南极海冰过去200年的演变特征

Variability of Antarctic sea ice extent over the past 200 years

南极海冰是影响南半球与全球气候的重要因子.与北极海冰减少相反, 1979年以来南极海冰呈缓慢增加趋势.受限于观测资料缺乏,南极海冰的变化规律和机理仍不清楚.本研究基于南极地区5支年分辨率冰芯记录和1组快速冰流数据,重建了威德尔海(WS),别林斯高晋海(BS),阿蒙森海(AS),罗斯海(RS),以及印度洋-西太平洋(Ind WPac)五个扇区的海冰最大北边界(NLSIE)序列.结果表明过去100~200年中, WS、BS、AS、RS和Ind WPac的趋势分别为-0.08°、-0.17°、+0.07°、+0.02°和-0.03°/10 a (≥95%信度水平).南极海冰范围总体在过去100年呈现显著减少趋势(-0.03°/10 a, 99%信度水平),其中1955~1980年出现快速减少,之后转为显著增加趋势.分析气候模态的可能影响,发现各扇区海冰的趋势变化主要受南半球环状模(SAM)的影响,多年代际变率在WS、BS和AS区域为太平洋年代际振荡主导,而在In WPac和RS区域为SAM主导.

While Arctic sea ice has been decreasing in recent decades that is largely due to anthropogenic forcing,the extent of Antarctic sea ice showed a positive trend during 1979–2015, followed by an abrupt decrease. The shortness of the satellite record limits our ability to quantify the possible contribution of anthropogenic forcing and internal variability to the observed Antarctic sea ice variability. In this study,ice core and fast ice records with annual resolution from six sites are used to reconstruct the annualresolved northernmost latitude of sea ice edge(NLSIE) for different sectors of the Southern Ocean, including the Weddell Sea(WS), Bellingshausen Sea(BS), Amundsen Sea(AS), Ross Sea(RS), and the Indian and western Pacific Ocean(Ind WPac). The linear trends of the NLSIE are analyzed for each sector for the past100–200 years and found to be à0.08°, à0.17°, +0.07°, +0.02°, and à0.03° per decade(!95% confidence level) for the WS, BS, AS, RS, and Ind WPac, respectively. For the entire Antarctic, our composite NLSIE shows a decreasing trend(à0.03° per decade, 99% confidence level) during the 20 th century, with a rapid decline in the mid-1950 s. It was not until the early 1980 s that the observed increasing trend occurred. A comparison with major climate indices shows that the long-term linear trends in all five sectors are largely dominated by the changes in the Southern Annular Mode(SAM). The multi-decadal variability in WS,BS, and AS is dominated by the Interdecadal Pacific Oscillation, whereas that in the Ind WPac and RS is dominated by the SAM.