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John Pohlman, PhD

John Pohlman is a Research Chemist with the Woods Hole Coastal and Marine Science Center Gas Hydrates Project.

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Image: Gas Hydrates Burning

U.S. Geological Survey Gas Hydrates Project

The USGS Gas Hydrates Project has been making contributions to advance understanding of US and international gas hydrates science for at least three decades. The research group working on gas hydrates at the USGS is among the largest in the US and has expertise in all the major geoscience disciplines, as well as in the physics and chemistry of gas hydrates, the geotechnical properties of hydrate...
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Natural Hazards Mission Area, Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center, Deep Sea Exploration, Mapping and Characterization
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U.S. Geological Survey Gas Hydrates Project

The USGS Gas Hydrates Project has been making contributions to advance understanding of US and international gas hydrates science for at least three decades. The research group working on gas hydrates at the USGS is among the largest in the US and has expertise in all the major geoscience disciplines, as well as in the physics and chemistry of gas hydrates, the geotechnical properties of hydrate...
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Area in northern Alaska where subsurface temperature and pressure conditions are conducive to the occurrence of gas hydrates

Gas Hydrates- Climate and Hydrate Interactions

The USGS Gas Hydrates Project focuses on the study of natural gas hydrates in deepwater marine systems and permafrost areas.  Breakdown of gas hydrates due to short- or long-term climate change may release methane to the ocean-atmosphere system. As a potent greenhouse gas, methane that reaches the atmosphere from degrading gas hydrate deposits could in turn exacerbate climate warming.
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Natural Hazards Mission Area, Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center
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Gas Hydrates- Climate and Hydrate Interactions

The USGS Gas Hydrates Project focuses on the study of natural gas hydrates in deepwater marine systems and permafrost areas.  Breakdown of gas hydrates due to short- or long-term climate change may release methane to the ocean-atmosphere system. As a potent greenhouse gas, methane that reaches the atmosphere from degrading gas hydrate deposits could in turn exacerbate climate warming.
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Hydrate Molecule

Gas Hydrates - Primer

What is Gas Hydrate? Gas hydrate is an ice-like crystalline form of water and low molecular weight gas (e.g., methane, ethane, carbon dioxide). On Earth, gas hydrates occur naturally in some marine sediments and within and beneath permafrost. Gas hydrates have also been inferred on other planets or their moons.
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Natural Hazards Mission Area, Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center
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Gas Hydrates - Primer

What is Gas Hydrate? Gas hydrate is an ice-like crystalline form of water and low molecular weight gas (e.g., methane, ethane, carbon dioxide). On Earth, gas hydrates occur naturally in some marine sediments and within and beneath permafrost. Gas hydrates have also been inferred on other planets or their moons.
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Water column properties and temporal hydrologic and chemical records from flooded caves (Ox Bel Ha and Cenote Crustacea) within the coastal aquifer of the Yucatan Peninsula, Quintana Roo, from December 2013 to January 2015

Natural cave passages penetrating coastal aquifers in the Yucatan Peninsula (Quintana Roo, Mexico) were accessed to investigate how regional meteorology and hydrology control dissolved organic carbon and methane dynamics in karst subterranean estuaries, the region of aquifers where fresh and saline waters mix. Three field trips were carried out in December 2013, August 2014, and January 2015 to ob
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Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center, Gas Hydrates Project Biogeochemistry Laboratory

Water column physical and chemical properties of Cenote Bang, a component of the Ox Bel Ha cave network within the subterranean estuary coastal aquifer of the Yucatan Peninsula, from December 2013 to January 2016

Subterranean estuaries extend inland into density-stratified coastal carbonate aquifers that contain a surprising diversity of endemic animals (mostly crustaceans) within a highly oligotrophic environment. How complex ecosystems thrive in this globally-distributed, cryptic habitat (termed anchialine) is poorly understood. The northeastern margin of the Yucatan Peninsula contains over 250 km of map
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Woods Hole Coastal and Marine Science Center

Comparison of methane concentration and stable carbon isotope data for natural samples analyzed by discrete sample introduction module - cavity ring down spectroscopy (DSIM-CRDS) and traditional methods

