Project traces climate history


Scientists are using Lake Ohau to reconstruct the climate of the past 17,000 years, which will be one of the most detailed, long-term terrestrial records of the South Island’s climate to date.

The Oamaru Mail spoke to GNS Science Quaternary Paleoclimate scientist Marcus Vandergoes about the project and what the research team hopes to uncover.

Collecting short (6m) sediment cores from the bottom of the lake, they hope to build an annual record of climate in the central South Island extending back 1500 years, with the ultimate goal being to recover a 100m core from beneath the lake bed to reconstruct climate for the past 17,000 years.

Dr Vandergoes said Lake Ohau became a prime target due to its ideal location to capture the way South Island rainfall responds to changes in the Southern Hemisphere’s westerly wind circulation.

The project involves teams from New Zealand, Germany, Italy, America and Australia.

Within New Zealand alone, GNS Science, NIWA, University of Otago, Victoria University of Wellington and Meridian Energy are also involved.

Work to try and develop detailed records of rainfall and climate change from the Makenzie Basin lakes had previously begun at Lake Tekapo and Lake Pukaki, but in more recent years has focused on Lake Ohau.

The amount of sediment entering Lake Ohau can be more easily related to rainfall in the catchment and Dr Vandergoes said: “We simply see Lake Ohau a large natural rain gauge.”

The sediment is deposited at the bottom of the lake in alternating light and dark coloured layers. Their generalised understanding is that the lighter coloured sediment represents higher inflow and larger storms that often occur during summer. The darker sediment represents winter, with lower inflow.

PhD student Heidi Roop is developing techniques to determine the direct relationship between the sediment layers and rainfall and thereby use the sediment core to identify changes in annual or seasonal rainfall back through time.

Although the team still needs to validate a few results, based on the cores taken from Lake Ohau, they can assume from the prominent periods of light and dark sediments that there were distinct times of high and low inflow over the past 1200 years.

They are also able to see how the landscape changed from pre-human to when Polynesians arrived and when Europeans settled in the area.

The project team has recently applied for funding through the New Zealand Marsden Fund to progress with the research. It will take more than three years to analyse the 17,000 year record and cost about $1 million.

“When you’re asking somebody for this amount of money, you’ve got to make sure you’ve got your science right,” he said.

“It’s not something that anybody can pull out of their back pocket,” he said.

To drill the lake alone, it will cost a substantial amount of this total.

“It is exciting but we’ve got to be aware of what we’re doing and attention to detail is paramount.”

He said to get this type of climate record out of a lake would be quite spectacular.

“There are very few places in the world you can do this,” he said.

The proposed deep core would be extracted using a barge-mounted drilling rig.

“This will be an interesting piece of equipment sitting on the lake if we go ahead,” he laughed.

They have received a lot of interest in the project and support from the local community, he said.

Even local children have become interested, through a visit by Heidi Roop to talk to them about the project as part of their home school curriculum.

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