Canterbury Basin drill cores hold clues to our climate

Scientists on an American research drill ship, the Joides Resolution, have docked in Wellington to offload kilometres of core samples from sediments in the Canterbury Basin.

The scientists drilled four holes on the continental shelf and slope off south Canterbury during the past month.

Two of the sites broke records for their drilling programme, one being the deepest hole drilled on the shallow continental shelf (1024m) and another being the deepest hole drilled on a single, integrated ocean drilling programme (IODP) expedition (1928m).

Although the expedition was aimed at recovering a 10 million-year record of sea level cycles across the basin, the deepest drill hole hit limestone thought to have been laid down 35 million years ago.

Data yet to be extracted from the core samples is expected to reveal relationships between climate and sea level, and how the ocean currents and sediment deposits from the Southern Alps have changed over millions of years.

Research from the samples is expected to cast light on cold, nutrient-rich water carried up New Zealand's east coast from the Antarctic circumpolar current that has isolated that continent's climate for millions of years.

The current running northwards through the Canterbury Basin was thought to be a key ocean "conveyer belt" carrying cold water to the tropics.

The New Zealand expedition also completed a technically difficult drill hole in only 85m of water - a depth which gave the vessel crew very little latitude in keeping it still above the drill stem.

A co-chief scientist on the trip, Craig Fulthorpe, said a preliminary paper will be published in a few months, but detailed analysis of the cores will take years.

"We have a huge amount of information - it was incredible how much good data we got," he said.

"We see a lot of indications that the cycles of sea level that we're looking for are present ... within the cores."

"We have cores in environments that have never been cored before."

Three New Zealand scientists were part of the scientific team for the Canterbury Basin expedition - Greg Browne and Martin Crundwell from GNS Science, and Kirsty Tinto from University of Otago.

One New Zealander, Rob McKay from Victoria University's Antarctic Research Centre, will participate in the drillship's next voyage, to Wilkes Land - the portion of Antarctica directly south of New Zealand and Tasmania - in a bid to further explore climate change, including variations in the East Antarctic ice sheet and the circumpolar ocean current.

Dr McKay took part in the ice-based Andrill (Antarctic geological drilling) programme carried out by New Zealand drillers in the Ross Sea, and has a research background in deciphering ice sheet behaviour from sediment samples.

New Zealand participates in IODP through the Australian and New Zealand IODP Consortium.

The Joides Resolution is financed by the US National Science Foundation, and managed by a US consortium, including the Texas A&M University, Lamont-Doherty Earth Observatory of Columbia University, and a consortium for ocean leadership.

- NZPA