Last night the weather was still too rough for pelagic fishing, so we were not able to get the samples we hoped for. Nevertheless we were able to get some nice acoustic results using the EK60 mentioned in the last blog, logging data until 0600 this morning.
The PAL Lander was successfully recovered, with new information and pictures from the ridge. The lander is a baited tripod with a downward facing camera (the casing along costs ₤ 30000,- ), taking picture (see photo) every minutes for 12/24 hours. The oceanlab team is currently analysing the pictures. This concluded the work on the SE station.
We then steamed to the SW station, which was today’s study site. Since the weather has cleared up, the Plymouth crew (Gavin Tilstone and Victor Martinez) were able to collect satellite imagery of the western ridge (see previous posted cross-section). Two US satellites and one European are currently detecting the reflectance of sunlight from the surface of the sea. A part of the light is reflected or absorbed by phytoplankton. The PML optic group compare these images to data from CTD transects (the CTD rosette, which measures salinity, temperature, and depth, was sent to 1600 m and took two hours to get back to the surface!) and from the optic profiler. The optic profiler measures the absorption, backscatter, attenuance of light by phytoplankton. There is also a sensor at the bow of the ship that is taking optical measurements to validate the satellite data. This knowledge is used by PML to map primary productivity over the globe.
At 1644 a permanent mooring, consisting of two sediment traps, a current meter and an acoustic release, was deployed at 2500 m, and will for the next year record data on deep sea currents and the contribution of surface productivity to the sea floor.
At 1830 the acoustics team will start another EK60 survey, in order to prepare for this night’s fishing. The weather will hopefully be calm enough for us to fish with a RMT (rectangular midtwater trawl), which is designed to open and close, in order to sample a discrete depth range. Combining this technique with the information collected with the EK60, we will thus be able to describe the main proponents of the pelagic realm. The Perg team is waiting in anticipation for the chance to get some samples!
Tom Bech Letessier, PhD student,
PERG, St Andrews