DOE/NETL METHANE HYDRATE PROJECTS
Characterizing Ocean Acidification and Atmospheric Emission Caused by Methane Released from Gas Hydrate Systems along the US Atlantic Margin Last Reviewed December 2017

DE-FE0028980

Goal
The primary objective of this project is to determine how methane seepage from the US Atlantic Margin (USAM) upper continental slope near the up-dip limit of gas hydrate stability affects ocean chemistry and sea-to-air greenhouse gas flux in three-dimensions and how this seepage interacts with oceanographic phenomena (e.g., southwardly flowing currents) to create hypothesized hotspots of decreased pH (i.e., acidification potential). A complementary objective is to collect physical data to constrain the location of the methane seeps, the height of plumes above the seafloor, the intensity of seepage, and the estimated volumetric flow rate of methane. Synthesizing the data required to meet these objectives will elucidate the sources and sinks for seep methane and track the flow of methane carbon through the ocean-atmosphere system once released at the seafloor.

Performers
The University of Rochester, Rochester NY
The U. S. Geological Survey, Woods Hole MA (through associated Interagency Agreement DE-FE0026196)

Background
Gas hydrate is known to exist widely within shallow marine sediments where ocean depths exceed ~500m. Gas hydrate that may occur along the landward edge of the zone of gas hydrate occurrence is particularly susceptible to destabilization in response to natural environmental changes, including changes in bottom water temperature. The methane emitted during destabilization can have a range of implications, including the potential transmission of methane to atmosphere, the conversion of methane to carbon dioxide in ocean waters, which may then be transmitted to the atmosphere and contribute to acidification of seawater.

In recent years, surveys of the Atlantic Margin have revealed the presence of numerous, previously-undocumented methane seeps in locations that appear to coincide with the landward edge of hydrate stability. This project will conduct targeted acquisition of field data during a 13-day research cruise from the UNOLS R/V Hugh R. Sharp to acquire water column samples and complete thorough surveys of sea-to-air greenhouse gas flux and seafloor gas emissions on the upper continental slope between Cape Hatteras and Wilmington Canyons. These data will then be analyzed to address the key questions related to the environmental impact of methane seeping from the margin near the up-dip limit of gas hydrate stability. The project will also continue to develop and refine laboratory procedures to help determine whether sampled methane was derived from recently-dissociated gas hydrate or was perhaps generated by another source.

Impact
The resulting data will 1) advance our understanding of the sources, source strengths, and distribution of methane emission from deepwater gas hydrate systems; 2) measure the concentration of methane near the seafloor and in the water column; and 3) assess the vigor of aerobic methane oxidation in ocean waters and the linked change in seawater buffering capacity and acidification along the edge of gas hydrate stability on the US Atlantic margin. The project will also characterize ocean currents that transport emitted methane and its byproducts southward toward Cape Hatteras; the amount of water column methane carbon derived from gas hydrate dissociation; and the emission intensity of methane derived from gas hydrate to the atmosphere.

Accomplishments (most recent listed first)

  • Completed a research expedition to collect data, seawater, and dissolved gas samples along the Atlantic continental shelf.
  • Evaluation of the suitability of the intended research vessel has been completed.
  • An ultra-high resolution technique has been established which enables the detection of isolated methane "hotspots" of emission from the surface waters to the atmosphere.
  • A technique to extract sufficient methane from surface water such that the natural radiocarbon content of that methane can be determined has been established.
  • The Project Management Plan was submitted and approved.

Current Status (November 2017)
Scientists from the University of Rochester and the USGS conducted a research expedition aboard the R/V Hugh Sharp from August 24, 2017 to September 7, 2017. The purpose of the expedition was to collect seawater and dissolved gas samples between Wilmington Canyon and Cape Hatteras, to constrain the amount of methane released from gas hydrate systems that reaches the atmosphere. In total, 5 transects running perpendicular to the continental slope were conducted between Cape Hatteras and Wilmington Canyon. Each transect contained 4 to 5 stations, sampling water from 12 different depths. In total, over 1,000 samples were collected. All data collected at sea (acoustic, high-resolution surface water CH4 concentration mapping, dissolved methane concentration, and high-resolution pH), are currently being investigated and interpreted.

In the coming months, the data and samples collecting during the research cruise will be analyzed. Specific analyses to be conducted are the natural radiocarbon content of methane and dissolved inorganic carbon (DIC), and δ13C-CH4. In addition to the analysis of these samples, the data collected at sea for [CH4], high precision pH of seawater, and the ultra-high resolution sea-to-air flux data will be processed and quality control/quality assurance analyses will be conducted.

Project Start: October 1, 2016
Project End: September 30, 2019

Project Cost Information
DOE Contribution: $797,607 (to U. Rochester)
Performer Contribution: $223,850 (U. Rochester)

Contact Information:
NETL – Skip Pratt, Project Manager (skip.pratt@netl.doe.gov or 304-285-4396)
The University of Rochester – Dr. John Kessler, Principal Investigator (john.kessler@rochester.edu)

Additional Information:

Quarterly Research Performance Progress Report [PDF] July - September, 2017

Quarterly Research Performance Progress Report [PDF] April - June, 2017

Quarterly Research Performance Progress Report [PDF] January - March, 2017

Quarterly Research Performance Progress Report [PDF] October - December, 2016