Marshall W. Bowles

Marshall W. Bowles
Louisiana Universities Marine Consortium

PhD

About

33
Publications
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Publications

Publications (33)
Article
Humanity's search for extraterrestrial life is a modern manifestation of the exploratory and curious nature that has led us through millennia of scientific discoveries. With the ongoing exploration of extraterrestrial bodies, the potential for discovery of extraterrestrial life has expanded. We may better inform this search through an understanding...
Article
Full-text available
Plain Language Summary The search for extraterrestrial life has long captured our collective imagination, but it is hindered by the difficulty of actually visiting extraterrestrial planets, moons, asteroids, etc. to search for life. An alternative strategy is to remotely analyze the atmospheres of these planets to look for trace gases that exist in...
Chapter
Microorganisms catalyze elemental cycling in the ocean and regulate geochemical processes that are crucial for the maintenance of planetary habitability. This chapter provides an overview of marine carbon, oxygen, nitrogen, phosphorus, sulfur, and trace gas cycling with an emphasis on modern processes in pelagic and sedimentary habitats. Microorgan...
Article
Documenting anaerobic microbial metabolisms in hypersaline perennially ice‐covered lakes in Antarctica further refines the environmental limits to life and may reveal rare biogeochemical mechanisms and/or novel microbial catalysts of elemental cycling. We assessed rates of sulfate reduction, methanogenesis, and anaerobic oxidation of methane using...
Article
Full-text available
Anaerobic oxidation of methane (AOM), a central process in the carbon cycle of anoxic environments, moderates the release of methane from soils and sediments to water bodies and, ultimately, the atmosphere. The regulation of AOM in the environment remains poorly constrained. Here we quantified AOM and sulfate reduction (SR) rates in diverse deep se...
Article
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Previous evidence suggests enhanced pyrite oxidation on exposed continental shelves during glacial phases of low sea level. While pyrite oxidation directly consumes atmospheric oxygen, acid generated by this reaction should increase the release of CO2 through carbonate dissolution. This scenario represents a climate control loop that could temper o...
Article
Lake Vanda is a permanently ice‐covered lake in the McMurdo Dry Valleys of Antarctica. Its bottom waters remain stratified year‐round because of a strong salinity‐driven density gradient. We have assessed spatial patterns in and relationships between major biogeochemical processes in the water column of Lake Vanda. Samples were collected in the aus...
Article
Full-text available
Marine sediments host an unexpectedly large microbial biosphere, suggesting unique microbial mechanisms for surviving burial and slow metabolic turnover. Although dormancy is generally considered an important survival strategy, its specific role in subsurface sediments remains unclear. We quantified dormant bacterial endospores in 331 marine sedime...
Article
Methylated amines and sulfides are ubiquitous organic nitrogen and sulfur compounds in the marine environment and could serve as important energy substrates to methanogens inhabiting anoxic sediments. However, their abundance and isotopic values remain largely unconstrained in marine sediments. In this study, we investigated the distribution of tri...
Article
The microbial communities thriving in deep-sea brines are sustained largely by energy rich substrates supplied through active seepage. Geochemical, microbial activity, and microbial community composition data from different habitats at a Gulf of Mexico brine lake in Alaminos Canyon revealed habitat-linked variability in geochemistry that in turn dr...
Article
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The Integrated Ocean Drilling Program (IODP) Expedition 337 was the first expedition dedicated to subseafloor microbiology that used riser-drilling technology with the drilling vessel Chikyu. The drilling Site C0020 is located in a forearc basin formed by the subduction of the Pacific Plate off the Shimokita Peninsula, Japan, at a water depth of 11...
Article
Lake Fryxell, McMurdo Dry Valleys, Antarctica contains a constantly cold water column and perennial ice-cover. Although carbon and sulfur cycling in this amictic lake have been studied previously, a paired investigation of 16S rRNA gene based microbial diversity and geochemistry of Lake Fryxell is lacking. Here, we used a combination of radiotracer...
Article
We collected 69 sediment cores from distinct ecological and geological settings along the deep slope in the Northern Gulf of Mexico to evaluate whether specific geochemical- or habitat-related factors correlated with rates of microbial processes and geochemical signatures. By collecting replicate cores from distinct habitats across multiple sites,...
Article
