DE-NT0005667

Goal
The goal of this project is to assess the efficacy of aerobic methanotrophy in preventing the escape of methane from marine, hydrate-bearing reservoirs to the atmosphere and ultimately to better define the role of aerobic methanotrophy in the global carbon cycle

Methane seeps with the resulting methane plume, Geophysical Research Letters, November 2007

Performers
University of California-Santa Barbara, Santa Barbara, CA 93106

Background
The global methane reservoir in the form of gas hydrate is estimated at 500- 10,000 Gt (KVENVOLDEN, 1995; MILKOV, 2004). This pool of carbon resides in permafrost/sub-permafrost and sub-seafloor settings. Neither the rates of methane generation / loss from the reservoir are known, nor is it known if the reservoir is currently growing, shrinking or at steady state. Evidence suggests that the hydrate reservoir has been unstable in the geologic past (JAHREN et al., 2001; THOMAS et al., 2002), and the reservoir is now considered as a capacitor on geologic timescales (DICKENS, 2003). Given the magnitude and potential instability of at least some portion of this reservoir, combined with the potency of methane as a greenhouse gas, it is critical to understand the natural processes that act to control the release of subsurface methane to the ocean and atmosphere.

One fundamental knowledge gap standing between methane hydrates and the carbon cycle at Earth’s surface is an understanding of the physical, chemical, geological and biological controls on methane release from the subsurface to the ocean and atmosphere. Physical, chemical and geological controls tend to trap or otherwise hinder methane transport from the subsurface, and are of primary importance in determining the magnitude, distribution and phase of subsurface methane reservoirs, as well as the flux of methane departing the subsurface toward the ocean and atmosphere (ETIOPE and KLUSMAN, 2002; ETIOPE and MILKOV, 2004). However, only methanotrophy (biological methane consumption) is known to destroy methane in the ocean and shallow subsurface, and the efficiency of this “methanotrophic biofilter” through space and time is a critical factor controlling how much subsurface methane ultimately reaches the atmosphere.

The potential impacts of methanotrophy in marine waters extend beyond the issue of methane transport to the atmosphere. The biological consumption of methane in the ocean is potentially an important process in the global carbon cycle in its own right, particularly at times of enhanced subsurface methane flux, as might be associated with broad hydrate destabilization. Methanotrophy not only removes methane, but also consumes O₂ and produces both CO₂ and abundant biomass (HANSON and HANSON, 1996). These processes have potentially far reaching consequences including contributions toward ocean anoxia (SLUIJS et al., 2007), ocean acidification (ZACHOS et al., 2005), and direct inputs of organic carbon to the deep ocean. In order to understand the linkage between methanotrophy and these factors, and how they might feed into the carbon cycle and broader earth system, it is critical to first understand the nature of the process and the associated controls.

A) Methanotroph-containing mat from Coal Oil Point, CA (COP), B) In-situ incubation of a methanotrophic mat at COP, C) Ongoing in-situ incubation of mats at Santa Monica Basin (SMB), D) Vein filling orange mats at the SMB methane seep, E) Mosaic of orange and white mats at SMB site, F) Methane hydrate was formed from an active seep at the SMB site-released here.

Potential Impacts
This project will provide insight into the relationship between the global carbon cycle and methane hydrate in regions of submarine methane hydrate occurrence and gas seepage. Results should create awareness of how benthic microbial communities impact the flux of methane from subsurface reservoirs to the ocean, and what organisms are involved, how active they are in several settings, and how they go about metabolizing methane. Results from both the closure of a basin-scale methane budget and identifying the factors that most impact the aerobic biofilters can potentially be fed directly into global carbon cycle models to predict what might happen to the carbon cycle if a period of large scale methane release into the oceans were to occur (i.e. gas hydrate dissociation).

Accomplishments
Project was initiated October 1, 2008. There are no technical accomplishments under the project to date.

Current Status
Project was awarded September 30, 2008 with a start date of October 1, 2008. The project is to be carried out over 3 years. Planned activity within the first year includes:

• Field Sampling of Microbial Mats from Coal Oil Point
• Calculation of methane turnover rate in microbial mats collected from Coal Oil Seep
• Initiation of Molecular Analyses of Methanotrophs
• Performance of Stable Isotope Probing of Coal Oil Point samples
• Shallow water sampling and current velocity measurements in Santa Barbara Basin
• Analysis of methane oxidation rates and methane turnover times throughout the Santa Barbara Basin
• Field Sampling in Santa Barbara Basin to determine primary controls on aerobic methane oxidation
• Sensitivity analyses of methane oxidations rates and turnover times

Project Start: October 1, 2008
Project End: September 30, 2011

Project Cost Information:
Phase 1 - DOE Contribution: $210,461, Performer Contribution: $80,642
Phase 2 - DOE Contribution: $178,460, Performer Contribution: $33,524
Phase 3 - DOE Contribution: $173,663, Performer Contribution: $29,262
Planned Total Funding (if project continues through all project phases):
DOE Contribution: $562,584, Performer Contribution: $143,428

Contact Information:
NETL – Traci Rodosta (Traci.Rodosta@netl.doe.gov or 304-285-1345)
University of California – Santa Barbara– David Valentine (Valentine@geol.ucsb.edu or 805-893-2973)

Additional Information

Project Kick-Off Presentation [PDF-4.69MB]

Technology Status Assessment [PDF-83KB]