Stable carbon isotopes in scallop shells: A proxy of Antarctic sea-ice persistence

Abstract

Sea ice is fundamental to global climate and its multiannual persistence or seasonal absence shapes Antarctic marine ecosystems. With sea ice in rapid decline in the Southern Ocean, it is imperative to understand its variability prior to satellite data. The Antarctic scallop Adamussium colbecki has a broad geographic distribution and long fossil history in the Southern Ocean, and its shells could be ideal bioarchives for sea ice with the potential to resolve subannual sea-ice dynamics over multiple years or decades. Here, we evaluate stable isotopes of carbon in A. colbecki shells from two sites on western McMurdo Sound. Each site maintains stable, frigid seawater temperatures, but they differ in sea-ice duration. Explorers Cove has semi-permanent multiannual sea ice, whereas Bay of Sails has annual sea ice that breaks out every year. Our results indicate that seasonal variation in δ13Cshell values may proxy sea-ice persistence. Scallops living under annual sea ice — adults from Bay of Sails and juveniles collected during a fortuitous recent sea ice breakout at Explorers Cove — had higher δ13Cshell values during summer growth than winter growth. Scallops living under multi-annual sea ice had no difference in δ13Cshell values between winter and summer growth. We posit that phytoplankton blooms leverage the seasonal δ13C values of the dissolved inorganic carbon under ice-free conditions, which is in turn recorded in δ13Cshell values and that A. colbecki shells could be used to understand past variability in sea-ice persistence in coastal Antarctica.