Looking out at the rolling waves after another delicious dinner from the Atlantis galley crew, it occurred to me that I hadn’t been outside in about 36 hours. Describing what we’re doing out here as a “cruise” can be misleading; it involves early mornings, late nights, and no weekends off, because we have specific goals to meet. When the weather and technology cooperate, you take advantage of it, sleep or no. So, we have primarily spent the last couple of days in the Jason control van, preparing instruments in the ship’s laboratories, or analyzing water samples in the wet lab. Not exactly a pleasure cruise, but it’s still an extraordinary experience!
Leg 3 of the cruise has been particularly productive. It is only day 3, and we’re already at our third location, and have swapped out all of the cabled infrastructure at the Oregon Shelf Site, Oregon Offshore, and a portion of Southern Hydrate Ridge (a total of 22 instruments across all of the sites). Oregon Offshore was exciting, because it involved multiple quick dives in a relatively shallow location, to replace the benthic experiment package, a digital still camera, and recover an instrument for Clare Reimers (Oregon State University), who had deployed her equipment near the OOI sensors so that she could compare her data to the OOI data and increase the value of the experiment. It was also thrilling to see so many healthy Sun Stars (Solaster spp.), which had been almost absent from the site over the past few years, because they were decimated by sea star wasting disease.
After Shelf and Offshore, we headed to Southern Hydrate Ridge, a long-studied site where methane produced by microbes deep beneath the seafloor rises upward and (when it’s cold and deep enough) gets trapped in water crystals to form gas hydrate, a kind of methane ice. Huge outcrops of this strange material get pushed upwards by the gas pockets below, and eventually either dissolve in warmer waters (releasing the methane slowly) or break free from the seafloor and explode upwards in sudden ‘blowouts’. This is all happening in this site because a small tectonic plate (named the Juan de Fuca) is currently moving towards North America and being pushed underneath it, scraping all of the mud lying on top of the plate (and the associated methane reservoirs) into ridges that rise upward towards the sea surface. In short, it is a very active system that is constantly changing. In addition, the methane supports large numbers of chemosynthetic bacteria and clams, as well as sea stars, soft corals, crabs, snails, rockfish, flatfish, hagfish, and other organisms that gather around or attach to the rough topography of the site.
We’ll be at Hydrate Ridge for the next couple of days, doing surveys for methane bubble plumes and deploying new fluid samplers, cameras, seismometers, and sonar systems. The cameras and scanning sonar are useful for imaging bubble releases, which seem to be connected to daily tidal signals. Tides affect the pressure of the water column on the seafloor, so at high tide we see fewer bubbles than at low tide, which is a reminder of the enormity of the volume of water we are sitting above at this intriguing site.