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Microbial life inhabits deeply buried marine sediments, but the extent of this vast ecosystem remains poorly constrained. Here we provide evidence for the existence of microbial communities in ~40° to 60°C sediment associated with lignite coal beds at ~1.5 to 2.5 km below the seafloor in the Pacific Ocean off Japan. Microbial methanogenesis was ind...
Article
The anoxic sediments of the White Oak River (WOR) estuary comprise a distinctive sulfate-methane transition zone (SMTZ) and natural enrichment of the archaea affiliated with the Miscellaneous Crenarchaeota Group (MCG). Archaeal biphytanes were generally depleted in 13C, with δ13C values being less than -35‰, indicative of production by active sedim...
Article
Sulfate reduction is a globally important redox process in marine sediments, yet global rates are poorly quantified. We developed an artificial neural network trained with 199 sulfate profiles, constrained with geomorphological and geochemical maps to estimate global sulfate-reduction rate distributions. Globally, 11.3 teramoles of sulfate are redu...
Article
Nitrogen (N2 ) fixation was investigated at Mound 12, Costa Rica, to determine its spatial distribution and biogeochemical controls in deep-sea methane seep sediment. Using (15) N2 tracer experiments and isotope ratio mass spectrometry analysis, we observed that seep N2 fixation is methane-dependent, and that N2 fixation rates peak in a narrow sedi...
Article
Full-text available
We measured potential nitrate removal and denitrification rates in hydrothermally altered sediments inhabited by Beggiatoa mats and adjacent brown oil stained sediments from the Guaymas Basin, Gulf of California. Sediments with Beggiatoa maintained slightly higher rates of potential denitrification than did brown sediments at 31.2 ± 12.1 versus 21....
Technical Report
Integrated ocean Drilling Program (IODP) Expedition 337 was the first expedition dedicated to subseafloor microbiology that used riser drilling technology. IODP drill Site C0020 is located in a forearc basin formed by the subduction of the Pacific plate off the Shimokita Peninsula at a water depth of 1180 m. Seismic profiles strongly suggested the...
Article
A robust and convenient method was developed to evaluate rates of microbial activity in gas-charged deepsea sediments at in situ hydrostatic pressure, temperature, and gas concentration. The method used a hydrostatic chamber to maintain high pressures of 50 bar and greater, and a modified Hungate tube and plunger to contain samples. This technique...
Article
We investigated coupling between sulfate reduction (SR) and anaerobic oxidation of methane (AOM) by quantifying pore water geochemical profiles, determining rates of microbial processes, and examining microbial community structure at two sites within Mississippi Canyon lease block 118 (MC118) in the Northern Gulf of Mexico. Sediments from the north...
Article
Microorganisms and the processes they mediate serve as the metabolic foundation of cold seeps. We characterized a suite of biogeochemical constituents and quantified rates of two key microbial processes, Sulfate Reduction (SR) and Anaerobic Oxidation of Methane (AOM), to assess variability between habitats at water depths exceeding 1000 m in the no...
Article
Full-text available
We measured denitrification and nitrate removal rates in cold seep sediments from the Gulf of Mexico. Heterotrophic potential denitrification rates were assayed in time-series incubations. Surficial sediments inhabited by Beggiatoa exhibited higher heterotrophic potential denitrification rates (32 μM N reduced day(-1)) than did deeper sediments (11...
Article
Nitrous oxide is a potent atmospheric greenhouse gas that contributes to ozone destruction. Biological processes such as nitrification and denitrification are thought to drive nitrous oxide production in soils, which comprise the largest source of nitrous oxide to the atmosphere. Here we present measurements of the concentration and isotopic compos...
Article
Full-text available
Many of the world's productive deepwater hydrocarbon basins experience significant and ongoing vertical migration of fluids and gases to the modern seafloor. These products, which are composed of hydrocarbon gases, crude oil, formation fluids, and fluidized sediment, dramatically change the geologic character of the ocean floor, and they create sit...
Article
Recent investigations at the Pito Deep collected on the order of 80,000 electronic still images of rock outcrop in the upper oceanic crust formed at the ultra-fast spreading EPR. Using Alvin and Jason II during 9 long (>2km) Jason II transects and 12 Alvin dives, the images cover an area of > 200,000 meters squared. Jason II was equipped with a hig...
Article
The SMARK region is approximately 100 km south of the Kane Transform on the Mid-Atlantic ridge (MAR). The region is noteworthy for its west-facing Eastern Median Valley wall (EMVW), a 2300 m-high seismically active fault scarp that exposes the upper 1-2 km of
Article
Project (B.S.)--James Madison University, 2003. Includes bibliographical references.