春季和秋季东海挥发性卤代烃的时空分布与海-气通量研究

Spatial and temporal distribution and sea-to-air fluxes of volatile halocarbons in the East China Sea in spring and autumn

海洋中挥发性卤代烃(VHCs)的产生和释放在调节全球气候方面发挥着至关重要的作用。本研究分别于2021年4月1日至19日搭乘“向阳红18号”科考船和2021年10月9日至30日搭乘“东方红3号”科考船对东海海域进行了大面积调查,探讨了春季和秋季东海海水和大气中CFC-11(一氟三氯甲烷)、CH_(3)Br(溴甲烷)、CH_(3)I(碘甲烷)和CH_(2)Br_(2)(二溴甲烷)4种VHCs的时空分布及其影响因素,并对海水和大气中VHCs的分布和海-气通量进行了季节对比。结果表明,受气团来源、海表温度、水团、生物释放和河流输入的影响,VHCs在大气和海水中的分布呈现显著的季节变化。表层海水中VHCs的浓度高值主要出现在闽浙沿岸和东部外海某些站位。CFC-11的分布主要受油气开采平台和陆源气团输送的影响。浮游植物释放是秋季表层海水CH_(2)Br_(2)的主要来源,而CH_(3)I主要受到河流输入和海表温度的影响。大气中CH_(3)Br和CH_(3)I在两个季节均呈现显著正相关性。春季CFC-11、CH_(3)Br、CH_(3)I和CH_(2)Br_(2)的海-气通量平均值分别为-535.17 nmol/(m^(2)·d)、10.17 nmol/(m^(2)·d)、16.69 nmol/(m^(2)·d)和24.18nmol/(m^(2)·d),秋季分别为-1621.03nmol/(m^(2)·d)、41.96nmol/(m^(2)·d)、94.32nmol/(m^(2)·d)和57.23 nmol/(m^(2)·d),表明东海是大气中CFC-11的汇,是CH_(3)Br、CH_(3)I和CH_(2)Br_(2)的源。较低的海水温度导致春季CFC-11的海-气通量比秋季高,较高的风速和表层海水浓度是CH_(3)Br、CH_(3)I和CH_(2)Br_(2)秋季海-气通量高于春季的主要原因。

The production and release of volatile halogenated hydrocarbons(VHCs) in the ocean play a crucial role in regulating global climate. The extensive voyage surveys in the East China Sea were conducted on board the R/V “Xiangyanghong 18” from April 1 to 19, 2021 and on board “Dongfanghong 3” from October 9 to 30,2021. This study conducted the temporal and spatial distributions of 4 VHCs including Trichlorofluoromethane(CFC-11), bromomethane(CH_(3)Br), iodomethane(CH_(3)I), and dibromomethane(CH_(2)Br_(2)) in the seawater and atmosphere of the East China Sea in spring and autumn, and the environmental parameters affecting their concentrations were also studied. The distribution of VHCs in seawater and atmosphere and the sea-to-air fluxes were compared seasonally. The results showed that the distributions of VHCs in the atmosphere and seawater exhibited significant seasonal changes, which were influenced by the source of air mass, sea surface temperature, water mass, seasonal differences in biological release, and river input. The high concentrations of VHCs in surface seawater mainly appeared in the coastal waters of Fujian and Zhejiang provinces and some stations in the open sea. The distribution of CFC-11 was mainly affected by oil and gas production platform and terrigenous air mass transportation. Phytoplankton release was the main source of CH_(2)Br_(2) in autumn surface seawater, while CH_(3)I was mainly affected by river input and sea surface temperature. Atmospheric CH_(3)Br and CH_(3)I showed a significant positive correlation in both seasons. The mean sea-to-air fluxes of CFC-11, CH_(3)Br,CH_(3)I and CH_(2)Br_(2) in spring were-535.17, 10.17, 16.69 and 24.18 nmol/(m~2·d), respectively, while those in autumn were-1621.03, 41.96, 94.32 and 57.23 nmol/(m~2·d). These results indicated that the East China Sea was the sink of CFC-11 in the atmosphere but the source of CH_(3)Br, CH_(3)I and CH_(2)Br_(2). Lower sea temperature led to higher sea-to-air flux of CFC-11 in spring than in autumn, and higher wind speed and surface seawater concentration were the main reasons for the higher sea-to-air fluxes of CH_(3)Br, CH_(3)I and CH_(2)Br_(2) in autumn than in spring.