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

We present the δ 18 O 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. 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. The Freshwater Depth Equivalent ( FDE ) of the contribution from the meteoric (snow) fraction to the Arctic Ocean would be 0.29 ± 0.14 m for MYI and 0.06 ± 0.04 m for FYI (snow fraction contribution to ice mass of 10% and 4%, respectively). These results indicate that once MYI is replaced by FYI, due to continuing Arctic warming and sea ice retreat; the seasonal cycle, the timing and the location of meteoric freshwater input to the surface Arctic Ocean could be altered. Our results indicate that there is significantly more meteoric freshwater stored in MYI, which will be released into the Arctic Ocean when MYI is completely melted, often after it has traveled far distances. In contrast, FYI releases the meteoric freshwater in the first summer shortly after deposition and therefore closer to the precipitation origin. This shift in ice type coverage will likely have consequences for meteoric freshwater distribution in the surface Arctic Ocean. Arctic freshwater budgets and fluxes already integrate freshwater differences between FYI and MYI based on the differential bulk salinities of FYI and MYI (e.g., Haine et al., 2015), but do not address the processes driving the salinity differences, the timing of inputs, the sources of the freshwater (e.g., desalinated sea ice vs. meteoric origin) and the redistribution of the freshwater from the source (e.g., precipitation) to potential downstream regions. These are factors required to model the oceanic implications of future changes in sea ice conditions and freshwater cycling.