Wave gliders | South African National Antarctic Programme

Our Wave Gliders have arrived back from the Southern Ocean. Last Friday 5^th April we picked up our second carbon Waveglider WG027 a few tens of metres from the breakwater in Granger Bay at the end of an exciting but problem free transit of 1500km from the Sub-Antarctic Zone (43^oS 8^oE)(Video). Its twin WG052 had completed its even longer transit of 2800km from the Polar Upwelling Zone (54^oS O^oE) 9 days earlier. Both units arrived in excellent shape in what was a first for us, bringing our gliders home with a ship pick-up. Both gliders completed 4-month long missions of which 10 weeks were sampling at their respective locations and 6 weeks transiting back to Cape Town.

VIDEO: WG052 waiting to be picked up off Granger Bay in a cold misty morning in Cape Town a couple of weeks ago after its 2800km epic from 54^oS.

https://www.facebook.com/AntarcticLegacySA/videos/322703648445517/

Bringing the gliders home under their own means opens the door towards the direction of reducing the dependency on ships and reduces the long-term costs of long-term observations. It is a significant technical challenge for the robots and the engineers. The biggest problems we encountered, apart from the vicious storms, were the very strong mesoscale jets west of the Agulhas retroflection area. Jets with flow speeds of over 2kn posed navigation challenges for the pilots but we also learned much from the experience and despite a few necessary deviations (Figure 1a,b) that probably added a week to the transit we got them home in really good shape (Figure 2).

: Figure 1a: shows part of the route of the gliders from the Sub-Antarctic Zone (SAZ) to highlight how the transit routing had to be adapted to follow the mesoscale jets to the west of the Agulhas current retroflection area.

: Figure 1b: shows the location of those jets SW of Cape Town.

: Figure 2: Wave glider WG027 on its dolly after recovery last week and displaying a few goose barnacles as a memory of its 4-month in the Sub-Antarctic Zone.

The decision to bring them home was shaped by two main considerations: firstly, we wanted to avoid the expensive physical damage to the gliders that often happens with ship recovery, especially under the typically rough conditions in the Southern Ocean. As it turned out we made the right call especially for WG052 which would have been all but impossible to retrieve such were the conditions. Secondly, we wanted to evaluate if wave gliders can be combined to address mesoscale differences in the response of the ocean to synoptic scale atmospheric forcing.

As mentioned in earlier posts each of these gliders was paired with a buoyancy glider over the entire period of deployment at their respective long-term observational sites in the SAZ and the PUZ as part of two NRF-funded SOCCO SOSCEX-Storm projects. This pairing enabled us to simultaneously observe the air-sea fluxes of CO and the ocean physics dynamics that influence them in the upper 1000m of the ocean. This is necessary because it is not clear how important these ocean dynamics are in predicting the climate sensitivity of the carbon cycle in the Southern Ocean. This learning will be used to improve the Earth System Models used to predict regional and global climate change, particularly the South African CSIR-VrESM model being developed as a collaboration between SOCCO, Global Change Institute-Wits University and the MaRe Institute at UCT.

All the instruments were fully operational over the entire time and the initial look at the data suggests that we have excellent accuracy and precision. This was the first operational test for our newly developed VeGAS pCO2 units on both gliders and we will do a deep dive into the data later this week.

This science work would not have been possible without the expertise and dedication of our engineering partners at Sea Technology Services who run SA-RobOTIC and their student engineers.

– Dr. Pedro M. Scheel Monteiro & SOCCO & SA-RobOTIC team, 08 April 2019 (posted 16 April 2019)

The S.A. Agulhas II is now on its homeward journey having finished all logistical and scientific work at SANAE and in the Weddell Sea (track the ship here). The work is not yet over for all aboard, however. Scientists from the University of Cape Town (UCT), the Council of Scientific and Industrial Research (CSIR) and the South African Weather Service (SAWS) continue to collect oceanographic and meteorological data. UCT and CSIR are both sampling seawater as the ship sails, measuring chlorophyll, nutrients, ammonium and phytoplankton community composition, to name a few.

Over and above this, CSIR—more particularly, CSIR SOCCO—and Martin Mohrmann of the University of Gothenburg and ROAM-MIZ deployed oceanographic instruments on the voyage south to Antarctica (see photos below). CSIR SOCCO, or the Southern Ocean Carbon & Climate Observatory, is a South African research programme focused on the Southern Ocean. ROAM-MIZ, according to their website, “is a multi-institutional initiative to observe the full seasonal cycle of the upper ocean in the marginal ice zone near the Greenwich Meridian”. CSIR SOCCO deployed two wave gliders, a Seaglider and a Slocum glider. ROAM-MIZ deployed two Seagliders and a Sailbuoy, christened SB Kringla. These instruments continuously record oceanographic data while they move through the water. The wave gliders and the Sailbuoy remain at the surface, harnessing wave and wind power, respectively, to propel them through the water. The Seagliders and Slocum glider alter their buoyancy to dive and sample sea water during their journeys to the deeps (deep parts of the ocean) and back to the surface. All these vehicles transmit their data to satellites at regular intervals or when they surface after a dive.

Deployment of Gliders

: Martin Mohrmann (University of Gothenburg and ROAM-MIZ)

: Colin de la Harpe, CSIR team leader, lending a hand with the preparation of a CSIR SOCCO wave glider.

: Mfezeko Rataza, of Sea Technology Services (STS), leading the CSIR SOCCO wave glider setup.

: ROAM-MIZ’s two buoyancy gliders making satellite contact in preparation for deployment.

: A successfully deployed wave glider gets an avian escort.

: A wave glider being deployed off the poop deck of the S.A. Agulhas II.

: A wave glider being deployed off the poop deck of the S.A. Agulhas II.

: Deployment of a ROAM-MIZ buoyancy glider.

: Deployment of the Sailbuoy, SB Kringla.

With the S.A. Agulhas II now making for home, the time has come to recover these instruments in order that they can be serviced and used again in future deployments. The wave gliders, in a true feat of engineering, are being piloted home to Cape Town. This is due to reducing sunlight available for the solar panels of the southernmost glider as the receding summer light wanes at these high latitudes. This will entail a journey of 1200 km and 2500 km for the respective wave gliders (click here for the update on the position of the gliders). Two Seagliders, the Slocum glider and the Sailbuoy will be recovered on the voyage home. The third Seaglider is to be recovered by another vessel, the Norwegian RV Kronprins Haakon, sailing from Punta Arenas in Chile.

On the 1^st of March, the Sailbuoy and a ROAM-MIZ Seaglider were both safely recovered in fair weather at 60°S 0°E. The speed and success of the recovery were entirely down to the skill of the S.A. Agulhas II’s crew and the prevailing calm weather. Next, the Slocum glider will be recovered at 54°S 0°E and then CSIR SOCCO’s remaining buoyancy glider at 43°S 8°E. The S.A. Agulhas II is now making for 54°S 0°E after having sailed to South Thule and South Georgia for SAWS deployments and commitments.