A CLOSER LOOK AT THE ROLE OF PRECIPITATION AND AIR-SEA GAS EXCHANGE OF CIRCUMPOLAR WATERS IN THE EASTERN AMUNDSEN SEA, ANTARCTICA

• Main Author: Cousens, Virginia
• Format: Text
• Language: unknown
• Published: DigitalCommons@URI 2023
• Subjects: Amundsen Sea; Pine Island Glacier; Antarc*; Antarctica; Ice Shelf; Pine Island
• Online Access: https://digitalcommons.uri.edu/theses/2300; https://digitalcommons.uri.edu/context/theses/article/3294/viewcontent/Cousens_uri_0186M_13099.pdf

Pine Island Glacier in the remote Amundsen Sea has exhibited some of the most pronounced thinning and retreat in Western Antarctica in recent decades, resulting in significant influx of freshwater to the region. These dynamic changes are caused by climate sensitive processes from warming ocean currents to changing air temperature. Glacial melt in this region has been thought to dominate the freshwater budget, but meltwater tracers suggest precipitation may also be significant in terms of freshwater flux. Here, we take a closer look at the magnitude of precipitation derived from oxygen-18 and noble gases as freshwater tracers and seek to explain its accumulation in the ocean. Using a model for air-sea gas exchange, constrained by the evolution of helium-3 from deep circumpolar waters to the observed continental shelf isotopic values, we find that gas-exchange ventilates nearly the entire Eastern Amundsen Sea down to 450 m. In particular, gas exchange leads to a decrease in the saturation anomalies of both neon (DNe) and argon (DAr) by an average of 0.75 % and 1.3 %, respectively. Gas exchange also leads to an average increase in oxygen concentrations of 69 mmol kg-1 on the Eastern Amundsen Sea continental shelf, though the distribution varies across this shelf with the smallest contribution in front of Pine Island Ice Shelf. Insight into gas exchange also permits us to reconstruct the oxygen budget. After accounting for oxygen derived from the freshwater budget, we find that the oxygen derived from biology is generally negative though the distribution across the shelf varies, indicating that waters in the Amundsen Sea are net heterotrophic. We used the estimates of gas exchange to put lower and upper bounds on the estimates of glacial meltwater and this uncertainty is propagated into the estimate of precipitation. We find that precipitation accounts for an average of 2.3 m of water per m2 or nearly 30 % of the freshwater inventory in the ocean column, and it likely accumulates during the 3.5 to 7 years that water ...