Mercury content in Atlantic sediments as a new indicator of the enlargement and reduction of Northern Hemisphere ice sheets

The total mercury content of Quaternary sediments over the last 1.1 Ma from IODP Site U1308 drilled in the North Atlantic Ocean has changed, varying with periodicities of 100 000 and 41 000 years. The Hg content of the sediment increased during glacial periods, associated with increases in ice-rafted debris (IRD), and correlates positively with the total organic carbon (TOC) content and inversely with the absolute abundance of surface-dwelling nannoplankton species. TOC/total nitrogen ratios and δ13Corg values of TOC indicate that the TOC deposited during glacial periods was marine and associated with increased Hg deposition. These observations suggest that marine Hg is incorporated into the organic matter produced by deep-dwelling phytoplankton in the lower photic zone. Mercury- and IRD-bearing icebergs flowed out to this area during glacial periods melt, increasing the Hg content of photic water, and depositing IRD on the ocean floor, where increased marine Hg during glacial periods was consumed by deep-dwelling phytoplankton. Therefore, the change in the sediment Hg content from the North Atlantic Ocean is controlled by climatic change and can be used as a chemical indicator of Northern Hemisphere ice sheet variability.