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Research cruise to the Celtic Sea

21st July 2008 - Week 4

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Cruise Diary - Week 4

POL scientist Jonathan Sharples is leading a research cruise to the Celtic Sea that aims to understand how the physics of different parts of the ocean lead to changes in the numbers of fish. Dr Sharples will be writing a cruise diary which will posted here. Another of the scientists on the cruise will be writing a blog which can found at - cmarhab.blogspot.com. For more information about the cruise read below.

Friday 25th July 2008

We sailed over the edge of the continental shelf today. The physics at the shelf edge is responsible for driving large amounts of nutrients into the Celtic Sea, so we wanted to get some nutrient information to provide the boundary for our work in the Celtic Sea. It was a fabulously calm, sunny day, so observing dolphins, whales, and sunfish became a key activity. Even a fire alarm doesn’t empty a ship’s lab faster than a message that a whale has been spotted ahead of us.

Our final CTD profile was in the NE Atlantic, in a water depth of almost 3000 metres. This is a real novelty for shelf-sea oceanographers as we are used to working in less than 200 metres depth. But then we quickly realise just how long it takes to get a CTD from the surface to the seabed and back in such deep water (a CTD is lowered typically at 1 metre per second); the novelty wears off rapidly. The last sampling at this deep site finished at 2200. We then deployed Scanfish for a tow all the way back onto the shelf, through the Celtic Sea, and over the top of Jones Bank. Tomorrow we are due to berth in Falmouth at 0900.

Scientists gather for a reported whale sighting ahead of us.		The ship's echosounder trace as we cross the edge of the continental shelf. It looks like we went over a cliff, but remember that the plot is considerably compressed. The whole length of the plot represents about 18 nautical miles (33 km).

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Thursday 24th July 2008

		After a slow but uneventful night towing the "Crystal Sea" we met the St Mary's lifeboat at 0900 just off the Isles of Scilly and handed the tow over. The fishing boat was towed into harbour, where they got a diver to help them untangle a virtually new trawl net from the propeller. There are lots of these discarded "ghost" nets in the sea – it was sheer bad luck that the "Crystal Sea" caught one, though some compensation in that it was a useable net. We left them and headed rapidly back to Jones Bank, arriving back at the site of one of the moorings by about 1600. This was the mooring we had all the difficulty with yesterday; within 20 minutes we had contacted it, released it, and it was floating on the sea surface ready for us to pick it up. Quite a relief. Once it was safely on board we set off for the final mooring site, and all of that was successfully retrieved by 1930. We immediately set off south to visit 3 final sites near the shelf edge. The timetable is now getting a bit tight. We have dropped several measurement sites on the way to the shelf edge because of the time taken out to tow the fishing boat. With fairly conservative estimates of the ship's speed I reckon we can make these last 3 sites and then tow Scanfish all the way back into the Celtic Sea and over Jones Bank; we are due at the Falmouth pilot at 0800 on Sunday. Picture left - A seabed current meter lander is brought alongside the ship ready to be pulled aboard.
The St Mary's lifeboat meets us ready to take over the tow.

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Wednesday 23rd July 2008

Our final turbulence station finished at 0700, and we began what we expected to be a full day of mooring recoveries. All of the current meters and temperature loggers that we moored to the seabed when we first came out 3 weeks ago have to be retrieved. Things went quite well initially, with everything from the flat site away from the bank and from the NE end of the bank recovered. Then we had some problems with the seabed lander + current meter halfway up the bank. There is an acoustic release on the lander that allows us to send acoustic codes to it and find out where it is. The signals we were getting back were patchy and made very little sense. Having watched the photos from Inigo's seabed camera at this site, we suspect that the lander has been at least partially covered in mud and is having difficulty in hearing us. We decided to head for the final mooring, and come back later for another try. However, our trawler buddy "Crystal Sea" had got her propeller seriously fouled by some drifting fishing gear - the boat was adrift. We immediately headed for the "Crystal Sea" to help, and in the evening passed a couple of tow ropes across and began towing them back to the Isles of Scilly.

The surface buoy of one of the moorings is hauled back onto the ship.		Towing the "Crystal Sea" begins.

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Tuesday 22nd July 2008 - An exciting day!

