Dolphins everywhere

Ocean research cruise blog of Jonathan Sharples

 

We had an astonishing display of dolphins last night. While sat carrying out a couple of measurements with the CTD for the iron work, lots of small fish had been attracted to the ship probably because of the deck lights. They in turn attracted something like 40-50 dolphins, cruising up and down the ship, accelerating to chase fish, and leaping out of the water to catch fish that were trying to escape. The acceleration and the rate at which the dolphins could turn through 180 degrees were incredible to watch. [A good question for the Oceans Sciences and Marine Biology students back at Liverpool University – the dolphins were reaching easily 10 metres per second, what Reynolds number were they operating at?] With the light from the ship we could see the dolphins 2 or 3 metres below the surface, streaking along after their food. Two sharks also turned up for the feast – much more sedate than the dolphins, cruising slowly into the foray and just wandering about as the dolphins flashed around them. We got a good look at one of them as it passed right below us at the side of the ship – at least 2 metres long. Dolphins and sharks paid each other no attention at all. This whole theatre lasted a good 90 minutes. My camera wasn’t quite up to the task of night-time photography, but the best effort is below.

dolphin watching

A glorious morning for us today. The wave height has dropped below 3 metres for the first time this trip. We have now started our 3 day stint at the station at the shelf edge.
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dophins at night

End of the iron line

We have nearly finished our transect sampling iron from the deep ocean back to the shelf. The iron group is fairly excited, because in all of the profiles we have done gradually working along and up a seabed canyon there has been evidence in the CTD data of lots of suspended particles near the seabed. There must be some flow of water down there that is pulling sediments, along with trace metals such as iron, up off the seabed which is exactly what the scientists are looking for.

iron nerve centre

Other lab work continues also, as the iron chemists need to know what else is happening in the water to help understand what they are seeing. Chata, a PhD student from the University of East Anglia, has spent the past 3 days trying to fix a machine she uses to measure argon, oxygen and nitrogen gas dissolved in seawater. The machine is refusing to work properly, so she is having to store samples for analysis later back at University. Oxygen and argon behaviour similarly in seawater, and in the rates they can be transferred from the atmosphere to the ocean. However, oxygen also has a biological component to how it changes – if the ocean’s microbial plants are growing, then (like all plants) they produce oxygen. Chata can compare what she sees the argon and the oxygen doing in the water, and any differences between them will tell her about how the biology in the ocean is working. She is also helping us by doing chemical analyses of water samples to measure the oxygen concentration, which will allow us to calibrate the oxygen sensor that we have on our CTD.

chata titrating oxygen samples

Due to finish this transect at about 0100 tomorrow. We then plan to start th second of our main study stations, this time sat at the edge of the continental shelf.

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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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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

The first data

Right on schedule, at 0500 our main set of instruments hit the water to collect the first data. This package of instruments (the "CTD") is made up of several sensors that measure water temperature, saltiness, oxygen concentration, and also how many of the microscopic ocean plants there are. The long grey tubes around the outside are used to trap water (20 litres at a time) from depths where the scientists want samples for their experiments.

CTD into sea

The first data is exactly what I was hoping for. Throughout the summer this part of the sea would have had a warm, sunlit layer above deeper, colder water. As autumn and winter approach this surface layer cools and starts to get thicker, until eventually the whole of the water from the surface to the seabed (140 metres deep here) reaches the same temperature. The red lines in the left panel of the computer screen show the temperature. It’s about 14 deg C in the upper 40 metres, then drops to 12 deg C in the deeper water. In summer it would have been about 18 deg C in the upper 30 metres, and 11 deg C below. So, we’ve got here just in time to see the change in conditions towards winter.
These early morning "CTD casts" are sampled a lot by the scientists. There was a big meeting last night to discuss who required how much water from what depths. Also the order in which the samples are taken is really important (samples for dissolved gases need to be taken first, while samples for salt can wait until the end).

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orderly queue

Leaving Falmouth

Bang on time we left Falmouth Docks at 0830. The ship is so quiet many of us didn’t realise we’d started moving. We dropped the pilot off once clear of the docks. Ship pilots work for the port, rather than they ship. They know the sea in and around the port very well, so ships use them to guide into and out of the docks. Once we were clear of Falmouth, a fast boat came alongside us to pick up the pilot and take him back to shore.
The weather is remarkably sunny and calm. In fact we have some spare time as our first planned work is to start at 0500 tomorrow, and it’s about 15 hours to get to the work site. So, the ship’s crew have been testing one of the lifeboats – making sure that the davits (or cranes) that are used to lower it into the water work, and that the lifeboat’s engine is fine.
 

lifeboat recovery

Preparation of the laboratories continues, with the lab space gradually becoming clearer. Note in the picture below the typical fashion of the scientist at sea: lab coat, hard hat, lab groves, and also stell-toecapped boots. This is Matthew Bone (from the University of East Anglia); he will be working on how nutrients are released from the seabed at the start of winter.

