Helicopter-borne sea ice thickness measurements during cruises ARK-XX/2 and ARK-XXII/2 (SPACE) in the Arctic Ocean@en

Helicopter-borne electromagnetic sea ice thickness measurements were performed over the Transpolar Drift in late summers of 2001, 2004, and 2007, continuing ground-based measurements since 1991. These show an ongoing reduction of modal and mean ice thicknesses in the region of the North Pole of up to 53 and 44%, respectively, since 2001. A buoy derived ice age model showed that the thinning was mainly due to a regime shift from predominantly multi- and second-year ice in earlier years to first-year ice in 2007, which had modal and mean summer thicknesses of 0.9 and 1.27 m. Measurements of second-year ice which still persisted at the North Pole in April 2007 indicate a reduction of late-summer second-year modal and mean ice thicknesses since 2001 of 20 and 25% to 1.65 and 1.81 m, respectively. The regime shift to younger and thinner ice could soon result in an ice free North Pole during summer.本数据集包含2001年、2004年与2007年夏末在跨极漂移带（Transpolar Drift）开展的机载电磁海冰厚度测量数据，该观测序列延续了1991年启动的地面监测工作。观测结果显示，自2001年以来，北极区域海冰厚度的众数与均值均呈持续缩减趋势，最大降幅分别可达53%与44%。基于浮标的海冰年龄模型（buoy-derived ice age model）表明，海冰变薄的主要原因是海冰格局发生转变：早年该区域以多年冰（multi-year ice）与二年冰（second-year ice）为主导，至2007年已转变为以一年冰（first-year ice）为主；当年夏季，一年冰的厚度众数与均值分别为0.9米与1.27米。2007年4月仍留存于北极的二年冰观测数据显示，自2001年以来，夏末时节二年冰的厚度众数与均值分别缩减了20%与25%，最终分别降至1.65米与1.81米。这种向更年轻、更薄海冰的格局转变，或很快将导致夏季北极出现无冰状态。