Following two days of a force 9 storm with the RRS James Cook being thrown around by an angry sea, we resumed our position at a station to the North West of the Charlie Gibbs Fracture Zone at 03:00 GMT where the sediment traps were deployed on 01 August. We are now at the same latitude as Northern Scotland, at the end of the Reykjanes Ridge, an underwater lava sea mount that extends from the tip of Iceland and separates the North American and European tectonic plates.
Today saw a hive of activity; much to the relief of the scientists and crew after a few days of literally holding on!!!! Shortly after 03:00 the CTD (see Colin’s blog of 28 July for a description of the CTD) was deployed to 2.5 km depth so that Jane and Andy could characterise the dominant water types in this area from the temperature, salinity and oxygen profiles and from water samples collected at specific depths to determine the nutrient contents. This was followed by another three hour CTD at 06:00 at a station further to the North to not only look at the temperature, salinity and nutrients, but also to identify the dominant phytoplankton and to determine how much carbon they are fixing through photosynthesis. With the CTD still in the water, there was an optics cast at 08:30 to determine how much light the phytoplankton are absorbing during photosynthesis and how much they are scattering back to the sea surface which can be detected by satellites (see Williams blog of 30 July).
Shortly after lunch, the Southampton group lead by Alan Hughes deployed the MEGA-CORER. This instrument consists of a number of 10 cm diameter Perspex cylinders that are lowered onto the sea floor by a wire to collect sediment cores from the seabed. As the mega corer nears the seafloor, it is hydraulically dampened so as not to disturb the tiny benthic animals that live in the uppermost surface layer of the sediment, which would otherwise be disturbed and washed away. Once dampened, the instrument is activated automatically using a series of levers that thrust the Perspex tubes into the soft muddy substrate and then seals the tubes with a metal plate on the bottom and o ring on the top. This ensures that the mud does not fall out of the tubes when it is being hauled back onto the ship. The resulting cores can be anything from 20 to 30 cm deep. Today the sediment consisted of a 10 cm light brown top layer overlying dark brown and grey mud. Once back on board they are fixed in a preservative and stored for analysis back in the laboratory, which can take up to three months. Alan’s group are studying the abundance and diversity of Benthic Formanifera, single celled animals that live in the sediments that are formed from the raining down of detrital material from the upper ocean. There have been very few studies of these tiny creatures and with each mega-core there is a high chance of discovering new species.
Next to be launched from the deck at 15:00 were BATHYSNAP and PALANDER (described in Tom’s blog of 26 July). BATHYSNAP consists of a time lapse camera mounted on a stainless steel frame. The instrument is weighted to the sea floor with an iron anchor and is equipped with a series of buoys which carry it back to the surface when an acoustic release mechanism is activated. BATHYSNAP is left on the sea floor for one year, taking photographs every 12 hrs onto 35 mm Cinema film and records the seasonal changes on the sea floor. Instruments like this have revolutionised our understanding of how the deep oceans change over time and season.
Last, but by no means least, SHRIMP was deployed at 18:00. SHRIMP stands for Seafloor High Resolution Imaging Platform and was originally developed in the early 1990’s and has been updated at regular intervals since, most significantly with the addition of a fibre optic link giving scientists a real-time view of the seafloor. It is now part of the NMFSS deep platforms group lead by Ian Rouse, who is running it on this cruise. It consists of a very heavy duty stainless steel frame (approximately 1 meter high and wide and 3 meters long) loaded with very powerful high intensity lights (400w), underwater CCD colour video and photographic cameras which relay real time footage of life on the deep sea floor back to the scientists and crew through a fibre optic cable. As it was lowered through the water column, myriads of tiny copepods rushed past us like shining stars, skeletal jellyfish ambled by and the occasional fish darted from view. There was a moment of suspense at 200 metres from the bottom when something seemed to hit the instrument making the cameras shake and causing momentary loss of the lights and images. Ian fortunately managed to regain communications!! The instrument was suspended at 2.5 mts above the seafloor guided by Charlie, Bob and Steve, the Winch men who use a downward facing camera focused on a weighted target to guide the instrument as it is towed at 0.5 knots. The atmosphere on board was electric as we witnessed for the first time images 2.5 kms below us of the deep ocean floor on the Northern Mid Atlantic Ridge plateau. As the instrument neared the bottom it caused small plumes of sediment creating interest for the carnivorous Blue Hake and disturbing Snail fish and Rats tails. As it moved along the plateau and eventually down the slope of the ridge we saw Brittle Stars, Sea Cucumbers, Sea Urchins, Sponges and Grenadieres gliding past us. We spotted the elusive Dragon Fish (Bathyosaurus Ferox) which has an array of massive front teeth and lies in wait for unsuspecting prey. We also saw the Spiral Poo Worm, which until 3 years ago on a voyage to the same area, was only known in fossil records. The suspense and excitement in the scientists’ faces captured it all. The deep sea truly is an incredibly exciting and undiscovered world!!!!!
Plymouth Marine Laboratory, UK.