Role of snow in sea ice mass balance in a thinner Arctic ice pack - lessons learned from the N-ICE2015 campaign

Abstract:

Observations from the N-ICE2015 campaign in the Arctic Ocean north of Svalbard showcased for the first time that snow can contribute substantially to the mass balance of Arctic pack ice, through snow-ice formation. This was earlier considered negligible due to the rather thick ice and relatively thin snow on Arctic sea ice, that would not allow for seawater flooding of the ice due to the weight of the snow on the ice. However, with rapid thinning of Arctic sea ice this could change, to more closely resemble the seasonal sea ice pack in the Southern Ocean where relatively thick snow on thinner sea ice result in significant contributions to ice mass balance from transformation of snow to ice.

Here we summarize recent modeling work on the role of snow in Arctic sea ice mass balance, through its effects on mass and thermodynamics of the ice cover. This work supported the observations from N-ICE2015 that multi-year ice, ice that has survived summer melt and thus accumulates snow from early fall has greater potential for snow-ice formation in the Atlantic sector of the Arctic. The thinner the ice is at the end of the summer the larger the potential for snow-ice formation. First-year ice that forms later fails to capture the largest accumulation of snow in late autumn and early winter, which will in turn support rapid thermodynamic growth. Thick snow on older ice can limit the thermodynamic bottom growth in regions with thick snow. However, there are large regional differences across the Arctic Ocean, which are largely related to the patterns of precipitation. Thus the potential for snow-ice is largest north of Fram Strait, north of Svalbard and north of the Barents Sea, where frequent synoptic weather systems bring moisture into the central Arctic. For example, snow accumulation on level ice on MOSAiC appeared much smaller than observed on N-ICE2015, likely showcasing the significant regional gradients in precipitation. Snow on sea ice appears to play a critical role in the thermodynamic effects of winter warming events, with thicker snow cover reducing winter ice growth considerably more than transient atmospheric winter warming events do.

The overall effect of snow in a thinner Arctic sea ice pack is complex, but a critical aspect of the sea-ice system, and needs to be well represented in future projections of the Arctic sea ice cover.