海气交换与呼吸作用调控下杭州湾碳酸盐体系的特征

杭州湾作为典型的高浑浊度海湾，对其水体碳酸盐体系分布特征的研究相对较少。本文基于两个夏季航次(2018年和2019年)获取的调查资料，阐述夏季杭州湾水体中碳酸盐体系参数的空间分布特征，并进一步分析影响溶解无机碳偏离保守混合作用的主要过程及相对贡献。数据结果表明，杭州湾内表层溶解无机碳浓度与总碱度的变化范围分别为1 553～1 964 μmol/kg和1 577～2 101 μmol/kg，略低于长江口(1 407～2 110 μmol/kg和1 752～2 274 μmol/kg)，溶解无机碳浓度和总碱度的空间分布受控于淡水与外海水混合的影响，在潮汐作用下，总体呈现出湾内低，向湾外逐渐升高的趋势。影响表层溶解无机碳非保守混合分布的主要过程中，海?气交换降低溶解无机碳浓度，呼吸作用增加溶解无机碳浓度，两个过程对溶解无机碳浓度变化量的贡献分别为(?42.3±11.7)%与(34.2±14.3)%，净效应呈现为相对平衡的状态。通过计算获得表层海水pCO₂的平均值为799 μatm (675～932 μatm)，海湾总体表现为大气CO₂的源。此外，湾内海水碳酸盐缓冲因子的范围为12.8～23.8，对CO₂的缓冲能力弱于邻近东海海水(缓冲因子平均值约为11.9)，指示其与外部水体的交换可能会降低附近海域的酸化缓冲能力。相对其他河口/海湾而言，杭州湾内高浊度与强潮汐的特点使其湾内水体的碳酸盐体系分布特征具有区域特殊性。

Characteristics of carbonate system in the Hangzhou Bay: Under the regulation of air-sea exchange and respiration

As a typical high-turbidity bay, the carbonate systems in the Hangzhou Bay are not well documented. In this paper, the spatial distributions of inorganic carbonate paramenters in the Hangzhou Bay were analyzed based on data collected from two summer surveys in 2018 and 2019. The results showed that dissolved inorganic carbon (DIC) concentration and total alkalinity (TA) in surface layer of the Hangzhou Bay ranged from 1 553 μmol/kg to 1 964 μmol/kg and from 1 577 μmol/kg to 2 101 μmol/kg, respectively, which were lower than that of the Changjiang River Estuary (1 407?2 110 μmol/kg and 1 752?2 274 μmol/kg). The spatial distributions of DIC concentration and TA were controlled by the mixing of fresh water and offshore sea water. They were affected by strong tide, which gradually increased DIC concentration from inner bay to outlet of the bay. Air-sea carbon exchange and biological respiration led to decrease and increase of DIC concentration, with the contributions of (?42.3±11.7)% and (34.2±14.3)%, respectively. Such two compensate processes resulted in a net balanced state. The average surface pCO₂ in the Hangzhou Bay was 799 μatm (675?932 μatm), indicating that bay waters were source of atmospheric CO₂. The revelle factor in the Hangzhou Bay varied from 12.8 to 23.8, suggesting a weaker CO₂ buffering capacity than the adjacent East China Sea (the mean value was 11.9). Compared with other estuaries/gulfs, the characteristics of high turbidity and strong tides in the Hangzhou Bay made the spatial distributions of the carbonate system in the bay water had regional specificity.