Frederick S. Colwell

In the summer and fall of 2023, the University of Texas (UT) Deepwater Hydrate Coring Expedition (UT-GOM2-2) drilled, cored, made downhole measurements, and analyzed samples from the seafloor to the base of the gas hydrate stability zone at Site H, in the Walker Ridge Protracted Area Block 313 (Site H, WR313), in the Terrebonne Basin, deepwater Gulf of America (Gulf of Mexico). Analyses of data and samples from the expedition will inform biological, geochemical, and geomechanical models to constrain the role of gas hydrates in the carbon cycle and the potential for gas hydrates as an energy resource.

Freshwater wetlands are major sources of global methane emissions through biogenic methanogenesis, a process increasingly influenced by climate change. High latitude wetlands are subject to uniquely altered biogeochemical inputs due to disproportionate warming. For example, glacial meltwater delivers metal‐rich sediments that are easily reducible. Additionally, if the wetland is located upon a subduction zone, periodic and dynamic geological forces, such as megathrust earthquakes, can disrupt these systems further. To explore these interactions, we analyzed the genomic potential of microbial communities across a glaciated wetland located in an active forearc region subject to repeated megathrust ruptures. We found that sediment microbial communities contained the complete potential for methanogenesis and iron cycling, yet the relative abundance of key methanogenic genes was reduced in recently deposited freshwater sediments despite high levels of organic matter and iron. These findings suggest that megathrust fault activity and associated uplift exerts broad, abrupt change on microbial metabolic potential, and that overlying sediments reflect modern glacial input which modify the development of metabolic potential. Glacial influence likely disrupts methanogenesis by supporting communities capable of dissimilatory iron reduction, which may increase metal‐dependent methanotrophy. As climate change accelerates glacial melt, extant and newly developing microbial communities will likely respond rapidly to shifting carbon and mineral inputs, altering carbon cycling dynamics in these sensitive ecosystems. Our work links small scale microbial metabolic potential with some of the largest processes on our planet, revealing how cyclical tectonic events can overprint broad scale biogeochemistry by homogenizing microbial metabolisms and disrupting elemental cycling.

Methods used during the University of Texas (UT) Deepwater Hydrate Coring Expedition (UT-GOM2-2) include work done onboard the Helix Q4000 in the offshore Gulf of America (Gulf of Mexico), herein “the Gulf”, “dockside” in Salt Lake City, Utah, and some shore-based work in individual laboratories. The goal of this report is two-fold: to provide enough detail on the methods so they can be repeated by others; and to provide a reference document for the team to enhance cross-disciplinary understanding and knowledge. Methods include drilling operations, depth references and depth modification, downhole tool deployment, coring tool performance assessment, core processing, lithostratigraphy, biostratigraphy, as well as physical properties, including core logging and imaging, rock magnetism, dissolved methane concentration, hydrate saturation, microbiology, and geochemistry. An extensive amount of operational work and planning was required before mobilization of the expedition to permit, build mobile labs, and test downhole tools for deepwater drilling.

