Recovering the Smart Buoy’ systems

We recently recovered two ‘Smart Buoy’ systems operated by Cefas. Several such observing systems have been deployed at various stations around the Celtic Sea since March of 2014. These systems allow us to understand variation in the ocean in a way that is similar to weather monitoring. The sensors can record a variety of variable crossing physics to biogeochemical themes. These systems allow us to see how weather and climate affect surface ocean conditions and the growth of marine algae via primary production. It can measure changes in salinity, primary production nutrients, chlorophyll fluorescence, dissolved oxygen, and suspended particles. There is also a string of temperature sensors down to 60 m depth.

Recovering a 'Smart Buoy' system

We used the ship’s sensor and sampling systems to calibrate the buoy sensors, both when deployed and recovered to check that everything is working as expected and calibrate any sensor drift. Together with the sediment samples being take in the area, these long-term observatory observations allow us to better understand the variation in way that can be achieved when ships are not present. This helps bridge understanding between site visits over the change of seasons. 

Collecting images from the seafloor.

By Henry Ruhl

We have completed sediment core sampling at our four main study sites. This is a key achievement for the trip. We are now sampling one other site that allows us to cross-reference our findings with those of other studies and a long-term study station with the nickname Candyfloss. This site is closer to the continental shelf edge and open ocean than we have been for most of the trip. Marine life spotting has been good and we even laid eyes on the RRS James Cook about ten miles from us. The James Cook is researching life in the canyons that extend just beyond the shelf edge. We will soon return northward to for the more AUV deployments, the fourth deployment of the NOC lander, as well as a few other remaining tasks.

We are using the Autsub3 autonomous underwater vehicle (AUV) during our cruise to collect photographic images of the seafloor, as well as sonar-based images of the shape and texture of the seafloor. We have been running the AUV in a ‘mowing the lawn’ pattern of parallel lines that are about ~5km long. After checking our seafloor shape and texture mapping for any obstacles, we ‘fly’ the AUV as close as 2.5 meters from the seafloor to collect colour photographs in the moderately cloudy waters of the Celtic Sea.

The images will be geo-referenced, which effectively turns the photo into a map like you see in Google Earth. As you can see below, that 2.5 m height above the seafloor still gives us images that are very useful for determining the identity size, and location of all the observed images. This can provide a landscape scale view of the seafloor and its inhabitants, which we can then use to improve estimates of ecological and biogeochemical patterns and processes.

The seafloor and its inhabitants

 

AUV photographs are particularly useful in estimating the distribution of biomass of larger animals that are not sampled well by trawls or sediment cores. Observed animals include crabs, shrimps, and anemones as well as fish. The images above and below come from a Celtic Sea site where the seafloor is dominated by sandy mud.

The seafloor and its inhabitants

Mini-Flume Experiments

Sarah Reynolds. Senior Research Associate and Lesley Chapman-Greig, MRes student,  are Marine Biogeochemists with the University of Portsmouth, and their research is looking at how the processes in marine sediments can contribute to the carbon and nitrogen cycles in shelf seas.

For one of their experiments, sediment from the seabed is collected from a NIOZ core and brought up to deck, where it is stored in a mini-flume alongside water collected from the just above the bottom of the seabed by the CTD. The mini-flume simulates resuspension events on the seabed. The sediment lies at the bottom of the mini-flume, with the water from the CTD above, which is stirred by paddles of the flume to simulate the action of currents on the bottom of the seabed, which can disturb the seabed sediments causing them to be mixed (the scientific term is re-suspended) into the overlying water column. During resuspension events nutrients and carbon stored in the sediments can be released into the water column.

Mini Flume

Over the course of the experiment (~3 hours), samples of water are collected from the mini-flume at certain time points and collected for inorganic nutrients, dissolved organic carbon, particulate organic carbon and suspended particulate matter. These measurements can then be used to determine the concentration of nutrients and carbon that are released into the overlying water column. As the mini-flume experiment progresses the paddles of the flume are moved faster and faster until complete bed failure occurs.

The increases in speed of the water moving  above the sediment in the mini-flume, make it possible to measure how different current speeds close to the surface of the seabed may change the concentration of carbon and nutrients that are released from the sediments.

Sediment is collected for mini-flume experiments at three cohesive sediment sites, with each site having a different type of sediment, ranging from very muddy sediment with fine particles sizes to muddy sand and sandy mud. Depending on the type of sediment, the concentration of carbon and nutrients and the energy required to lift the sediment off the seabed varies, so by conducting this experiment with a variety of sediment types it is possible to discover how the concentration of carbon and nutrients mixed into the water column by seabed currents varies between different sediment types.

