Driving Mechanisms of Very Rapid Sea Ice Loss Events

Abstract

Forecasting Arctic sea ice is a complex, open problem in polar science, exasperated by climate change and Arctic amplification. Climate models consistently under represent sea ice processes on subseasonal timescales which may contribute to the forecasting challenges. Very rapid sea ice loss events (VRILEs) are substantial sea ice loss events that occur on the timescale of days. There are three mechanisms proposed to cause VRILEs: heat transport by surface cyclones, wind driven ocean waves, and ocean heating from vertical mixing. We hypothesize that ocean waves play as much if not more of a role in causing VRILEs as atmospheric heat transport.

We approach this problem from three perspectives. First, a detailed comparison of sea ice properties in observations and the Community Earth System Model version two large ensemble (CESM2 LENS). Of note is that neither CESM2 or any other model couples ocean waves to sea ice. We find that model performance in this area is insufficient to study short term phenomena meaningfully. Next we take a statistical approach, utilizing multivariate EOFs to examine the relative importance of various atmospheric and ocean fields to subseasonal changes in sea ice concentration. In general, heating terms more strongly co-vary with sea ice concentration than ocean waves with seasonal difference in the importance of 2-m temperature anomalies. Finally we construct a one-dimensional, Finite Element Analysis model to study how effective ocean waves are at fracturing sea ice in the Marginal Ice Zone (MIZ). Ocean waves, particularly low frequency waves, are capable of fracturing large ice floes over a kilometer deep in the MIZ. Taken all together, we find that ocean waves likely play an causal role for VRILEs but one intertwined with the other mechanisms. That is, there is not a single most important factor but VRILEs are related to increased storminess caused by a surface cyclone interacting with a preexisting high pressure system that generated ocean waves and upwelling. They cyclone itself transports heat, especially in its warm sector, and its winds can drive sea ice both deeper into the central Arctic and out of the Arctic depending on the cyclone's local winds.