On this part of the voyage S.A. Agulhas II spent a total of 18 days, 13 hours and 50 minutes inside the Antarctic Circle (66° 33' 55" South), and our Antarctic experience ended when we left the Ekström Ice Shelf on 15 February. Despite the previous day's icy wind on the observation deck, the late evening atmosphere just had to be enjoyed once again for the last time. The moon rising over an iceberg drifting in Atka Bay and the play of colours in the heavens over Ekström Ice Shelf and Neumayer-Station III were a worthy conclusion.
Evening mood in Atka Bay on 14 Feb. 2020.
The return trip began, heading in an east-northeast direction, after the last containers were loaded in the afternoon. The Sentinel-1 images that had been made available guided our route along the southern edge of the sea ice and then north across an unproblematic region of sea ice. An analysis of the route in this segment of the journey clearly showed us that despite existing sea ice a rapid passage usually exceeding 10 knots was possible. Only when we entered the area with sea ice cover was our velocity briefly reduce to under 10 knots.
For the last time a Sentinel-1 recording was consulted to analyse the sea ice situation as we departed northward. And we took a last look back at the Ekström Ice Shelf: Farewell Antarctica!
The route continued along the Good Hope Line, the prime meridian, always heading north. Now the oceanographers on board got their reward. Marine measurement instruments are regularly dropped along this stretch by research vessels. Depending on their design, they can provide data for several months, or even years. Many are buoys that drift with the ocean currents around the Antarctic continent, routinely relaying their measurement data via satellite. Other instruments also move with the currents but collect vertical profile data down to ocean depths of 2000 m, thereby supplying information on temperature, salinity and oxygen content at various ocean depths. Other instruments function like drones. They measure diverse parameters along specified vertical profiles and then head for programmed waypoints. They can be retrieved weeks to months later from ships so that the recorded data can be read out and the instrument platform reused for a new measurement campaign after refurbishing.
Retrieving this kind of underwater glider requires the skilful coordination of scientists and crew. First, the ship heads for the latest coordinates sent by the underwater glider every five minutes via satellite. When this location has been reached, every eye available is welcome to search the ocean surface around the ship for the little antenna on the underwater glider. After it is discovered it has to be cautiously recovered with a specially-equipped crane. Especially if there are high winds and waves such a recovery requires the crew's total attention – from the captain to the crane operator to the men at the ropes whose job it is to stabilise the recovery device. If everything goes smoothly – as was the case on 18 Feb. 2020 – the data will contain important information about the state of the ocean. Such a recovery is not only a special event for those on board. A group of humpback whales was also extremely interested in the activities on the red giant that had entered their territory in the morning of 18 February – and that in turn considerably delayed use of the retrieval equipment.
Retrieving an underwater glider at the prime meridian at 58°S. Before, S.A. Agulhas II was observed for several hours at close range by a group of humpback whales.
Since Wednesday evening S.A. Agulhas II has been on the way to Marion Island, where two passengers will join us on Monday. Arrival in Cape Town is planned for 28 Feb. 2020. Until then the Furious Fifties and Roaring Forties will guarantee us a high seas feeling. The wave activity has increased considerably and the ship's roll is can be definitely felt – and seen! But rocking belongs to the Fifth Season, after all, and so I sign off with a high sea's carnival greetings: Alaaf!