2011−2020年间南大洋印度洋扇区冬季水的年际变化特征及其成因

Interannual variability of winter water in the Indian Ocean Sector of the Southern Ocean and its causes during 2011−2020

已有多个研究证实南大洋自海表到底层的海水特性存在长期变化特征,并指出其与大尺度外部强迫的改变紧密相关。然而,截至目前海洋学界对各水团的更高频年际变化特征及其影响原因依然了解甚少,其中包括了近海表最易受外部强迫影响的冬季水(Winter Water,WW)。本文结合2011−2020年间每年1月沿110°E断面采集的重复观测资料和再分析气象资料,研究季节性冰区内WW层10年间的年际变化。结果发现,该海域WW特性具有显著的时空变化特征。WW核心温度距平与前一年的南极涛动(Antarctic Oscillation,AAO)指数距平具有显著正相关关系(R=0.69),而AAO指数与局地纬向风转向所在纬度呈负相关关系(R=−0.61),说明AAO指数越大(小)时,辐散带会向南(北)移动,季节性冰区的WW核心温度升高(降低)。局地净降水量距平变化与WW核心盐度距平的变化相反,2016年之后负的净降水量距平(大气向海洋输送淡水减少)促使WW核心盐度距平增大。另外,局地涡动能距平与WW厚度距平呈负相关关系(R=−0.70),据此推测该海域持续存在的气旋式涡旋的强度增强(减弱),引发向上抽吸作用增强(减弱),导致绕极深层水的深度变浅(加深),进而引起其上层WW层厚度的变化。通过本研究工作,有助于深入理解南大洋海洋水柱对外部强迫高频变化的具体响应。

Multiple studies have confirmed the long-term property modification of water columns from the bottom to the sea surface at the Southern Ocean and pointed out that it is closely related to the changes of large-scale extern-al forcing.However,the higher frequency interannual variability of the water masses and its causes are still poorly understood,including the winter water(WW),which is the most vulnerable to external forcing near the sea surface.Based on repeated hydrographic observations along 110°E in Januaries 2011 to 2020 and meteorological reanalysis datasets,this study estimated interannual variability of the WW layer in the seasonal ice zone(SIZ)and its possible causes over ten years.Results show that WW properties have significant temporal and spatial variability in this re-gion.A significant positive correlation between the WW core temperature anomaly and the previous-year Antarctic Oscillation(AAO)index anomaly(R=0.69)and a negative correlation between the AAO index and the turning lat-itude of the local zonal wind component(R=-0.61),indicate that a larger(smaller)AAO index corresponds to a southward(northward)shift of the divergence zone,and the increase(decrease)of the WW core temperature in the SIZ.A negative correspondence between the local net precipitation anomaly and the WW core salinity anomaly in-dicates the negative net precipitation anomaly(less freshwater transport to the ocean)after 2016 contributes to an increase in the WW core salinity anomaly.Meanwhile,the local eddy kinetic energy anomaly is negatively correl-ated with the WW thickness anomaly(R=-0.70),which supports the idea that the enhancement(decrease)in the intensity of persistent cyclonic eddies in this region may strengthen(weaken)the upward pumping to shoal the depth of the circumpolar deep water,and further affect the WW thickness.This study contributes to an in-depth un-derstanding of the specific response of water columns in the Southern Ocean to the high-frequency variability of ex-ternal forcing.