February 11, 2009

Ocean Kelp Studied To Learn About Ice Age Climate

A New Zealand research team has produced data that could improve predictions of climate change, after discovering sea ice extended further north in the Southern Ocean during the last Ice Age than scientists previously thought, Reuters reported.

Researchers from the University of Otago examined the genetic code of modern-day bull kelp from samples taken from many sub-Antarctic islands, as well as New Zealand and Chile.

They found that southern bull kelp, Durvillaea antarctica, had only recolonized the sub-Antarctic islands in the past 20,000 years after the retreat of sea ice. The kelp live in the shallow inter-tidal zone and were destroyed by the scouring motion of sea ice across the sea bed.

The studies leader, PhD student Ceridwen Fraser told Reuters: "We found this pattern that there is a lot of genetic diversity further north and next to no diversity further south, which suggests that it's just recently been colonized by the species."

Current data of the estimated extent of sea ice based on sediment core samples from the Southern Ocean seabed are now highly questionable. Because of the remoteness of the vast ocean, some areas had abundant data, while others had very little.

The researchers said none of the sediment data suggests sea ice extended as far north as the sub-Antarctic islands between about 50 and 55 degrees latitude, such as Macquarie island, south of New Zealand, or South Georgia, in the far south Atlantic.

In regard to ocean and wind circulation patterns and the amount of solar radiation sea ice reflects back out to space, Fraser said if the sea ice was more extensive than previous studies suggested then that's going to call for a re-assessment of other things science understands about climate change and how all these systems interact.

She added that a very small change in the extent of sea ice would make a huge difference in the amount of radiation that is reflected, as well as ocean circulation patterns.

The findings suggested temperatures were a little cooler than some previous studies had reported.

"This helps us understand better what sort of patterns we might expect in the future and also the rate of climate change," she said.

The study marks the first time scientists had looked at modern-day genetic data to study past climate in the southern hemisphere, according to research supervisor Jonathan Waters. He said the purpose was to expand the concept to study other species in the sub-Antarctic zone.

"It's important to understand historic climate and how inaccurately estimating it can give us false impressions of what can happen in the future," he said.


Image Caption: Durvillaea antarctica stipes on Second Bay, Otago, New Zealand. Courtesy Wikipedia


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