Kowalski, L., Nakayama, Y., and Loose, B. (2025)
Presented at:
AGU Annual Meeting 2025The Winter Water mass reveals the role of deep winter mixing on 'warm' and 'fresh' shelf regions of the West Antarctic. In this study, we investigate how the production of Winter Water within the Amundsen Sea leads to ventilation by introducing a surface tracer into a regional configuration of MITgcm with ECCO-constrained forcing conditions for the years from 1998 to 2023. The annual average in ventilation flux ranges from -0.34 up to -1.34 Sv, with the largest fluxes occurring in early spring. The modeled mixed layer depths routinely reached depths of 200 to 300 m in coastal polynyas driven by changes in salinity from sea ice formation and wind stress. Seasonal and multiyear variations in ventilation flux correlate with sea surface salinity as well as surface buoyancy flux. Overall, we find that ventilation taking place in the Amundsen Sea completely renews 25% of water on average down to 200 m every year, with ventilation by vertical mixing beginning in winter and continuing through late spring even after the surface ocean restratifies. Changes in simulated fields revealed a suspected regime shift in the Amundsen Sea with less ventilation after 2014 coinciding with progressive freshening and stratification of the modeled surface ocean. This simulated regime shift is consistent with observations of decadal shifts in other marginal Antarctic seas illustrating how ventilation, renewal, and continental shelf overturning are all sensitive to the secular changes impacting West Antarctic regional seas.
