Circulation of Circumpolar Deep Water and marine environment traced by 127I and 129I speciation in the Amundsen Sea Polynya, Antarctica

Abstract

The long-lived anthropogenic 129I released from human nuclear activities has been widely employed as an effective oceanographic tracer to investigate circulation of water masses in marine environment. Depth profiles of seawater collected from the Amundsen Sea Polynya, Antarctica were analyzed for total 129I and 127I, as well as their species of iodide and iodate. The measured 129I concentrations ((1.15–3.43) × 106 atoms/L) and 129I/127I atomic ratios ((0.53–1.19) × 10−11) indicate that anthropogenic 129I has not only reached the Antarctic surface marine environment but also the deep water due to a strong vertical mixing of water masses. The Circumpolar Deep Water (CDW) flowed southward along continental shelf towards the ice shelf zone (74.25°S) at a depth of 1025 m and then migrated upward and northward to the polynya and finally to the sea ice zone (71.95°S). The maximum upwelling depth of the CDW was around 200 m in the polynya. The source of 129I− in the polynya is predominantly the intrusion of source waters rather than the in-situ reduction of iodate by phytoplankton, implying a considerably slow reduction process of iodate to iodide in this region.