Natural methane leakage from the seafloor is far more widespread on the U.S. Atlantic margin than previously thought, according to a study by researchers from Mississippi State University, the U.S. Geological Survey, and other institutions.
Methane plumes identified in the water column between Cape Hatteras, North Carolina and Georges Bank, Massachusetts, are emanating from at least 570 seafloor cold seeps on the outer continental shelf and the continental slope. Taken together, these areas, which lie between the coastline and the deep ocean, constitute the continental margin. Prior to this study, only three seep areas had been identified beyond the edge of the continental shelf, which occurs at approximately 180 meters (590 feet) water depth between Florida and Maine on the U.S. Atlantic seafloor.
Cold seeps are areas where gases and fluids leak into the overlying water from the sediments. They are designated as cold to distinguish them from hydrothermal vents, which are sites where new oceanic crust is being formed and hot fluids are being emitted at the seafloor. Cold seeps can occur in a much broader range of environments than hydrothermal vents.
“Widespread seepage had not been expected on the Atlantic margin. It is not near a plate tectonic boundary like the U.S. Pacific coast, nor associated with a petroleum basin like the northern Gulf of Mexico,” said Adam Skarke, the study’s lead author and a professor at Mississippi State University.
The gas being emitted by the seeps has not yet been sampled, but researchers believe that most of the leaking methane is produced by microbial processes in shallow sediments. This interpretation is based primarily on the locations of the seeps and knowledge of the underlying geology. Microbial methane is not the type found in deep-seated reservoirs and often tapped as a natural gas resource.
Most of the newly discovered methane seeps lie at depths close to the shallowest conditions at which deepwater marine gas hydrate can exist on the continental slope. Gas hydrateis a naturally occurring, ice-like combination of methane and water, and forms at temperature and pressure conditions commonly found in waters deeper than approximately 500 meters (1640 feet).
“Warming of ocean temperatures on seasonal, decadal or much longer time scales can cause gas hydrate to release its methane, which may then be emitted at seep sites,” said Carolyn Ruppel, study co-author and chief of the USGS Gas Hydrates Project. “Such continental slope seeps have previously been recognized in the Arctic, but not at mid-latitudes. So this is a first.”
Most seeps described in the new study are too deep for the methane to directly reach the atmosphere, but the methane that remains in the water column can be oxidized to carbon dioxide. This in turn increases the acidity of ocean waters and reduces oxygen levels.
Shallow-water seeps that may be related to offshore groundwater discharge were detected at the edge of the shelf and in the upper part of Hudson Canyon, an undersea gorge that represents the offshore extension of the Hudson River. Methane from these seeps could directly reach the atmosphere, contributing to increased concentrations of this potent greenhouse gas. More extensive shallow-water surveys than described in this study will be required to document the extent of such seeps.
Some of the new methane seeps were discovered in 2012. In summer 2013 a Brown University undergraduate and National Oceanic and Atmospheric Administration Hollings Scholar Mali’o Kodis worked with Skarke to analyze about 94,000 square kilometers (about 36,000 square miles) of water column imaging data to map the methane plumes. The data had been collected by the vessel Okeanos Explorer between 2011 and 2013. The Okeanos Explorer and the Deep Discoverer remotely operated vehicle, which has photographed the seafloor at some of the methane seeps, are managed by NOAA’s Office of Ocean Exploration and Research.
"This study continues the tradition of advancing U.S. marine science research through partnerships between federal agencies and the involvement of academic researchers,” said John Haines, coordinator of the USGS Coastal and Marine Geology Program “NOAA's Ocean Exploration program acquired state-of-the-art data at the scale of the entire margin, while academic and USGS scientists teamed to interpret these data in the context of a research problem of global significance."
The study, Widespread methane leakage from the sea floor on the northern US Atlantic Margin, by A, Skarke, C. Ruppel, M, Kodis, D. Brothers and E. Lobecker in Nature Geoscience is available on line.
USGS Gas Hydrates Project
The USGS has a globally recognized research effortstudying natural gas hydrates in deepwater and permafrost settings worldwide.USGS researchers focus on the potential of gas hydrates as an energy resource, the impact of climate change on gas hydrates, and seafloor stability issues.
For more information about the U.S. Geological Survey’s Gas Hydrates Project, visit woodshole.er.usgs.gov/project-pages/hydrates/.
