Issue 11, 2023

The emission of low pH water from Gulf of Mexico seeps as revealed by δ13C–CO2 and methane oxidation data

Abstract

Seawater was collected around the MC118 hydrocarbon seep in the Gulf of Mexico and was used previously for a study of aerobic methane (CH4) oxidation. During that experiment, changes in the dissolved concentrations and δ13C isotopes of CH4 and CO2 were recorded. Originally, the CO2 concentrations and isotopes were recognized to qualitatively follow trends supporting the microbial conversion of CH4 to CO2via aerobic oxidation, however, no attempt was made to quantitatively explain this CO2 data. The present study models the δ13C–CO2 changes that occur as a result of CH4 oxidation, accounting for the carbon already present as dissolved inorganic carbon (DIC), DIC added via CH4 oxidation, and the pH of seawater. This study discovers that to accurately model the measured concentration and isotopic data for CO2, the seawater emitted from this seep site must have a pH which is at most between 6.49 and 7.24, and possibly up to 0.43 ± 0.08 pH units lower. These results are corroborated by direct measurements of pH from seeps in the Mediterranean Sea. A first-order extrapolation indicates that while cold seeps in the Gulf of Mexico may be a source of low pH water influencing the carbon dynamics of the deep ocean environment, this influence is likely less than that of current surface ocean acidification caused by the infiltration of atmospheric CO2.

Graphical abstract: The emission of low pH water from Gulf of Mexico seeps as revealed by δ13C–CO2 and methane oxidation data

Supplementary files

Article information

Article type
Paper
Submitted
03 Maijs 2023
Accepted
09 Okt. 2023
First published
09 Okt. 2023
This article is Open Access
Creative Commons BY license

Environ. Sci.: Adv., 2023,2, 1600-1606

The emission of low pH water from Gulf of Mexico seeps as revealed by δ13C–CO2 and methane oxidation data

S. I. Louden and J. D. Kessler, Environ. Sci.: Adv., 2023, 2, 1600 DOI: 10.1039/D3VA00117B

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