|Characterizing the Response of the Cascadia Margin Gas Hydrate Reservoir to Bottom Water Warming Along the Upper Continental Slope
||Last Reviewed 5/27/2014
The goal of this project is to investigate the response of the Washington margin gas hydrate system to the contemporary warming of bottom water along the upper continental slope.
University of Washington – Seattle, Washington
This up-slope limit of hydrate stability represents one of the most climate-sensitive boundaries for the global hydrocarbon reservoir. Compared to other climate-sensitive gas hydrate accumulations—including those associated with thinning Arctic permafrost—continental slope hydrates are located in close proximity to actively circulating seawater. This close physical association promotes hydrate dissociation over relatively short timescales (i.e., periods of tens of years vs. 100s to 1000s of years for other climate-sensitive deposits) in response to modest seawater warming at intermediate depth. Documenting the vulnerability of these hydrates to ocean warming and quantifying the fate of methane during transit through the sediment and water column are high priorities and have implications for the global ocean-atmosphere inventory of greenhouse gases. This hydrate-derived flux could contribute to ocean acidification and hypoxia through microbial oxidation of methane, initiate large-scale collapse of continental slopes producing coastal tsunamis, and increase the emission of methane-derived CO2 from the ocean to the atmosphere.
This project focuses on the upper limit of gas hydrate stability along the Washington segment of the Cascadia margin. The Washington margin has been the focus of an impressive array of recent scientific initiatives and programs including Earthscope, the Plate Boundary Observatory, the Ocean Observatories Initiative, GeoPRISMS, the ARRA Cascadia Initiative, as well as several large National Science Foundation research projects including the COAST 2-D multi-channel seismic (MCS) survey on the R/V Langseth in 2012, the Johnson/Solomon heat flow and fluid flux experiment on the R/V Atlantis off Grays Canyon in August 2013, and multiple ocean bottom seismic deployments in 2012, 2013, and 2014. Because of this high level of scientific activity, many of the parameters associated with the distribution and stability of methane hydrates are already well-characterized making the Washington margin a rich target area to examine the response of methane hydrate to environmental changes.
Washington margin bathymetry map identifying key sites. Yellow circles are methane plume sites. Numbers next to plumes are the water depth of the emission sites. Yellow dashed box is the R/V Langseth MCS survey that identified large areas of BSRs (Holbrook et al., 2012). Broad yellow line is schematic trackline for the planned 2014 expedition following 500 m contour. Blue boxes are areas for detailed CTD, water sampling, and coring sites.
This project constitutes one of the first field programs outside the Arctic focused primarily on the response of a methane hydrate system at the upper limit of gas hydrate stability to environmental change. This detailed study of gas hydrate and methane dynamics in a mid-latitude margin, one that is highly susceptible to the warming of bottom water, is relevant to current research priorities that have been identified by the gas hydrate science community on the response of methane hydrate systems to climate change. Understanding this response to climate forcing, and quantifying the flux and sinks of methane associated with these hydrate occurrences, is important for constraining the significance of methane/gas hydrate dynamics to the global ocean-atmosphere system and how this process contributes to hypoxia and ocean acidification.
- Compiled all relevant and available multi-channel seismic (MCS) profiles, swath bathymetry, high-resolution CTD temperature profiles, and acoustic backscatter data on the WA margin.
- Compiled sediment core archives from legacy coring programs on WA margin for determining sediment lithology in order to provide guidance regarding the distribution and partitioning of the sediments into turbidites and pelagic sediments.
- Converted MCS data to P-wave Velocity (Vp) vs. depth profiles for estimating sediment porosities.
Current Status (May 2014)
The University of Washington is currently using lithology and estimated sediment porosity data to convert seismic velocities and structural components into a plausible thermal conductivity model. In collaboration with Oregon State University, the University of Washington is conducting 2-D modeling of conductive heat flow to simulate the change in temperature distribution in the shallow sediments at the upper limit of gas hydrate stability resulting from the warming intermediate-depth water. Preliminary results indicate that, averaged over the entire region, the temperature at the upper limit of gas hydrate stability displays a constant and significant warming trend off the WA margin over the last 40 years. Results of modeling using long-term bottom water temperature series data also shows the influence of the Pacific Decadal Oscillation at the upper limit of gas hydrate stability. These early modeling efforts will be used to help guide systematic geophysical and geochemical surveys along the upper continental slope of the WA margin during a field program scheduled in October 2014.
Project Start: October 1, 2013
Project End: September 30, 2016
Project Cost Information:
Phase 1 – DOE Contribution: $360,808, Performer Contribution: $200,000
Phase 2 – DOE Contribution: $270,161, Performer Contribution: $0
Planned Total Funding:
DOE Contribution: $630,969, Performer Contribution: $200,000
NETL – Robert Vagnetti (Robert.Vagnetti@netl.doe.gov or 304-285-1334)
University of Washington – Dr. Evan Solomon (firstname.lastname@example.org or 206-221-6745)
University of Washington – Dr. H. Paul Johnson (email@example.com or 206-543-8474)
Research Performance Progress Report [PDF-472KB] January - March, 2014
Research Performance Progress Report [PDF-473KB] October - December, 2013