累积海冰密集度及其在认识北极海冰快速变化的作用

为定量分析北冰洋海冰密集度年际差异,提出并采用累积海冰密集度(ASIC)概念。利用SSMR/SSMI的分辨率为25 km的海冰密集度数据,分别研究了1979—2011年北极海冰在融冰期(4~9月)和结冰期(10月至翌年3月)的变化过程以及2个冰期内ASIC的区域差异。研究发现,在1979—1989年、1989—1999年和1999—2009年期间,融冰期海冰发生明显变化的范围都远远大于结冰期海冰发生明显变化的范围。1998—2010年,融冰期内发生加速融化的海区并没有都出现结冰期冰量减小的现象。在此期间融冰期ASIC减小,结冰期ASIC也减小的海域仅集中在楚克奇海、新地岛北部海域以及格陵兰岛东西海岸。融冰期ASIC减小,而结冰期ASIC无明显变化的海域包括波弗特海、东西伯利亚海、拉普捷夫海和喀拉海。这些区域与局地陆地径流侵入的海域重合。研究发现,在这些区域,融冰期ASIC减少是陆地径流增大加速海冰融化引起的。在结冰期,陆地径流加速海水结冰的作用消除融冰期海水吸收大量太阳辐射能后发生推迟结冰的现象,使得ASIC无明显变化。融冰期ASIC减小,而结冰期ASIC增大的区域只有白令海。研究结果证明累积海冰密集度能够去除海冰高频变化而只表现低频变化,能够描述海冰的年际变化特征。同时由于海冰变化与海洋中其他物理参数存在显著关系,变T的ASIC可以更加方便地描述次表层叶绿素最大值层深度的变化。

Accumulation Sea Ice Concentration and Its Action on Understanding Arctic Sea Ice Dramatic Change

Accumulation Sea Ice Concentration (ASIC) is developed to quantitatively measure the regional difference of Arctic sea ice concentration. During the periods of 1979-1989, 1989-1999 and 1999-2009, the linear trends of ASIC in melt period (April-September) and in ice-formation period (October-March) were obtained from SSMR/SSMI sea ice concentration, respectively. Retrospective analysis reveals that there exits greater areas, where dramatic change happens for ASIC in melt period than in ice-formation period. It is revealed that during 1998-2010, in most areas where sea ice was rapidly melted, sea ice amount did not yet decrease in ice-formation period. These areas of ASIC in melt period decreased and in ice-formation also decreased in Chukchi Sea, northern Nova Zembla, and the east and west coast of Greenland. These areas of ASIC in melt period decreased and in ice-formation did not obviously change in Beaufort Sea, East Siberian Sea, Laptev Sea and eastern Kara Sea, where sea ice was influenced by continental runoff. Continental runoff can accelerate the melt of sea ice in melt period and can accelerate the freeze of sea water in ice-formation period. It is concluded that its action is enough to compensate for the delay due to regional sea water absorbing more radiation in summer, as a result of freezing sea ice on time in these areas. The area of ASIC in melt period decreased and in ice-formation increased only in Bering Sea. Conclusively, ASIC is regarded as a useful parameter presenting low frequency of sea ice change and eliminating the high frequency, and is used to illustrate annual variation characteristics of sea ice. Meanwhile, due to sea ice change consistent with other parameters in sea water, using ASIC can better understand the change of sea water’s properties. There is a negative correlation between ASIC calculated by changeable time-scale and the depth of subsurface chlorophyll maximum layer.