Editing IPCC:AR6/SROCC/Chapter-3 (section)

===== 3.2.1.1.6 Snow on ice =====

Snow accumulation on sea ice inhibits sea ice melt through a high albedo, but the insulating properties limit sea ice growth (Sturm and Massom, 2016 <sup>[[#fn:r167|167]]</sup> ) and inhibits photosynthetic light (important for in- and under-ice biota) from reaching the bottom of the ice (Mundy et al., 2007 <sup>[[#fn:r168|168]]</sup> ). If snow on first-year ice is sufficiently thick, it can depress the ice below the sea level surface, which forms snow-ice due to surface flooding. This process is widespread in the Antarctic (Maksym and Markus, 2008 <sup>[[#fn:r169|169]]</sup> ) and the Atlantic Sector of the Arctic (Merkouriadi et al., 2017 <sup>[[#fn:r170|170]]</sup> ), and may become more common across the Arctic (with implications for sea ice ecosystems) as the ice regime shifts to thinner seasonal ice (Olsen et al., 2017 <sup>[[#fn:r171|171]]</sup> ; Granskog et al., 2018 <sup>[[#fn:r172|172]]</sup> ) ( ''medium confidence'' ).

Despite the importance of snow on sea ice (Webster et al., 2018 <sup>[[#fn:r173|173]]</sup> ), surface or satellite derived observations of snowfall over sea ice, and snow depth on sea ice are lacking (Webster et al., 2014 <sup>[[#fn:r174|174]]</sup> ). The primary source of snow depth on Arctic sea ice are based on observations collected decades ago (Warren et al., 1999 <sup>[[#fn:r175|175]]</sup> ) the utility of which are impacted by the rapid loss of multi-year ice across the central Arctic (Stroeve and Notz, 2018 <sup>[[#fn:r176|176]]</sup> ), and large interannual variability in snow depth on sea ice (Webster et al., 2014 <sup>[[#fn:r177|177]]</sup> ). Airborne radar retrievals of snow depth on sea ice provide more recent estimates, but spatial and temporal sampling is highly discontinuous (Kurtz and Farrell, 2011 <sup>[[#fn:r178|178]]</sup> ). Multi-source time series provide evidence of declining snow depth on Arctic sea ice (Webster et al., 2014 <sup>[[#fn:r179|179]]</sup> ) consistent with estimates of higher fractions of liquid precipitation since 2000 (Boisvert et al., 2018 <sup>[[#fn:r180|180]]</sup> ) but there is ''low confidence'' because surface measurements for validation are extremely limited and suggest a high degree of regional variability (Haas et al., 2017 <sup>[[#fn:r181|181]]</sup> ; Rösel et al., 2018 <sup>[[#fn:r182|182]]</sup> ).

Although there are regional estimates of snow depth on Antarctic sea ice from satellite (Kern and Ozsoy-Çiçek, 2016 <sup>[[#fn:r183|183]]</sup> ), airborne remote sensing (Kwok and Maksym, 2014 <sup>[[#fn:r184|184]]</sup> ), field measurements (Massom et al., 2001 <sup>[[#fn:r185|185]]</sup> ) and ship-based observations (Worby et al., 2008 <sup>[[#fn:r186|186]]</sup> ), data are not sufficient in time nor space to assess changes in snow accumulation on Antarctic sea ice.

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