Ground-based electromagnetic (EM) and drill-hole ice and snow thickness measurements during Polarstern cruise ARK-XVII/2 in 2001

Late-summer thickness distributions of large ice floes in the Transpolar Drift between Svalbard and the North Pole in 1991, 1996, 1998, and 2001 are compared. They have been derived from drilling and electromagnetic (EM) sounding. Results show a strong interannual variability, with significantly reduced thickness in 1998 and 2001. The mean thickness decreased by 22.5% from 3.11 m in 1991 to 2.41 m in 2001, and the modal thickness by 22% from 2.50 m in 1991 to 1.95 m in 2001. Since modal thickness represents the thickness of level ice, the observed thinning reflects changes in thermodynamic conditions. Together with additional data from the Laptev Sea obtained in 1993, 1995, and 1996, results are in surprising agreement with recently published thickness anomalies retrieved from satellite radar altimetry for Arctic regions south of 81.5°N. This points to a strong sensitivity of radar altimetry data to level ice thickness.1991、1996、1998及2001年，斯瓦尔巴（Svalbard）与北极点之间的穿极漂流（Transpolar Drift）区域内大型浮冰的夏末厚度分布得到对比分析。本次研究的数据集通过钻孔钻探与电磁测深（electromagnetic (EM) sounding）方法获取。结果显示，该区域浮冰厚度存在显著年际变率，1998年与2001年的浮冰厚度明显降低。平均厚度从1991年的3.11米下降至2001年的2.41米，降幅达22.5%；众数厚度（modal thickness）则从1991年的2.50米降至2001年的1.95米，降幅为22%。由于众数厚度代表平整冰（level ice）的厚度，本次观测到的厚度减薄现象反映了热力学环境的变化。结合1993、1995及1996年在拉普捷夫海（Laptev Sea）获取的补充观测数据，本研究结果与近期发布的、针对北纬81.5°以南北极区域的卫星雷达测高（satellite radar altimetry）反演厚度异常数据高度吻合，这表明雷达测高数据对平整冰厚度具备极强的敏感性。