The sea freezes

Pancake Ice, April 2003.
Pancake Ice, April 2003. (Photo: J Smith)
Elephant seals on Davis beach, and their 'snail trails' on the new sea-ice offshore, April 2003.Ice monitors Sharon, Jim, Jeff and Paul skiing over the sea-ice away from Davis, April 2003.Chad, Jeff and Sharon drilling the new sea-ice, April 2003.

15 April 2003

The sea has frozen at last. This is what we have been waiting for. We are now observing the sea-ice as it gradually thickens, drilling, measuring and recording its progressive solidification.

Since the helicopters left on the last ship in early March, our scientists have been unable to get themselves and their equipment back to their research sites. Recreational walking in the Vestfold Hills inland of Davis has also become increasingly difficult as snow-drifts have built up, day length has diminished, and temperatures have plummeted. Soon the sea-ice will provide a road network allowing us once more to access our hinterland for scientific, operational and recreational reasons alike.

We watched the progressive congelation during March with considerable interest. At first the grey sea became streaked with smoother patches of floating ice crystals called frazil ice or grease ice. Then, during one calm, cold night, a soft crust formed which, with the wind and swell to continually stir it, broke into rounded plates up to a few metres in diameter called pancake ice. Each pancake had a raised crust around its perimeter where it had bumped against its neighbours, pushing up the slush into peripheral ridges.

Rising winds blew the pancakes away twice. Finally, near the end of the month, they stayed in place long enough to freeze together in a continuous thickening sheet. At first the elephant seals on the beach easily broke through it when they went for their morning swims, but before long they were restricted only to a small area of water kept clear by their own activities. Those that left to go back to sea after completing their moult then had to drag themselves across kilometres of ice, leaving 'snail trails' in the snow that had settled on the surface.

Once it looked thick enough, the sea-ice monitoring team cautiously went out to measure it. They travelled on skis, which is the safest way to go on thin ice as the weight of the body is spread more widely. Skiers require 100 mm thickness, walkers 130 mm, quad riders 300 mm, and to go securely on the ice in the larger tracked vehicles, called Hägglunds, requires a thickness of 500 mm.

Drilling holes and measuring the ice thickness that first day showed it to be up to 200 mm in most places, with one thinner patch of only 100 mm. The next survey a few days later revealed a more uniform thickness of 180-210 mm in all places, so the sea-ice within station limits was opened to full pedestrian recreational access. The next Sunday several groups were out walking or skiing to the neighbouring islands. There is talk of a fishing competition this coming weekend, lowering baited hooks through holes in the ice.

A series of monitoring stations has been established, extending to 6 km offshore. Measurements will be made carefully at these stations throughout winter, as part of a long-term glaciological research program. For now the monitors must ski to the sites, and the operation takes most of a day. Before long it will be possible to ride quads (otherwise known as all terrain vehicles, or four-wheeled motorbikes) making things much quicker and easier.

John and Cal walked further afield a couple of days ago, to check the ice towards Ellis Fjord. There are some well-known danger spots down there, in narrow channels through which the tide is funnelled and where the ice forms slowly. They found patches of thin ice and in some places open water, so our access in that direction will have to wait a while. But with temperatures mostly staying below –10 degrees now, it won't be too long before we have our road network, and will be able to ride around the coast in a few minutes to places that can now only be reached by a few hours of hard walking.