Microbial sulfate reduction rates and sulfur and oxygen isotope fractionations at oil and gas seeps in deepwater Gulf of Mexico

From 2015 to 2018, TGS conducted a comprehensive multiclient oil and gas seep hunting survey in the Gulf of Mexico. The basis for identifying seeps on the sea bottom was a high-resolution Multi-Beam Echo Sounder survey, mapping approximately 880,000 km2 of the sea bottom deeper than 750 m water depth, at a bathymetric resolution of 15 m and a backscatter resolution of 5 m. We have identified more than 5000 potential oil and/or gas seeps, and of those, we cored approximately 1500 for hydrocarbon geochemical analysis. The sea bottom features best related to hydrocarbon seepage in the GoM are high backscatter circular features with or without bathymetric expression, high backscatter features with “flow” appearance, mud volcanoes, pock marks, brine pools, “popcorn” texture, faults, and anticlinal crests. We also tracked gas plumes in the water column back to the sea bottom to provide an additional criterion for hydrocarbon seepage. Cores from sea bottom targets recovered liquid oil, tar, and gas hydrates. Oil extract and gas analyses of samples from most target types produced values substantially higher than background in oil and gas.

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Hydrothermal alteration and microbial sulfate reduction in peridotite and gabbro exposed by detachment faulting at the Mid-Atlantic Ridge, 15°20′N (ODP Leg 209): A sulfur and oxygen isotope study

Geochemistry Geophysics Geosystems ◽

10.1029/2007gc001617 ◽

2007 ◽

Vol 8 (8) ◽

pp. n/a-n/a ◽

Cited By ~ 80

Author(s):

Jeffrey C. Alt ◽

Wayne C. Shanks ◽

Wolfgang Bach ◽

Holger Paulick ◽

Carlos J. Garrido ◽

...

Keyword(s):

Sulfate Reduction ◽

Oxygen Isotope ◽

Hydrothermal Alteration ◽

Microbial Sulfate Reduction ◽

Mid Atlantic Ridge ◽

Isotope Study ◽

Detachment Faulting

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Oxygen isotope effects during microbial sulfate reduction: applications to sediment cell abundances

The ISME Journal ◽

10.1038/s41396-020-0618-2 ◽

2020 ◽

Vol 14 (6) ◽

pp. 1508-1519 ◽

Cited By ~ 4

Author(s):

E. Bertran ◽

A. Waldeck ◽

B. A. Wing ◽

I. Halevy ◽

W. D. Leavitt ◽

...

Keyword(s):

Sulfate Reduction ◽

Oxygen Isotope ◽

Isotope Effects ◽

Microbial Sulfate Reduction

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Active microbial sulfate reduction in fluids of serpentinizing peridotites of the continental subsurface

Communications Earth & Environment ◽

10.1038/s43247-021-00157-z ◽

2021 ◽

Vol 2 (1) ◽

Author(s):

Clemens Glombitza ◽

Lindsay I. Putman ◽

Kaitlin R. Rempfert ◽

Michael D. Kubo ◽

Matthew O. Schrenk ◽

...

Keyword(s):

Sulfate Reduction ◽

Dna Sequences ◽

Low Molecular Weight ◽

Coast Range ◽

Sulfate Reducing ◽

Microbial Sulfate Reduction ◽

High Fluid ◽

Low Levels ◽

Sulfate Reduction Rates ◽

Strong Control

AbstractSerpentinization of peridotites in Earth’s mantle is associated with the generation of hydrogen and low molecular weight organics that could support subsurface life. Studies of microbial metabolisms in peridotite-hosted environments have focused primarily on methanogenesis, yet DNA sequences, isotopic composition of sulfides and thermodynamic calculations suggest there is potential for microbial sulfate reduction too. Here, we use a sulfate radiotracer-based method to quantify microbial sulfate reduction rates in serpentinization fluids recovered from boreholes in the Samail Ophiolite, Oman and the California Coast Range Ophiolite, USA. We find that low levels of sulfate reduction occur at pH up to 12.3. These low levels could not be stimulated by addition of hydrogen, methane or small organic acids, which indicates that this metabolism is limited by factors other than substrate availability. Cellular activity drops at pH > 10.5 which suggests that high fluid pH exerts a strong control on sulfate-reducing organisms in peridotites.

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