Sea ice thickness and sea ice area transport in the Laptev Sea

Recent studies based on satellite observations have shown that there is a high statistical connection between the late winter (Feb-May) sea ice export out the Laptev Sea, and the ice coverage in the following summer. By means of airborne sea ice thickness surveys made over pack ice areas in the southeastern Laptev Sea, we show that years of offshore directed sea ice transport have a thinning effect on the late winter sea ice cover, and vice versa. Once temperature rise above freezing, these thin ice zones melt more rapidly and hence, precondition local anomalies in summer sea ice cover. The preconditioning effect of the winter ice dynamics for the summer sea ice extent is confirmed with a model sensitivity study where we replace the inter-annual summer atmospheric forcing by a climatology. In the model, years with high late winter sea ice export always result in a reduced sea ice cover, and vice versa. We conclude that the observed tendency towards an increased ice export further accelerates ice retreat in summer. The mechanism presented in this study highlights the importance of winter ice dynamics for summer sea ice anomalies in addition to atmospheric processes acting on the ice cover between May and September. Finally, we show that ice dynamics in winter not only precondition local summer ice extent, but also accelerate fast ice decay.

基于卫星观测的近期研究表明，拉普捷夫海（Laptev Sea）晚冬（2月至5月）的海冰输出量与次年夏季海冰覆盖率之间存在显著的统计相关性。本研究通过对拉普捷夫海东南部密集浮冰区开展机载海冰厚度勘测，证实海冰向海输送较强的年份会使晚冬海冰覆盖层变薄，反之亦然。当气温升至冰点以上时，此类薄冰区的融化速度更快，进而为夏季海冰覆盖的局地异常预先奠定了条件。通过一项将年际尺度夏季大气强迫替换为气候态的模式敏感性试验，本研究验证了冬季海冰动力过程对夏季海冰范围的预调制效应。在该模式中，晚冬海冰输出量偏高的年份总会导致海冰覆盖范围缩减，反之亦然。本研究据此得出结论：观测到的海冰输出量增加趋势，会进一步加快夏季海冰的消退进程。本研究提出的机制表明，除5月至9月间作用于海冰覆盖的大气过程外，冬季海冰动力过程对夏季海冰异常同样具有关键影响。最后，本研究证实，冬季海冰动力过程不仅会预先影响局地夏季海冰范围，还会加速固定冰的消融。