2013年南沙海域混合层深度的季节变化特征

Seasonal variability in mixed layer depth in Nansha area in 2013

基于2013年在南沙海域开展的4个航次生态环境综合调查的实测资料,研究了该海域混合层深度(MLD)的季节变化特征。结果表明,南海南部海域MLD季节变化明显,海域均值以秋季最深(65 m),冬季次之(54m),夏季居第3位(49 m),春季最浅(37 m),主要受季风、环流和海面净热通量的影响。其中春季时中南半岛对开的海域MLD较深,夏季时整个海域MLD分布较均匀,秋季时海域中部MLD最深,冬季时高值区出现在海域东北部。Ekman输运导致水体在巴拉望岛西侧、南沙南部以及加里曼丹岛西北侧产生的堆积作用,以及9°N以北海域冬季存在的失热效应,是MLD存在区域差异的可能原因。南海南部海域混合层水温始终大于27℃,其中夏季大于28℃,混合层内水温的季节变化很小。海表温度(SST)区域差异大时,MLD空间差异亦大;MLD与SST的关系在调查海域的南部和北部存在差异,代表性站位的研究结果显示,海域北部MLD与SST的变化刚好相反,而海域南部由于靠近赤道太阳辐射全年变化小致使SST变化亦小,SST与自春向冬急速加深的MLD关系不明显。

Based on the observed data during four comprehensive investigations on ecological environment of Nansha area in 2013,we investigated the seasonal variability in mixed layer depth（ MLD） in that area. Significant seasonal variability in MLD in that area was observed. In autumn,the MLD reached its maximum（ 65 m）,followed by winter（ 54 m）,summer（ 49 m） and spring（ 37 m）.These seasonal variabilities were closely related with variations in monsoon,ocean current and sea surface heat flux. The MLD in the southeast area to the Indo-China Peninsula was deeper in spring; the MLD distribution was uniform in summer; the deepest MLD appeared in the central area in autumn; high value appeared in the northeastern area in winter. Ekman transport led to the effects of accumulation of water in the west Palawan Island,the south Nansha area and northwest Kalimantan Island,as well as heat lost effect on north of 9°N area in winter,which might be the reason for regional difference of MLD. Moreover,the water temperature of mixed layer in that area was always over 27 ℃（ more than 28 ℃ in summer）,and seasonal change of water temperature in the mixed layer was very little. When the regional difference of sea surface temperature（ SST） was huge,so was the space difference of MLD. Difference was found in relationship between MLD and SST between north and south in the surveyed area. Representative stations results revealthat MLD was contrary to the change of SST in the northern area,while in the southern area,the relationship between SST and MLD was not obvious. Since the southern area is near the equator,the change of solar radiation was little throughout the year which led to the little SST change. MLD rapidly deepened from spring to winter,which was not obviously related with SST.