VARIATIONS IN MERCURY DEPOSITION TO ANTARCTICA OVER THE PAST 34,000 YEARS

POLAR ice contains a valuable record of past atmospheric mercury deposition, which can provide information about both the natural biogeochemical cycling of this toxic trace metal and the impact of recent anthropogenic emissions. But existing studies of mercury in polar ice and snow cores1-5 suffer from sample contamination and inadequate analytical procedures. Here we report measurements of mercury concentrations spanning the past 34,000 years from the Dome C ice core, Antarctica, using the stringent trace-metal clean protocols developed by Patterson and co-workers6. Although this record does not extend into the industrial period, it provides an important baseline for future attempts to identify anthropogenic mercury in Antarctic ice and snow. We find that mercury concentrations were strikingly elevated during the last glacial maximum (18,000 years ago), when oceanic productivity may have been higher than it is today7. As oceanic mercury emission is correlated with productivity8,9, we suggest that this was the principal pre-industrial source of mercury to Antarctica; mercury concentrations in Antarctic ice might therefore serve as a palaeoproductivity indicator for the more distant past.