2019年夏末长江口及其邻近海域走航pCO_(2)变化及控制机制

Spatial variation of underway surface pCO_(2) and its controls in the Changjiang(Yangtze River)Estuary and adjacent sea area in late summer of 2019

利用2019年8月获得的长江口及其邻近海域表层海水pCO_(2)的走航观测数据,结合温度、盐度、溶解氧等理化参数,初步探讨了该区域夏末表层海水pCO_(2)的空间分布特点及控制因素。研究结果显示,整体上pCO_(2)呈现近岸高而离岸低的特点,其中在长江冲淡水的中盐度区域出现了一个pCO_(2)的极低值区。去除温度的影响,温度归一化后的pCO_(2)与溶解氧饱和度具有良好的负相关关系,这表明生物过程是造成研究区域pCO_(2)巨大空间差异的主要原因,其中高初级生产造成了中盐度区的强汇现象。同时河、海混合区断面的温度、盐度和溶解氧的分布显示水体层化致使垂直混合作用对pCO_(2)的影响较小。整体而言,研究区域的海-气界面CO_(2)通量为-2.0±5.2 mmol·m^(-2)·d^(-1),表现为大气CO_(2)的汇。随着环境的改变和人为活动的干扰(如长江径流量的减少),长江口及其邻近海域可能存在由大气CO_(2)的汇转为源的风险,需要持续关注和研究。

Base on underway surface CO_(2)data obtained from Changjiang(Yangtze River)Estuary and adjacent area in August 2019,combined with the temperature,salinity,dissolved oxygen and other parameters,the spatial variation of pCO_(2)and its controls during late summer were discussed briefly.The results show that the pCO_(2)generally decreases with distance offshore,and is the lowest in the mesohaline zone of river plume.After removing temperature effect,the good negative correlation between temperature-normalized pCO_(2)and DO%indicates that biological processes are the main reason for the spatial variation,and the strong sink for atmospheric CO_(2)just results from high biological production.Moreover,the section distributions of temperature,salinity and DO%in the river-ocean mixing zone show that the influence from vertical mixing on pCO_(2)is minor due to the water stratification.On the whole,the air-sea CO_(2)fluxes for the study area are-2.0±5.2 mmol·m^(-2)·d^(-1),showing a carbon sink with respect to atmospheric CO_(2).However,with environment changes and human perturbation such as the decrease of Changjiang runoff,Changjiang Estuary and its adjacent area may gradually shift from a sink to a source,which is necessary for us to pay more attention and further study.