北部湾东北部春、夏季表层海水CO2分压的24 h变化及其调控机制研究

周日观测对掌握近海碳酸盐体系变化和海-气CO₂交换过程是必要的，有助于降低碳源汇评估的不确定性。针对北部湾东北部的英罗湾-安铺港海域，于2018年4月和8月利用24 h定点逐时采样观测了该区域表层海水碳酸盐体系及相关要素，分析了春、夏季的表层海水CO₂分压(p CO₂)24 h逐时变化规律及其调控因子。观测结果表明，春、夏季p CO₂变化范围分别为530～628μatm和427～748μatm，平均海-气CO2通量分别为(1.7±0.8)mmol/(m²·d)和(1.2±0.8)mmol/(m²·d)，均表现为大气CO₂的弱源。其中春季p CO₂ 24 h逐时变化受温度的影响相比夏季更显著，而夏季p CO₂对潮汐作用以及区域内沿岸河流、地下水等淡水汇入引起的生物生产和呼吸代谢过程增强的响应更明显。海水升温主导了春季区域表层高p CO₂的形成，夏季咸淡水的物理混合过程中增...

Hourly variations of partial pressure of CO2 in surface sea water and its controlling mechanisms in the northeastern Beibu Gulf in spring and summer

Diurnal observation is necessary for grasping the variability of carbonate system in coastal waters and sea-air CO₂ exchange process and is helpful to reduce the uncertainty of assessments for carbon source/sink. Surface carbonate system and related parameters were obtained during twice 24 hours fixed sampling and observation conducted in April and August 2018 in the Yingluo Bay-Anpu Harbor, located in the northeastern Beibu Gulf. In this paper, we analyzed the hourly variations of partial pressure of CO₂ in surface sea water (pCO₂) and discussed the corresponding environment factors controlling pCO₂ in both seasons. The pCO₂ values ranged from 530?628 μatm in spring to 427?748 μatm in summer, with the average sea-air CO₂ flux in spring and summer for (1.7±0.8) mmol/(m2·d) and (1.2±0.8) mmol/(m2·d), respectively. The study area acted as a weak CO₂ source during both seasons. The hourly changes of pCO₂ in spring were more significantly affected by temperature effects than in summer. During summertime, pCO₂ had more sensibly response to tidal action, enhanced biological production and respiration with inflow of coastal freshwater such as rivers and submarine groundwater discharge. Water warming dominated the formation of high pCO₂ in spring. The enhanced biological production during the physical mixing of saline and fresh water played a role in the drawdown of surface dissolved inorganic carbon (DIC) and the mangroves and salt marshes ecosystems along the bay had a certain contribution to the addition of DIC on the freshwater end-member in summer. The variations of the ratio of DIC concentration and total alkalinity (TA) in the water masses could imply the overall distribution pattern adjacent to the Yingluo Bay-Anpu Harbor that high values exists in the bay and lower values exists in offshore water.