A discrete sample introduction module (DSIM) was developed and interfaced to a cavity ring-down spectrometer to enable measurements of methane and CO2 concentrations and 13C values with a commercially available cavity ring-down spectrometer (CRDS). The DSIM-CRDS system permits the analysis of limited volume (5 - 100-ml) samples ranging six orders-of-magnitude from 100% analyte to the lower limit o
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Natural Hazards Mission Area, Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center

Geochemical data supporting investigation of solute and particle cycling and fluxes from two tidal wetlands on the south shore of Cape Cod, Massachusetts, 2012-19 (ver. 2.0, October 2022)

Assessment of geochemical cycling within tidal wetlands and measurement of fluxes of dissolved and particulate constituents between wetlands and coastal water bodies are critical to evaluating ecosystem function, service, and status. The U.S. Geological Survey and collaborators collected surface water and porewater geochemical data from a tidal wetland located on the eastern shore of Sage Lot Pond
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Woods Hole Coastal and Marine Science Center

Vertical chemical profiles collected across haloclines in the water column of the Ox Bel Ha cave network within the coastal aquifer of the Yucatan Peninsula in January 2015 and January 2016

Natural cave passages penetrating a coastal aquifer in the Yucatan Peninsula (Mexico) were accessed to test the hypothesis that chemoclines associated with salinity gradients (haloclines) within the flooded cave networks of the karst subterranean estuary are sites of methane oxidation. Two field trips were carried out to the fully-submerged cave system located 6.6 km inland from the coastline in J
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Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center

Temporal hydrologic and chemical records from the Ox Bel Ha cave network within the coastal aquifer of the Yucatan Peninsula, from January 2015 to January 2016

Natural cave passages penetrating a coastal aquifer in the Yucatan Peninsula (Mexico) were accessed to investigate how regional meteorology and hydrology control methane dynamics in karst subterranean estuaries. Three field trips were carried out in January 2015, June 2015, and January 2016 to obtain year-long high-resolution temporal records of water chemistry and environmental parameters below a
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Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center

Data and calculations to support the study of the sea-air flux of methane and carbon dioxide on the West Spitsbergen margin in June 2014

A critical question for assessing global greenhouse gas budgets is how much of the methane that escapes from seafloor cold seep sites to the overlying water column eventually crosses the sea-air interface and reaches the atmosphere. The issue is particularly important in Arctic Ocean waters since rapid warming there increases the likelihood that gas hydrate--an ice-like form of methane and water s
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Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center
Infographic showing forest and storm overlying underwater cave. Arrow shows stormwater bringing oxygen into the cave as dissolved oxygen. Methane enters cave, oxygen supports the ecosystem and helps microorganisms break down food such as methane. Water flows through the cave, causing less methane to be released into the atmosphere
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Infographic showing forest and storm overlying underwater cave. Arrow shows stormwater bringing oxygen into the cave as disso
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Drawing of the Chesapeake Bay research vessel
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counterflow device capable of isolating and holding a single gas bubble link
Two men standing in front of laboratory equipment link
Aerial view of coastline, water, and sky
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divers deploy acoustic devices in centoes in the Yucatan Peninsula, Mexico
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Filter Total Items: 53

Oxygenation of a karst subterranean estuary during a tropical cyclone: Mechanisms and implications for the carbon cycle

Seasonal precipitation affects carbon turnover and methane accumulation in karst subterranean estuaries, the region of coastal carbonate aquifers where hydrologic and biogeochemical processes regulate material exchange between the land and ocean. However, the impact that tropical cyclones exert on subsurface carbon cycling within karst landscapes is poorly understood. Here, we present 5-month-long
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David Brankovits, John Pohlman, Laura Lapham
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Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center

Barkley Canyon gas hydrates: A synthesis based on two decades of seafloor observation and remote sensing

