Lost and found in the Atlantic Ocean: MIDAS researchers help out TREASURE colleagues
Lagrangian models are not only good at simulating the dispersion of virtual mining plumes and larvae in a virtual ocean. They also prove their merits in tracking objects in real life, as recently demonstrated by the successful salvaging of a runaway bottom lander of NIOZ.
In the early hours of 2 May 2016, a stream of alerts received via satellite link warned NIOZ biologists Gerard Duineveld and Marc Lavaleye that one of their bottom landers was floating at the surface 250 nautical miles southwest of the Azores. The lander, equipped with CTD, current meter, sediment trap and time-lapse baited video camera, had been deployed in April 2015 in 2100 m water depth on the Mid Atlantic Ridge near the Rainbow hydrothermal vent field, as part of the Dutch TREASURE project. Along with two other landers and one mooring deployed in the same area, it was meant to be recovered in July 2016 by the Dutch RV Pelagia. For unknown reasons this lander had prematurely released its anchor and had surfaced. Urgent action was needed to salvage it. U-Azores biologist Telmo Morato, called in for assistance, was quick to find a skipper based on the Azorean island of Faial who was willing to sail out with his fishing vessel to rescue the lander. Many days of precious time was lost, however, as storm depressions swept over the Azores, forcing skipper Jorge Gonçalves to wait for a window of calm weather. Far out at sea, in the meantime, the lander was drifting 10 miles per day along an irregularly meandering track. The chances of ever finding the costly equipment back depended heavily on how long the batteries of the satellite beacon would last. Without regular updates of the lander’s position, a rescue action would almost certainly be deemed to fail. Coincidence or not, on Friday 13 May the dreaded scenario became true: while weather forecasts finally were improving, the satellite beacon expired. As a last recourse, U-Azores oceanographer Manuela Juliano was called in for help. Would she by any chance have an ocean circulation model running for the Azores region, which might predict the track of the lander? Not by chance but thanks to her modeling work in MIDAS she did. And while skipper Jorge headed out with his small fishing vessel toward the approximate lander position, Manuela made her Lagrangian model simulate the track of a 1000 virtual landers swarming out and dispersing in the meanders and eddies of the Azores Current. A search line, running through the center of the simulated swarm, was then communicated via satellite telephone to the skipper. On Tuesday 17 May, when the ship was approaching the end of the search line, the satellite beacon which had been dead for more than three days miraculously revived and transmitted a single position, which turned out to be less than four miles away from the search line. Within an hour the ship reached the indicated position and there the bright orange flag marking the lander was soon sighted. With skill and ingenuity the 650 kg structure was hoisted on board the small fishing vessel, thus ending its errant journey of approximately 180 miles across the ocean.
On behalf of the TREASURE team a huge thank you to the heroes of this story: Telmo Morato, Manuela Juliano and Jorge Gonçalves and crew of FV Manuel de Arriaga!