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Matthew Bone

Everyone aboard

Everyone has made it aboard now. We had our safety briefing this afternoon, learning about where to go if there were to be an emergency, how to operate the watertight doors, as well as other practical information such as where the laundry is and what time meals are served.

Snowcatcher Discussion

The scientists have continued getting the gear ready, and then all strapped down so that once we get to sea things don’t start rolling around the deck. We have two enormous "marine snow catchers" on the aft deck. These are used to capture 400 litres of water from key depths, which is then brought back onto the ship and sampled to see what particles are in it. For instance tiny animals (zooplankton), or bits of sediment from the seabed, or – very importanly – bits of zooplankton poo. Particles in the ocean sink, taking with them lots of carbon which ultimately was removed from the atmosphere. It’s what happens to these particles, and the carbon that they carry, that forms the basis of a large component of our work. One of the mooring components was also completed and strapped down, ready to take out into the middle of the Celtic Sea and dropped onto the seabed. This seabed lander has two devices for measuring the water currents using pulses of sound. It will sit on the seabed measuring currents until March next year.

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adcp bedframe

Preparation continues

Things are gradually finding their place inside the ship. Everything is now aboard, and slowly being put together or stored. Jo Hopkins (from the National Oceanography Centre in Liverpool) is putting together the wirewalker mooring. This is a device that uses wave action to crawl up and down a wire between the seabed and the sea surface. As it does this, instruments on it measure the water temperature, saltiness, and the amount of the microbial plants (the phytoplankton) in the water. The wirewalker doesn’t work if the sea is flat calm, which we suspect won’t be a problem on this cruise.

jo assembling wirewalker

 Malcolm Woodward (nutrient chemist from Plymouth Marine Laboratory) has, perhaps a little early, got into the Christmas spirit. His nutrient autoanalyser and its control computer are festooned with flashing coloured lights.
We are all keeping a wary eye on the weather forecast. Looks to be fairly good still for the first day, which will at least allow us to get out to the first sampling site in the middle of the Celtic Sea. After that the wind is forecast to pick up, but it doesn’t look like it’ll be strong enough to worry us for a few days.

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Well lit autoanalyser

Loading the ship begins….

The various groups of scientists gradually began to arrive in Falmouth today. People have travelled from Plymouth, Norwich, Oban, Aberdeen, Southampton, and of course Liverpool. Each van load of equipment was loaded onto the ship, and stacked in the ship’s laboratories. Tomorrow the hard work starts, sorting all the boxes of stuff into the correct labs, setting up all of the equipment and beginning to see if it all works OK after the journey here. The plan is to sail 0830 Sunday morning.

Disco Loading

I met the captain to chat about the plans for the next few days. This is her first cruise as captain on this ship. Before this she worked for several years with the British Antarctic Survey on their research vessel. It’s interesting to see how things have changed since my first cruise way back in 1989. Then the crew was entirely male, and the scientists tended to be predominantly male. This is my first cruise where there are more women scientists on board than men, and the ship has several women, including the captain, one of the engineering officers and the head chef.

Disco Laoding

Next cruise: RRS Discovery, Celtic Sea

My next research cruise is due later next week. I’ll be at sea for 23 days aboard the RRS Discovery, leaving Falmouth on November 9th and returning to Southampton on December 3rd. This cruise is a part of the Shelf Sea Biogeochemistry research programme.

On an earlier cruise, with a collection of meteorological buoys ready for deployment.

The shallow seas around the world’s landmasses, called the shelf seas, cover about 5% of the ocean’s surface area, but they generate somewhere between 15 and 30% of the total amount of biological production in the ocean. We are not entirely sure how they do that. In particular we know that they must receive nutrients from the deep ocean to fuel this biological growth, but we don’t know how that happens. This biological growth supports all of the main commercial fisheries in the sea, and it is also important to our climate. The growth of plankton results in the sea surface absorbing carbon from the atmosphere’s CO2; the shelf sea biological production is thought to remove about one third of the total carbon we put into the atmosphere each year by burning fossil fuels. So, we want to understand how the plankton do this and, importantly, if they are sensitive to changes in our climate.