|Abstract Title:||A change in Arctic mercury and bromine chemistry during the Glacial-Holocene transition|
|Presenter Name:||Delia Segato|
|Company/Institution:||Ca' Foscari university|
|Session:||Atmospheric Hg cycling: Source and Emissions|
|Day and Session:||Wednesday 27th July - Session Three|
|Start Time:||14:00 UTC|
Abstract Information :
Mercury (Hg) is a pollutant of concern especially for the Arctic ecosystems and local populations. Present-day Hg levels have declined thanks to global mitigation policies such as the Minamata Convention and to initiatives focused on the Arctic region such as the Arctic Contaminants Action Program. However, while present-day Arctic anthropogenic Hg is extensively studied, the control of past climate changes on natural Hg variability remains unknown. Sea ice variability influence Hg oceanic evasion to the atmosphere and reactive bromine (Br) in the polar boundary layer, which in turn leads to Atmospheric Mercury Depletion Events (AMDEs) that scavenge Hg to the snowpack.
As part of the East Greenland Ice-Core Project (EGRIP), we report the first ice core record of Arctic Hg, Br and sodium covering the Last Glacial Termination and Early Holocene (9000 ? 15700 years before 2000 AD). To relate Hg with sea ice variability, we employ bromine enrichment (Brenr), with respect to bromine-to-sodium sea water ratio, as a first-year sea ice tracer. Low mercury depositional fluxes and Brenr during the Last Glacial Termination are associated with multi-year sea ice conditions (MYSI) in the subpolar North Atlantic and limited Hg oceanic evasion. At the onset of the Holocene the climate drastically warmed, leading to melting of MYSI and first-year sea ice/open ocean conditions, as suggested by higher Brenr levels. The three-fold increase in Hg depositional flux is likely the results of the interplay between 1) higher Hg evasion from the open ocean and 2) enhanced scavenging of Hg mediated by reactive Br emitted from the higher fraction of first-year sea ice in the subpolar North Atlantic at the onset of the Holocene.