Flat, almost mirror-calm sea today. And quite an eventful day. The "Crystal Sea", a trawler out of Newlyn and working on this project with us, met us early morning and began fishing. The data from this will be invaluable, telling us which species are found over and away from the bank. About 1130 we heard that the Crystal Sea, while fishing close to one of our moorings, was getting quite a bit of attention from another trawler who clearly didn’t want the Crystal Sea on "his patch". While trying to cut close in front of the Crystal Sea the other trawler neatly picked up our seabed current meter and frame (clearly marked by a surface buoy). He was not very happy, judging by what was heard on the radio, and eventually cut the frame free and dumped it back into the sea. We were able to recover it OK. The Crystal Sea, initially still being harassed by an apparently testosterone-fuelled trawler, went back to fishing for us. After all this had settled down, but shortly afterwards the crewman on the Crystal Sea damaged his hand badly while hauling in their nets; we went to sit by them in case they wanted some medical help, and very soon after that a Royal Navy helicopter arrived and picked the crewman off to take him back ashore. Just as the helicopter left a group of 20 dolphins appeared around us. Finally we made it to the off-bank site, deployed the seabed camera, and began our final station with the turbulence profiler.

A Royal Navy helicopter moves in the take the crewman off the Crystal Sea.

A common dolphin, one of a group of 20 or so that spent some time playing around our ship.

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Monday 21st July 2008

The day began with a pre-dawn CTD profile and water sampling on top of the bank, so that meant the labs were very busy. We started a second go at a 25 hour turbulence profiler station at a site we tried in the first week of the cruise. This is a spring tide repeat, also with a remarkable contrast in the weather. In the first week we were struggling to work in force 6/7 and a heavy swell, while today the winds dropped below 5 knots, the sea was flat calm, and it even felt hot standing outside on the deck. In the afternoon the aft hatch cover was littered with scientists taking breaks from their lab work for a lie in the sun. The turbulence profiling will carry on until mid morning tomorrow. We are hoping to see another bout of strong mixing driven by internal waves. Compared to the first visit here there was no clear evidence of this by the end of the day, so we could be looking at a situation that is sensitive to both the state of the tide and the weather.

The CTD returns to a lovely clear, blue sea surface.		Scientists soaking up a bit of sun between experiments..

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More about the cruise

POL scientist Dr Jonathan Sharples and the Royal Research Ship James Cook preparing to depart for the Celtic Sea

POL scientist Jonathan Sharples is leading a research cruise that aims to understand how the physics of different parts of the ocean lead to changes in the numbers of fish. A team of 26 scientists, technicians and engineers from POL, Scottish Association for Marine Science, the University of Aberdeen, and the Joint Nature Conservation Committee will be sailing aboard the Royal Research Ship James Cook to the Celtic Sea. They will be deploying instruments on the seabed for measuring the physics and biology of the region, and analysing waters samples in the ship's laboratories. Physicists in the science team will be measuring the turbulence caused by tidal currents. The biologists then want to understand how that turbulence affects the phytoplankton (single-celled plants in the ocean and form the base of the marine food chain) and ultimately controls where the fish, marine mammals, and seabirds go to feed.

"ith so many scientists, covering everything from the fundamental physics, through the phytoplankton, and up to the fish, seabirds, whales and dolphins, this is the most complex and ambitious research cruise I've been involved in" said Jonathan Sharples of POL. "If all the science instruments work well, and the weather is kind to us, we expect to gain some exciting and novel understanding of how the marine ecosystem responds to changes in the physical environment".

The ship is due to depart from the National Oceanography Centre in Southampton on July 3rd, and the research cruise will finish on July 27th.

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Notes

The Proudman Oceanographic (POL) scientific research focuses on oceanography encompassing global sea-levels and geodesy, numerical modelling of continental shelf seas and coastal sediment processes. This research alongside activities of surveying, monitoring, data management and forecasting provides strategic support for the wider mission of the Natural Environment Research Council.

As a public funded body it is part of our remit to inform the public of the science and research undertaken at the laboratory. Attending events like the 'Ocean Awareness Weekend' at the Blue Planet Aquarium offers the opportunity for our scientists to meet members of the public and present the laboratory's work.

The Natural Environment Research Council is one of the UK's eight Research Councils. It uses a budget of about £ 350m a year to fund and carry out impartial scientific research in the sciences of the environment. NERC trains the next generation of independent environmental scientists. It is addressing some of the key questions facing mankind, such as global warming, renewable energy and sustainable economic development.