Into the deep water

We’re in deep water now. Not the deepest in the ocean, but enough to make a normally shelf-focused oceanographer a little nervous. The forecast suggests things should quieten a little over the next day or two, so we headed out over the shelf edge and into the deep ocean aiming for a depth of 2,500 metres. Crossing the shelf edge always looks like we are going over a cliff when you look at the echosounder. On the shelf the depth had increased from 150 to 200 metres in about 100 km, but then over the shelf edge the depth suddenly increases from 200 to 2000 metres in about 30 km. So a change of 1800 metres over 30 km: if you cycled a slope like that you might get a bit out of breath, but it’s not the cliff edge that the echosounder makes it look.

cup creations

 Scientists can be easily amused. The one thing we really like to do when we work in deep water is decorate polystyrene cups and then send them down with the CTD. Amber Annett from Edinburgh University remembered to bring a supply of cups, pens, and a pair of old tights to hold the cups on the CTD frame. The lab is a hive of creative activity. Why do we do this strange ritual? The cups compress under the pressure of the water; the greater the pressure the smaller the cups become. The decorations also compress, so that you end up with miniature, highly-detailed cups when the CTD returns to the deck. We are due to work gradually back up the shelf slope to the shelf edge, lowering the CTD into 2,000, 1,500, 1,000 and 500 metres, so we could produce a series of cups scaled by the depth of the water. It’s fun, and also a great way of demonstrating the concept of water pressure to school kids.

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deep ctd

At the shelf edge, and rolling….

Ocean research cruise blog of Jonathan Sharples

 

November 14th. We are out at the edge of the continental shelf. Work had to stop early this morning as the waves reached 7 – 8 metres, making it too difficult to get our instruments over the side safely. We are now sat here trying to get a weather forecast, so that we can decide whether to stay out here and wait for the waves to settle down, or turn back onto the shelf and work in the shallow water.

Yesterday’s work started off very well. We managed to do 5 out of 6 sets of measurements as we headed southwest from the central Celtic Sea. We have collected a great set of information on the distribution of the autumnal nutrients out towards the shelf edge. Unfortunately we couldn’t collect any information on iron in the sea, as the instruments used to do that use a wire that has a lower breaking strain – we are fairly sure it wouldn’t survive the sudden snatches the wire gets when getting gear back onto the ship in these waves.

We’re rolling heavily now! The ship has turned direction slightly to try to get a signal to our back-up internet connection – then we can get a weather forecast and start to plan the next few days.

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13 November, 2014 21:38

Ocean research cruise blog of Jonathan Sharples

 

We finally finished our work at the mooring site yesterday evening. The marine snowcatcher work was not terribly successful. We are having difficulty in keeping them sealed, and also with the brass “messenger” that slides down the wire to trigger the catcher to shut. However, as usually happens, the Marine Facilities engineers on board have some ideas that might solve our problems so we’ll get another try in a couple of days.

We are heading southwest now, making a series of measurements with the CTDs across the continental shelf and to the shelf edge. There was some nasty weather during the night, with winds over 50 knots – dropped to 15 knots or so today, but it has left a decent swell for us to ride over on our way out. Over the next day the depth will increase slowly from 150 metres to 200 metres, then within about 2 hours the seabed will drop down to about 3000 m as we leave the continental shelf and head briefly into the open ocean. We will be doing a lot of iron chemistry out there, but I’ll explain more on what that is all about once we get started.

For now, work in the labs continues, on the samples we have collected since Monday and on those we collect during today. Invariably the lab work involved filtering lots of seawater, either because we want to analyse the pure seawater without any organisms in it (e.g. for dissolved nutrients), or because we want to filter out the organisms to study them more closely.

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Catching snow in the sea

Ocean research cruise blog of Jonathan Sharples

 

The last day on this station began with another 0500 early CTD, so that those scientists working on how fast the plankton are growing can start another set of experiments. During the afternoon we released another glider. This one has a special chemical sensor on it that has been designed at the National Oceanography Centre. It measures the amoung of nitrate in the water, a key nutrient required by the plankton. As with the glider yesterday, we are leaving this one in the water just while we are at sea; we aim to retrieve it just before we head back to Southampton in early December.

glider 2 deployed

We also had a go at using our “Marine Snow Catcher”. This large tube is designed to trap 400 litres of water at one depth. The tube is then brought back on deck, and all of the tiny particles in the water (plankton, bits of detritus)are allowed to settle in the tube. After 2.5 hours the scientists collect particles from near the top of the tube (which will be very tiny and will not have settled far), the middle of the tube and the bottom (containing the coarsest particles which settled quickly). We want to see how the organic matter in these different particles is being recycled by bacteria in the ocean; particularly we want to know if the bacteria recycle nutrients, such as nitrogen and phosphorus, more quickly than they recycle carbon.

snowcatcher

 
Our communications are still suffering. It looks like we may be down to a limited email connection for the rest of the trip, with the problem with the main system having been narrowed down to a component that we don’t have a spare of.

