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Research cruise to the Celtic Sea

14th July 2008 - Week 3

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Cruise Diary - Week 3

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 20th July 2008

Our spring tide repeat of the Scanfish survey around the mooring at the "flat" site, away from the bank, began at 0500. The weather was a bit lumpy, with the ship steam beam on the a moderate swell. This gradually decreased during the day. On alternate legs of the circuit the aft hold hatch was covered in scientists trying to catch a bit of sunshine before heading back into the labs and their experiments. A trawler appeared in the morning and began to work in the same area as us. This irritated the observers; the trawler acted as a seabird magnet, attracting all birds within a radius of about 6 km and fundamentally wrecking the seabird component of the survey. Still, we have been lucky on this cruise, with far fewer fishing vessels that the last time I was out here.

We broke off the circuit at 2020 and towed Scanfish back towards the bank along the line that we surveyed with the CTD and grab yesterday. Tomorrow will be our first turbulence station since neap tides.

Another of the more common birds that we see: fulmers.		A sunfish, photographed by Clare Embling while she was trying her skills in seabird observing. The Sunfish is a strange fish, with a large chubby body and tiny fins it seems to flop about at the sea surface rather than make any serious efforts at swimming.

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Saturday 19th July 2008

The last of the dye surveys finished at 0100 this morning, and it looks as though it has been a remarkable success. A key finding from the dye experiments is the consistent average flow southeastward from the bank. That means that any impact that the internal mixing has on the bank will then be pushed away to the southeast. Bearing that in mind we spent the rest of the day running a transect line of CTD profiles and sediment grabs from 12 miles northwest of the bank, over the top of the bank, to 12 miles southeast. Our aim with those is to see if we can detect any "before" and "after" effects of the bank within the water or within the seabed sediments. The end of the day saw us running some echo sounder lines over the "flat" site to the east of the bank. This site was chosen because the chart suggests it is devoid of any significant bumps in the seabed. However, we have picked up one or two string mixing events there so we want to run some extra bathymetry surveys just to see how flat or bumpy the site really is.

Nick Owen, from Trinity College Dublin, takes his bucket of seabed mud from the Day grab. Nick is analysing the mud to see what small creatures are living in it..		A gannet, one of the more common birds we are seeing out here. The gannet is a diving seabird. It looks for fish while flying 10-15 metres above the sea surface, then plunges into the water to depths down to 20 metres to catch fish.

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Friday 18th July 2008

We carried out the 3rd and 4th dye patch surveys today. Mark and Claire have worked out that we can use the tide to move the patch past us as we continuously Scanfish along one transect line. There is always a bit of tension initially as we try to pick up the edge of the patch, but then we settle into a routine of tracking. The resulting course we follow can look very convoluted. The dye release results have been very interesting, showing a consistent average easterly drift away from the bank. This has made us reassess our planned sampling strategy. A new station has been added to our work, on the west of the bank "upstream" of the average flow. Between the 2 dye surveys today we deployed the seabed camera at this new station. All of the biochemistry, within the water and the sediments, will be carried out there tomorrow morning. It looks like the weather might worsen briefly; we are expecting a force 6 possibly 7 tomorrow.

The ship's track over the 2 dye patch surveys today. The distance between the mooring sites MS1 and MS2 is about 8 km. The dye was originally injected into the thermocline early yesterday morning.		Romain Pete, from the Scottish Association for Marine Science, checking the deck incubators. These tanks hold bottles of seawater, incubated under different light intensities, and later analysed to assess how fast the phytoplankton were growing

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Thursday 17th July 2008

The second release of rhodamine dye took place in the morning at 0200. Not quite a smoothly as the first release - some residual dye left in the hosepipe escaped onto the ship as the pipe was recovered, so there are a couple of people walking around with very pink hands today. We carried out two surveys of the expanding dye patch, one shortly after its release and one about 12 hours later. The survey involves towing Scanfish in lines near the buoy that was thrown in with the dye. Scanfish has an fluorometer that identifies rhodamine down to remarkably low concentrations; once the patch is identified we tow Scanfish through it several times, mapping the patch size.

