What happens when warm water from the Antarctic Circumpolar Current finds its way under ice shelves is something that polar researchers have been observing for the past few decades in the Amundsen Sea. Here, the ice shelves begin melting from below; as a result, they gradually lose contact with the ground, and with it, their buttressing effect on the glaciers pushing from behind. The ice streams of the Amundsen Sea lost over 334 gigatonnes of ice in 2013 alone, i.e., roughly 110 gigatonnes more than in 1994. If we compare the current melting and calving rates with data from 1977, they’re now losing 77 percent more ice than they did 40 years ago. At the same time, nearly all glaciers are now forcing their ice masses out to sea much faster than they did in the 1970s – a fact that also helps explain why this region alone accounts for ten percent of the global sea level rise.
Taken together, the hinterland of the Filchner-Ronne Ice Shelf holds so much ice that the global sea level would rise by twelve metres if this giant brake suddenly disappeared and all the inland ice poured out into the ocean. But will the Filchner-Ronne Ice Shelf share the fate of the ice streams in the Amundsen Sea?
To answer that question, oceanographers at the AWI are combining climate models (see the graphic on p. 20/21) with extensive measurements gathered in the Weddell Sea, both below and even inside the ice shelf. “Our models indicate that the Antarctic will grow warmer over the next few decades. As, this progresses, we’ll likely see less sea ice forming, which could cause the cold-water barrier to collapse in the second half of this century,” says AWI oceanographer Dr Hartmut Hellmer. “If that happens, the warm water could then flow directly under the ice shelf. Whether or not this development has already begun is something we’re investigating right now, on various Polarstern expeditions to the Weddell Sea and with the sensor chains that we’ve placed in and below the ice.”
To successfully install the devices below the ice, in the course of two summer expeditions Tore Hattermann and his German-British team drilled seven holes in the up to 900-metre-thick ice. “Three of our boreholes are to the north, roughly 60 kilometres behind the calving front; another four are located 200 kilometres farther south,” he explains. At all sites, thermistor chains deployed directly in the ice shelf are now documenting how cold the ice is in the different layers.
In the water below the ice shelf, sensors measure the water masses’ temperature, salinity, and their flow speed and direction. The readings are then sent to Tore Hattermann by satellite every night. “Every morning I receive 28 mails from the Filchner Ice Shelf, with the latest readings in the attachments,” says the 33-year-old researcher.