Shelf Sea Biogeochemistry blog

Showing posts with label SSB. Show all posts
Showing posts with label SSB. Show all posts

Tuesday 25 August 2015

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. 

Saturday 22 August 2015

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

Thursday 20 August 2015

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.

Monday 17 August 2015

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.

Wednesday 12 August 2015

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

Monday 10 August 2015

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.



Friday 7 August 2015

Starting Out

By Sebastian Sims

My name is Sebastian Sims, and I have just finished my first year at the University of Southampton, studying MSci Marine Biology. Cruise DY034 is my first voyage out to sea, and I feel honoured to start my scientific career with the opportunity of joining RRS Discovery on a shelf sea biogeochemistry research cruise.

DY034 is the last cruise of the SBB series, and "This is an exciting time for the Shelf Seas Biogeochemistry Programme as we finish the last of nine cruises aboard RRS Discovery" says Principle Scientist, Henry Ruhl.


RRS Discovery
"We'll mainly be conducting seafloor research, but also making measurements and taking samples in the overlying waters. The key use of these observations is to better characterise how seawater chemistry and other factors drive carbon cycling and storage, including the role of biology and ecology. In addition to using UK's most advanced research vessel, we've got robotic subs and other tools to hand that mark a real evolution in how we can observe and understand the seas around us."

I first set foot on the ship on 4th August, to receive some training as to the sampling I'll be doing. I work in WP1, and my role involves oxygen calibrations and processing for phytoplankton and other variables. Initially, this did feel like a lot to take in, but once I had practiced some of the essential skills, and after receiving some more training the next day, I began to feel a lot more confident.



Leaving Southampton
I boarded the ship for the voyage on the 5th. After seeing my cabin, I was surprised at the high quality of the cabin, and the food also surpassed my expectations. We also had a science meeting to plan additional details of our expedition, which gave me a good overview of the research happening on board, as well of the anticipated order of events.

Yesterday, the 6th of August, we had a presentation and tour about life on the ship with a focus on health and safety. Following this, there was another brief science meeting. Then at last, Discovery left berth 106 at around 7pm. A few of the scientists and I then made our way to the bow, where we spent quite a while outside enjoying the evening transit. I was particularly impressed by the departure of the pilot, and also the incredible view of the Needles and Alum Bay at sunset.

Sebastian Sims

Friday 24 July 2015

Diagnosing Transmission Problems


By  Julie Wood, NMF Technician

Thursday marked the end of the second iron transect of the cruise and for the technicians, it certainly was an eventful transect.

As technicians, one of the most important pieces of equipment we are responsible for is the CTD. This is a short name for the large metal frame carrying conductivity, temperature and pressure (measuring depth) sensors along with a whole suite of other instruments such as sensors to measure current, turbidity and fluorescence. It also carries large water bottles which can capture water from any depth visited.

On this cruise, we have two CTDs. One is a normal stainless steel frame with 20L bottles, while the other is made of titanium with 10L water bottles. Apart from titanium, this second frame contains as little metal as possible because it is used to collect water for investigating trace metals. The 10L water bottles are kept in the trace metal laboratory on the ship. Before each trace metal CTD, they are individually carried out to the frame to limit exposure to the metal on the ship.
Clean Sampling room with bottles

The CTD is lowered in the water by a wire of over 7000m long stored on a large drum. The cabling from the CTD is joined to the wire by an electrical splice near the mechanical termination (this is the conical part between the wire and the CTD frame). This allows real-time data from the sensors to be transmitted from the CTD along the wire. This means we can see profiles of ocean parameters while the CTD is in the water which can help the scientist select the depths that they would like to take water samples.

The first CTD of the iron transect was to commence on Tuesday morning at around 4am. Nick and Tom, the technicians on duty, prepared the CTD as usual for its journey down to 2400m. At around 1050m, the sensor readings indicated that the communications between the deck computer unit and the CTD had failed. The CTD was brought back on deck and the sensor readings all returned to normal. A second deployment was attempted for diagnostic purposes, however once the CTD was back in the water, the sensor readings stopped again confirming that there was a problem with the termination.
Julie and Dougal working on the CTD

The senior technician, Dougal, was called to assist in diagnosing and rectifying the fault. Based on the observations, initially 2m of cable was removed from the end of the wire. However, when the wire was tested, the electrical characteristics were found to be unsatisfactory. A further 400m of wire was removed and then the wire performed perfectly.

With assistance from Andy, the mechanical engineer, and Steve from the Glider group, the team started to build a new termination which is time consuming and requires attention to detail. A new mechanical termination needed to be put on along with a new electrical splice in order to communicate with the sensors. Both activities required concentration to ensure they were correctly and safely attached.

The final test, the load test, was performed on the new termination. This involved attaching the termination to the deck and progressively applying increasing force to a final weight of 1.2 tonnes. This ensures that it is well able to hold the CTD frame.

By 7:30pm, the titanium CTD was back in the water. Despite passing the load test, the first deployment following a new termination is always a nervous affair. The frame safely made it down to 2430m, just 20m shy of the bottom. All bottles were filled successfully with recovery of the CTD at 9:15pm.

The Metal Free CTD Winch

Unfortunately, this incident did caused delay to the science program. Some careful re-jigging of the timetable by the Principle Scientist meant that the iron line was still completed successfully. We deployed the titanium CTD at seven stations along the iron transect.

The final titanium CTD was retrieved on Thursday at 2pm, amid much excitement from the team of iron scientists collecting these water samples. With a completed transect, we hope they find lots of interesting features about iron on the shelf.