How Much Methane Comes Out of The Seafloor

Tuesday, September 02, 2014
Mosquitos Installed on at a Methane Seep
Sampling Pore Fluids, Sediments, and Bacteria

A push core is taken with the ROV ROPOS adjacent to an OOI-RSN "Mosquito" flow meter built by E. Solomon at the University of Washington. The entrapped sediment, pore fluids, and bacterial mats were brought back to the ship for ship- and shore-based analyses. Photo credit: NSF-OOI/UW/CSSF; Dive R1772; V14.  

Measuring Methane At Southern Hyrate Ridge

An in situ, cabled mass spectrometer is installed at a methane seep at the summif to Southern Hydrate Ridge. The OOI-RSN mass spectrometer was built by Peter Girguis, Harvard University. The intake host is on a small tripod and the mass spectrometer is housed inside a titanium housing within a half-size junction box frame. It is installed adjacent to an instrument to measure fluid flow in and out of the seafloor (Mosquito) and an osmo fluid sampler for seep chemistry. Photo credit: NSF-OOI/UW/CSSF; Dive R1772; V14.  


We are currently working at Southern Hydrate Ridge getting ready to install the first underwater cabled mass spectrometer at this active methane seep. The past few days have been a whirlwind of activity, diving at both the EA Oregon Offshore site and Southern Hydrate Ridge. At the Oregon Offshore site, the ship- and shore-based personnel have been working hard to trouble shoot a couple of pieces of infrastructure there, and are continuing to narrow down the issue. At Southern Hydrate Ridge, we are very far along in the completion of both cabled and uncabled instruments at this site.

Over the past few days at Southern Hydrate Ridge, we have installed the digital-still camera, upward-looking ADCP that will measure currents, and three short-period seismometers on extension cables that range from ~400 m to 600 m in length. The seismometer locations form a triangular pattern on the seafloor so that we can obtain good locations for seismic events beneath the seep site. A broadband seismometer was deployed at the seafloor and awaits final placement inside a caisson enclosed by sediment, which was installed last year.

This morning we also installed a flow meter an an active seep, as well as an osmotic fluid sampler, and we recovered three flow meters that were tested at this site over this past year. They provide fluid chemistry, but also information on fluid flow both in and out of the sediments. These data will allow flux calculations to be made, which along with methane concentrations via the cabled mass spectrometer will provide constraints on the flux of methane out of the seafloor - an important measurement for many scientists working at seep environments. Methane flux to the overlying hydrosphere may impact the biology over the vent sites at much shallower depths than the seeps themselves, methane release rates may be impacted by seismic events as well as global warming (the methane-ice compounds are metastable and only a few degrees increase in temperature can cause increased methane release), and methane is a very powerful greenhouse gas. So, many different kinds of scientists have interest in this problem. Push cores were taken with the ROV to obtain chemistry on pore fluids. The cores also provided samples of the thick white bacterial (Beggiatoa) mats that characterize the active seeps.

We are blessed by sunny skies today with little wind, but weather is supposed to worsen later today, so we are working hard to get instruments to the seafloor. The students onboard are enjoying the food on the R/V Thompson, watches in the ROPOS control room, and are working hard on their science and outreach projects. A subset of students is working on obtaining wonderful images and video of all the sea creatures that live around the seeps and in the water column above Southern Hydrate Ridge, for distribution via the InteractiveOceans site. This should be a great resource for folks interested in deep-sea biology.