南大洋混合层的时空变化特征

过去对南大洋的研究受限于长期观测的缺乏,而现在地转海洋学实时观测阵(Arrayfor Real-timeGeostrophicOceanography,Argo)项目自开始以来持续提供了高质量的温度盐度观测,使系统地研究南大洋海洋上层结构成为可能。本研究使用2000—2018年的Argo浮标观测数据,分析了南大洋混合层深度(Mixed Layer Depth, MLD)的时空分布特征。结果表明:南大洋混合层存在明显的季节变化,冬春两季MLD在副南极锋面北侧达到最高值并呈带状分布,夏秋两季由于海表加热导致混合层变浅,季节变化幅度达到400m以上;在年际尺度上,MLD受南半球环状模(Southern HemisphereAnnularMode,SAM)调制,呈现纬向不对称空间分布特征,这与前人结果一致;本文指出在所研究时段,南大洋混合层在90°E以东,180°以西有加深趋势,而在60°W以西,180°以东有变浅趋势,显示出偶极子分布特征,并且这种趋势特征主要是风场的作用。

SPATIO-TEMPORAL VARIATIONS OF MIXED LAYER DEPTH IN SOUTHERN OCEAN

Researches on the Southern Ocean in the past were limited by the lack of long-term observations. The Array for Real-time Geostrophic Oceanography (Argo) project has continued to provide high-quality temperature-salinity observations since 1997, making it possible to comprehensively study the upper layer structure of the Southern Ocean. We used the Argo buoy observation data from 2000 to 2018 to analyze the temporal and spatial pattern characteristics of mixed layer depth (MLD) in the Southern Ocean. The results show that there is significant seasonal variation of mixed layer depth of the Southern Ocean. The MLD in winter and spring reaches its maximum in the north of the sub-Antarctic front in a strip shape. In summer and autumn, MLD becomes shallow due to surface heating, and the seasonal amplitude exceeds 400 meters. On interannual time scales, MLD is modulated by the southern hemisphere annular mode (SAM), which is consistent with previous results, showing an asymmetric zonal pattern. This research reveals that during the study period, the Southern Ocean MLD deepens within the eastern of 90°E and the western 180°W, while it shoals within the western of 60°W and the eastern of 180°. This spatial characteristic of dipoles is primarily driven by winds.