Influence of snow depth and surface flooding on light transmission through Antarctic pack ice, supplementary data

Snow on sea ice alters the properties of the underlying ice cover as well as associated physical and biological processes at the interfaces between atmosphere, sea ice, and ocean. The Antarctic snow cover persists during most of the year and contributes significantly to the sea-ice mass due to the widespread surface flooding and related snow-ice formation. Snow also enhances the sea-ice surface reflectivity of incoming shortwave radiation and determines therefore the amount of light being reflected, absorbed, and transmitted to the upper ocean. Here, we present results of a case study of spectral solar radiation measurements under Antarctic pack ice with an instrumented Remotely Operated Vehicle in the Weddell Sea in 2013. In order to identify the key variables controlling the spatial distribution of the under-ice light regime, we exploit under-ice optical measurements in combination with simultaneous characterization of surface properties, such as sea-ice thickness and snow depth. Our results reveal that the distribution of flooded and nonflooded sea-ice areas dominates the spatial scales of under-ice light variability for areas smaller than 100 m-by-100 m. However, the heterogeneous and highly metamorphous snow on Antarctic pack ice obscures a direct correlation between the under-ice light field and snow depth. Compared to the Arctic, light levels under Antarctic pack ice are extremely low during spring (< 0. %). This is mostly a result of the distinctly different dominant sea ice and snow properties with seasonal snow cover (including strong surface melt and summer melt ponds) in the Arctic and a year-round snow cover and widespread surface flooding in the Southern Ocean.海冰表面的积雪会改变下伏海冰的物理属性，同时也会扰动大气-海冰-海洋界面处相关的物理与生物过程。南极地区的积雪覆盖全年多数时段持续存在，且由于广泛发育的表面融水淹没现象及伴随的雪冰形成过程，积雪对海冰总质量的贡献极为显著。积雪还会提升海冰表面对入射短波辐射的反射率，进而决定被反射、吸收以及传输至上层海洋的光照总量。本研究展示了2013年在威德尔海，利用搭载观测设备的遥控无人潜水器（Remotely Operated Vehicle）开展南极浮冰下光谱太阳辐射测量的案例研究成果。为明确调控海冰下光照格局空间分布的关键变量，本研究结合海冰下光学测量数据与同步获取的海冰厚度、积雪深度等表面属性特征开展分析。研究结果显示，在100米×100米的小尺度区域内，融水淹没与未淹没海冰区域的分布格局主导了海冰下光照变化的空间尺度特征。但南极浮冰上的积雪兼具极强的非均质性与高度变质特征，掩盖了海冰下光场与积雪深度之间的直接关联。与北极地区相比，南极浮冰下的春季光照强度极低（不足0.%）。这一现象主要源于南北极海冰与积雪属性的显著差异：北极地区为季节性积雪覆盖（包含强烈的表面融蚀与夏季融池），而南大洋地区则为全年积雪覆盖且广泛存在表面融水淹没现象。