DNV Wants Increase Focus on Plastic Deg
Contracts Awarded in New Generation Ocea
WOC Sustainable Ocean Summit Charts Cour
CSA Holds Ocean Sciences Innovations Wor
New Technology for Harvesting Energy fro
Ocean Power Technologies Announces Award
Western Indian Ocean Earthquake and Tsun
Scientists Discover New Marine Life in A
Gateway Technology Emerges for Critical
The Birth of the Atlantic Ocean
A World of Ocean Research Awaits RV Inve
Polarstern Expedition Team Departs for t
Reef Subsea Dredging & Excavation Comple
Ocean Sonic’s Launches icTalk Smart Pro
Ocean Sonics Celebrates World Oceans Day
Ocean Alliance New Headquarters in Glouc
Makai Ocean Engineering Receives Prestig
Ocean Specialists Inc. Achieves Major
Ocean Power Technologies Demonstrates So
World Authority Leads Ocean Energy Resea
CSA Ocean Sciences Inc. Mobilizes for 31
CHOIRS: Characterization of Hazardous Oc
NSF Awards Grant to Measure Changes in O
CSA Ocean Sciences Inc. Launches GeoSpat
World Ocean Systems Undermined by Climat
World Ocean Council Organizing Ocean Bus
Ocean Power Technologies Awarded $2.6 Mi
Lockheed Martin and Reignwood Group sign
First Ocean Energy Company Joins World O
CSA Ocean Sciences Inc. Educates at Hous
Marine Conservation Institute Announces
Speedcast Expands Its Global Maritime VS
Maine Marine Composites Wins Federal Gra
MAKAI Awarded $3.6M to Continue Work on
Dr. Michele Halvorsen Joins CSA Ocean Sc
New Generation of Micro Sensors for Moni
Respiratory Disorder in the Ocean
NOAA Announces Regulations to Protect Ma
WOC Working to Ensure Ocean Industry Inp
The Role of the Ocean for Climate Change
CSA Ocean Sciences Inc. Awarded Gulf of
Indian Ocean Phenomenon Helping to Predi
Kongsberg Maritime Delivers First Set of
Ocean Drilling Support Office Honors Scr
Chelton Receives 2013 Award for Achievem
Willard Marine Wins Contract for 42 Sola
Science Team Member Describes U.S. Arcti
NOAA: Coastal Ocean Aquaculture can be E
Greenhouse Gas Measurements in the Ocean
Taubman Foundation Invests in Ocean Drug
Ocean Networks Selects Xtera for the Tu
Global Ocean Commission Welcomes Carol B
Global Ocean Commission Welcomes Carol B
Keppel Offshore and Marine Joins World O
Keeping an Eye on the Indian Ocean
Is There an Ocean Beneath our Feet?
OceanGeo Receives Ocean Bottom Seismic C
World Ocean Council Partners with the Ec
Bio Robots Make a Splash in the Indian O
First Offshore Wind Project Proposed for
Industry Input Sought in Setting U.S. Oc
Ocean Sonics Ltd. to Launch icListen AF
Marlink Helps French Ocean Research Team
CSA Ocean Sciences Inc. Project Wins Pre
Unstable Atlantic Deep Ocean Circulation
First animals oxygenated the ocean, stud
Smart Ocean / Smart Industries for Canad
National Oceanography Centre Wins €1.8 M
Florida State University: Researchers Fi
Corals Track Strongest Indian Ocean Curr
Planet Ocean Ltd Announces the Selection
New 3D Atlas Makes Trace Metals in the O
WOC to Convene Business Forum on Ocean P
Greater Atlantic Region Expected to Rece
CSA Ocean Sciences Inc. to Continue Long
Deep Ocean Current May Slow Due to Clima
ClassNK Establishes Department of Ocean
NRDC: Milestone in Ocean Noise Fight (Ma
UCSB Researchers Create First Regional O
SCF Partners Invests in Seanic Ocean Sys
Demand Grows for new Generation Ocean Ro
Ocean Sonics Announces New Partnerships
Inquisitive Students Meet with Scientist
Scientific Mission Will Explore One of t
Smart Ocean / Smart Industries for Canad
CSA Conducts Benthic Habitat Surveys for
Private Sector Participation in Stakehol
UGA Research Examines Fate of Methane Fo
The Red Sea - An Ocean Like All Others,
Ocean Sonics Welcomes Industry Partner f
Ocean Industries Engage In EU Maritime P
ASL Builds Custom Acoustic Instrument fo
Ocean Sonics Officially Opens the First
Ocean Sonics Officially Opens the First
A Snapshot of our Nation’s Scientific Oc
Cell Simplicity Betters Complexity in Su
CSA Ocean Sciences Partners with CENTRE
FAU Signs Lease to Install World’s Firs
OceanGeo Receives Ocean Bottom Seismic C
ASL to Build an Ocean Data Geoportal for
Ocean News & Technology is a publication of TSC
7897 SW Jack James Drive
Suite A, Stuart, FL 34997
(772)-221-7720