Shelf Sea Biogeochemistry blog

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.

Friday 17 July 2015

Meanwhile, science continues

By Mark Moore

Around the drama of Wednesday afternoon (see Lucie’s recent blogpost), the science on board continues apace. Over the 5 intensive days of science to date we have already completed 72 ‘Events’ each of which effectively corresponds to a deployment of one of the many pieces of equipment which you may have read about during previous log entries, including deployments of moorings and gliders, CTDs, net sampling (see picture below) alongside snow catchers, in situ pumping systems, etc, etc ....  

Picture: The ongoing event log in the main laboratory
Others: A CTD coming on deck
Net sampling
Mooring deployments
A glider being ballasted on board before being deployed

With all this activity occurring on board it is important that we keep detailed, accurate and up to date records. The first stage in making sure everyone knows where we are with planned activities is a running event log which we keep in the main lab of the ship (see picture). Here we provide a rough record of what has happened to date, allowing the person leading the next activity to confirm the event number and providing a record for checking against more detailed logs. Simultaneously the officers on watch also keep a separate ongoing record of all activities from up on the bridge. One of my jobs as principal scientist then involves keeping a check to make sure that all these logs are aligned. It pays to have multiple redundancy as although a research ship is a reasonably small space, with everyone working in different areas of the ship and at different times of the day and night effective communications can sometimes still be a challenge!

Work wise we are currently around half way through another of our CTD (Picture) sampling transects down the shelf edge aimed at understanding the processes by which iron (Fe) may be transported off the shelf. Working where the water depth shoals so steeply has its own challenges. We have to be extra careful lowering sampling equipment near to the bottom as there are regions of the shelf break where the water depth can change by 1000m in under a km, i.e. a >45% slope!

Wednesday 15 July 2015

Call of Duty - Receiving a distress call

This week we were all reminded that RRS Discovery is more than just a research ship. On the open ocean, every vessel has a responsibility to play their part in the safety of the rest of the sea-going community.

Sampling activities at our first process station; Central Celtic Sea (CCS), were drawing to a close. All on board were starting to get into the swing of things. Most operations had run smoothly so far, including two pre-dawn sampling points, which at this time of year begin at 02.00 am!

At approximately 13.00 pm many scientists and technicians were on deck sampling seawater from the midday CTD; the piece of equipment which is deployed over the side of the ship to collect water from many different depths. Although sampling at CCS was not yet complete we noticed the ships engines rumble to life and the ship beginning to move. Soon after, Captain Jo appeared on deck with some somewhat startling news, at least for those of us who are not seasoned seamen.

RRS Discovery had received a distress call. The hull of an upturned vessel had been sighted from an aircraft, and we were in close vicinity and were required to respond immediately. The steam west to the site of the incident took approximately 3 hours, and it was all eyes on deck to keep a look out for anything unusual. Needless to say the atmosphere was tense, but the crew were incredibly calm and professional.

Cargo Ship and spotter plane look on as the boat from Discovery investigates
upturned hull.

When recovered Goose Barnacles indicate that the rusty old open boat has
clearly been at sea for a considerable time!

At around 16.00 we spotted a tiny brownish speck bobbing in the swell; the hull of a very small upturned boat. A light aircraft from the Irish coast guard was surveying from above, and a large container ship had reached the scene first, but neither had the means to move in for a closer look. 

With a readily deployable rib, RRS Discovery is better prepared than most vessels for the situation. Three brave crew members rose to the challenge of boarding the rib; 2nd Officer Vanessa, 3rd Engineer Angus and Petty Officer Willie. Watched anxiously by the rest of us they motored out to make an inspection, where to everyone’s great relief they found that the boat had clearly been adrift for quite some time, and was not a recent capsize. It was reddish-orange with rust, spattered with white bird poo, and hundreds of barnacles clung to its submerged surfaces. Some skilful manoeuvring by both the crew on the rib and on board the Discovery brought the old wreck alongside, and it was carefully winched aboard, in order that it would not cause an alarm to be raised in the future. The biologists among us ogled the stalked goose barnacles; beautiful yet slightly repulsive as their fleshy parts struggled and groped in vain for cool seawater. Meanwhile, the trace metal group shuddered at the amount of rust on the deck, and gave it a wide berth. 

The boat has been carefully stowed atop Alex and Chris’s container lab. They look forward to the stench of rot that will inevitably ensue if the sun decides to make an appearance.