Characteristics of carbonate system in the Hangzhou Bay: Under the regulation of air-sea exchange and respiration
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摘要: 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。Abstract: 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.
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Key words:
- carbonate systems /
- dissolved inorganic carbon (DIC) /
- distribution /
- Hangzhou Bay
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图 5 TA、DIC浓度与盐度之间的相互关系
虚线与直线分别表示2018年、2019年的趋势线;红圈内展示的是北部沿岸高值站位
Fig. 5 The correlation among TA, DIC concentration and salinity
The dotted line and the straight line represent the trend lines of 2018 and 2019, respectively; the high-value stations along the northern coast are shown in the red circle
表 1 航次信息与水文参数
Tab. 1 Cruise information and hydrological parameters
航次名称 采样时间(阳历) 温度/℃ 盐度 深度/m 潮汐 2018年航次 2018年8月12日、2018年8月15日 29.87±0.52 16.02±4.89 8.2±2.1 大潮 2019年航次 2019年8月25−29日 28.45±1.58 17.34±7.85 15.7±12.5 小潮 注:温度、盐度和深度数据为各个航次调查站位的平均值±相对偏差,潮汐以农历推算。 表 2 两个航次表层DIC浓度、TA、pCO2的变化范围
Tab. 2 The variation range of DIC concentration, TA and pCO2 in surface layer of two field cruises
航次年月 DIC浓度/(μmol·kg−1) TA/(μmol·kg−1) pCO2/μatm 2018年8月 1 789~2 015 (1 921) 1 822~2 100 (1 982) 778~1 271 (1 085) 2019年8月 1 553~1 964 (1 805) 1 577~2 101 (1 886) 675~932 (799) 注:DIC浓度、TA为实测值,pCO2为计算值,括号内为平均值。 表 3 7个北半球中高纬度河口/海湾碳酸盐体系的对比
Tab. 3 Comparison of carbonate systems in seven different estuaries and gulfs in the North Hemisphere
河口/海湾 DIC浓度 pCO2/μatm 主要影响因素 数据来源 斯海尔德河口 3 300~7 100 μmol/L 2 200~15 500 呼吸作用 文献[9] 卢瓦尔河口 2 200~2 700 μmol/kg 700~2 900 呼吸作用/
碳酸盐溶解文献[12] 黄河口 2 155~2 927 μmol/L 400~750 初级生产/
碳酸盐析出文献[11] 长江口 1 407~2 110 μmol/kg 177~1 036 初级生产 文献[25, 28] 珠江口 798~1 572 μmol/kg(雨季);
2 744~3 329 μmol/kg(旱季)− 碳酸盐浓度 文献[55] 切萨皮克湾 800~1 900 μmol/kg − 初级生产/呼吸作用 文献[13] 杭州湾 1 553~1 964 μmol/kg 675~932 呼吸作用/海−气交换 本文 注:−代表对应时期数据不可用。 -
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