Kiwi seas were as hot as spas, scientists say

If you lived in New Zealand 50 million years ago, you could have had a warm dip in the sea all year round, scientists say.

The spa-pool-like conditions that existed in the early Eocene period a time of significant global warming suggest scientists may be underestimating the likely effect of climate change.

Using sedimentary rocks from the bed of the Waipara River in North Canterbury, an international research group led by GNS Science palaeontologist Chris Hollis has reconstructed ancient sea temperatures.

They found surface sea water exceeded 30 degrees celsius, and water at the sea floor hovered around 20C during an episode of greenhouse gas-induced global warming that lasted for between two million and three million years.

"These temperatures are at the extreme end of modern tropical water masses," Dr Hollis said. Year-round sea surface temperatures of 25C to 30C are today found only at the equator.

In a study to be published in the international scientific journal Geology next month, scientists have inferred warm conditions in New Zealand for this period from a wide range of fossil evidence showing the country was once covered in lush tropical forest. But, till now, the degree of warmth was uncertain.

Dr Hollis said similar freakishly warm conditions had been reported for this period in high-latitude regions of the northern hemisphere. "It now seems likely that some, as yet unknown, heat-transport mechanism comes into play during times of extreme global warmth."

Co-author Matt Huber, of Purdue University, Indiana, said the new findings were at least 10C higher than previous estimates, which indicated climate models had underestimated past warming episodes. "It is possible that models are also underestimating future warming projections."

Dr Hollis said research into extreme climatic changes in the past would benefit from New Zealand's recent decision to join the Integrated Ocean Drilling Programme an international project extracting 2000-metre sediment cores from the ocean floor.

The recent findings, part of an eight-year study, will be presented at an international conference on climate change at Te Papa next month.

Funded by the New Zealand Government through the Foundation for Research, Science and Technology, the project involves an international team of 12 research scientists and graduate students.

- © Fairfax NZ News