The Start: DY030

By Gary Fones 

4^th May 2015 saw the commencement of DY030 aboard the RRS Discovery, the latest cruise in the Shelf-Sea Biogeochemistry (SSB) programme. The aim of the NERC Shelf Sea Biogeochemistry research programme is to take a holistic approach to the cycling of nutrients and carbon, and the controls on primary and secondary production in UK and European Shelf Seas, and to increase understanding of these processes and their role in wider biogeochemical cycles.

RRS Discovery. Photo credit: Jessy Klar

Of the 4 main work packages this cruise will mainly focus on Work Package 2 (Biogeochemistry, macronutrient and carbon cycling in the benthic layer) and Work Package 3 (The Supply of Iron from Shelf Sediments to the Ocean), but with facets of the CANDYFLOSS Pelagic Work package. All Work packages contribute to the overall Integrated modelling effort of Work Package 4.

Aboard RRS Discovery. Photo credit: Richard Cooke

This mainly benthic focussed cruise is the third of four benthic cruises following on from DY008 in Spring 2014 and DY021 in March 2015. DY030 will include the use of a number of benthic lander systems, Autosub 3, gliders, benthic trawl equipment, benthic flumes, CTD water column sampling, Sediment Profile Imaging (SPI) camera and various coring systems.

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…

Ship's inbuilt equipment that science uses on the cruise

Jon Seddon, National Oceanography Centre, Southampton

I look after the science equipment that is permanently fitted to Discovery. I am also responsible for the storage of all the data that we record and the satellite system that we use for communicating with the shore.

On this cruise we’re using several of the instruments that are permanently fitted to the RRS Discovery. We have a weather station that every second records the air temperature, humidity, air pressure, the intensity of the light coming from the sun, and the wind speed and direction. Every second we also measure the properties of the sea 5 metres under the surface. We record the temperature, salinity, how much the phytoplankton in it fluoresce and also how clear the water is, from which we can work out how much is growing in the water (see picture with measurements below). The whole cruise is looking at how the phytoplankton start to grow in the Celtic Sea in spring. The data from the ship allows us to continuously observe how much phytoplankton there is at the surface throughout all of the sea that we pass through.

A screenshot of the underway data that is continuously logged aboard 24-7.  Since 7 am this morning temperatures have increased and fluorescence (chlorophyll) has decreased.

We’re using the echo sounders on the ship to make a profile of how deep the sea underneath us is. There’s more information about how echo sounders work here. We’re using two types of echo sounder on this cruise. The single beam system sends a single pulse of sound down from the bottom of the ship to measure the water depth directly under the ship. We’re also using the multibeam system, which sends out 400 beams of sound out in a triangular pattern to measure the water depth underneath and out to the side of us. We’re currently on the flat shelf and so the sea bed is uniform and 118 metres deep. When we dropped off the edge of the shelf during the iron transect the water went as deep as 2650 metres. There were lots of canyons flowing from the shelf into deeper water that showed up in the multibeam data. 

Multi-beam data from the iron transect showing increasing depth with colours going from red (shallow) to deep blue (deep). Below the ship is a deep canyon running east to west.

This is the unprocessed multibeam data from the deepest part of the iron transect.  The yellow line is the course that the ship took. The blues show the deepest areas of the sea and the reds are the shallower parts that are on the edge of the shelf. The navigation charts that we have for this part of the sea are not that detailed. The echo sounder data allows us to know how deep to lower the CTD to make sure that we measure all of the sea but that we don’t bump the CTD into the sea bed.

There’s a 2.4 metre wide satellite dish on top of the ship that connects us to the Internet and gives us four phone lines (see picture below). Satellite data is very expensive and so our system only works at 256 KBits per second. This is about one-eighth of the speed of the data on a mobile phone and we have to share this amongst the 50 scientists, crew and technicians onboard. There are nine computers around the ship that we can use to access the Internet. You have to be very patient though – the BBC Sport page takes 30 seconds to load and even longer if all nine computers are in use at once.

Picture of the bridge of the RRS Discovery with satellite dome and lots of other aerials and instruments. Photo: Chata Seguro.

Everyone has a phone in their cabin and the ship has four lines with Aberdeen phone numbers because that’s where our satellite ground station is. Friends and family can call us on these numbers or we can call them using phone cards that we’ve bought in advance. Because of the Aberdeen number it only costs the same as a UK phone call and so is very affordable but there is a bit of delay on the line, which can be confusing if you’re not used to it. 

All change: half time in the Celtic Sea

Alex Poulton, National Oceanography Centre

This morning marked a key placeholder in this cruise: a boat transfer and change of scientists. After half a day's steam we arrived in Falmouth bay, although the ever present sea fog meant that we could have been anywhere from the depths of the South Atlantic to the icy waters of the Arctic. Out of the fog came our three new recruits: Angie Milne, Matthew Fishwick and Elaine Mitchell. 