Pressure and conventional cores were collected at Site H of the Walker Ridge Protracted Area Block 313 in the Terrebonne Basin, deepwater Gulf of America (Gulf of Mexico) during the University of Texas (UT) Deepwater Hydrate Coring Expedition (UT-GOM2-2). Pressure and conventional cores were collected continuously to a depth of 155.1 meters below the seafloor (mbsf). At deeper depths, cores were taken periodically from hydrate-bearing sands and their bounding muds to a total depth of 861.3 mbsf. 162.6 m of conventional core and 54.8 m of pressure core were recovered. Twelve temperature measurements were made between 27.1 and 144.5 mbsf to determine the geothermal gradient. At the seafloor, more than 4 m of sandy silt of unknown origin was encountered. Beneath this sand, to a depth of about 200 mbsf, the section was composed of interbedded mud and biogenic carbonate ooze. The ooze correlated to low density and high porosity intervals observed in the previously acquired logging while drilling (LWD) data and as measured. These ooze intervals also correspond to lighter sediment color, increased Ca content based on X-ray florescence (XRF) core scanning, and increased calcareous nannofossil abundance. Calcareous nannofossil biostratigraphy constrains the entire record to the Pleistocene (< 0.91 million years), with a pronounced increase in sedimentation rate with depth. Below 200 mbsf, the section was predominantly composed of mud with two thicker, hydrate-bearing coarse-grained intervals, which are commonly known as the Blue and Orange sands. The dissolved gas concentration was quantified from pressure cores. In the shallow section, dissolved methane concentration increased below the sulfate-methane transition zone (SMTZ) and reaches saturation (the limit of solubility for methane) at 147 mbsf. Gas expansion was very common in conventional and depressurized pressure (conventionalized) cores below the SMTZ. At deeper depths, the methane concentration within muds bounding the Blue and Orange reservoirs was generally found to be less than saturation. The dissolved and hydrate gas composition is consistent with a microbial source, containing greater than 99.99% methane and only trace concentrations of ethane, propane, and butane. The methane to ethane ratio (C1 /C2 ) and the methane to ethane plus propane (C1 /(C2 +C3 )) decrease with depth down to at least 678 mbsf, mainly driven by the increase in ethane with depth. It is unclear if this trend continues through the Orange sand interval. The δ13C isotopic signature of methane ranges between -69.9 and -78.5 ‰ relative to the Vienna Pee Dee Belemnite (VPDB) standard. Pressure core recovery in sandy intervals was poor. However, pressure core logs of the Orange sand show intervals of low density and high velocity, which are indicative of high hydrate saturation. One pressure core was degassed and the average hydrate saturation in the core was determined to be 24%. One core from within the Orange sand was composed of interbedded graded sandy silt and mud. The sandy silts from this core are composed of mainly quartz and feldspar with some lithics. Most of the recovered pressure core samples are maintained at near in-situ pressure and temperature (within the hydrate stability field) at the University of Texas Pressure Core Center awaiting analysis. In the shallow section, samples will be used to determine the flux of organic carbon through the basin system, find the rate at which that carbon was consumed, and understand the microbial population responsible for these processes. In the deeper section, samples from in and around the hydrate reservoirs will be used to determine the petrophysical properties of the reservoir and bounding seals in these systems.

In the summer and fall of 2023, the Gulf of Mexico Deepwater Hydrate Coring Expedition (UT-GOM2-2) drilled, cored, made downhole measurements, and analyzed samples from the seafloor to the base of the gas hydrate stability zone in one location (Site H, WR313) in the Terrebonne basin, deepwater Gulf of Mexico. Analyses of data and samples from the expedition will inform biological, geochemical, and geomechanical models to constrain the role of gas hydrates in the carbon cycle and the potential for gas hydrates as an energy resource. Pressure and conventional cores were collected continuously to a depth of 155.1 meters below the seafloor (mbsf). At deeper depths, cores were taken periodically from hydrate-bearing sands and their bounding muds to a total depth of 861.3 mbsf. 162.6 m of conventional core and 54.8 m of pressure core were obtained. Twelve temperature measurements were made between 27.1 and 144.5 mbsf to determine the geothermal gradient. At the seafloor, more than 4 m of sandy silt of unknown origin was encountered. Beneath this sand, to a depth of ~200 mbsf, the section was composed of interbedded mud and biogenic carbonate ooze. The biogenic ooze correlated to low density and high porosity intervals observed in the previously acquired logging while drilling (LWD) data and as measured. Calcareous nannofossil biostratigraphy constrains the entire record to the Pleistocene (< 0.91 million years) with a pronounced increase in sedimentation rate with depth. Beneath 200 mbsf, the section was predominantly composed of mud with two thicker, hydrate-bearing coarse-grained intervals, which are commonly known as the Blue and Orange sands. The dissolved gas concentration was quantified from pressure cores. In the shallow section, dissolved methane concentration increased below the sulfate-methane transition zone (SMTZ) and reaches saturation (the limit of solubility for methane) at 147 mbsf. Gas expansion was very common in conventional and depressurized pressure (conventionalized) cores below the SMTZ. At deeper depths, the methane concentration within muds bounding the Blue and Orange reservoirs was generally found to be less than saturation. The dissolved and hydrate gas composition is consistent with a microbial source, containing greater than 99.99% methane and only trace concentrations of ethane, propane, and butane. The methane to ethane ratio (C1/C2) and the methane to ethane plus propane (C1/(C2+C3)) decrease with depth down to at least 678 mbsf, mainly driven by the increase in ethane with depth. It is unclear if this trend continues through the Orange sand interval. The δ13C isotopic signature of methane ranges between -69.9 and -78.5 ‰ Vienna Pee Dee Belemnite (VPDB). Pressure core recovery of all sandy intervals was poor. However, pressure core logs of the Orange sand show intervals of low density and high velocity, which are indicative of high hydrate saturation. One core from within the Orange sand was composed of interbedded graded sandy silt and mud. The sandy silts from this core are composed of mainly quartz and feldspar with some lithics. Most of the recovered pressure core samples are maintained at near in-situ pressure and temperature (within the hydrate stability field) at the University of Texas Pressure Core Center awaiting analysis. In the shallow section, samples will be used to determine the flux of organic carbon through the basin system, find the rate at which that carbon was consumed, and understand the microbial population responsible for these processes. In the deeper section, samples from in and around the hydrate reservoirs will be used to determine the petrophysical properties of the reservoir and bounding seals in these systems.

