Sea ice melt onset dynamics in the northern Canadian Arctic Archipelago from RADARSAT

Abstract:

Sea ice melt onset, the appearance of liquid water in its snow cover, decreases surface albedo which increases shortwave absorption and thereby accelerates snow and sea ice melting. Earlier melt onset leads to the earlier formation of open water which enhances the ice-albedo feedback. Sea ice melt onset timing and duration vary considerably, both spatially and temporally, owing to variability in atmospheric forcing; this in turn influences the September sea ice extent. Sea ice melt onset variability has been investigated using coarse resolution passive microwave observation in Canadian Arctic Archipelago (CAA); however, this does not provide sufficient information about sea ice melt dynamics. We developed a new melt onset algorithm using high resolution synthetic aperture radar (SAR) images from RADARSAT to better understand sea ice melt onset dynamics in northern Canadian Arctic Archipelago (fig 1) from 1997 to 2014. The algorithm is based on the temporal evolution of the SAR backscatter coefficient (σ^o), using separate thresholds for seasonal first-year ice and multi-year ice. Results indicated that the mean annual average melt onset date in the northern CAA was on year day 164 (mid–June) with a standard deviation of 4 days over the 18 year period. No significant trend for melt onset date was found over the 18 year period (fig: 2) but extreme early melt onset was detected in 1998 and 2012 associated with anomalous atmospheric forcing. Spatially, sea ice onset over the entire northern CAA varied from a 10-day minimum in 2007, to a 35-day maximum in 2011 and exhibited negative correlation (r=0.70) with the rate of increase in surface air temperature (fig 3) derived from Extended AVHRR Polar Pathfinder (APP-x) dataset. An earlier (later) melt onset also results in light (heavier) September sea ice area in the northern CAA (fig 4).