PhD Thesis Defense: David Clemens-Sewall

For Zoom link, email david.w.clemens-sewall.th@dartmouth.edu.

"Snow redistribution and apparent thermal conductivity on Arctic sea ice"

Abstract

Arctic sea ice has declined dramatically due to climate change which impacts Arctic communities, ecosystems, international trade and the world's climate. However, due to uncertain physical processes, climate models generally do not capture the severity of the observed decline, which adds uncertainty to projections of future climate change. The greatest uncertainty in the Arctic sea ice component of climate models is how much heat passes through the snow on top of the ice in the winter. This heat flux controls how much ice grows each winter, impacting how much ice survives the summer melt. Snow is an excellent thermal insulator (about ten times more effective than ice), so the snow depth is a critical parameter. Wind redistribution produces highly spatially variable snow depth. Due to logistical and technological challenges, there are few measurements of snow redistribution on free-floating Arctic sea ice throughout the winter.

We measured snow accumulation and redistribution on drifting Arctic sea ice from October 2019 to May 2020 on the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC). In addition to traditional, manual snow depth measurements, we made approximately biweekly observations of the changing snow surface topography at cm-scale vertical accuracy on an area of approximately 0.5 km² via Terrestrial Laser Scanning. Furthermore, we collected the first measurements of blowing snow loss into open water through cracks in the ice. Our findings suggest that less snow is lost into open water than assumed in models. However, once the open water has refrozen into young ice, it preferentially accumulates 2.5-8 cm of wind-blown snow, depressing ice growth. This preferential accumulation is not represented in climate models, and its omission may cause models to overestimate wintertime heat flux by 3-8% on average in the Arctic.

Finally, we observed that snow redistribution from level ice to snow drifts around pressure ridges can significantly reduce snow depth on level ice. For level, second-year ice at MOSAiC, this snow redistribution may have increased ice growth by 28-45%. Collectively, our findings deepen our understanding of snow redistribution on Arctic sea ice and will enable better representation of snow processes in climate models.

Thesis Committee

• Christopher Polashenski, PhD (Chair)
• Donald Perovich, PhD
• Matthew Parno, PhD
• Marisa Palucis, PhD
• Colin Meyer, PhD

Contact

For more information, contact Theresa Fuller at theresa.d.fuller@dartmouth.edu.