ICMGP - Conference Presentation

Abstract Information :

Ocean plays a critical role in the global mercury (Hg) cycling, due to the in-situ formation and bioaccumulation of neurotoxic methylmercury (MeHg), but the sources and transformations of Hg in ocean are not fully understood. Previous studies on marine Hg cycling have been mostly focusing on the Northern Hemisphere. However, only a few attempts have been made to study the marine Hg cycle in the Southern Hemisphere, where oceanic Hg is less affected by direct anthropogenic emission and thus may record the background Hg cycling. Here we measure Hg stable isotopes in two deep-sea sediment cores (SX-09 and SX-10) in the North Ross Sea to investigate the source of Hg to the Southern Ocean and the impact of the glacial-interglacial climate change on marine Hg cycling. Sedimentary Hg isotope data suggests significant changes in Hg sources with time. In SX-10, atmospheric deposition via long-range transport was the dominant Hg source before the Last Glacial Maximum (LGM), as evidenced by slightly positive mass independent fractionation (MIF, ?199Hg and ?200Hg) and negative mass dependent fractionation (MDF, ?202Hg), which are similar to those of modern open-ocean sediments. In contrast, the SX-09 core shows strongly negative ?199Hg but positive ?200Hg before LGM, which are similar to the Hg isotope signatures of Antarctic snow. We suggest that the SX-09 core was dominated by Hg input from glacial materials transported from the Antarctic icesheet during the expansion of glacial. However, after LGM, ?199Hg and ?200Hg in both cores shifted consistently towards zero together with increases of Hg concentration and ?202Hg, which may have recorded enhanced volcanic Hg emission (near-zero MIF) and terrigenous input (negative MIF) from Antarctica due to the retreat of glacial. Our results show that Hg isotopes in the Southern Ocean can record the historical Hg cycling and its responses to climate changes.