Anaerobic alkalinity and dissolved inorganic carbon production in the Northern Gulf of Mexico hypoxic waters

Seawater total alkalinity (TA) and dissolved inorganic carbon (DIC) are influenced by various biogeochemical processes, such as aerobic and anaerobic remineralization, as well as carbonate precipitation and dissolution. During the summer months, bottom water hypoxia, i.e., dissolved oxygen concentration less than 2 mg L^-1, has been observed in the northern Gulf of Mexico (nGoM). Using water samples collected from the nGoM between 2006 and 2019, we attempted to examine TA and DIC production from anaerobic processes, by applying a three end-member mixing model. The TA and DIC production signals were determined by calculating the difference between the observed and mixing-expected values, with corrections for photosynthesis and aerobic respiration based on dissolved oxygen changes. We found detectable TA and DIC in anoxic waters, with maximum anaerobic contributions of up to 180 and 210 µmol kg^-1, respectively. In the meantime, aerobic oxidation contributes to an increase in DIC by 80-140 µmol kg⁻¹ and a decrease in TA by approximately 20 µmol kg⁻¹. This study underscores the significance of TA and DIC production in hypoxic waters of the nGoM and offers a preliminary quantification of the various biogeochemical factors influencing carbonate chemistry.

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Primary Presenter: Hang Yin, The University of Texas at Austin (hangyin.phd@gmail.com)

Authors:

Xinping Hu, Marine Science Institute, The University of Texas at Austin, USA  (xinping.hu@austin.utexas.edu)