First-year and second-year snow properties on sea ice in the Weddell Sea during POLARSTERN cruise ANT-XXII/2 (ISPOL) during the drift@en

Observations of snow properties, superimposed ice, and atmospheric heat fluxes have been performed on first-year and second-year sea ice in the western Weddell Sea, Antarctica. Snow in this region is particular as it does usually survive summer ablation. Measurements were performed during Ice Station Polarstern (ISPOL), a 5-week drift station of the German icebreaker RV Polarstern. Net heat flux to the snowpack was 8 W/m**2, causing only 0.1 to 0.2 m of thinning of both snow cover types, thinner first-year and thicker second-year snow. Snow thinning was dominated by compaction and evaporation, whereas melt was of minor importance and occurred only internally at or close to the surface. Characteristic differences between snow on first-year and second-year ice were found in snow thickness, temperature, and stratigraphy. Snow on second-year ice was thicker, colder, denser, and more layered than on first-year ice. Metamorphism and ablation, and thus mass balance, were similar between both regimes, because they depend more on surface heat fluxes and less on underground properties. Ice freeboard was mostly negative, but flooding occurred mainly on first-year ice. Snow and ice interface temperature did not reach the melting point during the observation period. Nevertheless, formation of discontinuous superimposed ice was observed. Color tracer experiments suggest considerable meltwater percolation within the snow, despite below-melting temperatures of lower layers. Strong meridional gradients of snow and sea-ice properties were found in this region. They suggest similar gradients in atmospheric and oceanographic conditions and implicate their importance for melt processes and the location of the summer ice edge.本数据集针对南极洲（Antarctica）威德尔海（Weddell Sea）西部的一年海冰（first-year sea ice）与二年海冰（second-year sea ice），开展了积雪属性、叠置冰（superimposed ice）以及大气热通量（atmospheric heat fluxes）的观测研究。该区域的积雪具有独特性，通常可在夏季消融（ablation）期内得以留存。本次观测依托德国破冰船‘极星号’（RV Polarstern）布设的为期5周的漂流冰站——极地星冰站（Ice Station Polarstern，简称ISPOL）开展。作用于雪层（snowpack）的净热通量（net heat flux）为8 W/m²，仅使两类积雪（薄型一年海冰积雪与厚型二年海冰积雪）减薄0.1至0.2米。积雪减薄过程以压实与蒸发为主导，消融仅占次要比重，且仅发生于表层或近表层内部。研究发现，一年海冰与二年海冰上的积雪在厚度、温度与层理结构（stratigraphy）上存在显著特征差异：二年海冰上的积雪厚度更大、温度更低、密度更高，且层理结构更为发育。两类海冰上的积雪变质作用（metamorphism）与消融过程（即质量平衡（mass balance））并无显著差异，这是因为其更多依赖于地表热通量，而非地下属性。冰干舷（ice freeboard）大多为负值，但海水漫溢（flooding）现象主要出现在一年海冰区域。观测期间，雪冰界面温度未达到熔点，但仍观测到了不连续叠置冰的形成。彩色示踪剂实验表明，尽管积雪下层温度低于熔点，仍存在大量融水在积雪层内渗透。本区域积雪与海冰属性存在显著经向梯度（meridional gradients），这暗示大气与海洋环境也存在类似梯度，并表明这些梯度对融冰过程以及夏季冰缘线（summer ice edge）的位置具有重要影响。