Moorings, landers, and squid

It’s only been a week and a half since we left Panama behind, though we’ve accomplished a lot of science since then. As well as numerous CTD casts mentioned in the previous post, we’ve done almost as many VMP deployments (vertical microstructure profiler) which measure the turbulence in the water column, indicating the extent of water mixing. Additionally, we have deployed 5 semi-permanent moorings, which will measure the hydrography of the ocean for the next few months until collection on a different cruise, 12 MT (magnetotelluric) landers, and started our heat flow measurements. This goes to show that although this is a long cruise (at 6 weeks), time is absolutely of the essence. It’s very lucky to get so many days of sea time to do this research, and we must make the most of it.

Three of the moorings we deployed consist of a set of several instruments, connected in a long vertical array with a weight to keep them anchored to the seafloor. They are supported by buoyancy along the length of the chain, resulting in a floating set of instruments from the seabed to approximately 1500 m above it. These instruments include: 

- micro-CATs, which stands for Conductivity And Temperature (and doesn’t refer to small felines). These are like a smaller version of CTDs and give measurements of the salinity and temperature of the water. 

- Current meters, which measure the strength and direction of the currents throughout the water column. 

- And a bottom pressure recorder, which sits on the seabed at the base of the mooring and measures the pressure every minute, which can tell us about the changes in water depth over time, such as that caused by the tides.

Paul and John attaching an instrument to the mooring rope

The moorings are specially designed for their position to best measure changes in the hydrography of the water column, depending on what is already known about the location. Each length of rope or chain is measured and cut to the specific size long before the ship sails, and then the mooring is put together on deck as it is being deployed, piece by piece. Our first mooring was assembled in an incredibly heavy rain storm, with everyone assisting soaked through within 10 minutes, and staying that way until the last piece went over the side an hour and a half later. Naturally the rain stopped almost as soon as we had finished.

The bottom-pressure recorder and weight going over the side

The last two moorings were ADCP moorings, which stands for Acoustic Doppler Current Profiler. These float 50 m above their anchor on the seafloor and measure the currents in the water column using the Doppler Effect (from movement of particles in the water) to about 500 m above their position. With these, we hope to measure the flow of water into and out of the Panama Basin.

A quick wildlife update

For a few days, we had a blue-footed booby accompanying the Cook on its voyage. Christened Glinda, the bird settled on the aft-deck to oversee the mooring deployments, and obviously pleased with the crew's efforts, flew to the forecastle deck afterwards to sun herself. Glinda has sadly left us now, perhaps to oversee mooring deployments elsewhere.

We were also visited by a squad of squid during one of our CTD casts. They were hunting little whitebait-sized fish that were leaping out of the water, and you could see their tentacles reaching above the surface sometimes to try and grab them. 

Glinda, the blue-footed booby