Distribution of dissolved inorganic radiocarbon in the Amundsen Sea, Antarctica

Abstract

The Amundsen Sea is experiencing rapid change in sea-ice cover and ice shelf melting. It has the most productive polynya, the Amundsen Sea polynya. However, the inorganic carbon cycling associated with this polynya is yet poorly determined. In this study, I have examined the distribution of dissolved inorganic radiocarbon (DIC) in three different oceanographic regions in the Amundsen Sea: in the sea-ice zone (SIZ), inside the Amundsen Sea polynya, and near the Dotson Ice Shelf. In the upper 300 m layers, the average radiocarbon value in ∆14C in the polynya (−135 ‰) was considerably higher than that in the SIZ (−150 ‰). ∆14C value of Winter Water (WW) end-member was −147 ‰. The ∆14C values near the sea floor at each site were close to the value of the Circumpolar Deep Water (CDW), reflecting the intrusion of this water mass to the shelf near the sea floor. Contribution of carbon from processes such as glacial meltwater (GMW) input, benthic efflux, and remineralization of sinking organic particles in the water column was negligible to change the radiocarbon values of DIC in the water column. Air-sea gas exchange appears to be the primary process to increase radiocarbon content in the upper layer. Based on the observed discrepancy in ∆14C value between the SIZ and the polynya, absorption of atmospheric CO2 during the polynya opening in the austral summer was estimated. This study provides the preliminary data to understand the inorganic carbon cycling in this climate-sensitive region.