Physical oceanographers on ice

“How long do you think this will take?” the first mate asks me. The answer – anything between 15 minutes and 12 hours – does not seem to what he wants to hear. We are about to board one of the two helicopters on Araon to fly onto the western end of the Getz ice shelf. If it turns out that the weather there is not as good as it is at the ice shelf front, we will be back in 15 minutes. If all goes to plan, we will deploy phase sensitive radars and do seismic surveys at four sites within the next twelve hours.

 

The phase sensitive radars were developed and built at the British Antarctic Survey (BAS) and very precisely measure changes in ice thickness. This means that we get a direct measurement of the ice shelf melt rate. Satellites can also be used to measure this, but will only give average values over several years, while we will get a value every 2 hours from the phase sensitive radars. In combination with the moorings that we have deployed at the ice shelf front, this will allow us to directly link changes in ocean temperature to changes in the ice shelf melt rate. The aim of the seismic surveys is to find out how much seawater there is between the floating ice shelf and the bedrock. While radar can find the base of the ice shelf, it isn’t powerful enough to reach the seafloor through the water. In fact few things besides seismic surveys are, which is why very little is known about the shape of the seabed under the floating ice shelves and even as few as our four points will make a difference. Bigger seismic surveys normally use explosives as the sound source, but we are doing a more basic version with a sledgehammer and steel plate as the sound source and a set of wireless geophones that we have borrowed from Pennsylvania State University.

As we rise above the ice shelf front, the ice spreads out in front of us.

It is vast, flat and white and rather magnificent.

After flying for 30 minutes we get to the first site, the Korean mountaineering guide hops out and checks that there aren’t any crevasses. We unload the helicopter and start to work. The first site takes a while as we work out the quirks of the equipment that we have only used in tests at home before. A few tests show that the helicopter pilot is the best seismic source. This means he gets to strike 120 blows with the sledgehammer over the four sites. He seems to be happy to do this and by site three we have worked out a pretty good routine of deploying the geophones, doing the survey and collecting them again. The mountaineering guide joins Povl from BAS and Kyoung Ho from KOPRI in setting up the radar sites. This involves digging holes, putting up a mast for the Iridium antenna to send the data back to us, and building antenna boxes.

Our west site on Getz ice shelf

Our west site on Getz ice shelf

Just under 11 hours later, at 5.30 in the morning, we arrive back at the ship after successfully completing our four sites.

/Karen

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