Dr Bruno Tremblay - Projections of sea ice conditions in Nunatsiavut (Labrador)

Of all sub-regions of the Canadian Arctic, the Labrador and Baffin Bay display the largest negative trend in summer sea ice area, raising important questions regarding the length of the “usable-sea-ice season” for coastal communities of Nunatsiavut. In this work, we focus on projected changes in sea ice thickness and extent in the Labrador Sea and Baffin Bay, and more specifically on changes in sea ice season length around four coastal communities, namely Nain, Hopedale, Postville and Rigolet using output diagnostics from the High-Resolution (0.1 ◦) Community Earth System Model version 1.3 (CESM1.3-HR) for the period 1850-2100. Given that CESM1.3-HR does not simulate landfast sea ice, nor does it resolve the fjords along the Labrador coast in which the coastal communities are located, the sea ice season length is derived from surface air temperature data (resolved by the model) and a simple freezing degree day model, validated using in-situ, reanalysis and remote sensing data. Results for the Baffin Bay and Labrador Sea show a remarkably stable maximum march sea ice extent in the Labrador Sea followed by a rapid transition to winter ice-free conditions around 2060 at the same time the Arctic Ocean becomes seasonally ice-free and thick multi-year ice is no longer advected southward through the Nares Strait and along the Labrador coast. This is in contrast with the lower resolution CESM2-LE showing a re-expansion of the maximum sea ice extent starting in the middle of the 21st century followed by a sudden collapse at the end of the century due to a freshening of the Labrador Sea surface waters and shutdown of deep convection. These results show the importance of resolving small scale processes (i.e., the fresh coastal Baffin and Labrador currents) for regional climate projection. Also of interest is the gradual decline in the “usable-sea-ice” season and sporadic extremely large inter-annual variation in sea ice season length in the mid 21st century - a signal that is robust to model spatial resolution and presence or absence of deep convection in the Labrador Sea.