Building a ‘MAP’ for the chemistry of ocean bottom waters

By Will Homoky

“What does it do?” asked Neil, as he inspected the arrangement of tubing and whirring pumps.

“It measures radioactivity that’s escaped from the seafloor” I replied.

Having just heard myself, I clarified “Natural radioactivity. It’s found throughout the ocean, especially near the seafloor where much of it comes from”.

“Oh right” said Neil, “why do you want to do that then?”

MAPs being prepared for their first deployment. Photo credit: Torben Stichel.

 

I was glad Neil asked why, I could answer that, but how, is still pretty new to me. I just had my crash course in how to measure the activity of Radium when our ship was in Southampton dockyard. The expert, Amber Annett, walked me through her method before she disembarked, and passed me the baton for this DY030 expedition.

I want to learn how to measure Radium because I have a new instrument that will sample it from just above the seafloor. This bit of the ocean is a real mystery for us ocean chemists. Routinely the equipment we depend on cannot collect water samples just above the seabed for risk of smashing it as it dangles from a long wire. This means we struggle to measure the changes in chemical properties in this zone – we struggle to map the chemistry of ocean bottom waters.

My idea is to design new sampling equipment that can rest directly on the seabed, and DY030 has offered me the chance to try the newly built Miniature Autonomous Pumps (MAPs) for the first time. I have only made the first step; test MAPs ability to filter particles and collect the scarce quantities of radioactive elements that pass been the seabed and the overlying ocean, but the results are promising. 

 

Neil deploying MAPs on DY030. Photo credit: Torben Stichel

 

MAPs have been funded through a NERC Fellowship at University of Oxford, and designed and built in collaboration with the Ocean Engineering and Technology Group at NOC Southampton. For this cruise, MAP missions are on a borrowed ‘Lander’ from NOC Liverpool. Yesterday the bright orange Lander held two MAPs a metre above the seabed, where they automatically pumped seawater, filtered particles, scavenged elements, and monitored and recorded their performance. Samples recovered on deck have been divided for various analyses –nutrients, and ‘trace’ concentration elements including Iron and Radium - that will feed in to the programmatic goals of UK SSB.

Will Homoky is a NERC Fellow and Anniversary Ambassador at University of Oxford. For more information follow Will on twitter or visit his home page.

 

Working with mud!

By Sarah  Dashfield  and  Joana (Jo) Nunes

This is our first SSB cruise, as well as our first cruise overall!!! Exciting stuff!

Bulk coring team

On the second benthic cruise we are responsible for doing lots and lots of coring, i.e. lots of mud to shovel off the side of the ship!! Sarah’s work, who is mainly responsible for all the fauna (the beasties) that live in and on the seabed, involves both the NIOZ and the SMBA box corer. These corers collect a 0.1m² and a 0.5m² sample of the seafloor, respectively. Epifauna is collected with the Jennings trawl, a 2m net that is very slowly dragged over the seabed – the nets collect lots of bivalves, starfish and sea mice (furry and iridescent worms! Yes, really!),  snappy Nephrops norvegica (scampi!) and sometimes even some monkfish, which we don’t keep!

Sea mice

Monkfish

Jo is responsible for the flux coring. Here, we also use the NIOZ box corer, but each core is shared by several people. It is Dave who collects for nutrient flux incubation, Gangi who collects cores for oxygen profile incubations, and Helen who collects cores for a pulse-chase experiment.  This experiment quantifies the exchange of nutrients between the sediment and the overlaying water.

Jo sub-samples around everyone else:  50mL syringes for pigments and microbial analysis, surface scrapes for nitrification rates, and, the most fun of all, 10cm diameter cores for denitrification rates, which get whizzed up with a blender-like piece of kit.  The samples are treated with different chemicals to stop the nitrification process at different stages, incubated for a minimum of 24 hours and fixed with zinc chloride.  Finally, they are ready for analysis when we return back to PML.

Jennings trawl 

The fauna that we have collected from the trawls and cores will be identified, counted and weighed when we return to the benthic lab in PML.  This information together with the microbial data and the chemical analyses can be statistically analysed to discover whether there is a relationship between them. Finally, this information can be added to enhance marine models such as ERSEM (the European Regional Seas Ecosystem Model) which then will be used to predict how the marine environment may change in the future.

Flux coring

Calm Seas

By Gary Fones 

Calm seas: Credit: Gary Fones

12^th of May saw some much appreciated calm weather and lots of science activity aboard the RRS Discovery. Lunchtime saw the deployment of the PML Buoy Profiler, which is a SSB PhD project (more of this in a latter blog from Rich Sims, PML).

 Picture of PML Buoy. Credit: Gary Fones

Sediment coring followed this, this is a key activity of any benthic cruise. We are using a number of coring devices to collect sediment from the seabed beneath us, which is 100m down. On this research cruise we are using a NIOZ corer which is used to collect sediment (mud) from the ocean floor,  a mega-corer (able to take up to 12 undisturbed samples in clear plastic tubes),  and a large SMBA box corer which is designed to take a 600mm square, undisturbed sediment sample up to a maximum depth of around 450mm.

 NIOZ corer recovered to deck. Credit: Gary Fones

Wednesday 13^th of May started with calm seas and a lovely sunrise. This was followed by a very successful recovery of the NOCL mini-stable lander that has been on the seabed the last few days gathering in-situ data (more of this in a latter blog) which will be used by the scientists to understand processes happening at the boundary between the sea bed and water column.

Recovery of Lander: Credit:Richard Cooke

Rough seas and science finally starts

By Gary Fones 

Deploying the CTD. Credit: Gary Fones

The core aim of DY030 is to collect samples and data to understand how the chemistry and biology of the Celtic Sea link together to drive healthy and productive conditions, as well as how those conditions might change with climate change. After sailing we experienced some weather more associated with March than May – a number of scientists took to their cabins or just sat on deck staring at the horizon wishing the waves away! Those with their sea legs carried on and continued preparations in their various laboratories on the ship waiting for the science to start.

CTD. Credit: Torben Stichel

We eventually started work on the 6^th May at one of our main Benthic Process sites – Benthic G. First up is always some CTD work even on a benthic sediment sampling research cruise. CTD (Conductivity, Temperature and Depth) is the stock instrument of any oceanographic cruise and enables us to understand the water column structure using a number of on-board sensors and collecting water samples from per-determined depths for subsequent analysis. After a slow start it is always nice to get the first sampling underway.

CTD. Credit: Richard Cooke

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…