Core sampling to reveal South Island climate secrets

Lake Ohau, from which scientists hope to learn more about New Zealand's climate. Photo by Gerard O'Brien.

A scientific project to collect layers of sediment dating back to the end of the last Ice Age from the bottom of Lake Ohau has been granted more than $750,000 to create the most detailed climate study of South Island weather yet tackled.

A GNS Science-led international team of scientists began initial steps to create one of New Zealand's most detailed climate studies to date by taking core samples from Lake Ohau in March 2012.

The project has now been granted $782,609 from the Marsden Fund, and project leader Dr Richard Levy said the study would collect 150m of core samples from the bottom of Lake Ohau to build a detailed climate record over the past 17,000 years, "when the last ice age ended".

"It will be the longest record of on-land South Island climate to date. The core will reveal seasonal variations in lake inflow. Information gleaned from this record will be integrated with other New Zealand climate records and used to assess the effect of warming on New Zealand's climate processes."

The Marsden Fund, administered by the Royal Society of New Zealand and the New Zealand Government, received 1157 preliminary proposals all hopeful of receiving a share of the $59 million of funding on offer, and the Lake Ohau study was one of just 109 projects that were granted full-funding.

Dr Levy added that the three-year study, which would analyse sediment layers on the lakebed, would also help build a more detailed picture of the effects of climate change and southern hemisphere weather patterns.

"It will also help to improve the understanding of interactions between westerly winds, and large climate features such as El Nino and their influence on southern hemisphere rainfall and temperature variability.

"It will also provide a long-term benchmark for the effects of current climate change."

Core samples would show how sediment layers related to the history of river inflows to the lake, and how that in turn could be linked to precipitation in the South Island.

Although acoustic imaging of the lake had shown sediment was about 150m thick at its deepest point at the centre of the lake, a more sheltered area, with a sediment layer of about 70m to 80m, had been identified as the ideal location for drilling, he said.

Drilling was expected to start about February 2015, he said.

"It will take us a year at least to get the system sorted out so then we need to wait for the right weather window.

Some of the equipment required was in Antarctica at present and would be sent back to New Zealand.

Although initial 6m core samples were taken last year, background analysis on the project had been ongoing for the past three or four years.

"One of the key things we are really trying to understand here is what really controls precipitation or controls rainfall on the South island.

"Ultimately we are trying to figure out how the climate system in New Zealand works and obviously that sort of information can be useful to feed into models that try to simulate current weather patterns, plus patterns from the recent past.

"Once we can do that we can obviously start to better predict or understand what might happen in the next decades or hundreds of years."