Biogeochemical Impact of Snow Cover and Cyclonic Intrusions on the Winter Weddell Sea Ice Pack

Abstract

Sea ice is a dynamic biogeochemical reactor and a double interface actively interacting with both the atmosphere and the ocean. However, proper understanding of its annual impact on exchanges, and therefore potentially on the climate, notably suffer from the paucity of autumnal and winter data sets. Here we present the results of physical and biogeochemical investigations on winter Antarctic pack ice in the Weddell Sea (R. V. Polarstern AWECS cruise, June–August 2013) which are compared with those from two similar studies conducted in the area in 1986 and 1992. The winter 2013 was characterized by a warm sea ice cover due to the combined effects of deep snow and frequent warm cyclones events penetrating southward from the open Southern Ocean. These conditions were favorable to high ice permeability and cyclic events of brine movements within the sea ice cover (brine tubes), favoring relatively high chlorophyll‐a (Chl‐a) concentrations. We discuss the timing of this algal activity showing that arguments can be presented in favor of continued activity during the winter due to the specific physical conditions. Large‐scale sea ice model simulations also suggest a context of increasingly deep snow, warm ice, and large brine fractions across the three observational years, despite the fact that the model is forced with a snowfall climatology. This lends support to the claim that more severe Antarctic sea ice conditions, characterized by a longer ice season, thicker, and more concentrated ice are sufficient to increase the snow depth and, somehow counterintuitively, to warm the ice.

Variability in sulfur isotope composition suggests unique dimethylsulfoniopropionate cycling and microalgae metabolism in Antarctic sea ice

“…Following the same line, it is also likely that the high permeability and active brine cycling that developed in the relatively warm conditions of the AWECS study in the Western Weddell Sea might have homogenised the DMSP δ 34 S profiles towards oceanic values (Fig. 1a ), as observed for other biogeochemical variables during that study 30 .…”

“…1 ). Pack ice was sampled at three different stations in the Western Weddell Sea (AWECS field study 30 ), and at four different stations in the central Ross Sea and Ross Sea marginal ice zone (PIPERS field study 31 ). One land-fast ice station was visited seven times during a year-round time series study in the McMurdo Sound, Ross Sea (YROSIAE field study 13 ).…”

“…The YROSIAE study in the McMurdo Sound provided an opportunity to sample the same fast-ice site from the winter–spring transition (mid-September) to the spring–summer transition (late-November), covering the full seasonal cycle (growth and decay) of a sympagic bloom 13 . This set of ice cores was therefore selected to study the temporal/seasonal variability in sea ice DMSP δ 34 S, since the two other sets integrated spatial variability and were sampled over a much shorter time frame 30 , 31 . Temporal trends during the YROSIAE study are described here in four distinct sea ice horizons corresponding to distinct microalgal assemblages (surface, interior, bottom ice, and ice–ocean interface) 13 (Fig.…”

Chlorophyll‐a in Antarctic Landfast Sea Ice: A First Synthesis of Historical Ice Core Data

“…Recent studies and reviews on Arctic fast ice have shown a seasonally changing influence of snow cover on ice algal bottom communities (Campbell et al, ; Lange et al, ; Mundy et al, ) and demonstrated how snow dynamics can alter the timing, duration, and magnitude of ice algal spring blooms (Leu et al, ). Recent Antarctic studies have highlighted the importance of snow loading for algal biomass accumulation in pack ice during winter and spring (Meiners et al, ; Tison, Schwegmann, et al, ), but the role of snow in driving Antarctic fast ice algal dynamics remains poorly understood. Snow depth data were available for 57.4% of the AFIAC sites and showed relative low variability, including a very high number of zero snow depth sites ( n = 299, 57.1% of all snow measurements).…”

“…In this case the ice algal community cannot reposition to the ice‐water interface through vertical migration (Aumack et al, ) and gets trapped in sea ice interior layers. On the other hand, in snow‐covered sea ice, surface flooding inducing warm and permeable conditions is an alternative mechanism for the establishment of internal Chl a maxima (e.g., Meiners et al, ; Tison, Schwegmann, et al, ).…”