by Penny Holliday
This cruise is just one part of the international programme that is OSNAP. The cruise will provide a complete view of the circulation of the subpolar gyre for the time that we are at sea, but as we want to know how the ocean currents evolve over time we need to leave instruments in the water to measure them while we are not here. So as we near the end of our long cruise, other research vessels carrying more teams of scientists and technical experts are also sailing out into the North Atlantic. They are putting instruments including floats and moorings into the water at strategic points along the OSNAP line that we have been working all cruise.
Moorings are vertical lines of wire, anchored to the sea bed and held upright by air-filled spheres, with instruments to measure temperature, salinity and velocity placed at intervals along the wires. When we combine the data from all the moorings, floats and gliders (the OSNAP “array”) we will have a full record of the ocean currents at all depths through the subpolar North Atlantic. This has never been done before so it is a very exciting prospect.
Closest to us at the moment is the American ship the R/V Knorr which left Reykjavic in Iceland last Sunday. As I write this the US, UK and Dutch teams on the Knorr are laying moorings across the Reykjanes Ridge. From there they will follow us along the same track that we took, putting further moorings in the water in the Iceland Basin and eventually the Rockall Trough. I am swapping position updates with Stuart Cunningham who is on the Knorr, hoping that by some lucky chance the two ships will be able to see each other at some point. It is looking unlikely though; I think we will always be too far east of them to catch a glimpse.
We started our cruise working a CTD section across the Canadian shelf, and a couple of weeks ago a team from Canada on the CCGS Hudson laid some moorings on the shelf there. Our German partners had planned to place some moorings in deeper waters offshore from the Canadian moorings, but engine trouble on the German research vessel, Maria S. Merian has meant their work has been delayed.
Earlier in June the Knorr had been over in the Newfoundland Basin placing floats and their sound sources in the water there. The floats they released are rather different to the Argo floats I have written about. These are called “RAFOS” floats and unlike Argo floats that report their position at the surface every 10 days, RAFOS floats are continually recording their position underwater using the sound sources located on the seafloor.
The Knorr will be back over by Greenland to lay US and UK moorings in the Irminger Sea in August, and once they and the German team are finished, the full international OSNAP array will be in place though an enormous team effort. We then have to wait….. and wait…. until next year when we will come back again to recover our moorings, collect the data, and re-lay them for another year.
You can read more about RAFOS floats and our sister OSNAP cruises on the international OSNAP blog at www.o-snap.org/news-events/blog/
Images: So far we have done 195 CTD stations on JR302 (and 38 still to go!), here are just 4 of them in different conditions. You are looking at the starboard deck, facing forward, with the midships gantry extended out over the deck and holding the CTD wire away from the side of the ship. (all by Penny Holliday)