Tracing metals

By Torben Stichel, University of Southampton

When Prof. Rachel Mills (Head of Department in Ocean and Earth Science, University of Southampton) asked me if I’m willing to help out on one of the Shelf Sea Biogeochemistry Programme’s benthic cruises and carry out some own research, I didn’t hesitate to say yes. I love the ocean, studying it, and before joining the University of Southampton as a Research fellow, I had already thought about the particular role of shelf seas in the global marine system.

In previous years I have put my focus on the deep ocean. I have been analysing trace metals in seawater to look at the big picture – how water masses with billions of litres per second are distributed along the ocean conveyor belt. I have looked at different tracers to understand where water masses come from and how they mix with each other. One particular tracer, neodymium, has been my focus for more than five years now – a study that involves collecting and processing thousands of litres of seawater. 

Recovery of our trace metal clean rosette that collected seawater at various depths. It is equipped with a conductivity, temperature and pressure, i.e. depth, sensor (CTD). Credit: Torben Stichel

Neodymium is a lithogenic element, which means it comes from land into the ocean via various weathering sources. The cool thing about neodymium is that its composition in water masses gives direct information about their formation regions. For example North Atlantic Deep Water has a distinct isotope composition because its surrounding landmasses mix their isotope signal into the source region where this water mass forms. We can also reconstruct past ocean circulation to a certain degree with neodymium isotopes archived in marine sediments. The problem with this isotope system is that the observed values not always meet the expected ones. In other words: water mass mixing is not the only process that governs trace metal isotope composition of seawater. Even though we have quite a good understanding on how water masses move and how they mix thanks to the help of reliable proxies, such as salinity, temperature and nutrients, there are processes involved, which we haven’t quite understood about neodymium, particular when it comes to sources and sinks of this element. 

RRS Discovery. Image: Torben Stichel

For this reason I’m looking at ocean boundaries to better understand source and sink mechanisms that imprint the neodymium isotope signal on the water masses we are tracing. The shelf seas like the Celtic Sea are potentially significant sources of neodymium into the ocean. So connecting shelf seas’ processes with the global ocean conveyor belt will help us to better understand the cycle of neodymium and trace metals in general in the ocean. 

Why is that important for us? The climate of our planet has been changing on large (glacial to inter-glacial) and smaller scales (modern climate change). Much of these changes are closely linked with ocean circulation. Understanding proxies that trace water masses are therefore vital to reconstruct past, assess present, and predict future ocean conditions.

An Irish Observer onboard RRS Discovery

By Finn Ni Fhaolain

As an Irish Observer, my role onboard is to see that the scientific work being conducted and that the locations being sampled, are the same as those outlined in the initial report submitted to the Irish Marine Institute before the cruise began. Should the need ever arise, in certain situations, I am also to act as an intermediary between Irish officials and the ship. Irish Observer positions on foreign research vessels in and around Irish waters provide a fantastic opportunity for early career level researchers to gain experience on international projects and they are encouraged to actively participate in the research efforts of the cruise.

Finn (blue hat) onboard RRS Discovery: Image Credit: Torben Stichel

During the initial day of the cruise I found out which areas I was needed most to help with. This involved filtering water samples from the CTD stainless steel rosette for organic and inorganic, dissolved and particulate nutrients and chlorophyll in the water column. These samples were taken and filtered, as part of a small team, and then frozen for later analysis by different research institutes involved in the BSS project. I spent the rest of the time helping with the sediment coring and some species sorting as I’ve some experience in these areas. I tried to lend a hand with as many other activities as possible, like core slicing and Radium sampling which I had never done before. I also enjoyed photographing the deployment of landers, buoys, the Auto Sub and gliders.

Deploying the CTD rosette: Image Credit: Torben Stichel

Having previously sampled for macrofauna in deep sea and freshwater environments, I looked forward to sampling in shelf seas in a variety of substrates. I got to observe very different fauna, those more associated with soft substrates such as starfish and flat fish.

Caught by the trawl! 

It was very interesting to see the deployment of SMART buoys and landers having read so much about them at university and having used their observational data for college projects. I particularly enjoyed learning about the set up of the Auto Sub as autonomous equipment of this kind had not been present on any cruises I have been previously part of.

The cruise not only gave me the opportunity to observe different disciplines of marine science all working together – marine biology, chemical oceanography and biogeochemistry, to name a few – it made me more aware of the division of job types between technical and academic. I felt this was a significant differentiation to become aware of, as it aids early career level scientists in deciding where on the scientific spectrum they wish to work. 

Autosub: Image Credit Richard Cooke

CO2 Fluxes: Why pelagic WP1 Richard Sims jumps ship to join the benthic WP2 team on DY030?

Deploying the Near Surface Ocean Profiler (NSOP): Image Credit: Richard Sims

The existence or not of near surface gradients is of importance when attempting to calculate air sea fluxes, as measurements from a research ships underway system at 5-7m depth may not be representative of the oceans interface. Gradients may be created by physical gradients like temperature or chemical gradients induced by biology (plankton).

Richard Sims

Richard Sims is a PhD student at PML. His research is focused on measuring near surface (10m) trace gas gradients in shelf seas.  In order to obtain a good vertical resolution for his measurements of temperature, salinity, depth and fluorescence, he developed the Near Surface Ocean Profiler (NSOP), a free floating buoy which rides the swell and floats away from the local disturbances caused by the ship. Water is pumped back to the ship where it is passed through a membrane equilibrator for CO₂ analysis. Richard hopes to use his measurements to characterise gradients across the entire shelf. 

Near Surface Ocean Profiler (NSOP): Image Credit: Richard Sims

Near Surface Ocean Profiler (NSOP): Image Credit: Richard Sims

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