The goal of the Interagency Agreement between the National Energy Technology Laboratory and the Naval Research Laboratory is to conduct research to enhance understanding of the extent and dynamics of gas hydrate deposits and their relation to areas of focused fluid flux at and beneath the seafloor.

Marine Biogeochemistry Section, Naval Research Laboratory, Washington, DC 20375

Methane is a potent greenhouse gas necessitating a better understanding of the mechanisms controlling its contribution to the atmospheric carbon cycle. Active methane fluxes (from deep sediment hydrates and seeps) contribute to shallow sediment biogeochemical carbon cycles, which in turn modulate the methane flux to ocean waters and, ultimately, to the atmosphere. Currently, science largely focuses on methane-induced climate changes in the Arctic Ocean and tundra; however, a more thorough understanding of the Earth’s natural carbon cycle may be gained through other regional assessments. This task is a subset within a larger deep sea sediment gas hydrate research project. The task focuses on shallow sediment geochemical analysis across the Chatham Rise pock marks to analysis the influence of climate change on methane hydrate stability and subsequent vertical gas migration in a paleo-ocean environment. The study area is located east of South Island, New Zealand on the southwestern portion of the Chatham Rise where water depths range between ~500 and 1,100 meters. This region is influenced to the north by the Subtropical Front and to the south by Subantarctic Water. Sedimentation rates and composition vary in response to glacial-interglacial cycles. Geophysical and geochemical data interpretations will focus on the methane flux during the past interglacial period. In addition, data collected from this project will be used to evaluate the presence of petroleum and deep sediment methane hydrate deposits, contributing to current government supported exploration.

The University of Otago seismic data and IFM-GEOMAR multibeam profiles will be analyzed to target coring locations. Current and past vertical methane flux migrations evaluations include data interpretations of stable carbon, radiocarbon isotope, and methane in inorganic and organic sediments. Current day methane flux will be estimated through analysis of sediment pore water sulfate, dissolved inorganic carbon, and methane profiles. By comparing sediment radiocarbon data against sedimentation rates, the contribution of past deep sediment vertical methane flux to shallow sediment carbon will be evaluated.

Hydrate distribution and decomposition rates are important factors affecting oceanic methane concentrations, yet these parameters are not well characterized. Results of this research will lead to a better understanding of sediment methane geochemistry and help refine the Earth’s gas hydrate reservoir estimates. Geochemical data provided during this project will be used to determine the validity of current and past vertical methane fluxes in Chatham Rise pock marks as suspected from the seismic data. A combination of conservative age-dating and non-conservative radiocarbon data derived from piston cores will provide a 30,000 year timeline of the methane contribution to organic and inorganic sediment carbon. Further understanding of methane cycling during the past interglacial period will assist in interpretation of current and future global climate changes. Finally, data gained from this study will contribute to the New Zealand government’s assessment of coastal petroleum and methane hydrate deposits.

The Naval Research Lab (NRL) has completed piston and multi-coring at four sites on the Chatham Rise off the eastern coat of New Zealand. Coring was conducted during Leg 2 of the expedition from February 13 through 26, 2013, aboard the RV Sonne. In total, 37 cores were retrieved comprising a total length of 155 meters. Leg 2 included 22 scientists from New Zealand, Germany, and the United States. NRL’s contribution to this study included paleogeochemical assessment of the pockmark formations, estimation of organic and inorganic pools, and estimation of past and present methane flux in shallow sediments.

(May 2014)
The New Zealand Chatham Rise task has been completed.

$224,866 (current task) $1,227,895 (overall IA contribution)

Other U.S. Federal Government and international contribution: $50,000 (current task) $633,830 (overall IA contribution)

NETL – Robert Vagnetti (robert.vagnetti@netl.doe.gov or 304-285-1334)
Naval Research Lab – Rick Coffin (rcoffin@ccs.nrl.navy.mil or 202-767-0065)

Geochemical Cruise Report [PDF-4.58MB] Chatham Rise Expedition