Snow's Thermodynamical Effect on Southern Ocean Sea Ice Extent

Snow accumulation on sea ice is expected to change with future global warming. Understanding how the changing snow accumulation impacts sea ice growth and melting is important for climate modeling. Sea ice extent in the Southern Ocean has been evolving under the contemporary climate in ways people are yet to understand. Sea ice experienced a slight and gradual growth prior to 2008, a sudden increase to a large sea ice extent regime during 2008 to 2016, and a significant decrease to an unprecedentedly small sea ice extent regime after 2016 (Purich & Doddridge, 2023). In this thesis, I am curious about (1) what role the thermodynamic effect of snow has on sea ice and (2) how snow can potentially impact the intensity of sea ice extent regime shifts. This thesis contains three chapters. The first chapter gives a general introduction of snow on sea ice in the Southern Ocean. The second chapter, utilizing the new perspective of the three sea ice extent regimes in the past decades, compared three different types of Southern-Ocean-wide remote sensing data products to analyze the changes in snow depth on sea ice from 2002 to 2021. From these datasets I found that across different regions in the Southern Ocean, most saw an increase of snow depth during the 2008 to 2016 large sea ice extent period compared to that before 2008. During the sea ice extent retreating period, snow on sea ice showed a decrease of snow depth in more regions compared to that before 2008. This is true especially in regions with seasonal sea ice. In the third chapter of the thesis, I combined a 1-D snow-sea-ice thermodynamic model with a sea ice extent model. Because I isolate snow’s thermodynamic effects on sea ice in the Southern Ocean, my thesis pin points changes induced by thermodynamic processes, which is novel compared to most snow-sea-ice models. This updated model generates snow depth and sea ice thickness in the seasonal sea ice zone. The model experiments confirmed that snow insulation is the dominant thermodynamic effect of snow on sea ice. With an increase in snow accumulation, there is a thinning in sea ice at the pole and a smaller sea ice extent. The most significant negative thermodynamic impact for snow on sea ice is when snow accumulation increases in fall. The model experiments suggest that the sea ice extent regime change was muted due to the positively-correlating snow depth. This thesis presents an updated and comprehensive synthesis of snow depth on sea ice in the Southern Ocean, and the first idealized thermodynamic model to compare Antarctic snow depth, sea ice thickness, and latitudinal sea ice extent on a multi-year timescale.