Snow catching across the Celtic Sea

Alex Poulton, National Oceanography Centre

Picture 1. Snow Catcher going over the side of the ship. Photo: Jose Lozano.

Of particular interest during this cruise is the fate of the material that is produced in the upper part of the water column - this material sinks down through the water column as large particles called marine snow. Marine snow is formed in many different ways. Some is formed from phytoplankton sticking together to form large aggregates when growth conditions are not optimal in the surface ocean, for example when nutrients are limiting growth. Others are produced by zooplankton eating phytoplankton and then producing faecal pellets. These marine snow particles can sink through the water column at various speeds, with their sinking speeds linked to their composition and size. As they sink they act as a food source for zooplankton and other organisms that live in the lower depths of the water column.

Picture 2. Snow Catcher being deployed to 70 m. Photo: Jose Lozano.

Collecting marine snow is a challenging business. During this cruise we are using Marine Snow Catchers - large volume (100 L) water bottles which we send down to the depth of interest and then close, enclosing the sinking particles which we then bring back up onto the ship and allow to settle for an hour or two (pictures 1-4). After this settling period we can then remove the water from the Snow Catchers and examine the particles in the bottom of the Snow Catcher. 

Picture 3. Snow Catchers taking a rest. Photo: Jose Lozano.

These Snow Catchers have been used on multiple cruises from the Arctic to the Caribbean individually, but unique to the Celtic Sea is the deployment of not one or two, but four Snow Catchers twice - once in the upper 10 m and then again at 70 m. This is quite some operation, taking a large amount of organisation, (patience), timing and around five hours. Over the entire length of the cruise we will carry out this large-scale water collection and snow catching exercise at five different sites, including our Central Celtic Sea site (Candyfloss). Our hope is that as well as seeing changes in the surface community we will also see changes in the composition of the material leaving the upper sun lit ocean and sinking down to the seafloor.    

Picture 4. Team Snow Catcher celebrating success. Photo: Callum Whyte.

Game of Filters: A Song of Filters and Water

Clare Davis and Calum Preece, University of Liverpool (Westeros)

The University of Liverpool team (picture 1) is responsible for determining the composition and relative concentrations of dissolved and particulate organic nutrients, namely carbon, nitrogen and phosphorus. This is a key part of understanding both nutrient cycling and the fate of carbon fixed by primary production in the shelf system.  

Picture 1. The Liverpool team with [Jon] Snow Catcher enjoying some afternoon sunshine. Photo: Jose Lozano.

In real terms, this equates to an awful lot of filtering during the SSB cruises. To achieve this we travel down from Filterfell in the North to Southampton where we join the ship. From then on, we employ all of the Seven Filtrations to collect a wide range of samples. But first of all, we trot our little legs over to whichever device we are using for sampling that day, be it Jon Snow Catcher, CTD or Ned SAPS, armed with Tygon Lannister tubing and fill our bottles with as much seawater as we can get our hands on. There is one exception however, when we are working alongside the Fe Island team we aren’t trusted in the clean lab so they sample their fancy CTD on our behalf and deliver the water to us.

During transects and at designated stations we collect water samples from the CTD which we analyse for dissolved organic nutrients, including dissolved organic phosphorus (DOP), dissolved organic nitrogen (DON), dissolved organic carbon (DOC), amino acids (AA) and coloured dissolved organic matter (CDOM). We define these nutrients as those which pass through what is arguably the king of filters; King GFFrey with a pore size of 0.7μm.

We collect a selfish amount of water from the CTD for sampling particulate nutrients, including particulate carbon, nitrogen, phosphorus, lipids, amino acids, stable nitrogen isotopes and pigments. We define the particulate fraction as anything stuck to King GFFrey after filtering a couple of litres of seawater (picture 2).  We also collect particulate samples from the now infamous Jon Snow Catcher. 

Picture 2. A [King] GFF[rey] filter covered with particulate material. Photo: Chata Seguro.

A personal favourite for sampling particulate nutrients is the honourable and reliable Ned SAPS. With the help of Lord Commander Jon Short (picture 3), his Men of the NMF Watch, and good old Ned SAPS we can filter hundreds of litres of seawater in situ, separating out large particles from smaller ones which can give us useful insight into the composition and variability of the different sized particles in the water column.

Picture 3. [Lord Commander] Jon Short of the NMF [Watch] and good old [Ned] SAPS. Photo: Chata Seguro.

 

After all the samples have been filtered most are frozen in the freezer room which lies beyond the great hangar, but the Cercei CDOM samples must be analysed on Hodor Horiba…Horiba before they degrade. This is helps us calibrate the CDOM sensors on Samuel ‘Tarly’ Ward’s sea gliders that roam the Celtic Sea.

While many are currently playing in the Game of Filters, there is no denying that the North is a force to be reckoned with as they rule over their Seven Filtration rigs across the not-so-narrow Celtic Sea.

The bloom is coming! And soon the seabed will be covered with marine snow…

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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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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