Ice Shelf Team
The main goal for the Ice Shelf Team is to obtain sediment cores from the sea floor beneath the ice shelf, from within a few kilometers of where the glacier goes afloat, or the grounding line (where it’s still attached to the fjord bottom).
The ice near the grounding line is around 600 m thick and thins out to about 200 m thick or more at its terminus. To get the sediment cores we need first to make an access hole through the ice using a hot-water drill that is lowered slowly through the ice. Water at around 90°C is pumped at a rate of 80 litres per minute, giving a total heating power of around 0.5 MW.
It is important to remember that the ocean beneath the floating ice shelf is just like any other, except that there is a thick sheet of ice floating on top – ice that has flowed from the continental ice sheet. We know that the flow of ice from the Greenland Ice Sheet into the ocean is increasing, causing a rise in sea level. Being able to predict future loss of ice from both the Greenland and the Antarctic ice sheets is important for us to be able to plan for future rising sea level. In the Antarctic in particular, the role played by ice shelves in helping hold back the ice sheet is thought to be critical. In most environments, changes in ocean-driven melting at an ice shelf’s base, or basal melting, is the major cause of ice shelf thickness change, so we need to be able to predict how this melting is going to respond to an evolving climate.
Like a lot of ice shelves with a strongly sloped ice base (near the grounding line, at least) the base of the ice has deep canyons carved in it, a few km wide and hundreds of meters deep. We want to make measurements to understand how this extreme topography is formed and how it affects the rate at which this sort of ice shelf melts. To understand that, we need to measure the details of the oceanography going on in the canyons, the rate at which the ice is melting, and the ambient water properties, that is, the general oceanography in the “sub-ice shelf cavity”.
So, once the access hole has been made with the hot-water drill, as well as attempting to obtain sediment cores, we’ll lower an oceanographic instrument into the water column beneath the ice shelf to obtain our first view of the oceanographic conditions. Then we’ll suspend instruments beneath the ice shelf, which will be connected to data loggers and left for a year or more recording how the ocean conditions change with the seasons, and with changes in conditions seaward of the ice front.
To measure the rate at which the ice shelf is melting into the ocean, we’ll leave downward-looking radars that will measure very precisely how fast the ice shelf is thinning on the flanks of one of the basal canyons. In that way, it’ll be possible to determine the response of the melt rate to the changing ocean conditions measured by the instruments deployed in the water beneath.
Keith Nicholls, Ice Shelf Team Coordinator
Paul Anker, Drilling Engineer
Mike Brian, Field Assistant