This cruise is final cruise in a yearlong project, where the same data have been collected at different stages of the seasonal cycle of the Celtic Sea. The data collected by this experiment can be used alongside other measurements, collected from the different sites at different times of the year, to get a good picture of how the suspension of sediments affects the carbon and nutrient cycles in the Celtic Sea, with the hope that these can be extrapolated to the Western European continental shelf.

36 years of working on Discovery

By Peter Statham
Ocean and Earth Science, University of Southampton

When I first set foot on the old Royal Research Ship Discovery in 1979 in Cape Town I had little idea that in 2015 I would be on the Discovery once again but now on the most recent version of the vessel to carry this famous name. 

I am interested in the chemistry of the ocean and how chemical processes affect the biology and other parts of the marine system. This aspect of oceanography is important in terms of understanding how the sea works and can be impacted by climate change. 

On this trip we are studying where the essential nutrient iron comes from on the shelf and how it may move away into the open ocean.  In some areas the element is at such low concentrations that it limits plant growth and thus impacts ecosystems, so it is important to know where it comes from, and one potentially important source are the edges of shelf seas. 

Launching a glider from Discovery. Gliders move up and down through the water by altering their density and “glide” on their wings from one location to another in the upper ocean, whilst collecting data that is sent by satellite to shore when it is at the surface. This new model has a small propeller to help it occasionally overcome strong currents.

Whilst frequently demanding with long working hours I always enjoy the times at sea with the wide range of people on board, the constant challenges to be dealt with and the buzz when a long planned experiment finally works out.  Whilst new techniques such as satellites and gliders are developing rapidly, ships are still essential tools in the study of the oceans. Discovery is a world-class research platform for UK marine science that will support our new generation of oceanographers into the future.

The animals on the seafloor of the Celtic Sea

Yesterday we recovered some nice trawls from the sandy site. We also managed to get some images of the animals that live on the seafloor of the Celtic Sea, which is about eighty miles north by northwest of Land's End.

Octopod

Octopod_suckers

Ophiuroid_brittle star

Paguroidea_Hermit crab

Asteroid

Asteroid

Echinoid_ Sea Urchin

We've now finished most of the sediment sampling work at both our muddy and sandy sites. Tomorrow will likely be a busy day as we expect to pick up some lander, buoy and mooring equipment.

Shark!

By Henry Ruhl 

We have just about finished with sampling at one of our four key study sites, which range from muddy to having sandy mud, muddy sand, and sand. Each of these can have differences in their ecology and biogeochemistry. With the muddy site essentially complete, we have just moved onto our sandy site. Just like a visit to the beach, sand seashells are getting 'spread around'. 

Spotting the shark

 And one night, we even managed to spot a shark right next to the ship. It seems that he was also spotting us by the looks of it.

The Shark

One of the things we have been doing that is generating lots of enthusiasm is short bottom net trawls to get some samples of the animals on the seafloor for identification and other research. At the muddy site, these animals have been dominated by a small shrimp called Nephrops (a.k.a. the Norway Lobster, or Dublin Bay Prawn). There is an active fishery for these and we expect to take some live specimens back to the lab to investigate how sediments with and without these species present can change sediment mixing.

A sample of the animals on the sea floor

Measuring the metabolism of the seafloor

By  Megan Williams, National Oceanography Centre

Today we recovered our benthic lander. The frame had been deployed for two days and has nine instruments measuring a range of parameters including water velocity, nutrients, suspended sediment, sediment particle sizes, and benthic oxygen consumption. Our first deployment was at a site with sandy sediments.

Recovery of the benthic lander 

 The steps toward our first recovery were many (see pictures): after driving the instruments and frame down from the National Oceanography Centre in Liverpool to our sister location in Southampton, we built the frame and started attaching instruments, batteries, and routing cables. When the frame was in a state it could be moved (with fragile instruments not yet installed), the frame was driven to the mobilization dock and loaded onto the RRS Discovery. Once on the ship, we could install the fragile water sampler (which will be used for nutrients and suspended sediment measurements) and the eddy correlation system (which makes fast oxygen and velocity measurements near the bed). The eddy correlation system measures subtle turbulent currents (eddies) just above the seafloor with both up and downward elements as they move past the sensor as swirls of water 'rolling' over the seabed. The sum of the upward (positive) and downward (negative) movement of dissolved oxygen gives a measure of how much oxygen the seafloor is using (i.e. the metabolism of the seafloor).

With a planned deployment time, we programmed instruments to start, did last minute calibrations, and set up the mooring. The frame was then slowly lowered 100 meters (m) to the sea bed, a ground line was set out, and a weight and buoy are connected 300 m away so as to not interfere with measurements.

All has gone well so far! We have the frame back on the ship this afternoon. We have now started to collect all the data off the lander, changing batteries, and preparing for another deployment of the instruments at a site with muddy sediment.