Barkley Canyon is one of the few known sites worldwide with the occurrence of thermogenic gas seepage and formation of structure-II and structure-H gas hydrate mounds on the seafloor. This site is the location of continuous seafloor monitoring as part of the Ocean Networks Canada (ONC) cabled observatory off the west coast off Vancouver Island, British Columbia, Canada. We combine repeat remotely
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M. Reidel, M. Scherwath, M. Romer, C. K. Paull, E. Lundsten, D. W. Caress, P. Brewer, John Pohlman, L. L. Lapham, N. R. Chapman, M. Whiticar, G. D. Spence, R. Enkin, K. Douglas
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Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center

USGS tools perform gas source analysis in the field

Field studies of gas hydrate rely on gas sampling and analysis tools to determine the origins and alteration of methane and other hydrocarbons. The conventional strategy for deciphering gas origins has been to collect gas and other related samples in the field then pack, ship, store, and later analyze these discrete samples in a laboratory using instruments that require specialized training and de
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John Pohlman, Michael Casso, Lee-Gray Boze, Emile Bergeron
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Woods Hole Coastal and Marine Science Center

Northern Cascadia Margin gas hydrates — Regional geophysical surveying, IODP drilling leg 311, and cabled observatory monitoring

This article reviews extensive geophysical survey data, ocean drilling results and long-term seafloor monitoring that constrain the distribution and concentration of gas hydrates within the accretionary prism of the northern Cascadia subduction margin, located offshore Vancouver Island in Canada. Seismic surveys and geologic studies conducted since the 1980s have mapped the bottom simulating refle
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Michael Riedel, Timothy S. Collett, Martin Scherwath, John W. Pohlman, Roy Hyndman, George Spence
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Energy Resources Program, Central Energy Resources Science Center

Contribution of deep-sourced carbon from hydrocarbon seeps to sedimentary organic carbon: Evidence from radiocarbon and stable isotope geochemistry

Sulfate-driven anaerobic oxidation of methane (AOM) limits the release of methane from marine sediments and promotes the formation of carbonates close to the seafloor in seepage areas along continental margins. It has been established that hydrocarbon seeps are a source of methane, dissolved inorganic carbon, and dissolved organic carbon to marine environments. However, questions remain about the
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Dong Feng, John Pohlman, Jorn Peckmann, Yuedong Sun, Yu Hu, Harry Roberts, Duofu Chen
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Woods Hole Coastal and Marine Science Center

Discrete sample introduction module for quantitative and isotopic analysis of methane and other gases by cavity ring-down spectroscopy

Carbon dioxide (CO2) and methane (CH4) are natural and anthropogenic products that play a central role in the global carbon cycle and regulating Earth’s climate. Applications utilizing laser absorption spectroscopy, which continuously measure concentrations and stable isotope ratios of these greenhouse gases, are routinely employed to measure the source and magnitude of atmospheric inputs. We deve
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John Pohlman, Michael Casso, Cedric Magen, Emile M. Bergeron
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Woods Hole Coastal and Marine Science Center

Metabolic flexibility of aerobic methanotrophs under anoxic conditions in Arctic lake sediments

Methane (CH4) emissions from Arctic lakes are a large and growing source of greenhouse gas to the atmosphere with critical implications for global climate. Because Arctic lakes are ice covered for much of the year, understanding the metabolic flexibility of methanotrophs under anoxic conditions would aid in characterizing the mechanisms responsible for limiting CH4 emissions from high-latitude reg
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Ruoying He, Jing Wang, John Pohlman, Zhongjun Jia, Yi-Xuan Chu, Matthew Wooller, Mary Beth Leigh
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Woods Hole Coastal and Marine Science Center

Ideas and perspectives: A strategic assessment of methane and nitrous oxide measurements in the marine environment

>In the current era of rapid climate change, accurate characterization of climate-relevant gas dynamics – namely production, consumption, and net emissions – is required for all biomes, especially those ecosystems most susceptible to the impact of change. Marine environments include regions that act as net sources or sinks for numerous climate-active trace gases including methane (CH4) and nitrous
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S.T. Wilson, A.N. Al-Haj, A. Bourbonnais, C. Frey, R.W. Fulweiler, John D. Kessler, H.K. Marchant, J Milucka, N.E. Ray, P Suntharalingham, B.F. Thornton, R.C. Upstill-Goddard, T.S. Weber, D.L. Arévalo-Martínez, H.W. Bange, H.M. Benway, D. Bianchi, A.V. Borges, B.X. Chang, P.M. Crill, D.A. del Valle, L. Farías, S.B. Joye, A. Kock, J Labidi, C.C. Manning, John Pohlman, G. Rehder, K.J. Sparrow, P.D. Tortell, T. Truede, D.L. Valentine, B.B. Ward, S. Yang, L.N. Yurganov
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Woods Hole Coastal and Marine Science Center

