南极拉森北部冰架表面物质损失机制探讨

摘要

基于解密航片、光学遥感影像以及卫星雷达测高数据,完成一个较长时间序列的拉森A和B冰架的范围及表面高程变化监测.在此基础上,结合NCEP/NCAR夏季逐月平均气温数据和GPCP全球降水数据这两种气象数据来探讨拉森北部冰架表面物质平衡机制.结果表明:随着气温的升高,拉森A和B冰架自1968年以来总共消失了14000km2的浮冰.当前,拉森A冰架已经完全消失,拉森B冰架仅存2000km2.伴随着冰架的持续崩塌与退缩,拉森北部冰架展现出高程持续降低的趋势,而且拉森 A 冰架的降低速度(-0.45m/a)明显高于拉森 B 冰架(-0.09m/a).作为冰架表面物质平衡估算的两个主要参数,拉森A冰架的夏季平均气温从1968年的0.16℃升高到近期的0.84℃;拉森B冰架的夏季平均气温从1968年的0.04℃升高到近期的0.66℃.过去几十年的降水量变化对拉森北部冰架表面物质累积产生的影响很小,反倒是夏季温暖的降雨进一步加剧该地区的表面物质负平衡.对于持续崩塌与退缩型的拉森北部冰架来说,其高程降低除了受到冰架表面冰雪融化与再凝结导致的积雪致密化驱动外,还受到冰架后退导致的背向应力减少,进而导致的冰架物质输送加快的深刻影响.总之,在全球气候变暖的背景下,拉森A和B冰架的表面物质体现出越来越明显的负平衡趋势.%In this study, multiple data sets were selected, including declassified aerial photographs, optical remote sensing images and satellite radar altimetry data. A long time-series of monitoring the extent and surface elevation of Larsen A and B Ice Shelf was compiled. On this basis, combined with the two meteorological data of NCEP/NCAR summer monthly mean temperature data and GPCP global precipitation data, then the mass balance mechanism of the north Larsen ice shelf 2 was discussed. The results showed that Larsen A and B ice shelf had already diminished by 14000kmsince 1968 in the context of global warming. To date, Larsen A ice shelf has disappeared completely and Larsen B ice shelf remains an area only. Along with continuous collapsing and retreating of the ice shelf , Larsen A and B ice shelf have progressively thinned in recently decades, while lowering rate of the Larsen A(-0.45m/a)during 1992~2001 was significantly higher than that of the Larsen B (-0.09m/a) during 1992~2010. Air temperature and precipitation are two key parameters to estimate surface mass balance, the average summer temperature in Larsen A ice shelf raised from 0.16℃ in 1968 to 0.84℃ in recent years, and the average summer temperature in Larsen B ice shelf raised from 0.04℃ in 1968 to 0.66℃ in recent years. Meanwhile, the precipitation over the past several decades has little impact on surface mass balance of the northern Larsen ice shelf, but on the contrary the summer warm precipitation further aggravates the negative surface mass loss over the northern Larsen ice shelf. The main mechanism for continuous the northern Larsen ice shelf collapsing and retreating is attributed to warmer air temperatures and increased melt water production/refreezing, and it leads to surface lowering by firn densification. In addition, the retreat and even disappearance of Larsen ice shelf possibly lead to a reduction of back-stress with upstream flowing ice progressively thinned. In sum, the surface mass 2 of 2000km balance of Larsen A and B ice shelf show a clear and strong negative trend in context of global warming.