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 May 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)

  • The Project Management Plan was submitted and approved.
  • 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.

Current Status (May 2017)
The project will complete contracting with the ship owner within the next month. The Principal Investigators will continue to refine laboratory protocols related to the accurate measurement of dissolved methane in seawater, the measurement of the radiocarbon content of that methane, and sea-to-air methane flux over a wide range of expected occurrences, in preparation for the field program, which is planned to occur by October, 2017.

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 – Ray Boswell, Project Manager (ray.boswell@netl.doe.gov or 412-386-7614)
The University of Rochester – Dr. John Kessler, Principal Investigator (john.kessler@rochester.edu)

Additional Information:

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