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<p>This study investigates the spatial distribution and regulatory mechanisms of dissolved inorganic carbon (DIC) in Xiangshan Bay, East China Sea, addressing critical gaps in carbon cycling research within semi-enclosed bays. Through isotopic analysis (δ<sup>13</sup>C<sub>DIC</sub>, δD and δ<sup>18</sup>O) and hydrochemical measurements [salinity and dissolved oxygen (DO)] of surface and bottom seawater samples from 52 stations, we demonstrate that δ<sup>13</sup>C<sub>DIC</sub> values (surface: −3.6‰ to −2.1‰; bottom: −3.6‰ to −1.8‰) exhibit distinct vertical and spatial patterns, with higher values in surface waters and outer bay regions compared to bottom and inner bay areas. Conservative mixing between seawater (average contribution: 56%) and freshwater dominates DIC dynamics, while tidal hydrodynamics amplify the imprint of riverine inputs during low tides. Nutrient gradients driven by saline-freshwater mixing enhance primary productivity in outer bay regions, resulting in <sup>13</sup>C-enriched DIC and elevated dissolved organic carbon (DOC) concentrations. Conversely, bottom waters show <sup>13</sup>C-depleted signatures (−2.75 ‰ mean δ<sup>13</sup>C<sub>DIC</sub>), reflecting organic matter degradation under oxygen-depleted conditions. Aquaculture activities exacerbate localized eutrophication, with monsoon-enhanced runoff amplifying anthropogenic impacts. This work underscores the sensitivity of coastal carbon cycling to both natural hydrodynamics and anthropogenic perturbations in semi-enclosed bays.</p>

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Deciphering dissolved inorganic carbon dynamics in Xiangshan Bay: isotopic constraints on sources, hydrodynamic controls, and anthropogenic influences

  • 期刊论文

  • 发表日期：

    2025年9月1日

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  • Xue Li,
  • Xiaoyong Duan,
  • Gang Tong,
  • Ping Yin,
  • Fei Gao,
  • Ke Cao,
  • Bin Chen

摘要

This study investigates the spatial distribution and regulatory mechanisms of dissolved inorganic carbon (DIC) in Xiangshan Bay, East China Sea, addressing critical gaps in carbon cycling research within semi-enclosed bays. Through isotopic analysis (δ13CDIC, δD and δ18O) and hydrochemical measurements [salinity and dissolved oxygen (DO)] of surface and bottom seawater samples from 52 stations, we demonstrate that δ13CDIC values (surface: −3.6‰ to −2.1‰; bottom: −3.6‰ to −1.8‰) exhibit distinct vertical and spatial patterns, with higher values in surface waters and outer bay regions compared to bottom and inner bay areas. Conservative mixing between seawater (average contribution: 56%) and freshwater dominates DIC dynamics, while tidal hydrodynamics amplify the imprint of riverine inputs during low tides. Nutrient gradients driven by saline-freshwater mixing enhance primary productivity in outer bay regions, resulting in 13C-enriched DIC and elevated dissolved organic carbon (DOC) concentrations. Conversely, bottom waters show 13C-depleted signatures (−2.75 ‰ mean δ13CDIC), reflecting organic matter degradation under oxygen-depleted conditions. Aquaculture activities exacerbate localized eutrophication, with monsoon-enhanced runoff amplifying anthropogenic impacts. This work underscores the sensitivity of coastal carbon cycling to both natural hydrodynamics and anthropogenic perturbations in semi-enclosed bays.