Mercury cycling over the Southern Ocean during Polar Spring: Results from SIPEX II
Caitlin M. Gionfriddo

Authors

Caitlin M. Gionfriddo
School of Earth Sciences, University of Melbourne, Parkville, Australia

Michael Tate
Wisconsin Water Science Center, U.S. Geological Survey, Middleton, WI

David Krabbenhoft
Wisconsin Water Science Center, U.S. Geological Survey, Middleton, WI

Andrew Klekociuk
Australian Antarctic Division, Kingston, Australia

Klaus M. Meiners
Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Sandy Bay, Australia
Australian Antarctic Division, Kingston, Australia

Andrew Bowie
The Institute for Marine and Antarctic Studies, University of Tasmania, Sandy Bay, Australia
Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Sandy Bay, Australia

Delphine Lannuzel
The Institute for Marine and Antarctic Studies, University of Tasmania, Sandy Bay, Australia
Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Sandy Bay, Australia

Robyn Schofield
School of Earth Sciences, University of Melbourne, Parkville, Australia

John W. Moreau
School of Earth Sciences, University of Melbourne, Parkville, Australia

Abstract

Polar sea-ice plays a critical role in defining marine food webs. Despite of this, very little is known about the contribution of methylmercury (MeHg) from the sea-ice environment to resident aquatic organisms in the Southern Ocean. Sea-ice provides a unique ecological niche that may host microorganisms capable of methylating mercury (Hg). During the Sea Ice Physics Ecosystem eXperiment (SIPEX) II, snow, sea-ice, brine, and seawater samples were collected for total Hg (THg) and MeHg analysis to understand the speciation and distribution of Hg at the sea-ice/water interface. Real-time atmospheric elemental Hg concentrations were measured over the duration of the voyage, to identify Hg depletion events, which regularly occur in polar spring and result in Hg deposition in the snowpack. THg concentrations in snow, ice, and brine samples ranged from 0.20-179.1 ng/L, with a median value of 4.03 ng/L. MeHg concentrations ranged from 0.020-0.17 ng/L, median: 0.023 ng/L. The highest concentrations of MeHg and THg were found in ice core samples, but only ~0.7% was methylated. Seawater samples collected from depths of 15-1000 m had the lowest THg concentrations (0.22-2.48 ng/L, median: 0.47 ng/L), but higher methylation proportionally (11% MeHg). Thus, MeHg concentrations in the seawater profile were similar to ice core samples (median: 0.035 ng/L). In the snowpack, the highest concentrations of THg were found in the upper 2 cm, and decreased with depth, indicating Hg deposition, but loss over time. Our results provide useful constraints on fluxes and bioavailability for mercury across the atmosphere-sea-ice-seawater continuum for the under-sampled Antarctic region.