More jellies

Ocean research cruise blog of Jonathan Sharples

 

The children at Churchtown Primary School are I gather busy working on the questions we asked them about sinking salp poo. The zooplankton group on board are getting very excited about their results, and already planning the scientific papers that they want to write. We collected more of the zooplankton yesterday so that we can make better estimates of the rate at which they eat and the rate at which they release the faecal pellets. In an attempt to get an idea of what these delicate organisms look like in the ocean we attached a few waterproof cameras to the CTD, and lowered them into the sea surface to record pictures for half an hour or so. I set the challenge to get a picture of a jellyfish or salp in the process of releasing faecal pellets into the water. There was a clear winner (Clare Ostle, from the University of East Anglia), but she was working very early this morning and is currently in bed – so I’ll get the photo for tomorrow.

an interesting bucket of jellies

Meanwhile, to help the kids at Churchtown think about this problem, the picture below has some good examples of the salps (the long, tubular jellies, connected in spirals) and the tiny jellyfish. Another rally interesting organism in this photo can also be seen, just about. The photo looks like it has a fine sprinkling of sawdust in it. These are tiny colonies of a photosynthesising bacteria called trichodesmium. It’s special in the ocean because it is a nitrogen fixer – it is able to use nitrogen gas dissolved in seawater, rather than the form of inorganic nitrogen (nitrate) that most phytoplankton need. That means they can grow in areas where nitrate is in very low concentrations, such as the large areas of open ocean in the sub-tropics. Finding them here is odd, because there is enough nitrate around and so the trichodesmium should not have any advantage compared to other phytoplankton. I’ll find out a bit more about them for another blog entry.


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salps and tiny jellyfish

The importance of zooplankton poo

Ocean research cruise blog of Jonathan Sharples

 

At dawn this morning we reached the end of the iron sampling transect, crossing onto the edge of the continental shelf at a depth of about 250 metres. Quite a stunning sunrise, with flat calm seas. Not what you’d expect for November. The dreadful-looking forecast for the end of the week also appears to have dissipated, so we might be able to push our work further north into the Celtic Sea.

end of iron transect

We are about to head southeast for an hour or so, to return to the shelf edge site that we spent 3 days on earlier in the cruise. We need to repeat some of the Snowcatcher work there, and also the zooplankton biologists on board want to find some more salps and jellyfish to try out some experiments to determine how much they are eating and also what happens to the waste material that they excrete. I’ve asked the children at Churchtown Primary School in Southport to have a think about this problem – how quickly does a salp waste pellet (i.e. a salp poo) sink through the sea? It’s an important thing for us to know about. A fast sinking particle doesn’t give the bacteria in the water much time to breakdown the organic material before the pellet reaches the seabed. A slow-sinking pellet can be broken down into inorganic material before it reaches the seabed, and that inorganic material is then returned to the water where it is accessible to the phytoplankton. Also, sinking quickly means that the carbon in the pellet is removed from the ocean surface (and the atmosphere) very quickly – you could argue that the stability of Earth’s climate owes a great deal to zooplankton poo.

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Measuring growth of the microbes

Ocean research cruise blog of Jonathan Sharples

 

Yesterday started with another of our pre-dawn set of measurements. Fundamental biological measurements we need from these pre-dawn CTDs are how fast the microbial plants (the phytoplankton) are absorbing and using carbon and nutrients, and how fast the bacteria are growing by using the organic matter available in the water. Think of these as the two ends of a food chain, with the phytoplankton converting the inorganic elements into organic material, and the bacteria breaking down the organic material back into the inorganic. Between them we have the zooplankton, and other marine animals, eating the organic material provided by the phytoplankton, and in turn providing waste material that the bacteria use.

Radioisotope lab1

Measuring uptake of elements by phytoplankton and bacteria requires very careful laboratory work. The method involves using tiny quantities of radioisotopes of the elements we are interested in (carbon, nitrogen, phosphate, silicate) and incubating samples of seawater that have been treated with these isotopes. After a set period of time the sample is filtered to collect the phytoplankton or bacteria, and the activity of the samples counted to tell us how much of the element the organisms used. We have two laboratories dedicated to this work on the ship. Alex Poulton (National Oceanography Centre, Southampton) and Kyle Mayers (University of Southampton) are working in one to measure the phytoplankton rates. Sharon McNeill from the Scottish Association for Marine Science in Oban is dealing with the bacteria rates.
We steamed quickly over to the deep ocean side of the shelf edge yesterday afternoon, and at about 8 pm we started the second of our line of sample stations to measure iron in the seawater. This line started in a deep canyon, and we are working up the wall of the canyon back towards the continental shelf.

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Radioisotope lab2

22 November, 2014 08:49

Ocean research cruise blog of Jonathan Sharples

 

We had a very successful day yesterday – managed to get through all that was planned, plus most of what I’d planned for the next day as well. Deploying the moorings began shortly after 0800. This tends to be a long, careful process as the mooring wire is gradually unwound over the stern, instruments are clamped onto it at the planned depths, buoys are slotted in at key stages to hold it all up in the water, and then finally the 500 kg clump of chain is attached and dropped into the sea. By lunchtime we had deployed the long temperature/salt logger mooring and also the bedframe with the current meters. The second current meter mooring has been delayed until today, while the techs sort out an issue with the memory cards that it uses. That allowed us to go and hunt for the wandering wirewalker mooring and also the glider that we deployed when we first got here from Falmouth, but which has refused to dive.

