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Anqi Liu, Feng Zhou, Xiao Ma, Qiang Zhao, Guanghong Liao, Yuntao Zhou, Di Tian, Xiaobo Ni, Ruibin Ding. Inter-annual variations of dissolved oxygen and hypoxia off the northern Changjiang River (Yangtze River) Estuary in summer from 1997 to 2014[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-023-2244-0
Citation: Anqi Liu, Feng Zhou, Xiao Ma, Qiang Zhao, Guanghong Liao, Yuntao Zhou, Di Tian, Xiaobo Ni, Ruibin Ding. Inter-annual variations of dissolved oxygen and hypoxia off the northern Changjiang River (Yangtze River) Estuary in summer from 1997 to 2014[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-023-2244-0

Inter-annual variations of dissolved oxygen and hypoxia off the northern Changjiang River (Yangtze River) Estuary in summer from 1997 to 2014

doi: 10.1007/s13131-023-2244-0
Funds:  The National Natural Science Foundation of China under contract No. 41876026; the Scientific Research Fund of the Second Institute of Oceanography, Ministry of Natural Resources under contract No. YJJC2201; the National Programme on Global Change and Air–Sea Interaction Phase II under contract No. GASI-01-CJK; the Zhejiang Provincial Ten Thousand Talents Program under contract No. 2020R52038; the Project of State Key Laboratory of Satellite Ocean Environment Dynamics under contract No. SOEDZZ2105.
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  • Corresponding author: Feng Zhou, zhoufeng@sio.org.cn, phone: 086-571-81963106; Xiao Ma, maxiao@sio.org.cn, phone:086-571-81963089
  • Received Date: 2023-03-28
  • Accepted Date: 2023-06-16
  • Available Online: 2024-01-29
  • Hypoxia off the Changjiang River Estuary has been the subject of much attention, yet systematic observations have been lacking, resulting in a lack of knowledge regarding its long-term change and drivers. By revisiting the repeated surveys of dissolved oxygen (DO) and other relevant hydrographic parameters along the section from the Changjiang River Estuary to the Cheju Island in the summer from 1997 to 2014, rather different trends were revealed for the dual low-DO cores. The nearshore low-DO core, located close to the river mouth and relatively stable, shows that hypoxia has become more severe with the lowest DO descending at a rate of −0.07 mg/(L·a) and the thickness of low-DO zone rising at a rate of 0.43 m/a. The offshore core, centered around 40-m isobath but moving back and forth between 123.5°–125°E, shows large fluctuations in the minimum DO concentration, with the thickness of low-DO zone falling at a rate of −1.55 m/a. The probable factors affecting the minimum DO concentration in the two regions also vary. In the nearshore region, the decreasing minimum DO is driven by the increase in both stratification and primary productivity, with the enhanced extension of the Changjiang River Diluted Water (CDW) strengthening stratification. In the offshore region, the fluctuating trend of the minimum DO concentration indicates that both DO loss and DO supplement are distinct. The DO loss is primarily attributed to bottom apparent oxygen utilization caused by the organic matter decay and is also relevant to the advection of low-DO water from the nearshore region. The DO supplement is primarily due to weakened stratification. Our analysis also shows that the minimum DO concentration in the nearshore region was extremely low in 1998, 2003, 2007 and 2010, related to El Niño signal in these summers.
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