夏季琼州海峡表层海水二氧化碳分压时空变化

采用船载海?气CO₂连续观测系统于2011年和2014年夏季在琼州海峡开展了现场观测，分析研究了表层海水二氧化碳分压(pCO₂)时空变化及其影响因子。2011年和2014年夏季pCO₂分别为(516±29) μatm和(533±15) μatm，海?气CO₂交换通量分别为(8.4±1.7) mmol/(m2·d)和(4.5±0.4) mmol/(m2·d)，均是大气CO₂的强源，高于相邻及相似海域，主要受控于东口海域上升流和海峡中部狭管效应。2011年夏季东口上升流增大pCO₂的同时也促进了浮游植物繁殖，光合作用吸收水体CO₂，降低了pCO₂，而且受其影响，西口口门附近叶绿素a和溶解氧含量陡增，pCO₂突降。2014年夏季东口海域上升流较弱，且观测海域垂直混合作用显著，pCO₂和溶解氧分布特征与2001年夏季明显不同。海峡中部狭管效应造成水体输运速率大、混合作用强，浮游植物“来不及”生长，pCO₂较高。

Spatiotemporal variations of partial pressure of carbon dioxide in surface sea water in the Qiongzhou Strait in summer

The sea surface temperature(SST), salinity(SSS), dissolved oxygen (DO), chlorophyll a(Chl a) and surface partial pressure of carbon dioxide(pCO₂) was determined by underway measurement system in the Qiongzhou Strait in summer 2011 and 2014, and the spatiotemporal variations of pCO₂ were analyzed and its control factors were explained. The averages of pCO₂ in surface sea water were (516±29) μatm and (533±15) μatm, sea-air CO₂ fluxes were (8.4±1.7) mmol/(m2·d) and (4.5±0.4) mmol/(m2·d) in summer 2011 and 2014, the Qiongzhou Strait acted as strong atmospheric CO₂ source and was more higher than the adjacent and similar sea areas. The upwelling forced the CO₂-enriched subsurface water to intrude the surface water and elevated pCO₂ in the east mouth, also promoted biological productivity and absorbed CO₂ from sea water, and also made the pCO₂ drop and DO rise sharply in the vicinity of west mouth in summer 2011. The upwelling was weak in east mouth and vertical mixing was strong along ship-track in summer 2014, the distributions of pCO₂ and DO were obviously different from that in summer 2011. Narrow channel effect was significant in the middle of Qiongzhou Strait, high water transportation speed with strong mixing resulted in weak photosynthetic activity, they altogether maintained high pCO₂ in summer 2011 and 2014.