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ASCA 2018: The roller coaster ride continued

By Jethan d’Hotman, Jordan van Stavel and Rudzani Silima, SAEON Egagasini Node
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The mooring team in action during the retrieval of mooring A (Photo: Kay McMonigal)

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The CTD package being retrieved from sampling the Agulhas Current (Photo: Houraa Daher)

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Student Rudzani Silima (L) and ASCA coordinator Tamaryn Morris prepare to deploy a surface drifter (Photo: Kay McMonigal)

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Intern Lizelle Carolus (L) and student  Rudzani Silima assist during mooring retrieval operations on the back deck of the vessel (Photo: Shane Elipot)

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Interns Jordan van Stavel (L) and Whitney Samuels remove a MicroCAT and current meter from a bracket attached to a mooring line (Photo: Shane Elipot)

On 31 May the SA Agulhas departed Port Elizabeth Harbour for what would be a disappointing end to the current state of the Agulhas System Climate Array (ASCA). 

The 2016 ASCA cruise saw the first deployment of the array to its fullest extent.

Unlike previous cruises that were split into legs with a specific focus either on moorings or CTD operations, due to cost and time constraints this cruise was set out to be one non-stop 20-day cruise. The objectives of the 2018 cruise were to recover all moorings (seven tall moorings, two coastal moorings and five CPIES) and complete 23 CTD (conductivity, temperature and depth) full-depth stations including calibration dips for MicroCATs that were recovered from the moorings.

Crew

On board the cruise were 16 scientists, split between the South African Environmental Observation Network (SAEON) (6), the Department of Environmental Affairs (DEA) (2), the Rosenstiel School of Marine and Atmospheric Science (RSMAS) (6), with Bradley Blows and Ryno Else providing mooring and electronics support.

Also on board were 20 trainee cadets. These cadets (from various universities) were given the opportunity to work alongside high-ranking officers and gained invaluable practical experience throughout the duration of the cruise as part of their studies.

Operations

The plan for this cruise was to start operations from the most offshore station, to complete the deep stations and retrieve the longest moorings first and proceed inshore. With a constant eye on the weather and state of the sea, the plan of action was adapted on a day-to-day basis to optimise ideal working conditions. Fortunately, the weather only played a minor role in comparison to the technical and logistical constraints faced on the cruise.

As the CTD operations began, the operators realised just how stressful these would be. The ship was equipped with an echo sounder capable of providing depths to 2 000 metres only, while our deepest station was at a depth greater than 4 500 metres.

To add to this, the CTD winch had a faulty wire display so operators seldomly knew the orientation of the CTD package. This meant that CTD operators often had to 'fly the CTD blind’, with only the CTD’s own pressure sensor and altimeter to use as a guide.

These stresses were compounded when, while at the bottom of a CTD cast (~4000 m), the archimedes screw of the CTD broke, resulting in considerable panic and being forced to abort the station by retrieving the CTD manually. A new part was soon engineered and CTD operations began again the next day.

During one of the next CTD stations, all operations had to be aborted due to a malfunction in the ship's bow thruster. The CTD was recovered and a decision was made to return to port to have the bow thruster fixed. During the transit back to Port Elizabeth, a RSMAS student used this opportunity to deploy nine Argo floats and eight surface drifters which would be used in her PhD.

Fortunately the bow thruster was repaired overnight and the SA Agulhas left Port Elizabeth for what would be the last time for this cruise. Due to the delays it was decided that only mooring operations and calibration CTDs would continue. This resulted in just 11 completed CTD casts out of the initial 23 planned.

At the end of the cruise an unsuccessful attempt was made to recover the two coastal moorings. The mooring technician suspected this was due to biofouling on the acoustic releases. Another attempt to recover these moorings will be made on a future cruise.

The cruise was not only doom and gloom though. All mooring operations went relatively smoothly, with only a handful of instruments being damaged or flooded during their deployment. With good weather and food, along with a treasure hunt at the end of the cruise, all participants were in good spirits as the ship made its way back to Cape Town.

All in all this cruise provided the perfect platform for skills and knowledge sharing among scientists, technicians and students. A cruise of this nature shows that it is not always 'smooth sailing’. Marine science can be extremely challenging at times, which in hindsight provides the best opportunities to learn and grow.

If there was ever a cruise that epitomised the famous South African saying, ''n boer maak 'n plan' ('a farmer makes a plan') it would have been this one.

Jordan van Stavel and Rudzani Silima had this to say about their experience:

Rudzani (Cape Peninsula University of Technology BTech student): The actual mooring recovery was especially thrilling, from establishing the mooring’s position and spotting the floats to the anticipation of watching the crew tag a line on the surface buoy to be towed on the stern of the ship. The mooring was winched on deck and one by one, the instruments were recovered, inspected and shipped off to the lab where two years’ worth of data would be downloaded.

Jordan (SAEON intern): Subsequent to all mooring retrieval operations, instruments were cleaned off and set up in the lab in preparation for the data to be downloaded off each of them. This process was stressful at times, when issues would arise with damaged instruments, faulty cables or a rolling ship. Nevertheless, these issues were nothing we could not find a solution to, and after all downloads and back-ups of data were made, the instruments were carefully stored until the end of the cruise.

As challenging as the cruise was, it was an overall success. All moorings were recovered and sufficient data was collected to validate the data collected by the mooring array. As students and interns it was a privilege to participate in this cruise and we look forward to the continuation of the ASCA project in the future.

For more information or updates on ASCA, please visit http://asca.dirisa.org/

ASCA 2016 article: http://www.saeon.ac.za/enewsletter/archives/2016/june2016/doc04

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