气候变化情景下东南印度洋亚南极模态水的演变趋势研究

基于参与第六次耦合模式比较计划（CMIP6）的8个地球系统耦合模式所输出的历史模拟结果，本文通过与观测对比，评估了CMIP6模式对东南印度洋亚南极模态水的模拟能力，并预估了在中等强迫情景和高强迫情景下，该模态水潜沉率、体积及性质的变化趋势。结果表明：与Argo观测相比，CMIP6模式中南印度洋混合层偏深且上层海洋的位势密度偏小，因此其模拟的东南印度洋亚南极模态水潜沉率偏大而位势密度偏小。不同CMIP6模式之间模拟的东南印度洋亚南极模态水潜沉区存在差异，混合层侧向输入是导致这一差异的主要原因。此外，在历史模拟和两种情景试验中，东南印度洋亚南极模态水均呈现出潜沉率和体积减小、温度升高、盐度和密度降低的趋势。其中，在高强迫情景下，变化趋势最大，中等强迫情景次之，历史模拟中的变化趋势最小。这表明，辐射强迫越强，东南印度洋海表温度升高和淡水输入增加的趋势越大，导致混合层变浅及其南北梯度减小的趋势越快，东南印度洋亚南极模态水潜沉率、体积和性质变化的趋势也随之增大。

Projectied longterm trend of the Southeast Indian subantarctic mode water under climate change scenarios

Based on the outputs of eight earth system models involved in the Coupled Model Intercomparison Project Phase 6 (CMIP6), this study assessed the simulation skill of the Southeast Indian subantarctic mode water (SEISAMW) of these models by comparing with observations. Moreover, this study investigated the projected long-term trends in subduction rate, volume and properties of the SEISAMW under medium and high greenhouse gas emission scenarios (i.e., SSP245, SSP585). The results show that the CMIP6 models generally have produced artificially greater mixed layer depth and smaller upper layer potential density in comparison with those of the Argo observation. Consequently, the simulated SEISAMW in the CMIP6 models are generally with larger subduction rate and smaller potential density. Meanwhile, the subduction regions of the SEISAMWs show significant differences among the analyzed CMIP6 models, which are attribute to lateral induction in the mixed layer. Furthermore, in the historical, SSP245 and SSP585 outputs, the SEISAMWs show consistent decreasing trends in subduction rate and volume, increasing trend in temperature, and decreasing trends in salinity and potential density. The long-term trends of the SEISAMWs are largest under SSP585 scenario, followed by the SSP245 scenario and historical simulation. The projected trends of SEISAMW can be explained by the following mechanism: the temperature and freshwater flux in the southeastern Indian Ocean upper layer tend to increase under enhanced radioactive forcing, resulting in shoaling in mixed layer and flattening of the mixed layer gradient. As a result, the trends of SEISAMWs in subduction rate, volume and water properties show larger values in accordance with stronger radioactive forcing.