Marine and terrestrial subsurface sediments, rocks, and water may represent the largest habitat for microbial life on Earth. Despite the global importance of subsurface ecosystems for biogeochemical cycling and microbial diversity, essential questions remain unanswered. These concern the abundance of novel microbial clades in the subsurface, the difference between marine and terrestrial microbiomes, as well as between subsurface and surface microbiomes, and the adaptation of specific clades to environmental conditions of the subsurface. Here, we analyzed 523 archaeal and 1,211 bacterial 16S rRNA gene amplicon sequence datasets and 146 shotgun metagenomes from surface, interface, and subsurface ecosystems worldwide, including lakes, saltmarshes, hot springs, caves, mines, methane seeps, hydrothermal vents, and seafloor sediments. We found that archaeal and bacterial alpha diversity (per sample richness and evenness) and beta diversity (community differentiation) varied continuously between surface and subsurface biomes, but differed abruptly between marine and terrestrial subsurface ecosystems. Bacterial alpha diversity tended to be lower in subsurface than surface ecosystems. However, subsurface archaeal alpha diversity often exceeded that of surface ecosystems suggesting that the subsurface holds a considerable and largely underestimated fraction of Earth’s archaeal diversity. Overall, microbial communities of marine subsurface ecosystems exhibited greater alpha diversity, while gamma diversity (total richness and evenness) was higher in the terrestrial subsurface, potentially due to greater habitat diversity. We identify diagnostic clades, especially for the archaea, that are widespread in marine (e.g., Lokiarchaeia, Bathyarchaeia) and terrestrial (e.g., Hadarchaeia, Methanococci) subsurface ecosystems. The substantial community overlap along depth transects and between surface, interface and subsurface realms suggests a global gradient between the surface and subsurface rather than a discrete and defined subsurface biosphere. Finally, none of the included subsurface ecosystems seem to be exhaustively sampled, leaving much biodiversity and metabolic capability yet to be discovered.

High‐latitude, coastal wetland biogeochemistry is dynamic in response to climate change, and yet we do not understand, and thus cannot fully predict, how crucial aspects of these systems will change in the future. Temperatures in the Northern Hemisphere have disproportionately increased 4°C in 30 years causing the rate of deglaciation to increase significantly in global high‐latitude river deltas. This will have a prolonged effect on local microbiome metabolism and biodiversity of the subsurface, influencing solid, liquid, and gaseous compounds in the system. Using sediment geochemical analyses, autonomous sampling techniques, and 16S rRNA gene sequencing, we have identified key processes that occur in the Copper River Delta, AK, a model system to study high‐latitude watersheds during rapid climate change. We calculated carbon accumulation rates upwards of 520 ± 60 g C m⁻² yr⁻¹ in outwash pond sediments nearest to the glaciers, which co‐occurred with pronounced suboxic peaks in Fe (III) and Mn (II). Sediment microbial communities across the outwash ponds are structured on the basis of total iron and manganese concentrations, proximity to glaciers, and organic matter content. Additionally, we revealed no methane accumulation in the ponds during ice‐cover, despite high organic matter content. High‐latitude wetland ecosystems are not only influenced by the changing climate, but also have the potential to impact carbon cycling considering high carbon burial rates. These findings show the importance of understanding changing biogeochemical processes in high‐latitude wetlands, as they have the potential to influence carbon cycling.