Both the wirewalker and the glider have been sending us regular position information via a satellite link, which meant that finding them and getting them on board was very quick. We arrived back at the mooring site just after sunset, ready to do some more zooplankton work.

It’s a lovely day today – a glorious sunrise (complete with dolphins) and an almost flat sea. However, we’ve just heard that the long-term forecast is looking a little grim. A particularly nasty-looking low pressure system is due this side of the Atlantic next weekend. Forecasts that far out tend to be a little uncertain, but it’s worrying enough for us to think carefully about when we can get back to this site to recover the wirewalker and the 2 gliders that are here.

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21 November, 2014 09:05

Ocean research cruise blog of Jonathan Sharples

 

We arrived at the central Celtic Sea mooring site yesterday at 0930. Recovering the moorings was delayed a couple of hours while we waited for the wind to drop a little, but we began pulling them out of the sea shortly after lunch.

We have a fairly complex array of instruments on the moorings out here. There’s a weather buoy, provided to our project by the UK Met Office, plus a Cefas Smartbuoy that samples the surface biology and chemistry. The Met Office buoy doesn’t need servicing – they are designed to stay at sea sending back weather information for about 2 years. The Cefas buoy is looked after by Cefas scientists also working on this project. That leaves 3 other components that we need to service. The first mooring is a vertical line of acoustic current meters, anchored to the seabed and stretched upward by large buoys. These current meters are being used to measure turbulence in the sea, which allows us to calculate the supplies of nutrients towards the sea surface and how carbon is being mixed downward.

curretn meter buoy recovery

The second mooring is a relatively simple steel frame containing two acoustic current meters; this frame sits on the seabed, with the current meters looking upward and every 5 minutes measuring the flow of water in a series of 4 metre thick layers throughout the entire depth. Finally, the most complex of the moorings is a line holding about 25 temperature and salt loggers, anchored to the seabed and stretched up towards the sea surface by several buoys. These loggers, sampling every 1 minute, show us how stratified the water is, where in the water the thermocline is, and also if there are any waves running along the thermocline. All 3 moorings came up OK, though the string of loggers popped up about 1 km away from where we expected it to appear, requiring a bit of nifty ship manoeuvring by the captain to grab the mooring before it drifted onto the Cefas buoy. Once everything was on board, the National Marine Facilities engineers, along with Jo Hopkins and Chris Balfour from the Oceanography Centre in Liverpool, downloaded data, re-batteried instruments, and got the new mooring wires wrapped onto the winches ready for deployment.

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bedframe recovery

Off to collect the moorings

Ocean research cruise blog of Jonathan Sharples

 

We finished off the work at the shelf edge station with a set of samples collected using the Marine Snowcatcher. Quite a long process, with a good few misfires of the sampler, but all of the samples needed were eventually collected. At 0200 this morning we did another of the “pre-dawn” samples, collecting water from different depths to measure plankton growth rates and nutrient requirements, and the nutrients dissolved in the seawater. This was earlier than we would normally carry out pre-dawn work, but we need to get back up to the moorings further on the continental shelf with sufficient daylight to recover them all. We are due at the mooring site just after 0900. We’ll first collect a CTD profile of data adjacent to the moorings, which can later be used to help calibrate the mooring data, and then we’ll begin what will likely be a full day of manoeuvring and collecting the 3 mooring components.

 

Rainbow

We have a couple of hitchhikers aboard. Two storm petrels were found resting in the hangar by the CTDs last night. Both are currently having a sleep in a cardboard box, and Clare Davis is hopeful one of them will be OK to fly off later today. A few days ago we had an owl flying round the ship. Very exotic – cruises out here usually only attract tired homing pigeons.

Here’s a question for the year 3 ocean dynamic students back in Liverpool University. The water out here by the moorings will soon be completely vertically mixed, and I want to estimate the date when that will happen. The water is 150 metres deep, with a surface layer 60 metres thick and density 1025.6 kg m-3, and a bottom layer 90 metres thick and density 1026.0 kg m-3. The average tidal current amplitude is 0.45 m s-1, average wind speed is 12 m s-1, and the heat flux across the sea surface is 100 W m-2 (a heat loss to the atmosphere). That’s all the information you need, along with a handful of constants that are in your notes!

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Looking for particles (again….)

Ocean research cruise blog of Jonathan Sharples

 

We deployed the last of our gliders yesterday afternoon. This one is being piloted to patrol between the shelf edge and our mooring site, 100 km further onto the continental shelf; it will do this continuously from now until earl March when it will be picked up during another cruise. We then had a very successful night looking for particles. Starting just before sunset we deployed our two “Stand-Alone-Pumps” (SAPS). These pumps are lowered on a wire to a fixed depth, and programmed to pump water through large, dinner-plate sized filters typically for 1 or 2 hours.

Clare and SAPS

 Clare Davis, from the University of Liverpool, will analyse the filters to measure the ratios of carbon, nitrogen and phosphorus in the tiny organic particles caught on the filters – a vital part of the story of how carbon and nutrients are cycled through the sea, ultimately supporting the marine food chain and also absorbing carbon from the atmosphere. We also tried the large Marine Snowcatcher again, this time after some modifications carried out by the Ben and Tom the National Marine Facilities Engineers. It worked at last! Both the SAPS and the Marine Snowcatcher were deployed, first close to the sea surface and then at a depth of about 100 metres. This is quite a relief for us – knowing the make-up of the particles in the ocean is a vital part of what we are trying to measure.

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SAPS over the side