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.
The University of Rochester, Rochester NY
The U.S. Geological Survey (USGS), Woods Hole, MA (through associated Interagency Agreement DE-FE0026195)
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 University-National Oceanographic Laboratory System’s (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.
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 U.S. 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.
Scientists from the University of Rochester have completed an analysis of seawater and dissolved gas samples collected during a research expedition along the Atlantic Margin between Wilmington Canyon and Cape Hatteras. During the past quarter, researchers focused on interpretation of the data: 1) coordinating the sea-to-air flux with seafloor emissions; 2) fingerprinting the source of methane emitted from the seafloor and comparing that to the source of methane being emitted from the sea surface to the atmosphere; 3) determining the extent of aerobic methane oxidation in the water column; and 4) quantifying the influence that CO2, produced from aerobic methane oxidation, has on ocean acidification and inorganic carbon chemistry.
The USGS is continuing to compile all seep location data from this project’s cruise, as well as other cruises, to support the release of a preliminary updated seeps database to The National Oceanic and Atmospheric Administration’s Office of Ocean Exploration and Research.
Further work and revisions were conducted on four manuscripts prior to their submission to peer-reviewed scientific journals. In addition, two Ph.D. dissertations were submitted to the University of Rochester acknowledging support from this project.
The project ended on 09/30/2019. The project team is working on the final report
$797,607 (to University of Rochester)
$223,850 (University of Rochester)
NETL – Joseph Renk (email@example.com or 412-386-6406)
The University of Rochester – Dr. John Kessler, Principal Investigator (firstname.lastname@example.org)
USGS – Dr. Carolyn Ruppel, Principal Investigator (email@example.com or 617-806-6768)
Final Scientific/Technical Report [PDF]
OSTI Identifier: 1634089