The University of Texas (UT), Genesis of Methane Hydrate in Coarse-Grained Systems: Northern Gulf of Mexico Slope Project (GOM2), will perform the UT-GOM2-2 drilling and coring expedition in the Terrebonne Basin, Gulf of Mexico outer continental shelf. This is the scientific plan for the acquisition, storage, analysis, and distribution of core and other collected samples for UT-GOM2-2. The UT-GOM2-2 expedition will sample and analyze the physical, chemical, and biological properties of the hydrate-bearing layers, thereby illuminating the origin, dynamic behavior, and response of this system to perturbation (whether by climate or energy production). A systematic measurement program will sample the hydrate-bearing layer from the seafloor downward. Novel technology, developed during the project, will be used to extract cores from a mile beneath the ocean and study those cores in laboratories worldwide, while keeping the samples under their original pressure. Samples taken near the seafloor will constrain the flux of carbon from the sediment into to the ocean and determine whether there have been recent temperature perturbations at the ocean floor. Through sampling of the microbes, and analysis of the surrounding pore fluid, we will illuminate the depths and rates at which microbes are generating methane beneath the seafloor. Our analysesmore » will inform biological, geochemical, and geomechanical models to constrain the role of gas hydrates in the carbon cycle and the potential for gas hydrates as an energy resource. We will drill and core two vertical wells to 9652 ft below sea level in the offshore Gulf of Mexico in Terrebonne Basin, Walker Ridge Block 313. We will spend 41 days at sea mobilizing, executing and demobilizing. We will spend an additional 18 days performing dockside analysis to complete the analysis of the recovered core. We will characterize the Orange sand and Upper Blue sand hydrate reservoirs and their bounding units, contrast hydrate reservoir properties at different structural levels within the Upper Blue dipping sand, characterize dissolved methane concentration and gas molecular composition with depth, measure the in-situ temperature and pressure profile, and determine the high resolution geochemical, geobiological, and sedimentary profiles in the upper 250 feet below the sea floor (fbsf). Pressure core and conventional core will be collected in two holes adjacent to previously drilled wells. We will use the DOE Pressure Coring Tool with Ball Valve (PCTB) to obtain pressure core. In the first hole, only pressure core will be acquired using the PCTB in the face bit configuration (PCTB-FB). In the second hole, conventional core will be collected using Geotek’s APC or XCB coring tool and pressure core will be collected using the PCTB in the cutting shoe configuration (PCTB-CS). In the second hole, temperature and pressure measurements will also be made. We will use the Geotek’s Pressure Core Analysis and Transfer System (PCATS) to log and X-Ray image the pressure cores. PCATS will also be used to subsample the recovered pressure cores at hydrate-stable conditions and to transfer samples to pressurized storage chambers. On-board and dockside, subsamples will undergo quantitative degassing to determine dissolved methane and hydrate concentrations. Pressure core in storage chambers will be transported to UT and stored at the UT Pressure Core Center (PCC) and other institutions. Conventional cores will be processed on board and dockside. On-board, conventional core will be run through a Geotek IR Scanner to create a thermal image to identify where hydrate dissociation had just occurred. Sections of conventional and depressurized core will be cut for microbiology, pore water analysis, and moisture and density analysis (MAD). Sections for pore water analysis will be squeezed and ephemeral pore water measurements will be completed on board. Preserved pore water samples will be shipped to the University of Washington (UW) for analysis. Microbiology samples will be sent to Oregon State University for analysis. MAD samples will be sent to Tufts University for analysis. The conventional and depressurized core will be CT 3D scanning, Geotek MSCL whole core logging, core splitting, split core scanning, primary litho- and biostratigraphy. Additional whole core samples will be cut for geomechanical testing after whole core scanning. Subsamples of split core will be shipped to the University of New Hampshire (UNH), UT, and others for secondary litho- and biostratigraphy. Split core archival and working halves will be placed in long term cold storage at UT. The Preliminary Expedition Report will be issued 2 months post-expedition. The Expedition Report will be published 1-year post-expedition. We are eager to support hydrate science by the broader community and requests for data and/or samples can be made to UT. « less

Biogeochemical processes capable of altering global carbon systems occur frequently in Earth’s Critical Zone–the area spanning from vegetation canopy to saturated bedrock–yet many of these phenomena are difficult to detect. Observation of these processes is limited by the seasonal inaccessibility of remote ecosystems, such as those in mountainous, snow- and ice-dominated areas. This isolation leads to a distinct gap in biogeochemical knowledge that ultimately affects the accuracy and confidence with which these ecosystems can be computationally modeled for the purpose of projecting change under different climate scenarios. To examine a high-altitude, headwater ecosystem’s role in methanogenesis, sulfate reduction, and groundwater-surface water exchange, water samples were continuously collected from the river and hyporheic zones (HZ) during winter isolation in the East River (ER), CO watershed. Measurements of continuously collected ER surface water revealed up to 50 μM levels of dissolved methane in July through September, while samples from 12 cm deep in the hyporheic zone at the same location showed a spring to early summer peak in methane with a strong biogenic signature (18O-H₂O and δ²H-H₂O isotopes from the water column exhibited similar patterns to discrete measurements, while samples 12 cm deep in the hyporheic zone experienced distinct fluctuations in δ¹⁸O-H₂O, alluding to significant groundwater interactions. Continuously collected microbial communities in the river in the late fall and early winter revealed diverse populations that reflect the taxonomic composition of ecologically similar river systems, including taxa indicative of methane cycling in this system. These measurements captured several biogeochemical components of the high-altitude watershed in response to seasonality, strengthening our understanding of these systems during the winter months.