Antarctic study probes past climatic changes

Press, 21 January 1984, Page 5

Antarctic study probes past climatic changes

World-wide climatic changes in the last million years may be able to be interpreted as a result of discoveries made on a joint United States-New Zealand geological drilling project in Antarctica. Five holes in one of the continent’s dry valleys, the Lower Taylor Valley, are being drilled in the project, which is sponsored by the Antarctic Division of the Department of Scientific and Industrial Research and the United States Geological Survey. The Lower Taylor Valley is the only dry valley of Antarctica’s Victoria Land with an extensive record of glacial deposits exposed on the valley floor. They were left by the Ross Ice Sheet and glaciers from the Polar Plateau in the last eight million years and more. The present project is investigating the origin of glacial deposits within a few hundred metres of the surface, probably less than two million years old. It also involves mapping the glacial deposits to link the subsurface sedimentary layers to surface exposures. The glacial history of this period is being studied to determine what features- of the present landscape of the valley are the result of uplift, erosion, and glaciation, and a combination of all three.

Dr Don Elston, of the United States Geological Survey, said there had been a breakthrough in the pro? ject. Deposits on the floor of the Lower Taylor Valley could now be related to surface glacial expressions on the sides of the valley, so that glacial advances and retreats from the Ross Ice Sheet and the Polar Plateau could be interpreted. “Until now they had just been considered to be a pile of debris.” He said- that when a detailed record was compiled, it could serve as a base for interpreting world-wide climatic changes. Also involved in the project is Dr Paul Robinson, of the New Zealand Geological Survey, in Wellington, who is studying the character and origin of glacial sediment in the Lower Taylor Valley. He, Dr Elston, and two other members of the United States Geological Survey are also looking at the extent of the layers of glacial sediment and at the records of magnetism they contain.

The drilling team consists of Messrs John Hay, aged 32, of, Wakefield, Nelson, and Stephen Pilcher, aged 23, of Alexandra. They are using a Winkie drill. Thev have both worked in Austra-

lian drilling projects.

Their assistants are two geology students of Wellington’s Victoria University, Messrs Warwick Potter, aged 21, and Bruce Morris, aged 26.

The first hole was drilled being obtained.

near New Harbour to a depth of 66m. The second near Commonwealth Glacier reached 68m and the third near the Canada Glacier is at about the halfway point.

Two more holes will be drilled near Lake Fryxell, and drilling which began about a month ago is expected to be completed by mid-January. All five holes will be drilled to a similar depth.

Dr Elston said the drillers were obtaining complete, almost unbroken, cores from the holes. The cores measured about 7.5 cm in diameter and because of the extensive permafrost from which they were extracted could be up to three metres long.

As the core was extracted from the hole, it was oriented with reference to north to obtain the east or west declination and the up and down inclination. He believed it was the first time this had been done in Antarctica.

Because drilling was being done in permafrost, the drillers had to use diesel fuel Antarctic (DFA), a fuel specially developed for the cold conditions of the continent. This fuel cooled the drilling bit and removed cuttings from the hole.

Dr Elston said that water could not be used because it would freeze, and an antifreeze solution would melt the ice cement of the permafrost and prevent a core

The cores were broken into 60cm lengths to be returned to the United States McMurdo Station where they were logged and sampled for paleomagnetism, sedimentology, and diatom analysis.

More extensive paleomagnetism and diatom studies would be carried out in the United States and sedimentology studies would be done by the New Zealand Geological Survey at Lower Hutt. The study of the Earth’s

ancient magnetic field, or paleomagnetism, involves measuring the fossil magnetic record from oriented samples of sediment. The layers of sediment record the direction and polarity of the magnetic field through time. The study follows up the Dry Valleys drill project, carried out six to 10 years ago by the United States National Science Foundation, which concentrated on drilling widely spaced holes up to 326 m deep. The Longyear drilling rig will be used in the cenozoic investigations in the Ross Sea geological study, which will be done in McMurdo Sound next season. The same rig was also used in New Zealand’s McMurdo Sound tectonic study five years ago. Dr Elston said the project was producing fine cooperation, both operationally and scientifically, between the Antarctic Division and the United States Geological Survey. He hoped it would continue for the benefit of both programmes. The investigation could possibly resume after the cenozoic study was completed in the 1985-86 season, he said.