Abstract
Cold seep emissions of low temperature fluid from the marine sediment basins are mainly comprised of methane and other hydrocarbons. A series of biogeochemical processes related to methane lead to the formation of authigenic carbonate minerals. In this study, a self-built experimental device was used to study the formation process of carbonate minerals under cold seep conditions. The concentrations of pore water chemicals, HCO3− and Ca2+ at different heights of the reactor under flow conditions can be observed. According to the experimental results, the formation process of carbonate minerals under cold seep conditions was estimated, that 1 m carbonate growth needs 12,000 and 7000 years, respectively, under fast (5 mL·min−1) and slow emission (1 mL·min−1) conditions. Furthermore, TOUGHREACT was used to simulate the diagenesis process. A 1D unsteady react-transport model was developed, and the experimental data was used to constrain the simulation. The results of simulation show that the carbonates need 17,000 and 9700 years to grow 1 m under the condition of fast and slow flow scenarios, respectively. The results of this work will contribute to the study of foundation on the formation of authigenic minerals in cold seep areas, and for the physical properties of sedimentary media as well.
Highlights
Cold seep is a phenomenon involving emissions of methane-rich fluid, occasionally accompanied by heavier hydrocarbons and CO2, from marine sediments
A self-developed biogeochemical experimental device was used to carry out an experiment to simulate the diagenesis of cold seep authigenic carbonates under different flow scenarios
The bicarbonate solution was injected into the reactor containing calcium ion solution at a constant rate of 5 mL·min−1 and 1 mL·min−1, respectively, followed by sampling the pore water at different reactor heights
Summary
Cold seep is a phenomenon involving emissions of methane-rich fluid, occasionally accompanied by heavier hydrocarbons and CO2 , from marine sediments. The temperature of the fluid is close to the temperature of the surrounding seawater [1]. Most of the ascending methane is consumed by anaerobic oxidation (AOM) mediated by anaerobic methanotrophic archaea (ANME) during the fluid migration in marine sediments. Unconsumed methane may enter the water column or even reach the atmosphere, causing an increase in the concentration of methane in the atmosphere, which due to its strong greenhouse effect may affect regional and global climates [2]. The AOM process produces the bicarbonate and changes the pore water composition and pH, bicarbonate react with metal ions such as calcium and magnesium and eventually forms aragonite, Int. J. Public Health 2019, 16, 1433; doi:10.3390/ijerph16081433 www.mdpi.com/journal/ijerph
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