1000 Year Record of Heavy Metal Contamination from the RICE Ice Core, Roosevelt Island, Antarctica

Abstract:

Since the onset of industrialisation, atmospheric concentrations of heavy metal pollutants have increased. We present a new record from Antarctica for the past 1000 years, which provides a unique opportunity to establish a baseline of natural heavy metal concentration variability and allows us to distinguish anthropogenic contributions.

As part of the Roosevelt Island Climate Evolution (RICE) project, a 764m deep ice core was drilled in 2012 and 2013 at Roosevelt Island. The site is located at the north-western edge of the Ross Ice Shelf, and as such is highly influenced by weather systems derived from the South Pacific sector of the Southern Ocean. This presents the opportunity to develop a high-resolution record of background environmental contamination that is representative of the Southern Hemisphere. The isolation of Roosevelt Island from local sources of heavy metals results in a record that is indicative of large-scale source and transport changes.

Over 2000 samples from the top 300m of the ice core, as well as snow pit and firn core samples, have been analysed for concentrations of 37 different elements. Analyses were made using a Thermo Scientific Element XR with front end modifications to maximise sensitivity to ensure high-quality data for the extremely low concentrations – parts per quadrillion (ppq) for some elements. The transition metal/metalloid elements selected for detailed investigation are Pb, Fe, Al, Co, Mn, Tl, As. High resolution (sub-annual) heavy metal data over the 20^th Century are presented and contrasted with lower resolution (three year averaged) data for the past 1000 years.

Snow samples collected during storm events at Roosevelt Island suggest heavy metal concentrations are associated with long range transport paths over the Southern Ocean, as modelled in Hysplit. By accounting for changes in source strength over the industrial period (using enrichment factors), the RICE heavy metal record can be used to infer large-scale transport changes. The relationships between heavy metal concentrations and ratios and major climate drivers such as the Amundsen Sea Low, the Southern Annular Mode, and the Southern Oscillation are investigated using ERA Interim reanalysis data from 1979 to the present, and the use of heavy metals as a proxy for these climate modulators is evaluated.