Mark Inall (SAMS) and Claire Neil (Strathclyde University) keeping an eye on the real-time Scanfish data as they attempt to find the rhodamine dye patch.		Scanfish has a 90 kg weight attached to it in order to profile vertically to collect calibration data.
		In the time between the dye surveys we calibrated Scanfish. Calibration is vital if we are to be able to present our results consistent with accepted international standards. Calibrating the CTD is relatively straightforward; sample bottles on the CTD rosette are used to collect water, which is then analysed (e.g. for salt, chlorophyll, dissolved oxygen) in the laboratories. The analysis of the water samples allows us to correct the data from the instruments on the CTD. Scanfish does not have sample bottles, so instead we carried out two CTD casts, and between them lowered Scanfish vertically over the stern of the ship. I can then use the calibrated CTD data to correct the instruments on Scanfish. A laborious task, but vital if we are to have confidence in the results. Picture left - Matthew Palmer (POL) takes advantage of a bit of sunshine at the same time as working through turbulence data from the recent turbulence profiler stations.

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Wednesday 16th July 2008

No early morning calls today; Scanfish behaved perfectly overnight, and ran throughout the rest of today without a hitch. By 1700 we had completed our 25 hour circuit over the bank, running round the circuit 12 times over a total distance of 192 nautical miles. The "birders" were sat in their wooden boxes forward of the bridge during daylight, and were disappointed to see very few birds. Potentially an interesting result though. We recovered the seabed camera again at the end of the Scanfish circuit - 2 conger eels this time, and both larger than the one we saw a couple of days ago. Once the camera was inboard we began a series of seabed grabs and cores, and bongo net hauls for zooplankton at a site on the NE edge of the bank. That took us to almost midnight, when preparations for our 2nd (and last) dye-tracking experiment began.

		The megacorer is prepared for an evening of coring the seabed. Coring the bank is proving to be a bit of a lottery. The corer can collect samples if the seabed is muddy, but fails completely if it’s sandy. Jones Bank seems to be an unpredictable patchwork of sand and mud.
Our first decent sunset of the cruise.

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Tuesday 15th July 2008

I was woken up at 0230 with the news that the VMP turbulence profiler had lost connection with the computer and needed hauling in to have the connections re-terminated. Just when we thought the profiler was getting into the swing of things. So, a bit of rapid re-arranging of the plan and we filled in the freed-up time with a test of the multibeam bathymetry system. Part of this project, once we gat back from the cruise, will involve detailed numerical models of the physics of the bank; that requires a better knowledge of the seabed than we currently have from the charts of the region. The multibeam system has 128 acoustic beams (individual echo sounders) that are transmitted in a fan shape below the ship. This produces a swath picture of the seabed under the ship as we steam along. We spent over 4 hours running the system during the morning - it produces great data, but to map the entire bank will take 10 times that effort as the "swath" of data under the vessel is only 200 - 300 metres wide. Given all of the other work we need to get done we'll have to re-assess the use of the multibeam. The group of scientists on the vessel who seem to most enjoy steaming up and down straight lines at 8 knots are the observers from the Joint Nature Conservation Committee. We have two wooden boxes, one either side of the ship just below the bridge (referred to as the "opera boxes" by the captain). The observers sit in these boxes throughout daylight hours, recording the numbers and behaviour of seabirds and marine mammals that they see every 5 minutes. Tremendously labour intensive, but they seem to enjoy themselves and apparently think the rest of us are mad for sitting in the labs all day. They are already producing some very interesting results on the spatial distributions of bird feeding compared to the patterns of internal waves that we have been recording.

One of the observer boxes just forward of the bridge.		Andy Webb and Mark Lewis (JNCC) and Clare Embling (University of Aberdeen) recording observations of bird distributions and behaviour.

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Monday 14th July 2008

We recovered Scanfish at 0400, after a successful and thankfully uneventful tow over the bank and back. Then we spent a bit of time looking for the drifting buoy that Mark Inall had deployed with the dye a few days ago. The buoy sends Mark an email with its GPS position every hour, so we had a good idea where it was - but there is little of it visible on the sea surface which makes it a challenge to find. But we did find it, then headed off to the top of the bank to put the seabed camera down again. The last deployment of the camera came up with some startling images. Inigo had been wondering what had been devouring the bait so quickly - in some cases in 2 hours or so - and which we had so far failed to get a photograph of. The mystery has now been solved; within a few minutes of the camera landing on the seabed, swarms of amphipods (sea lice), each about 3 - 4 cm long, found the bait and rapidly stripped the bones clean. Real horror movie stuff. Inigo's challenge now is to work out a way of making the bait last longer, otherwise we are not going to photograph many fish. After some more coring and bongo nets we began another 25 hour series of turbulence profiles, due to end tomorrow early afternoon. Initial results from those profiles show very little mixing, which is what we predicted as we are now at neap tides and there should be far less tendency for the flow to generate the sorts of large internal waves we saw last time we were here at spring tides.

A huge conger eel, 1.7 metres long, investigates the remains of the bait on the camera after the swarm of amphipods had left.

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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.