See more from this Division: Topical Sessions
See more from this Session: Mercury Cycling, Fate, and Bioaccumulation in Coastal Zones: The Next Big Stage for Mercury Research?
Abstract:
Mass dependent (d202Hg) and mass independent (Δ199Hg) variation in the isotopic composition of Hg has been observed in a wide range of natural materials. In this study we measured the Hg isotopic composition of marine sediments from the Baltic Sea that predate and post-date the Industrial Revolution to see whether anthropogenic inputs of Hg had altered the isotopic composition of the sediments. We analyzed surface (0-4 cm) and pre-Industrial (24-34 cm) sediments from spatially distributed, hydrographically separated locations in the Baltic Sea. Sediments from the Baltic Proper and Arkona basins demonstrate a three-fold enrichment in Hg concentration between pre-Industrial and post-Industrial sediments, with Hg concentrations increasing from an average of 19 ng/g to 51 ng/g in the Baltic Proper basin and from 51 ng/g to 155 ng/g in the Arkona basin. All sediments analyzed have a narrow range of d202Hg and Δ199Hg values. Deeper sediments from the two basins have d202Hg values ranging from -1.2 to -0.9 and Δ199Hg values of +0.14 to +0.15. Near-surface sediments from each site have d202Hg values ranging between -0.9 and -0.8 and Δ199Hg values of +0.09. The sediments analyzed have indistinguishable Hg isotopic compositions within analytical uncertainty (d202Hg = ±0.1, Δ199Hg = ±0.05). The isotopic composition of Baltic Sea sediments is nearly identical to mid-Pleistocene Mediterranean Sea marine sediments. The similar Hg isotopic composition of these marine sediments deposited at different times and locations suggests a characteristic marine Hg isotopic signature preserved in sediments of d202Hg » -0.9 and Δ199Hg » +0.1. Implications of this isotopic signature for global Hg cycling will be discussed.