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Deep Sediment Holds Clues To Past Climate Changes

Scientists are to drill two deep holes on the Wanganui coast to gain a better understanding of Southern Hemisphere climate and sea level changes over the past two and a half million years.

The sea level around New Zealand has risen and fallen 50 times in the past two and a half million years, due to expansion and contraction of ice sheets mainly in the Northern Hemisphere.

Sediment under the Wanganui coast contains one of the world’s best shallow marine records of these sea level changes.

Because of New Zealand’s unique geological setting the sediment profile under the Wanganui coast is detailed, highly accessible, and contains an uninterrupted record going back for millions of years. The only other sediment profiles in the world that come close are under several thousand meters of ocean.

The project is being led by the Institute of Geological & Nuclear Sciences Limited (GNS), with assistance from James Cook University in Queensland.

Project co-ordinator and GNS sedimentologist Tim Naish said sea level changes leave behind sedimentary deposits that can be analysed by geologists to gain a detailed understanding of the size and timing of past climatic changes.

“ Understanding past climate changes will help enormously in forecasting future climate trends,” Dr Naish said.

The information would also be valuable to petroleum exploration companies which would use the data to develop models to evaluate oil and gas potential in other parts of New Zealand.

Dr Naish said the sea level around New Zealand had been fairly static for 6000 years. Shorelines were 120m lower during the last ice age, 20,000 years ago. Each cycle, from low to high, lasted between 40,000 and 100,000 years.

“ Shorelines around New Zealand are currently at a high – the last time they were this high was 125,000 years ago.”

Until the mid-1970s it was thought there were only four main ice ages during the past two million years. The application of new investigative techniques had shown there had been 50 distinct glaciations during this period, Dr Naish said.

Sediment core from the drill holes will be brought to the surface for analysis in 3m lengths. One of the drill holes, near Castlecliff Beach, Wanganui, is to be 150m deep. The target depth at the other, 7km northwest of Castlecliff at Kai-iwi, is 250m.

This will be the first time that deep and continuous sediment cores from this area have been sampled for climate analysis. Petroleum exploration wells have been drilled near Wanganui in recent years, but were not studied for climate change.

Drilling is scheduled to start this week and will take about six weeks.

END

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