大尺度环流异常对南极印度洋扇区海表面高盐异常的影响

The role of large-scale circulation on the consistent positive salinity anomaly in the Indian sector of the Antarctic

南极印度洋扇区分布了许多南极底层水的生成区,此海域海水盐度变化对全球的气候变化有着深远影响。本文采用EN4再分析数据、实测海豹资料和WOD18数据,结合大气再分析和海冰密集度数据,对南极印度洋扇区表面盐度长期变化及其对大尺度环流异常的响应进行探究。2008年以来,南极沿岸出现显著的海表面持续性高盐异常,其中印度洋扇区变化最为显著,表层高盐水主要集中在达恩利冰间湖附近与沙克尔顿冰架以北的海域。沿岸海域的高盐陆架水向北扩张且影响深度不断加深,高盐的绕极深层水上涌也更加明显。此高盐异常与南极涛动(Antarctic Oscillation,AAO)、印度洋偶极子(Indian Ocean Dipole,IOD)两种大尺度环流密切相关。AAO与IOD正位相下,西风显著增强,促进海冰大量生成,为海表面提供了大量的盐通量。同时,海表面出现更显著的风场旋度负异常与低压异常,促进高盐深层水上涌,对高盐异常有重要维持作用。此外,纬向风剪切与蒸发增强也是影响该高盐异常的重要局地过程。

The key regions for formation of the Antarctic Bottom Water occupied in the Indian sector of the Southern Ocean.The salinity change of the region has a profound influence on the global climate change.EN4 reanalysisgridded data,measured seal data,WOD18 data combined with atmospheric reanalysis and sea ice concentration data were all used to explore the sea surface salinity changes in the Indian sector of the Southern Ocean and the response to large-scale circulation anomaly.The observation and reanalysis data both illustrated a significant positive surface salinity anomaly occurred in the Antarctic coast since 2008,especially in the Indian sector.The surface positive salinity anomaly was mainly centered in the Darnley Polynya and the north of Shackleton Ice Shelf.The high salinity shelf water expanded northward from the Antarctic coast and deepened.Meanwhile,the upwelling of Circumpolar Deep Water became increasingly distinct.Our study showed that this positive salinity anomaly was connected with the Antarctic Oscillation(AAO)and the Indian Ocean Dipole(IOD).During the positive AAO and IOD phases,the westerly wind enhanced significantly in the Indian sector and promoted the formation of sea ice,which increased surface salt flux.The significant negative wind curl and low pressure anomaly resulted in the upwelling of salty Circumpolar Deep Water and maintained the positive salinity anomaly.Additionally,increased locally zonal wind shear and enhanced evaporation were important factors as well.