Landfast sea-ice and platelet-layer thickness and conductivity of Atka Bay, Antarctica, December 2012@en

Ice shelves strongly impact coastal Antarctic sea-ice and the associated ecosystem through the formation of a sub-sea-ice platelet layer. Although progress has been made in determining and understanding its spatio-temporal variability based on point measurements, an investigation of this phenomenon on a larger scale remains a challenge due to logistical constraints and a lack of suitable methodology. In this study, we applied a laterally-constrained Marquardt-Levenberg inversion to a unique multi-frequency electromagnetic (EM) induction sounding dataset obtained on the landfast sea ice of Atka Bay, eastern Weddell Sea, in 2012. In addition to consistent fast-ice thickness and -conductivities along > 100 km transects; we present the first comprehensive, high resolution platelet-layer thickness and -conductivity dataset recorded on Antarctic sea ice. The reliability of the algorithm was confirmed by using synthetic data, and the inverted platelet-layer thicknesses agreed within the data uncertainty to drill-hole measurements. Ice-volume fractions were calculated from platelet-layer conductivities, revealing that an older and thicker platelet layer is denser and more compacted than a loosely attached, young platelet layer. The overall platelet-layer volume below Atka Bay fast ice suggests that the contribution of ocean/ice-shelf interaction to sea-ice volume in this region is even higher than previously thought. This study also implies that multi-frequency EM induction sounding is an effective approach in determining platelet layer volume on a larger scale than previously feasible. When applied to airborne multi-frequency EM, this method could provide a step towards an Antarctic-wide quantification of ocean/ice-shelf interaction.冰架（Ice shelf）通过海冰下血小板层（sub-sea-ice platelet layer）的形成过程，对南极沿岸海冰及其关联生态系统造成显著影响。尽管基于点位测量在探明与理解该现象的时空变异性方面已取得一定进展，但受限于后勤保障约束与适用方法的缺失，开展大尺度范围内的该现象研究仍为一项挑战。本研究于2012年针对威德尔海东部阿特卡湾（Atka Bay）的固定海冰（landfast sea ice）采集了一套独特的多频电磁（electromagnetic, EM）感应测深数据集，并将侧向约束的Marquardt-Levenberg反演方法应用于该数据集。除获取沿超100公里断面的一致固定海冰厚度与电导率数据外，本研究还发布了首套针对南极海冰的高分辨率、全面的血小板层厚度与电导率数据集。通过合成数据（synthetic data）验证了该反演算法的可靠性，反演得到的血小板层厚度与钻孔实测值在数据不确定度范围内保持一致。基于血小板层电导率计算冰体积分数后发现，相较于松散附着的年轻血小板层，老化增厚的血小板层密度更高、压实程度更强。阿特卡湾固定海冰下方的整体血小板层体积数据显示，该区域内海洋与冰架相互作用对海冰体积的贡献甚至高于此前的预估。本研究同时表明，多频电磁感应测深是一种可实现比此前更大尺度血小板层体积测算的有效手段。若将该方法应用于机载多频电磁系统，将有望推进南极全域范围内海洋与冰架相互作用的量化研究工作。