Contribution of Snow to Arctic First-Year and Multi-Year Sea Ice Mass Balance Within the Last Ice Area

We present the delta O-18 isotope composition of 16 multi-year ice (MYI) and eight first-year ice (FYI) cores collected during spring from the Lincoln Sea, a region within the Last Ice Area, which is expected to retain MYI longest into the future. Isotopic signatures were used to quantify the contribution of snow to sea ice mass. These estimates yield a higher total snow contribution in MYI (10 +/- 5%) than to FYI (4 +/- 2%). Converted to Snow Depth Equivalent (SDE), MYI had five times larger SDE (0.79 +/- 0.38 m) than FYI (0.16 +/- 0.11 m). The difference is explained by the contribution of refrozen surface and under-ice melt ponds as well as superimposed/interposed ice for MYI resulting from higher accumulation of snow over multiple, longer accumulation seasons compared to FYI. Given the impending replacement of MYI by FYI, the large difference in absolute snow contributions between MYI and FYI highlights the potential implications in terms of the redistribution of precipitation-derived (meteoric) freshwater throughout the Arctic Ocean. Furthermore, we observed high relative snow contributions to ice mass in the surface of one-third of older FYI cores, which we attributed to flooding and formation of snow-ice. Our results support the premise that flooding events on FYI may be more prevalent throughout the Arctic Ocean than previously assumed. Plain Language Summary Snow is important for the Arctic energy balance, ongoing climate change, and the disappearance of the sea ice. Snow acts like a blanket on the ice keeping the sea ice warmer in the winter by preventing heat loss into the cold atmosphere above. While in summer, snow can also insulate the ice from warm air temperatures delaying the start of ice melt. Snow can also be incorporated into the ice and contribute to the Arctic sea ice mass balance. How much of the Arctic ice is made up of refrozen snow is largely unknown. Our results indicate that the older, multi-year ice has a larger snow contribution to ice mass than younger first-year ice. This difference arises as the older ice accumulates more snow-melt water into its mass each melt season, which means that when the older ice melts it releases freshwater, accumulated over several years, far away from where it picked it up. The younger Arctic sea ice releases snow it has accumulated already in the first summer closer to the snow fall location. As a result of the disappearing older sea ice, the distance snow-melt water is transported across the Arctic will likely decrease.