白令海夏季水文结构年际变化特征研究

基于2008、2010、2012和2014年我国北极科学考察期间在白令海获取的水文观测数据,结合历史共享资料,通过对白令海水团、上层海洋热含量、净热通量变化、风场及海平面气压分布情况等的分析,探讨了白令海水文结构的年际变化特征及其原因。研究发现,白令海夏季的水团包括白令海上层水团(BUW)、中层水团(BIW)、深层水团(BDW)和白令海陆架水团(BSW)。白令海温盐分布差异最大、年际变化最剧烈的情况主要集中在上层水团。对比4年水团分布情况,最明显的变化是2012年7月调查区上层海水温度偏低,2014年7月上层海水温度偏高。这种异常变化在热含量方面表现为:2012年7月调查区各个测站上的热含量异常低,而2014年7月测站上的热含量都高于平均水平。着重研究了2014年7月海温偏高的原因,认为是由于陆架和海盆区分别有两种不同的形成机制造成:陆架区累积净热通量偏高,海水吸收热量升温;海盆区在异常强大而持久的海面气压(SLP)高压系统下,海面负的风应力旋度得到加强,从而引起持续的暖平流输送及强烈的Ekman抽吸作用,最终导致了上层海水偏暖。

Hydrographic structure and inter-annual variations of Bering Sea in summer

Based on conductivity–temperature–depth (CTD) data obtained by the Chinese National Arctic Research Expeditions (2008, 2010, 2012, and 2014), in combination with shared historical data, the water mass, upper-ocean heat content, net heat flux change, wind field, and sea level pressure were analyzed to investigate the interannual variability of the hydrologic structural characteristics of the Bering Sea. It was found that the waters of the Bering Sea could be divided into four masses: Bering Upper Water (BUW), Bering Middle Water (BIW), Bering Deep Water (BDW), and Bering Shelf Water (BSW). Variations of temperature and salinity were concentrated mainly in the upper water. In July 2012, the sea surface temperature (SST) was below normal, whereas in July 2014, strong positive SST anomalies developed. These abnormal phenomena resulted because of lower or higher heat content. We investigated the reasons for the SST anomaly in July 2014 and found that the mechanism was completely different from basin to shelf. The higher SST of shelf waters was mainly caused by higher cumulative net heat flux, whereas in the basin, it was due to unusually strong and persistent high pressure. This meant that the sea surface wind stress curl was enhanced, which caused continuous warm advection, and strong Ekman pumping, function that led to warming of the upper water.