Oceanography

E-mails from the Filchner Ice Shelf

After two successful drilling expeditions to the Filchner Ice Shelf, AWI oceanographer Tore Hattermann is now gathering unprecedented data from the ice tongue and the sea below it

The Antarctic Filchner Ice Shelf is roughly the size of Sweden and up to 1600 metres thick at its grounding line. The area immediately below its massive ice tongue is home to what could be the coldest water masses in the world. 2.5 degrees below zero Celsius cold, the only thing keeping the water liquid is the high pressure it is under.

Just how this super-cold water flows underneath the shelf, and whether or not warmer water masses from the Antarctic Ocean have already found their way under the tongue and are melting the ice from below, are just two of the many questions that AWI oceanographers and glaciologists are investigating in a large-scale joint FISP project with the British Antarctic Survey. “There are several hypotheses on what the circulation under the shelf looks like, but no one has any hard evidence. That’s why we bored holes at seven points in the Filchner Ice Shelf and placed measuring devices in and below the ice over the past two summers,” explains oceanographer Tore Hattermann.

Thermistor chains deployed directly in the ice shelf are now documenting how cold the ice is in different layers. In the water below the ice, our sensors are measuring the temperature, salinity and flow direction of the water masses. 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.

A logistical masterpiece

This simple data transfer belies the logistical masterpiece it took to install all of the sensors. As Hattermann explains, “For our hot-water drilling we needed 13 tonnes of equipment, which had to be transported to the shelf on board the Polarstern and other ships, bit by bit, in the course of several consecutive summers. Plus there was all the fuel we needed for the Twin Otter flights, the snowmobiles and the generators. And the glaciologists took seismic readings on long transects to gain insights into the topography of the seafloor below the ice, which we previously knew nothing about.”

For the drilling in the summer of 2016/17, eight researchers and engineers from the British Rothera Research Station flew to the winter camp on Berkner Island. In twelve flights back and forth, they then transferred the necessary equipment to the Filchner Ice Shelf. “Once we reached a given drilling position, we needed two days just to set up the camp, plus two more to install the hot-water drill. On the fifth day, three of us spent twelve hours shovelling snow so that we could melt the first 10 cubic metres of drilling water,” recalls AWI engineer Jörg Brozek. 

Video by "The Guardian"

In January 2017 the British daily newspaper "The Guardian" reported on the joint Filchner drilling project of the Alfred Wegener Institute and the British Antarctic Survey.

There are no second chances in drilling

Once the signal has been given to start drilling (see box), the process can’t be interrupted. “Otherwise the water immediately freezes in the pipes and hoses, which can do tremendous damage to the equipment. As such, we kept a very close eye on the drilling process,” says Brozek.

Despite this risk, thanks to clearly defined responsibilities and good communication, the German-British team didn’t encounter any drilling problems. Now the scientists are anxious to see if all of the recording devices will actually transmit readings for the next five years, as planned. As Tore Hattermann relates, “Three of our boreholes are to the north, roughly 60 kilometres behind the calving front; another four are located 200 kilometres farther south. Based on the data coming in, we can already see that very different water masses circulate below the two areas.”

Are these waters growing warmer? According to Hattermann: “Our time series is still too short to identify changes. We’re currently documenting the status quo, and next we want to focus on more precisely mapping the circulation under the ice. However, our Norwegian colleagues have already detected the warmer water masses predicted by climate models – in a thermistor chain moored at the edge of the continental shelf. We’re curious to see if we’ll pick up the same signal at our boreholes.”

 

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