2011 J. Tuzo Wilson Lecture: Offshore gas hydrates

John Preece here, covering for Nicole while she’s away. Today I’m going to be talking about the J. Tuzo Wilson lectures, a series of (roughly) annual public presentations on excellence in geophysics. This year’s lecture was given at the University of Toronto by Professor R. Nigel Edwards, recipient of the 2010 J. Tuzo Wilson medal for outstanding contributions to Canadian geophysics.

John Tuzo Wilson is considered to be the founder of Canadian geophysics, and made important contributions to the (now universally-accepted) theory of plate tectonics (a big believer in interdisciplinary work, he also “greatly enjoyed disturbing other scientists”). Many endowments have been named in his honour, including the Canadian Geophysical Union‘s J. Tuzo Wilson medal (Wilson was the first recipient, in 1978) and the University of Toronto’s J. Tuzo Wilson Professorship in Geophysics (which Prof. Edwards has held since 2007).

Prof. Edwards was educated at Imperial College London and the University of Cambridge, and has held geophysics research positions in Canada, Japan and the USA. His J. Tuzo Wilson lecture was entitled, The assessment of offshore gas hydrate: Clean fuel for the 21st century?

Prof. Edwards’ talk focused principally on the need for good, reliable gas hydrate detection techniques. Methane hydrates (also called methane clathrates) consist of methane gas trapped in crystalline water, resulting in a soft, yellowish solid not unlike ice cream. They are only stable at relatively high pressures and low temperatures, and so are found on and just below the sea floor. They are of considerable interest to researchers because methane is a potent greenhouse gas – if sea temperatures rise too much due to climate change, the clathrates could collapse and release their methane into the atmosphere in a runaway feedback loop. It may also be possible to capture the methane and use it as a fuel (ideally on-site, sequestering the CO₂ produced back into the clathrates) – there is thought to be more carbon locked away in gas hydrates than in all other sources combined. This is where Prof. Edwards’ research comes in, as estimates for just how much hydrates there are vary by about a factor of 100.

Resource exploration outfits generally use seismic techniques to survey the sea floor and work out what might be there, but these methods cannot reliably detect gas hydrates. Prof. Edwards’ team uses a towed array to transmit an electromagnetic signal along the sea floor, and analyses the extent of electromagnetic diffusion to work out the resistivity of the different layers there. Electromagnetic signals travel fastest in layers containing gas hydrate, slower in normal sediment layers and slowest in sea water, allowing the detection and mapping of hydrate deposits. They tend to occur around subduction zones, where bacteria-produced methane is relased near the sea floor.

To close his lecture with a bit of showmanship, Prof. Edwards produced an actual methane clathrate sample, about the size of a lemon. A robotic submersible working on the sea floor at a depth of about 1.2 km had stirred an area of clathrate up, and the pieces had floated to the surface. A member of Prof. Edwards’ research team had then scooped them up with a net and preserved them in liquid nitrogen for later study, the sample in front of us being one of the pieces. After waiting a few minutes for the ice to warm up a little, Prof. Edwards unceremoniously set it on fire with a barbecue lighter, to general applause.

Prof. Edwards’ team is currently researching the Bullseye gas vent (off the coast of Vancouver Island) with NEPTUNE Canada, a regional-scale underwater observatory network.

All photographs in this article are courtesy of Roger Hallett.