One of the new arrivals (Matthew Fishwick) climbing up the ladder from the launch. Photo: Chata Seguro.

Like half time in a football match, though without the orange quarters and deep heat, our three new recruits were soon on the pitch – after a brave climb up the ladder and onto the deck of the RRS Discovery. This was a straight like for like substitution for us: two new iron chemists to replace the two leaving and a new bacterial ecologist to replace the departing one. After a quick hello and bye from the new recruits to those getting off, the three leaving climbed down the ladder into the waiting launch and then disappeared off into the mist.

Farewell to those departing. Photo: Chata Seguro.

Before the new team members had a chance of relaxation they were informed that sampling would begin again in 12 hours - they had just half a day to orientate themselves on the ship (i.e. find their bed, their lab coat and the galley) before joining the rest of the team for a full night and day of sampling, firm in the knowledge that there was just over two more weeks to the final whistle.    

OMG - Glider glee!

Dr Charlotte Williams, Marine Physics and Ocean Climate, National Oceanography Centre

Today at our main sampling site (CANDYFLOSS) we are deploying our sixth and final ocean glider! Ocean gliders are robots which ‘glide’ up and down in the water whilst taking measurements of temperature, salinity, chlorophyll and oxygen (plus a few more things), and these are what I work with. They send their data back to us when they surface via satellite. The amazing thing about gliders is that we can see the data they are collecting from anywhere with an internet connection as soon as they surface (every 30 mins or so in 100m of water). In fact as I am writing this blog I am checking the data that is coming in from the 4 gliders we have out at the moment! This has been useful for our research cruise as we are trying to catch and sample the ‘spring bloom’. This is where light and nutrient requirements for phytoplankton in the surface become just right in spring, and so we see a bloom in phytoplankton growth. This can be observed by an increase in chlorophyll, which the gliders measure.  

The ‘OMG’ glider being ballasted in the tank. Photo: Jose Lozano.

Sam Ward, the glider engineer from National Marine Facilities, has been working very hard to ensure that the gliders are ready for the water. This includes ‘ballasting’ them in a big tank on the back deck. The gliders don’t have a propeller, they move up and down in the water by changing their buoyancy, which is much less power hungry. Sam has to check how buoyant the gliders are in the seawater that they are being deployed in, as the density of seawater changes according to its temperature and salinity. There will be more to come on how the gliders work in Sam’s future blog! The last glider being deployed today is particularly exciting as this is an Ocean Microstructure Glider (OMG). This glider measures all of the things listed above, but also measures the turbulent kinetic energy dissipation, which is a kind of fancy term for turbulence and mixing. Being able to estimate the mixing in the shelf seas is important because we can then estimate how nutrients and carbon move around.  We will have to see if the dolphins return to see the OMG glider!  

Another glider about to dive under the waves. Photo: Jose Lozano

Spring has sprung - here comes the bloom

Alex Poulton, National Oceanography Centre

After two weeks in the Celtic Sea we are seeing clear signs that the spring bloom has truly begun - nutrients are declining whilst levels of the pigment chlorophyll, used by phytoplankton for photosynthesis, are steadily rising. 

Just how green the water is at present (slightly cheating as this is a pigment extract rather than seawater). Photo: Chata Seguro.

The bloom appears to be patchy across the Celtic Sea; from the shelf edge where the bloom has not started to show strongly yet, to the central Celtic Sea (where our Candyfloss site is) where small phytoplankton are actively growing, to the northern Celtic Sea where we saw huge diatoms (images below) - a type of phytoplankton which often characterises blooms and productive waters - which were at least a hundred times larger than anything we have seen so far. 

Diatoms and zooplankton seen under the microscope. Photo: Chata Seguro.

A close up of one of the large diatoms we saw in the NE Celtic Sea. Photo: Chata Seguro. 

As the nutrient levels continue to decline we are keen to see what happens within the phytoplankton community: will there be a clear progression from large cells to smaller cells which needs less nutrients for growth, will the diatoms be succeeded by another phytoplankton group? How these changes are reflected in the rest of the ecosystem is a key question we will address over the next two weeks. For example, how will changes in which type of phytoplankton is present influence the different nutrients needed for their growth (nitrogen, phosphorus, silica), and will we see changes in the dominant types of zooplankton (tiny animals that eat the phytoplankton) across the Celtic Sea.

The ever present fog viewed from the bow of the RRS Discovery. Photo: Chata Seguro.

Though the bloom has arrived, we have lost the sun - a dense sea fog has descended on us over the last few days which means we can only see a hundred to two hundred metres in any direction (see image). The eerie silence that this has brought to the ship is broken up at regular intervals by the ear shattering sound of the ships horn announcing our presence. If the spring bloom didn’t know we were here before, you can be sure that it does now.