Focused fluid flow along the Nootka Fault Zone and continental slope, Explorer-Juan de Fuca plate boundary

Geophysical and geochemical data indicate there is abundant fluid expulsion in the Nootka fault zone (NFZ) between the Juan de Fuca and Explorer plates and the Nootka continental slope. Here we combine observations from > 20 years of investigations to demonstrate the nature of fluid-flow along the NFZ, which is the seismically most active region off Vancouver Island. Seismicity reaching down to th
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M. Riedel, K .M. M. Rohr, G. D. Spence, D. Kelley, J. Delaney, L. Lapham, John Pohlman, R.D. Hyndman, E.C. Willoughby
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Natural Hazards Mission Area, Woods Hole Coastal and Marine Science Center

Methane oxidation dynamics in a karst subterranean estuary

Chemical gradients between fresh, brackish and saline waters shape biogeochemical reactions and organic matter transformation within subterranean estuaries. In the Yucatán Peninsula’s karst subterranean estuary (KSE), methane and dissolved organic matter generated during the anaerobic decomposition of tropical forest vegetation are transported into flooded cave networks where microbial consumption
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David Brankovits, John Pohlman
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Woods Hole Coastal and Marine Science Center

India National Gas Hydrate Program Expedition 02 Summary of Scientific Results: Gas hydrate systems along the eastern continental margin of India

The primary objectives of the India National Gas Hydrate Program Expedition 02 (NGHP-02) were to obtain new data on the occurrence of gas hydrate systems and to advance the understanding of the controls on the formation of gas hydrate accumulations in the offshore of India. In accordance with the ultimate overall goal of the NGHP effort to assess the energy resource potential of marine gas hydrat
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Timothy S. Collett, Ray Boswell, William F. Waite, Pushpendra Kumar, Sandip Kumar Roy, Krishan Chopra, Sunil Kumar Singh, Yasuhiro Yamada, Norio Tenma, John Pohlman, Margarita Zyrianova
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Energy Resources Program, Central Energy Resources Science Center

Water salinity and inundation control soil carbon decomposition during salt marsh restoration: An incubation experiment

Coastal wetlands are a significant carbon (C) sink since they store carbon in anoxic soils. This ecosystem service is impacted by hydrologic alteration and management of these coastal habitats. Efforts to restore tidal flow to former salt marshes have increased in recent decades and are generally associated with alteration of water inundation levels and salinity. This study examined the effect of
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Faming Wang, Kevin D. Kroeger, Meagan Gonneea Eagle, John W. Pohlman, Jianwu Tang
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Natural Hazards Mission Area, Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center
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Storms Help an Underwater Cave Breathe in the Yucatan Peninsula, Mexico

New science shows that storms can provide an influx of oxygenated water into underwater caves, which supports the food web and enhances the biological...

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Anchialine Biogeochemistry Research Team returns to the Yucatan Peninsula, Mexico

The Anchialine Biogeochemistry Research Team has returned to the Yucatan Peninsula Mexico to continue investigating how life persists within...

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Life in Total Darkness–Investigating Underwater Cave Ecosystems

For more than 30 years, scientists have known that remarkably complex ecosystems thrive within underwater coastal caves, habitats that naturally...

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Mexico’s Yucatan Peninsula Reveals a Cryptic Methane-Fueled Ecosystem in Flooded Caves

In the underground rivers and flooded caves of Mexico’s Yucatan Peninsula, where Mayan lore described a fantastical underworld, scientists have found...

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Ocean Absorption of Carbon Dioxide More than Makes Up for Methane Emissions from Seafloor Methane Seeps

U.S., Norwegian, and German scientists report back on the surprising results of an Arctic Ocean research expedition. 

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