Scientific expedition: the Kerguelen archipelago, the forgotten oasis

The French territory of Kerguelen is a natural sanctuary, a marine and terrestrial reserve listed as a UNESCO World Heritage Site. But it's not just its raw beauty that attracts scientists. “We've been asking ourselves for a long time: why is there so much life on Kerguelen?” says Stéphane Blain, professor emeritus at the microbial oceanography laboratory of the Oceanological Observatory at Banyuls-sur-Mer.

The archipelago is home to king penguins, albatrosses, sea lions, elephant seals...and others. They all come here to nest and reproduce. But to survive, they must feed at sea. That's where the mystery begins: in this generally iron-starved ocean region, how does underwater life flourish?

In this nutrient-poor zone, a spectacular proliferation of phytoplankton—the microalgae that feed the entire marine food chain—is emerging. The bloom observed around Kerguelen is so large that it can be seen from space. “In the Southern Ocean, this is extremely rare. That's why we call it a biological oasis,” explains Stéphane Blain.
This oasis raises another question: where does the iron needed for this photosynthesis come from? Because this micronutrient is extremely rare in southern waters. “It's an ocean far from the continents, so there are no conventional atmospheric or fluvial inputs.

Stéphane Blain's team has been working on the site since 1995. It's only recently that a hypothesis has emerged: the Kerguelen ice cap could be the source of this iron. “It's the fastest-melting glacier in France. It's retreating at an impressive rate,” he observes. Glacial erosion generates a mineral-rich rock powder known as glacial flour. Accumulated in lakes, transported in estuaries and then carried out to sea, it could feed the iron bloom. 

The MARGO project is unfolding like an open-air investigation. Three questions structure the work of the research teams: is the glacier a significant source of iron? Is this iron capable of reaching the open sea, dozens of kilometers from the coast? Can it be biologically assimilated by phytoplankton? It's like us: we need iron, but it has to be bioavailable. We don't get our nourishment from sucking pebbles,” says Stéphane Blain.

Setting off for Kerguelen means embarking on three months of isolation. There's no airport there: you have to board the supply ship Marion Dufresne, pass through the Crozet archipelago and finally reach Kerguelen. “A week by boat, if all goes well. Once on the archipelago, the scientists are spread out over different sites: inland, in bays, offshore. “We live four to a room in basic shelters, set up mini-labs and walk several kilometers every day to collect samples.  

In these conditions, every piece of data collected is invaluable. Logistics are coordinated by the Institut Polaire Paul-Émile-Victor and the French Oceanographic Fleet, with the support of several research laboratories (see inset).

The latest mission collected hundreds of samples of water, sediment and suspended particles. Experiments have already been carried out in situ. “We can see that bacteria and phytoplankton react to glacial flour. There's real stimulation. So iron is indeed present. The final hypothesis remains to be verified: is it being transported offshore?

The MARGO project is not an applied ecology program. It is guided by a more fundamental desire to understand. “It's a project driven by curiosity,” insists Stéphane Blain. But understanding also means anticipating. Because if the glacier disappears—which seems inevitable—we need to know what it will leave behind. “If, in forty years' time, bird populations decline, we won't be able to say we didn't see it coming. We need to ask the right questions now.

The expedition is accompanied by a public outreach program. On the jetty opposite the Banyuls-sur-Mer Observatory, an open-air photo exhibition retraces the missions. 

Activities are also organized in the Biodiversarium, and children's drawings even decorate a panel in the exhibition. A website is also available to keep track of progress. “It's not our job, but we try to share what we do, why we do it and how we do it,” concludes Stéphane Blain.