Sediment cores sea-levels clue

Kirbati, Tuvalu and other Polynesian islands are an ocean away from Oamaru.

Still, their inhabitants could do worse than keeping an eye on proceedings in the North Otago town this week, as about 40 high-profile climate scientists from various countries meet to review results from an ocean drilling expedition off the South Canterbury coast early last year.

The main aim of the expedition was to learn more about the relationship between climate changes and global sea levels over the past 35 million years.

Using the sea-floor drilling ship JOIDES Resolution, operated by the Integrated Ocean Drilling programme (IODP), the scientists drilled at four sites on the continental shelf off Canterbury, recovering sediment cores up to 35 million years old.

One of those sites was at a depth of 1927m - the deepest hole ever drilled by the ship.

The cores were analysed by scientists from New Zealand, France, Spain, Italy, the United States, Japan, Australia, the United Kingdom, China and Germany over a 22-month period, before the meeting in Oamaru this week.

Expedition co-chief scientist Craig Fulthorpe, of the University of Texas, said the long record of changes contained in such areas as the Canterbury Basin could help scientists forecast how sea levels might vary in response of global warming.

"It's important to know what the Earth has thrown at us in the past," he said.

"One aspect of this is we are looking at times in the past when the amount of the CO2 in the atmosphere was higher than it is today."

Agreement between climate scientists about sea and CO2 levels being linked is "near total", he said.

And agreement, of sorts, was emerging from the meeting yesterday.

"I think we are starting to understand the timing of historical sea-level change," Dr Fulthorpe said.

The work comes as CO2 levels have risen sharply in recent times, after gradually decreasing over millions of years.

The sea level is also rising at a rate of about 3mm per year, in what Dr Fulthorpe described as looking like "a very rapid change relative to the longer time trends".

The expedition was not intended to produce predictions of future changes in sea levels.

Rather, it was meant to supply a historical context highlighting differences and similarities in levels over time.

Similar work has been carried out off the east coast of the US, near New Jersey, and off the coast of the Bahamas and Australia.

The information garnered from the various expeditions would be integrated to provide a better understanding of global trends in sea levels.

Prof Bob Carter, of James Cook University in Queensland, said the six-week multinational expedition likely cost between $10 million and $15 million.

The US and Japan provided more funds, so therefore had a greater influence on the group than the other countries, he said.

It was too soon to say what conclusions would be drawn from the complex work, which would continue for at least two more years, Dr Fulthorpe said.

"This ancient record is not easy to read because sea-floor sediments are also affected by local tectonic, sedimentary and oceanographic processes that can obscure the global sea-level record," he said.

"The expedition off the Canterbury coast was designed to untangle those confounding effects."

ben.guild@odt.co.nz

 

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