell Sea was suggested by the inverse relationship between chl a concentrations and trace metal residence time. A strong linear relationship between Cd and PO4 was observed, as in other oceans. The Cd/PO4 ratio along the western rim of the Weddell Sea was consistent with previous ratios reported for the northern part of the Weddell Sea and the Antarctic Circumpolar Current. However, those ratios were significantly higher than the previously reported Cd/PO4 ratio for the southern part of the Weddell Sea, suggesting that Cd/PO4 ratios within the same oceanographic basin are susceptible to temporal and spatial variability. We also showed that the Ag/Cu ratio could potentially be used as a geochemical tracer of different water masses in the world ocean. The Ag/Cu ratio in the Weddell Sea was essentially the same as the ratio reported for the Pacific Ocean, suggesting that Weddell Sea surface waters may influence the composition of trace metals in subsurface waters of the Pacific.