Oxygen Isotope Insights Into the Impact of Amundsen Sea Freshwater on Ross Sea Freshening

Abstract Over the past five decades, the Ross Sea has freshened, but the mechanisms remain unclear. This study uses oxygen isotopes to trace freshwater transport from the Amundsen Sea to the Ross Sea. Results show that Winter Water (WW) in the Antarctic Slope Current (ASC) has lower δ 18 O values (<−0.7‰) due to glacial meltwater (GMW) inputs from the Amundsen Sea shelf. Modified Circumpolar Deep Water (mCDW) in the Ross Sea, formed by mixing upwelled Upper Circumpolar Deep Water and ASC WW, has intermediate salinity and δ 18 O values. High Salinity Shelf Water (HSSW) forms from mCDW during sea ice formation and is further modified by mixing with GMW, resulting in distinctly low δ 18 O of <−0.8‰. In 2020, HSSW δ 18 O averaged 0.25‰ lower than in 2000, suggesting freshwater from the Amundsen Sea and local ice shelf melting contribute to the Ross Sea's freshening. This highlights the importance of understanding marginal sea interactions in climate change.