High Waves, Deep Methane

Tuesday, August 19, 2014
Crab at Southern Hydrate RIdge
Bubble plume on sonar

Bubble plumes above Southern Hydrate Ridge Summit as imaged by the R/V Thompson's sidescan sonar. These sonar surveys were used to plan CTD casts to sample for methane in the water column.

Photo Credit: Bob Collier, OSU

Soft Coral at Hydrate Ridge

A soft coral attached to hard substrate at Southern Hydrate Ridge, near Einstein's Grotto.

Photo Credit: NSF-OOI/UW/CSSF, Dive R1750, V14

When planning a scientific cruise, there are innumerable details to consider: lining up the correct personnel, procuring equipment, scheduling the vessel, buying supplies, packing and shipping everything, evenly loading the deck, mapping out the sites to be visited, writing up the plans and deployment procedures, etc. etc. etc. However, even with the most carefully designed and organized cruise schedule, there remains one vital ingredient that is completely outside of a chief scientist’s control: the weather. Without good weather, it is impossible to safely run deck operations, deploy an ROV, or complete most of the objectives of a research expedition.

That’s why it’s important to include a few activities that CAN be done in rough weather. On this expedition, that includes taking CTD casts (lowering sensors and remotely-triggered bottles on a wire from the ship to get samples from the water column), using the ship’s sonar to survey for bubble plumes (looking for backscatter signatures that reveal methane bubbles in the water column near seep sites), and, on marginally nice days, we can launch the ROPOS ROV without any heavy sensors or equipment on it to survey sites for future OOI infrastructure deployments.

Over the last few days we’ve done all three of those, while waiting for the weather to improve enough to do the activities that were higher on our priority list (like deploying the Slope Base seismometer and Deep Profiler mooring, and the Endurance Array two-legged mooring). We spent multiple nights doing hours of water sampling and one extremely long sonar survey, and ROPOS Dive 1750 went to Hydrate Ridge, an area where methane gas naturally bubbles out of the sediment, forming gas hydrate (a crystalline structure of water ice that forms around methane molecules under high pressure/low temperature conditions) and fueling a chemosynthetic ecosystem including mats of methanotrophic bacteria, clams with bacterial symbionts, and animals that graze on both of them (sea stars, soft corals, crabs, rockfish, eelpouts, and hagfish, among others). It was exciting to see such a strange assemblage of creatures, and the site appeared to have changed significantly since the last time the VISIONS expedition had surveyed the site. This was probably due to explosive gas venting or gas hydrate destabilization, where large chunks of hydrate “ice” break free from the sediment and float up into the water column, leaving a circular pockmark behind.

The weather appears to be improving, so hopefully we can make more progress towards the main goals of the cruise, but we’re getting a lot done in the meantime, and learning more about the strange deep-sea communities at Hydrate Ridge and the methane that feeds them.