Geochemistry of mercury in surface sediments of the Kuril Basin of the Sea of Okhotsk, Kuril-Kamchatka Trench and adjacent abyssal plain and northwest part of the Bering Sea

Abstract

Mercury concentrations in surface sediments collected from the Northwestern Pacific were analyzed by mercury Zeeman atomic absorption spectrometer with high frequency modulation of light polarization and a pyrolysis attachment. The range of total Hg concentrations in sediments was 19–158µgkg−1, with a mean of 77µgkg−1 (n = 50). The variation in mercury concentrations in sandy deposits of the slopes was 19–79µgkg−1 Hg; in clayey deposits from the Kuril Basin was 84–130µgkg−1 Hg; in clayey deposits from slopes of the Kuril Basin was 44–84µgkg−1 Hg; in clayey deposits from the abyssal area was 46–116µgkg−1 Hg; and in clayey deposits from the slopes and bottom of the Kuril-Kamchatka Trench was 42–143µgkg−1 Hg.Within the distribution of mercury across the study area, high mercury concentrations were observed in clayey sediments, which are enriched in organic matter and the remains of silicate phytoplankton. The Hg content of sandy deposits was minimal. The level of mercury in our deep-water sediments is somewhat overestimated by comparison to representative background values in clayey sediments from the impact areas (subject to anthropogenic pollution). Anomalies of mercury in bottom sediments near a hydrothermal source (Piip Volcano) have not been observed. The enrichment factor values at the stations range between 0.3 and 4.3. EF values of the most samples were generally more than 1, indicating that enrichment was by biogeochemical processes. Based upon four guideline values (ERL, ERM, ISQG and PEL) we can assume a minimal toxic mercury effect on the benthic marine biota.