12 Guaymas Basin and Gulf of California Subsurface Systems and Energy Applications

This session will present subsurface research in the Gulf of California, especially IODP Expedition 385 to Guaymas Basin that explored the linkages between tectonics, magmatism, sedimentation, hydrothermalism, carbon cycling, and microbial life. Merged sessions: Subsurface Research  in Guaymas Basin and the Gulf of California and Energy Resources and Economic Development in Baja California: Fossil, Renewable, and Transition Minerals.

Wednesday, 22 April 2026
1:30 PM - 5:30 PM
LMH, Isla Carmen

Sequence-based Survey of Methanogens and Methane Oxidizers in the Guaymas Basin Deep Subsurface (IODP Expedition 385)

Paper number: 12-6
Program: Technical Sessions
Time: 2:50 PM – 3:05 PM

Authors

Abstract

IODP Expedition 385 explored the microbial production and consumption of methane, the dominant fossil carbon compound in the Guaymas Basin subsurface. Here we summarize current efforts to identify the microbial catalysts of the methane cycle in deep subsurface sediments of Guaymas Basin using several approaches: Amplicon sequencing of mcrA genes using PCR primers for euryarchaeal methanogens and methane oxidizers, and for Methanophaga/ANME-1; archaeal 16S rRNA gene amplicons for PacBio sequencing; mcrA genes obtained from unbinned site- and sample-specific metagenomic libraries; and mcrA genes from MAGs obtained from specific drilling sites and sediment samples.

                  Methodology played a significant role in the detection of methane-cycling microbial populations. PCR surveys are by definition specific for the methanogen and ANME lineages for which the PCR primers have been designed and tested, whereas metagenomic surveys are not constrained in this way and detect gene variants beyond the phylogenetic range of previously established primers. Interestingly, PCR surveys yielded the majority of all sequence-based evidence for methanogenic and methane-oxidizing microbial communities in the Guaymas Basin deep subsurface, whereas screening metagenomic sequences (binned and unbinned) resembled searching for the proverbial needle in the haystack. We conclude that methane-cycling archaea are a minority among the generally heterotrophic bacterial and archaeal lineages of the Guaymas Basin deep biosphere, and are hard to detect in general metagenomic surveys without selective PCR amplification. Implicitly, subsurface methane build-up and consumption should be understood as cumulative activity of resident methanogens and methane oxidizers over long time spans.

We attempted to extend the detection of methane-cycling microbial activity by examining downcore trends of published δ13C-CH4 data. Plotting all currently available δ13C-CH4 values from Guaymas subsurface sediments and sills against in-situ temperature reveals a trend from isotopically heavier methane in hot, deep sediments towards relatively 13C-depleted, and thus biogenic methane in cooler sediments. Since this trend of gradually increasing biogenic methane begins in sediment samples at 200 to 300 meters depth that did not yield any sequence signatures of methanogens, microbial methanogenesis must be more widespread than the downcore detection of its sequence signatures. Considering the steep decline of cell numbers and DNA yield with depth and temperature, methanogens that initiate the microbial contribution to the methane pool at great depth and high temperatures must be very rare.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-410761

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