Abstract
Snow depth on sea ice is an essential state variable of the polar climate system and yet one of the least known and most difficult to characterize parameters of the Arctic and Antarctic sea ice systems. Here, we present a new type of autonomous platform to measure snow depth, air temperature, and barometric pressure on drifting Arctic and Antarctic sea ice. “Snow Buoys” are designed to withstand the harshest environmental conditions and to deliver high and consistent data quality with minimal impact on the surface. Our current dataset consists of 79 time series (47 Arctic, 32 Antarctic) since 2013, many of which cover entire seasonal cycles and with individual observation periods of up to 3 years. In addition to a detailed introduction of the platform itself, we describe the processing of the publicly available (near real time) data and discuss limitations. First scientific results reveal characteristic regional differences in the annual cycle of snow depth: in the Weddell Sea, annual net snow accumulation ranged from 0.2 to 0.9 m (mean 0.34 m) with some regions accumulating snow in all months. On Arctic sea ice, the seasonal cycle was more pronounced, showing accumulation from synoptic events mostly between August and April and maxima in autumn. Strongest ablation was observed in June and July, and consistently the entire snow cover melted during summer. Arctic air temperature measurements revealed several above-freezing temperature events in winter that likely impacted snow stratigraphy and thus preconditioned the subsequent spring snow cover. The ongoing Snow Buoy program will be the basis of many future studies and is expected to significantly advance our understanding of snow on sea ice, also providing invaluable in situ validation data for numerical simulations and remote sensing techniques.
Highlights
The sea ice cover of the polar oceans plays a dominant role in the Earth’s climate system, and at the same time, its evolution is a direct indicator of global changes
Status of the data in this article is from September 15, 2019. 47 units were deployed in the Arctic Ocean, including Snow Buoy 2014S25 on a buoy test site near Barrow, Alaska (Figure 1E). 32 units were deployed in the Weddell Sea, Antarctica, including three on the Ekström Ice Shelf on a test site near the German wintering station Neumayer III (Figure 1D)
The lifetime of an individual buoy depends in most cases on the sea ice conditions and most buoys fail in the marginal ice zone, predominantly due to drowning after sea ice melt
Summary
The sea ice cover of the polar oceans plays a dominant role in the Earth’s climate system, and at the same time, its evolution is a direct indicator of global changes. Due to its exceptional insulative properties and its own mass, snow plays a governing role in sea ice thermodynamics, and determines its mass balance to a great extent In particular it contributes to snow ice and superimposed ice formation and sea ice thickening from the top (Worby et al, 1998; Haas et al, 2001; Willmes et al, 2006; Nicolaus et al, 2009; Arndt et al, 2017). This thickening is mainly observed across large areas of the Southern Ocean, but is expected to be more important in a future thinner Arctic sea ice regime (Granskog et al, 2017). For the current radar (CryoSat, Sentinel-3A/B, AltiKa) altimeter missions, the interface and volume snow radar backscatter has a notable impact on the radar ranging in the freeboard retrieval process (Kurtz et al, 2014; Kwok, 2014; Ricker et al, 2015; Nandan et al, 2017; King et al, 2018)
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