Fossils help unearth climate history

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A Wanaka-based paleobotanist is helping to piece together the past by gathering globally significant plant fossils from Central Otago.

Since finding his first fossil at the age of 10, Mike Pole has gone on to have his research published in more than 80 papers and has developed one of the most extensive databases for plant cuticles.

Dr Pole’s research helps paint a picture of how climatic changes have occurred over time. His latest findings indicate Central Otago was once six to seven degrees warmer than it is today, and without frosts.

“The broader sequence of plant communities hint at changes in atmospheric circulation patterns that would be of global significance.

“The most useful thing palaeobotany can do, especially now, is to help climate scientists know what the climate was like at a particular place and time in the past – what the temperature was, how the rains varied over the year, what atmospheric phenomena were operating, and what the carbon dioxide levels were.

“Bannockburn and the now- flooded banks of the Kawarau River are possibly globally unique in the range of fossil vegetation communities represented over a short time.

“This diversity helps you figure out what may have been going on in terms of things like temperature, rainfall and fire.

“St Bathans is one of the most diverse fossil plant sites known anywhere. I’ve found 159 different species from that area, with more conifers than there are in all of New Zealand today.”

His research started with “reading geological or exploration reports going back into the 19th century, and ends with a lot of driving and walking”.

Lumps of sendiment are collected into numbered plastic bags, with GPS co-ordinates and other located data recorded at the same time.

Boiling water and bleach are then added to the samples to sieve out plant fossil concentrate, before the sample is added to further concentrate.

“I then search through this concentrate under a binocular microscope to find different types of fossil and mount them individually on numbered microscope slides.

“Then I can examine these under the higher power of a light microscope and take numbered photographs.

“These are all related in a database that seems to take up a third of my waking hours.”

Dr Pole said an iconic find was New Zealand’s first eucalyptus gum-nut fossil he sampled near Cromwell, which presented the first good evidence the species was once more widespread than its current location in Australia.

“It’s also a key piece of evidence that New Zealand forests may have once burnt like Australian ones.

There was also the overall “finding” that perhaps all of New Zealand’s vegetation had come over the sea.

“Until the early ’90s there was a general view that at least a core of New Zealand’s plants had been growing here since New Zealand broke away from Gondwana, a long time before the fossils of Bannockburn and St Bathans.

“Stimulated by what fossils I saw – or rather didn’t see – in places like Bannockburn, I wrote a paper that was instrumental in changing that view.”

Dr Pole is collaborating with Icelandic and Swedish colleagues to help narrow down the level of carbon dioxide in the atmosphere to ensure fossil dating is as accurate as possible.

“I always hope to find something new.

“It’s the feeling of exploration that makes each new sample exciting.”