Mercury profiles in sediments of the Arctic Ocean basins

Total Hg distributions have been measured far seven sediment cores collecte d from the major basins of the Arctic Ocean during the Arctic Ocean Section in 1994. Hg determinations were performed on the top 10 cm of the sectione d cores using gold amalgamation atomic fluorescence spectroscopy. in five c ores, Hg concentrations decrease downward from 34 to 116 ng g(-1) at the se diment surface to 10-65 ng g(-1) at 5 cm depth and then remain almost const ant with increasing depth. In the other two cores, the Hg decrease with dep th is interrupted by a maximum (96-107 ng g(-1)) at 7-8 cm. The obvious inf erence-pervasive Hg contamination from anthropogenic sources even at the No rth Pole-is discounted after a careful evaluation of sediment geochemistry. The evidence suggests that these Hg profiles have been produced by Hg redi stribution during diagenesis. In all seven cores, strong similarities are o bserved between the Hg and the reactive Fe profiles, implying that a portio n 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 enr ichments for Win and Fe. The crucial factors governing surface Hg enrichmen ts in Arctic basin sediments are the low sedimentation rates (<1 cm ka(-1)) and sediment mixing rates (<0.03 cm(2) yr(-1)) that permit even minor Hg f luxes to have a significant cummulative effect.