This is a first since 2008 on the Vendée Globe, skippers have encountered icebergs drifting outside the zone where they are prohibited from sailing. The progression of these enormous blocks of ice is under close surveillance, thanks to satellites. This is the specialty of CLS, a subsidiary of the National Center for Space Studies, based in Toulouse.
The essentials of the day: our exclusive selection
Every day, our editorial team reserves the best regional news for you. A selection just for you, to stay in touch with your regions.
France Télévisions uses your email address to send you the newsletter “The essentials of the day: our exclusive selection”. You can unsubscribe at any time via the link at the bottom of this newsletter. Our privacy policy
Stunning and frightening appearance, on January 1 and 2, 2025, in the Vendée Globe. For the first time since 2008, three skippers crossed paths with icebergs having crossed the “virtual line” of the zone prohibited to navigators for their safety. At the rear of the fleet, Oliver Heer is approaching the area where the ice blocks were detected. Specializing in tracking icebergs using satellites, the CLS company is on the alert.
How is this monitoring carried out to ensure the security of browsers? We asked the question to Franck Mercier, scientific expert within this CNES subsidiary, specializing in the detection and monitoring of icebergs.
Ahead of the race, detection specialists use altimeter radar satellites. Then, when the boats are in the area, CLS analysts use data from radar imaging satellites: Sentinel-1 from the Copernicus program and the Canadian commercial satellite, RadarSat-2.
For the safety of sailors, the Vendée Globe management has determined with the help of CLS an exclusion zone, “the boundary of the playing field“skippers involved in the race. For reasons of sporting fairness, this zone is frozen before the passage of the first competitor. This is what was done on December 16.”We had already taken around twenty satellite imagesFranck Mercier tells us. A few weeks ago, several large icebergs of a kilometer size were detected. These icebergs continued to move.“
CLS, a subsidiary of the National Center for Space Studies, monitors the drift of icebergs in the Pacific, using satellite images.
•
© CLS
Movement speed of an iceberg: between 1 and 5 km/h, depending on the specialist. “The speed of a pedestrian in a moderate hurry“.
“Since December 16, obviously, the icebergs which were around a hundred kilometers below the ZEA, have moved, mainly towards the east and a little towards the north. And on December 30, we had an image satellite which allowed us to confirm that we indeed had icebergs north of the exclusion zone.“The ice blocks are seen by Sébastien Marsset, Eric Bellion and Conrad Colman in the Point Nemo area, in the middle of the Pacific.
In addition to satellite images, iceberg detection and tracking specialists also use a drift model. “But it is relevant on the scale of a few daysrecognizes Franck Mercier. On a scale of 15 days or three weeks, the drift models remain very imprecise. You should know that the main driving force behind the drift of these icebergs is the currents at depth. The submerged part of the iceberg is probably at most a hundred meters deep. And these deep currents are not very well known. This is why the drift of icebergs remains something that is relatively imprecise.“
“We are able to detect icebergs that are around a hundred meters long. The example I give to skippers, because almost all of them have sailed in that area, is an iceberg the size of Fort Boyard. This is typically the size of icebergs that we are able to detect. And I think that’s about the size of what they must have seen on January 2nd.“
Eric Bellion and Sébastien Marsset would have seen the same iceberg, a little further north than a second ice giant seen by Conrad Colman. “What is quite intriguing is that these two icebergs have shapes that seem very, very similar. What we actually suspect is that it’s two pieces. Which would also correspond with an observation that we had been able to make by satellite before. What is very likely is that these are two pieces of a single, slightly larger iceberg that we observed south of the line a few days ago.s”, explains Franck Mercier.
The normal evolution of an iceberg is to move, both to melt and to fragment.
Franck Mercier, ice expert at CLS
An iceberg breaks up under the effect of “aging” and a long journey. The scientific expert tells us that the iceberg seen by the skippers has certainly left.its comfort zone on the immediate outskirts of Antarctica several months, even several years ago now.” And the block of ice is set to make a long journey.
One of the icebergs seen, outside the exclusion zone, by three Vendée Globe skippers at the start of 2025.
•
© Vendée Globe
It will be tossed around by the waves, will experience rain which can dig furrows and create fractures. “In this part of the Pacific Ocean, it is in relatively cold water, at 5 degrees. The pieces will therefore not melt very quickly. They can travel for a long time yet. Travel several hundred, probably several thousand kilometers“, estimates Franck Mercier. Until they get closer to the coasts of South America.
The next Vendée Globe competitor to approach the area where the icebergs were seen is Oliver Heer, aboard his Imoca Tut Gut. The Swiss skipper is almost on the line of the exclusion zone, a stone’s throw from Point Nemo.
CLS has already planned new satellite images to refine the presence or not of icebergs on the passage of skippers Oliver Heer, Antoine Cornic and JungKun Xu. “There are other icebergs a little further southFranck Mercier told us on January 3. There are some who can continue to go back up and also cross the line of the exclusion zone.“As for the two pieces of ice observed on the course a few days ago, they may have broken and transformed into three or four other icebergs. Pieces too small to be detected, warns the CLS specialist.
