东亚气候的年代际变化对中国近海生态的影响

Influence of interdecadal climate variation over East Asia on offshore ecological system of China

回顾了近几十年来中国近海赤潮的发生,利用长时间序列NCEP、ERA-40、HadISST和SODA等大气海洋高分辨率的再分析资料以及经验正交函数(EOF)方法,分析了近50a来东亚气候的异常变化,包括东亚夏季大气环流的年代际变化,东亚大气环流散度场、中国近海表层海温(SST)和经向海面风应力的时空特征及其与中国近海环境和生态异常的联系.结果表明,20世纪70年代末以来,中国大陆东部和东海近岸从长江口至台湾海峡附近海域上空的低层大气辐合表现为年代际增强,与该海域赤潮的发生在气候态时间尺度上有显著的对应关系,而低层大气辐合的偏强则有利于该海域上升流的形成和加强,易促使沉积于海底的营养盐和蛰伏的赤潮藻孢囊(休眠细胞)运移至海水表层;并且,近30a来中国近海出现了SST持续上升和经向海面风应力不断减弱等有利于赤潮发生以及海洋生物地理分布变化的年代际气候异常现象.这表明东亚海洋大气的年代际异常可能是该海域20世纪70年代末以来赤潮等生态灾害频发和中国近海海洋生物地理分布变化尤其是鱼类物种北移的重要原因之一.

A review of studies of harmful algal blooms（HAB,also known as red tide） in the offshore area of China indicates a clear increase in HAB events since the late 1970s.To explain this increase from a climatic point of view,variations of the East Asian climate and the relationship with the marine environment and offshore ecosystem of China were analyzed with an empirical orthogonal function（EOF） method using NCEP reanalysis,ERA-40 reanalysis,HadISST and SODA datasets.The climatic factors analyzed included the East Asian summer monsoon circulation,the atmospheric circulation divergence,sea surface temperature（SST） and sea surface meridional wind stresses.Results indicated that convergence in the lower atmosphere at 925hPa over the offshore area of East China Sea has intensified since the late 1970s.This corresponds well with the frequent HAB events in the area from the Yangtze estuary to the Taiwan Strait.The two phenomena are closely related,since stronger convergence in the lower atmosphere favors stronger upwelling in the ocean,which in turn helps to transport deposited nutrients and dormant algal cysts from coastal surface sediments to the sea surface layer and thus contributes to the occurrence of HAB.In addition,the continuous increase of SST and weakening of sea surface meridional wind stresses in the last 30 years has provided favorable conditions for frequent HAB occurrence and changes in the marine biogeographical distributions in this area.Overall,interdecadal oceanic and climatic anomalies over East Asia seem likely to be important factors underlying increasingly frequent marine ecological disasters,such as HAB and the northward movement of marine fish species in the offshore area of China.