东海海—气界面二氧化碳通量的季节变化与控制因素研究进展

通过对东海海—气界面二氧化碳(CO2)交换有关研究的总结,剖析了东海表层海水CO2分压(pCO2)的区域分布特征,探讨了海—气界面CO2通量(FCO2)的季节变化规律,诠释了影响海—气界面CO2转移的主要因素.结果表明,东海表层海水pCO2的区域分布具有明显的季节变化,可将其分为冬季、夏季、过渡季节(春季、秋季)3个时段.冬季西部近岸海域由于水体垂直交换强烈,造成表层水体pCO2较高,而中、东部陆架海域由于浮游生物的光合作用使得pCO2较低.夏季近岸河口海域由于陆源输入的影响导致pCO2较高,中、东部陆架海域受温跃层、长江冲淡水、浮游植物的综合作用pCO2较低.春季、秋季为过渡时段,表层海水pCO2分布变化剧烈,受控因素较为复杂.东海全年表现为大气CO2的净汇,其中冬、春、夏为碳汇,其海—气界面FCO2分别为(-6.68±6.93),(-4.94±0.80),(-3.67±1.09)mmol/(m2·d).秋季表现为碳源,通量约为(1.50±8.37)mmoL/(m2·d).东海全年平均通量约为-3.16 mmol/(m2·d),共可吸收CO2约为6.92×106 t C/a.不同季节海—气界面FCO2的年际变化凸显了人为因素的影响,近海富营养化加剧,三峡工程的运行都可能是造成东海冬季碳汇量减少、秋季碳源/汇格局转变的原因.

Advances of Seasonal Variations and Controlling Factors of the Air-Sea CO2 Flux in the East China Sea

Spatial variations of theCO₂ partial pressure (pCO₂) in surface water, seasonal variations of the air seaCO₂ exchange flux (FCO₂), and major controlling factors of theCO₂ transfer were reviewed based on the summary ofCO₂ exchange in the East China Sea (ECS). Spatial distribution of pCO₂ in the ECS underwent three different phases: the winter phase, the summer phase, and the transition phase (spring and autumn). The western coastal area acted asCO₂ source on account of vertical convection during the winter phase, whereas the shelf region acted asCO₂sink because of the phytoplankton activity. Estuary in the shallower shelf possessed highpCO₂ for terrigenous input in the summer phase while the major shelf had low pCO₂ under the comprehensive function of thermocline, Changjiang diluted water, and photosynthesis. During the transition phase in spring and autumn, the distribution ofpCO₂ varied dramatically and got complex controlling factors. The winter, spring, and summer could absorb atmosphericCO₂with the flux for （-6.68±6.93）, （-4.94±0.80）, （-3.67±1.09） mmol/（m²·d）, respectively, whereas the autumn could releaseCO₂with the flux for （2.64±7.06）mmol/（m²·d）. The ECS serves as a carbon sink with the annual air-seaCO₂ flux for -3.16 mmol/(m²·d),which equals to 6.92×10⁶t C/a. Anthropogenic activities and the aggregative of eutrophication were the principal reason for the annual variation of CO₂ flux probably.