Mercury Profiles in Sediments of the Arctic Ocean Basins

Abstract

Total Hg distributions have been measured for seven sediment cores collected from the major basins of the Arctic Ocean during the Arctic Ocean Section in 1994. Hg determinations were perfomed on the top 10 cm of the sectioned cores using gold amalgamation atomic fluorescence spectroscopy. In five cores, Hg concentrations decrease downward from 34 to 116 ng g-1 at the sediment surface to 10−65 ng g-1 at 5 cm depth and then remain almost constant with increasing depth. In the other two cores, the Hg decrease with depth is interrupted by a maximum (96−107 ng g-1) at 7−8 cm. The obvious inferencepervasive Hg contamination from anthropogenic sources even at the North Poleis discounted after a careful evaluation of sediment geochemistry. The evidence suggests that these Hg profiles have been produced by Hg redistribution during diagenesis. In all seven cores, strong similarities are observed between the Hg and the reactive Fe profiles, implying that a portion of the total Hg deposited is recycled along with Fe during redox changes. Intense redox processing in these cores is demonstrated by sharp decreases in organic content with depth and by vertical profiles showing surface enrichments for Mn and Fe. The crucial factors governing surface Hg enrichments in Arctic basin sediments are the low sedimentation rates (<1 cm ka-1) and sediment mixing rates (<0.03 cm2 yr-1) that permit even minor Hg fluxes to have a significant cummulative effect.