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Glider away….

Ocean research cruise blog of Jonathan Sharples

 

Two new pieces of equipment deployed yesterday. First, the Ocean Microstructure Glider (OMG). A glider does exactly what the name suggests – it glides through the sea. By making itself heavier than the water, and tilting its nose downward, it glides downwards. Then, when it gets to the depth at which it has been instructed to turn round, it makes itself lighter than the water, points the nose up and glides towards the surface. Inside a glider are instruments similar to those on the CTD – measuring water temperature, salt and plankton. The OMG also has some specialised instruments for measuring the amount of turbulence in the water. That’s what the “microstructure” part of the name refers to – the sensors measure tiny changes in water currents associated with turbulence. We are really interested in turbulence, as it mixes nutrients, plankton and carbon through the water. The really neat thing about gliders is that when they surface they can stick their tail end out of the water and communicate back to shore via a satellite link, transmitting data back and also receiving new instructions. Our gliders are not controlled by us on the ship, but by scientists back at the National Oceanography Centre in Southampton and in Liverpool.

wirewalker deployment

 Immediately the glider was away, we moved the ship clear and deployed a “wirewalker” mooring. This again has instruments for measuring temperature, salt and plankton, but it moves up and down a wire fixed to an anchor on the seabed and a buoy at the sea surface. The action of the waves on the buoy provides the energy that the wirewalker needs to ratchet itself down the wire (so, a note to my nephew Ben there – yes we do now have things that use the waves’ energy to power them! Your idea was spot on); it then releases its grip on the wire and floats back up to the surface. With decent waves (of which we’ve been having plenty) the wirewalker can profile up and down the cable every 15 minutes or so. Jo Hopkins for the National Oceanography Centre in Liverpool is running this instrument – she is keen to capture the details of how the water is mixing as the weather cools into winter.

omg glider deployment2

 
We’ve lost a lot of our communications at the moment – certainly internet and phones are out. Zoltan, the NMF computer tech, is working through all possible causes and he’ll be calling on the ships ELT tech as well. Hopefully we’ll be fixed soon. We still have access to the National Marine Facilities Webmail though, so I can get these posts through OK.

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omg glider off

Sampling iron

Fantastic weather today. Winds 5 – 10 knots, and we have lots of blue sky. Other than a long, 2 metre swell you’d have to describe the sea as calm.
We have a group on board, led by Maeve Lohan from the University of Plymouth, who are going to measure the amount of iron in the sea. Iron is a nutrient that the microbial plants in the ocean need. It occurs in the ocean in very small concentrations, and so is a real challenge to measure. Much of the challenge is because ocean scientists need to make the measurements from steel ships, so there is huge potential for contaminating the samples with iron from the ship or our equipment.

The instruments used by the iron scientists are all made from titanium or plastic, and they do all of their work is a special “clean lab” on the ship, into which the rest of us are forbidden to go. When their titanium instruments come on board after collecting water samples, Maeve and her colleagues rush forward with a bag of polythene gloves which are all put onto the taps of the sample bottles so that they don’t get contaminated while on deck.
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Salp soup

The weather deteriorated a bit after the first CTD cast. Wind reached about 40 knots, so we had to stop working as the motion of the ship was putting too much stress on some of the equipment hanging over the side. However, things have calmed down nicely for the afternoon. A group of 6 or so dolphins has been hanging around the ship, probably feeding on the fish that often congregate underneath us if we stay in one place for a while.

zooplankton net

Sari Giering (University of Aberdeen) has started her sampling of the zooplankton – the tiny animals that feed on the microbial plants (and on each other). There is general surprise that there is so much biological stuff in the water, given the time of year. The zooplankton net, which is hauled vertically upward through the water to catch any zooplankton on a mesh at the end of the net, has come back with all sorts of stuff. The latest haul had a large colonial salp – a gelatinous filer feeder about the size of your finger, but that lives in long connected ribbons of several dozen clones.
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bucket full of sulps