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Research cruise to the Celtic Sea

7th July 2008 - Week 2

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Cruise Diary - Week 2

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.

Sunday 13th July 2008

The calmest day yet. We finished a very successful 25 hours of profiling with the VMP turbulence instrument (about 280 profiles in total), and then deployed Scanfish to run a repeat circuit around this site off the bank. After piecing together all of the evidence for where fishing gear might be, it was decided to end the circuit at 2100 by making 2 long passes over the top of the bank. With Scanfish in the water everyone spent the day working in the labs. We have also set up a series of talks by the scientists to both explain what they do and to present any results that are emerging from this cruise. Mark Inall, from SAMS, gave us a presentation on why he likes to inject rhodamine dye into the thermocline - even though the first experiment was largely unsuccessful because of the problems we had with Scanfish, what it did show us has proved to be thought-provoking enough to make change some of our sampling plans.

		At 2100 we began the Scanfish tow over the bank, fingers crossed that we had an accurate picture of where any fishing gear might be. The picture to the left - Mark Inall shows us how the rhodamine dye patch changed after it was injected into the thermocline
The Queen Mary II passes us, doing about 25 knots on her way to Southampton

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Saturday 12th July 2008

The weather continues to get better. Today we are working a station away to the east of Jones Bank, looking for contrasts in the physics and biology that might help us identify the role of the bank. At 0300 we began a 25 hour station with POL's free-fall turbulence profiler. The profiler has had some modifications made to it since we had the cable snagging problems in the rough weather a few days ago - some delicate work with an angle-grinder, a length of hosepipe, and a large amount of gaffer tape has removed most of the likely catch points. As a result we had a virtually flawless series of profiles all day, every 5 minutes covering from the sea surface to the seabed. The seabed camera has also gone out again. Inigo had some problems with it on the last deployment, but the POL engineers seem to have a nose for jobs that need doing and Chris Balfour appears to have fixed the problems with the camera. We'll see when the camera is retrieved tomorrow morning.

POL scientists Matthew Palmer and Eleanor Howlett in the deck laboratory at the control and data acquisition computer for the VMP turbulence profiler.		The VMP turbulence profiler at the sea surface. The brush provides drag to slow the instrument as it drops to the seabed. Note the addition of the hosepipe to protect the first couple of metres of the cable from snagging on the profiler

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Friday 11th July 2008

The main event today was a concerted attempt to find out where the rhodamine dye, that we pumped into the thermocline a couple of days ago, has gone to. Scanfish had been fixed by the National Marine Facilities engineers, so we started to tow it in a grid search to see if we could find the dye. And we did! It was very dispersed, but we spent 7 hours mapping its distribution with Scanfish - considering the small patch we had put into the sea, the dye has now spread into an elongated patch about 5 km long, still within the thermocline. It has also drifted eastward off the bank, probably in response to the NW'ly winds we have had. We still have some dye left on the ship, so we plan to try this experiment again in a few days - hopefully this time without catching Scanfish on any fishing gear.

It feels like we have got into a decent stride now. The calmer weather makes all activities much easier, and the labs are full of people working through samples and data as it come aboard. It looks like we are getting some good initial results - more of that tomorrow when I get some decent plots of them.

Scientists from the Scottish Association for Marine Science working on the biochemistry of some of the water samples in the ship’s chemistry laboratory		The ship's main lab.

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Thursday 10th July 2008

Just as things were looking like they had settled into a nice routine with the calmer weather. I woke up to find a notice from Mark Inall pinned to my door. According to Mark the good news was that we had successfully mapped the dye patch just after midnight. The bad news was that just as the mapping survey was finishing, Scanfish got caught on something - possibly fishing gear, we don't know. After what Mark described as a "pretty hairy recovery" Scanfish was brought back aboard. The cable was badly damaged, which means 24 hours at least to cut the cable and re-terminate it to Scanfish. We filled the morning by running a few echo-sounder lines over Jones Bank to increase our knowledge of the bathymetry. Then we put Inigo's seabed camera down again at another mooring site, followed by putting our temperature-chlorophyll chain out and towing it round the 3 Bank mooring sites and out to the mooring on the flat seabed to the east. This became quite a convoluted course as we had to give a wide berth to some long gill nets put out by a fishing vessel late yesterday, uncomfortably close to one of our (well-marked!) moorings.

Inigo's first deployment of the camera has produced lots of seabed photos. Almost all of the pictures are obliterated by dense clouds of suspended material in the water probably because of the strength of the spring tidal currents - an interesting result, but not what Inigo was hoping for. There were a few clear images. A few small fish, and perhaps surprisingly a few large nephrops (Dublin bay prawns). The deployment of the camera today should give us more images of what fish are around here as the sediments at the new site are much coarser and the currents are reducing towards neap tides.

The seabed camera is recovered onto the aft deck.		Inigo Martinez (University of Aberdeen) removing the camera from the frame so that he can download the images.
An image from the seabed at a depth of 120 metres on the flank of Jones Bank. The large weights that hold the camera over the seabed are visible, along with a couple of hermit crabs and a nephrops (Dublin Bay prawns) investigating the bait on the weights.

