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ASCA teams up with floating university for landmark cruise

By Jethan d'Hotman, Tammy Morris and Juliet Hermes, SAEON Egagasini Node
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Only one month had passed since the end of the first Agulhas System Climate Array (ASCA) cruise for 2016 when SAEON's Egagasini Node were informed that their proposal for dedicated ship's time on the SA Agulhas II during July was successful.

This opportunity to collect extremely valuable data was grasped firmly by all scientists involved in ASCA, in order to validate moored instruments and water samples for multiple applications in a largely understudied area. Bad weather prevented this work from being completed on the previous ASCA cruise.

Once the announcement was made by the Department of Science and Technology (DST), the ASCA office immediately set to work. A wide variety of projects and researchers had to be coordinated and organised for the cruise, which was scheduled to depart on July 5. This included developing more stringent water rationing and sampling protocols for instrument operators and water samplers, as well as organising a number of science planning meetings.

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Sophumelela High School learner Tida Zukhanye deploying her school's Argo float

CTD being brought back on board after a 4 600-metre cast (Photo: Heather Forrer)

An agreement was signed between SAEON and the Council for Scientific and Industrial Research (CSIR) to use their 24 x 12L CTD rosette for the cruise. This CTD is four times larger than the CTD rosette previously used, which had a sampling capacity of only 12 x 6L. The agreement ensured that all researchers would have enough water to sample from just one CTD cast, instead of two casts planned for the previous cruise. A CTD rosette is lowered into the water to measure the salinity, temperature, depth and concentration of particles in the water column.

South Africa's floating university

The ASCA cruise was undertaken in collaboration with SEAmester, South Africa's floating university, which was conceptualised as a training course at sea where students participate in an intense lecture series combined with deck work (in collaboration with the ASCA science project) to gain practical experience. Since ASCA provides a large, international programme performing ground-breaking science and is also being used as a training platform for students, interns and junior staff, it was an excellent match.

One week before departure several meetings took place to finalise arrangements and for all personnel to get the appropriate training for their roles during the cruise. The cruise had a total of 86 people, SEAmester consisted of 40 students and 12 lecturers and ASCA had a total of 32 scientists and technicians, 15 of which were students and interns, as well as two learners and an educator.

Setting sail...

The first task of the cruise was to begin collecting Ship-borne Acoustic Current Doppler Profiler (S-ADCP) data, which would record the strength and direction of currents throughout the entire voyage. A Continuous Plankton Recorder (CPR) was also deployed to compare plankton samples along a similar transect followed during the previous ASCA cruises.

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Vertical bongo net tow being deployed to 200 metres to collect plankton and microplastics samples

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Hout Bay High learner Clarence Daniels collecting a water sample that will be analysed to calibrate instruments

After only two days the ship arrived at the most inshore mooring to be serviced (as it was not serviced during the last cruise). Unfortunately the mooring could not be retrieved, most likely due to large amounts of bio-fouling around the acoustic releases, meaning that the mooring cannot release its anchor.

The ship then steamed to the first station, where two vertical bongo tows, a full depth CTD cast and an oblique bongo tow took place. This was the order of events at every station to ensure the efficiency and safety of all personnel.

The two vertical bongo net tows were used for microzooplankton and microplastics analysis, the CTD cast and water samples were used for calibration (of oxygen and conductivity sensors on the CTD), phytoplankton identification, microbe analysis, flow cytometry, nitrogen isotope analysis, chlorophyll a analysis, nutrient analysis, primary production analysis, microzooplankton samples and phytoplankton community composition. The oblique bongo tow was used to collect zooplankton samples between the stations.

The transect was completed successfully, 23 full depth CTD casts were completed, including two additional casts in the Agulhas Current and one further offshore (from station 20, the furthest official station). The bongo net tows were not as successful - high winds and large swells forced almost half of the bongo net stations to be cancelled.

Learners deploy two Argo floats

Once the furthest station had been completed, an uninterrupted S-ADCP transect was undertaken, during which the four Argo floats adopted by high schools around the Cape Peninsula were deployed, two by the learners themselves.

SAEON would like to acknowledge, and thank, the DST and the National Research Foundation for making the Agulhas II available; Professor Isabelle Ansorge and her team for the opportunity to team ASCA with SEAmester; Chief scientist Gavin Louw and the rest of the Department of Environmental Affairs staff; the crew and Captain of the SA Agulhas II; all of the scientists, lecturers, students and learners involved; and lastly, the weather in making the cruise extremely successful.

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