Marine

MASTS Deep Sea Collaboration Project (Survey 0915S) – update 24 July 2015

July 24, 2015 by No Comments | Category Marine Directorate Science, Research Vessel Surveys

The latest update of the MRV Scotia Survey 0915S…

Day 4.

After yesterday’s tantalising glimpses of what might have been the cold seep, Jim Drewery, leads the watch in which we begin to deploy the more conventional seabed sampling gear. The first samples suggest we are indeed in the right area. Graham Oliver who did the formal identification of the new species is aboard and he confirms that the specimens are the same species we found 3 years ago. The lander is retrieved, but something is very strange – the bait has not been touched, all the pictures are black and the ‘feet of the lander’ are covered in a sooty substance. We decide to core the site to see what the seabed consists of. As the maxicore comes up, it’s clear it has only partially worked with 5 out of 8 cores containing samples. The most noticeable thing is a sulphurous pong, but when we decant the cores the overlying water is more like a slimey ooze. The core appears to contain very little in the way of life. Baffled we process the samples and preserve them. By evening time we get the TV going again and we fly straight back into the blizzard. So it seems to be typical of conditions down there. Eventually we come out it and we are back into the greenish ripple features. There are plenty of fish about. Its appears that in the very bottom of the trench is some extreme environment perhaps only inhabited by bacteria – but as you get further away life begins to get going again and there diverse ecosystems.

Day 5.

The sampling continues. One haul of the Agassiz trawl yields nearly 1 tonne of mud! We are all a mess after that, but there are some interesting specimens to be catalogued. The lander again comes up in a similar state as yesterday – no evidence of fish or much else other than bacteria in the slimey ooze at the centre of the trench. We move it further toward to edge of the trench and redeploy. We’ve had a few issues with the maxicoring today – misfires and wire tangles, but eventually we got 4 perfect cores which are carefully sectioned and preserved. Heather Stewart from BGS has had more success with deploying the gravity core which has done the business every time and we’re building up a good sample. Each core drives some 2.5 m into the sediment reaching down to deposits laid down before the last ice age. Tonight TV operations switched focus to a second deep basin area just a mile to north, separated by a ridge. Here the visibility was much better (no blizzards) and similar features were seen.

Day 6.

Overnight a camera tow was made along the east side of the trench and revealed a completely different environment – coral gardens and boulders that had presumably rumbled down the steep sides of the trench wall to the east. It was a busy morning with Agassiz trawl – a very diverse haul from the side of the trench. Problems with the depth sensors on the sampling gear meant we were unable to deploy SAMS’s epibenthic sledge. We continued with the Agassiz trawl – this time in the middle of the trench. A fraction of the bulk and diversity this time – only 1 km from the previous haul. There are some very steep environmental gradients here. After lunch we retrieve the lander. Tom Linley, a PhD student from Oceanlab is clearly relieved to see the bait has been eaten. The pictures are downloaded we finally see something – deepwater sharks, skates and cut-throat eels all attacking the bait. Also plenty of amphipods swarming around. Then its onto coring which goes well – finally we get a full set of cores from the green potential seep habitat we have been seeing on the video. There is a thick carpet of green slime sitting on top of very white and fine sediment. Above the slime the water is clear and normal, unlike the smelly ooze we encountered before. The wind is freshening and the forecast is for a 24 hour storm. We get 30 minutes of TV deployment, but by 21:00 the wind is gusting 40 knts and we abandon operations and get the chariot safely back on board.

Day 7

Well it wouldn’t be Rockall with a bit of rock and roll. 60 knt gusts overnight and a big old sea is now stopping us from doing anything more than opportunistic mapping of the seabed using the ship’s Olex system. Conditions moderate enough by 18.00 to resume work and we got going with the last gravity core deployment in the potential cold seep area. The baited lander was recovered and we did one final TV tow in the area before moving further west to the Hatton-Rockall basin Marine Protected Areas site.

Francis Neat, Marine Scotland Science

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