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

Studying radium concentrations in the muddy sendiments off the north west coast of Cornwall.

On Tuesday we continued with our coring as well as performing a few more CTDs.  Amber Annett (Edinburgh University) is taking water column samples from the CTD and sediment samples from an instrument called a megacorer, in order to study radium concentrations in the sediment and the overlying water, and she has written the following blog piece about her work.

Naturally occurring radium is a very useful element for studying many different shelf sea processes. This is because it is radioactive (no, not that dangerous sort of radioactive!), and we know the rate at which radium naturally decays. This means that radium can act as a kind of internal clock for a parcel of water, telling us how fast things happen.

Luckily, radium is also extremely rare in seawater, so even though it is a radioactive element it is present at concentrations thousands of times lower than anything we would need to worry about. Even though I use extremely sensitive detectors to measure radium (photo), because it is so rare I still need to sample a very large amount of water  to collect enough for a useful measurement– up to 150 litres for just one sample.

Amber's radium detectors on board the RRS Discovery

Radium comes from rocks, and there is plenty of lithogenic (rock) material in the sandy, muddy sediments on the UK continental shelf here off the north west coast of Cornwall. I am using a megacorer to collect pore water (water from in between the sand and mud particles inside marine sediments) and samples from the sediment-water interface, as well as a CTD to measure radium in the water column above. This lets me look at how much radium diffuses out of the sediments and into the sea, as well as how quickly this process occurs. This work is part of the trace metal group (SSB Work package 3), who are ultimately looking at how shelf seas can act as a source of iron, an essential nutrient for marine plant life, that is very scarce in many areas of the ocean. 

We will be using radium concentrations to help track iron that comes from sediments, where it goes and how fast it gets there.