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Hypoxic Effects on the Radiocarbon in DIC of the ECS Subsurface Water
Author(s) -
Wang ShingLin,
Fan Daidu,
Huang WeiJen,
Wu Yijing,
Su Jianfeng
Publication year - 2021
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2020jc016979
Subject(s) - oceanography , transect , continental shelf , estuary , bottom water , geology , outflow , dissolved organic carbon , water mass , hypoxia (environmental) , surface water , current (fluid) , seawater , mixing (physics) , environmental science , chemistry , oxygen , organic chemistry , environmental engineering , physics , quantum mechanics
Dissolved inorganic carbon (DIC) in the East China Sea (ECS) is physically and chemically affected by the northward intrusion of the Kuroshio Branch Current (KBC) and the Changjiang River (CR) outflow. We trace these processes using dual DIC isotopic compositions (Δ 14 C and δ 13 C) along transects that begin in the CR and estuary, and extend out into middle shelf waters of the ECS. We especially focus on frequently occurred nearshore hypoxia, as they appeared in the summer of 2017. The Δ 14 C values (28.8‰–35.3‰) from the ECS mid‐shelf water were comparable to the reported value from the Kuroshio Current (KC) at the continental slope (34.4‰ ± 7.4‰), but Δ 14 C values in the CR (−173.6‰ & −162.3‰) were substantially lower than observations made in 2014. We also found that the Δ 14 C of DIC in the bottom waters along the inner shelf, including hypoxic area, decreased from 25.0‰ to 18.5‰, from south to north. Water masses mixing between the CR and the ECS mid‐shelf waters with and without organic carbon degradation can be identified in plots of Δ 14 C versus DIC ‐1 . With simple mixing calculations, we show that the northward decreasing Δ 14 C of inner shelf bottom water is caused by downward transport of DIC with low Δ 14 C value mediated by biological process from the surface, as opposed to simple physical mixing.