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Wednesday 9th July 2008

After successfully running round the racetrack between the 3 moorings, the MVP was recovered at 0200 and we got ourselves positioned on one of the mooring sites ready for the pre-dawn CTD profile. At 0430 we began the CTD, followed by a series of other sampling including bongo nets to catch zooplankton and another set of seabed grabs and cores. The cores were remarkably unsuccessful. We were only 4 miles from the last coring site, where we collected decent sets of mud cores, but here the seabed is coarse sand and the corer simply can't get through it. We then headed back to the seabed camera that we had left on the seabed yesterday, and quickly recovered it.

Scanfish is recovered back onto the ship after the first successful trial		Mark Inall and John Beaton (Scottish Association for Marine Science) unroll the hose as it is deployed down to 35 metres to inject the dye into the thermocline.
		Picture left - For some reason (probably because it was the first sunny evening we have had on the cruise) the dye release activity attracted quite an audience. The big success today was our first use of the Scanfish towed profiler. A bit like the MVP in use, the Scanfish flies up and down through the water as it is towed behind the ship, continuously sending data back to us along the tow cable. We tested Scanfish for a few hours, then recovered it to get ready for the first of the two planned dye release experiments. Mark Inall and John Beaton (Scottish Association for Marine Science) and Claire Neil (Strathclyde University) have been preparing a large tank of rhodamine dye on the aft deck. This evening they injected the dye into the thermocline at 35 metres depth. The plan is to use a sensor on Scanfish to map the spreading of the dye patch 3 or 4 times over the next 48 hours. This will give us one of the more challenging parameters in ocean physics - the rate at which turbulent eddies disperse material horizontally.

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Tuesday 8th July 2008

A pleasant surprise this morning - I looked out of my cabin window and could not see any whitecaps on the waves. Finally the wind speed had dropped below 15 knots, and all day we have made excellent progress with our repeated circuit survey using the moving vessel profiler (MVP). Considerable excitement amongst the physicists at one point when we noticed that the fisheries echo sounder was providing superb images of breaking internal waves on the edge of the bank, probably the same structures that gave us the high turbulence we measured the other night. With the weather calmed down significantly all work is much easier, so a relatively relaxed day for people working in the labs. The only signs of tension was with the operators of the MVP, as they watch the instrument plummet towards the seabed each time to be snatched back just in time and hauled back to the surface by the winch. This kind of repeated circuit in invaluable for building up a series of pictures of how the water changes during the tide, and it would be impossible to carry out in the sort of weather we had been experiencing up until yesterday afternoon. Hopefully, if all continues to go well, we will have covered the whole circuit 12 times by 0200 tomorrow.

The ships navigation screen, showing the repeated circuit stretching over the 3 mooring positions on the bank.		An example of the fisheries echo sounder output, showing large internal waves over the edge of some steep bathymetry. The reddish curve is the seabed. The waves are visible on the boundary between the deep water (full of sound scatterers such as zooplankton) and the much clearer surface layer
		The picture to the left shows Jeff Benson and Dave Teare, from National Marine Facilities, cope with the tension of operating the MVP. The weather forecast looks unpleasant again. At least force 7, possibly a gale, meeting up with us tomorrow. The good side of that is that the forecast suggests it might drop away a lot quicker than the last gale we had - so we are all clinging on to that prediction.

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Monday 7th July

Very heavy swell during the night, causing cable snagging on the turbulence profiler that is deployed over the stern of the ship. Eventually this led to a small cut in the cable, stopping communication with the computer, so the profiler work had to stop so that we could remove the bad section of cable. While the weather got a little better, with winds dropping below 20 knots for the first time in 4 days, the profiler continued to have problems and we eventually had to stop using it completely in the afternoon.

But other things are going well! The turbulence profiler gave us some great results last night, indicating a period of 30 minutes or so when there was very high turbulence within the thermocline. Looking at the fisheries echo sounder at the same time showed that a series of large waves were moving along the thermocline - exactly the sort of thing we are looking for. POL's new temperature-chlorophyll sampling chain was recovered successfully, and it has worked well (thanks to a large extent to the nifty little quick-release clamps that POL engineer Dave Jones designed for us). The biochemists are all busy working through the samples they have collected from either the CTD water sampling or from the seabed cores. Overnight we will be trying out a couple of so far unused instruments. First we plan to deploy a seabed camera. Operated by Inigo Martinez from the University of Aberdeen, the camera takes a picture of fish on the seabed (attracted by bait attached to the camera frame) every minute. This tells us both what species of fish are around and when during the day (or the tide) they are active. Once the camera is deployed we hope to try the "moving vessel profiler" - a CTD system that is repeatedly dropped towards the seabed and hauled back to the surface as the vessel is under way.

POL engineers and ships crew recover loggers from the temperature-chlorophyll chain as it is winched back aboard the ship.		Morton Larsen, a biochemist at the Scottish Association for Marine Science, works in the constant temperature laboratory, measuring the microbe activity in the seabed sediment samples. This laboratory is kept at the same temperature as the seawater near the seabed, about 11 degrees C

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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.