Tidal‐Driven Submarine Groundwater Discharge and Its Influences on the Carbonate System of a Coastal Coral Reef in the Northern South China Sea. Issue 7 (25th June 2021)

• Record Type: Journal Article
• Authors: Jiang, Zong‐Pei; Lv, Jiacheng; Li, Quanlong; Dai, Minhan; Kao, Shuh‐Ji; Zheng, Nan; Fan, Wei
• Is Part Of: Journal of geophysical research. Volume 126:Issue 7(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-06-25
• Subjects: submarine groundwater -- coral reef -- carbonate system -- tidal pumping -- acidification; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2021JC017203
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: The driving mechanisms of submarine groundwater discharge (SGD) in Sanya Bay in the northern South China Sea were investigated using a combination of time‐series observation and modeling, as well as the influences of SGD on the carbonate system of a coastal coral reef. SGD flux, characterized by high variability on flood‐ebb and spring‐neap tidal cycles, was found to be mainly driven by tidal pumping. SGD posed more significant impacts on coastal water at the ebb phase during the spring tide (higher SGD flux and extended offshore reach of SGD impact), with nearshore water to be more heavily affected. Under the influence of SGD, the diurnal ranges of the carbonate variables observed in the coral reef system were 124 – 313 μmol kg −1 for dissolved inorganic carbon, 29 – 101 μmol kg −1 for total alkalinity, 179 – 717 μatm for partial pressure of CO2, and 0.20 – 0.45 for pH. The variations of the CO2 system were dominated by the enhanced SGD input during the spring tide, while biological metabolism of coral reef played a predominant role during the neap tide. The intensified SGD input resulted in higher diurnal variations of the carbonate variables, enhanced acidification, and oceanic CO2 emission during the spring tide. The SGD‐associated inorganic carbon flux is an additional stressor influencing coastal acidification in the context of rising atmospheric carbon dioxide. Plain Language Summary: Submarine groundwater discharge (SGD) is a barely noticed but significant source of nutrients and carbon to coastal marine ecosystems. Using observation and modeling, we studied the changes in the flux of SGD entering Sanya Bay in the northern South China Sea and how SGD affected the water chemistry of a coastal coral reef system. SGD flux was found to be driven by tidal movement showing distinct spatial and temporal variability. SGD posed greater impact on nearshore region in ebb tide and played a dominant role in controlling water chemistry during the spring tide. The carbon content carried by SGD acidified the seawater (pH decrease) in conjunction with the human‐induced increasing atmospheric CO2, which endangers the health of coral reef system. Key Points: Highly variable tidal‐driven submarine groundwater discharge (SGD) flux posed different impacts on coastal water on flood‐ebb and spring‐neap tidal cycles The carbonate chemistry was alternately dominated by SGD input during the spring tide and biological metabolism during the neap tide Changing SGD‐associated carbon flux increases the complexity of coastal acidification in the context of rising atmospheric carbon dioxide