OCE-PRF: Biomediated corrosion of methane-derived authigenic carbonates in the deep ocean and its implications for carbon fluxes from methane seeps

This research fellowship investigates the amount of carbon released back into seawater by biological processes that dissolve the carbonate rock structures formed at oceanic methane seeps. Throughout the worlds’ oceans, methane rises through seafloor sediments from subduction zones and old organic material buried below the seafloor. Most of this methane is consumed by unique microbial and chemical activity before it can reach the ocean or atmosphere.

Within this “methanosphere”, rocks form in the soft sediments near the seafloor when dissolved or gaseous carbon seeping up from below precipitates as solid carbonate. These rocks provide a hard surface for deep-sea organisms to inhabit and store carbon that would otherwise contribute to increased carbon dioxide in the ocean and atmosphere. Carbonate will dissolve back into seawater when the acid content of surrounding waters increases, which can be caused by the complicated biogeochemical reactions occurring on and around the carbonate rocks.

Without accounting for this dissolution of carbonate, the amount of carbon that reaches the atmosphere from the subseafloor on timescales relevant to anthropogenic climate change cannot be fully quantified. This research will support two undergraduates and provide training in Geographic Information Systems; image processing software; database management; and peer-reviewed manuscript development and publication.

In addition to training for undergraduate students at UCLA, the investigators are collaborating with the Alaska Native Science and Engineering Program and SoCalSeas, the Southern California network of teachers from 2-year and 4-year colleges designed to bridge education in oceanography. Results of the project will be disseminated to public and academic groups, including the Center of Diverse Leadership in Sciences at UCLA, as a variety of media content for a range of learning styles designed to inform and inspire participation in deep-sea science and related fields.

For example, the seafloor maps from this project will be adapted to GIS exercises for high school, community college, and university classroom instruction.

While the NSF-funded METHANOSPHERE project aims to redefine the footprint of deep ocean methane seepage for benthic ecosystems, the role of biomediated carbonate corrosion is not addressed. This study aims to directly evaluate the carbon loss over time associated with corrosion-driven dissolution of methane derived authigenic carbonate through U-series chronology to date carbonates; incubation of carbonates inoculated with living microbes to determine the carbon flux associated with different microbiological corrosion processes; scanning electron microscopy to quantify carbonate surface corrosion and identify its source; and geochemical modeling that combines these results with the relevant METHANOSPHERE project results to calculate the carbon loss over time from biomediated carbonate corrosion under canonical deep ocean conditions.

The METHANOSPHERE sites will allow the comparison of methane derived authigenic carbonate corrosion under the representative conditions of higher oxygen levels with lower photosynthetic food input (Aleutian) and lower oxygen with higher productivity conditions (California). Carbon fluxes associated with carbonate corrosion at these sites will be calculated and related to the organisms responsible to estimate a flux associated with a given environment and corrosion process.

The goals of this study are to produce 1.) An erosion mass balance of the Southern California Borderlands Seep, including experimental data, seafloor photomosaics, and substrate maps, 2.) An erosion mass balance of the Aleutian Margin Seep including experimental data, seafloor photomosaics and substrate maps, and 3.) A methane derived authigenic carbonate corrosion pattern identification guide (including data from both sites). The investigators are addressing these goals by surveying, sampling, and characterizing carbonates through shipboard and laboratory incubations and analyses.

Insights from the study will be presented at least once annually at an international conference; and as a guest lecture in the UCLA Freshman class "Methane the other greenhouse problem”, which targets non-STEM students, and the undergraduate/graduate course "Aquatic Geomicrobiology". As methane seeps and relic carbonates are widespread along the continental margins, carbon cycling through seep carbonates is likely a substantial component of the global subseafloor methane budget and its quantification is crucial to estimate long-term burial of methane-derived carbon.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.