Clamshells may provide most detailed record yet of global climate change

March 9th, 2010 - 3:48 pm ICT by ANI  

London, March 9 (ANI): A team of scientists, who studied a haul of ancient Icelandic mollusks, has said that oxygen isotopes in clamshells may provide the most detailed record yet of global climate change.

Most measures of palaeoclimate provide data on only average annual temperatures, William Patterson, an isotope chemist at the University of Saskatchewan in Saskatoon, Canada, and lead author of the study, told Nature News.

But molluscs grow continually, and the levels of different oxygen isotopes in their shells vary with the temperature of the water in which they live.

The colder the water, the higher the proportion of the heavy oxygen isotope, oxygen-18.

The study used 26 shells obtained from sediment cores taken from an Icelandic bay.

Because clams typically live from two to nine years, isotope ratios in each of these shells provided a two-to-nine-year window onto the environmental conditions in which they lived.

Patterson’s team used a robotic sampling device to shave thin slices from each layer of the shells’ growth bands.

These were then fed into a mass spectrometer, which measured the isotopes in each layer.

From those, the scientists could calculate the conditions under which each layer formed.

Technically, the molluscs record water temperatures, not air temperatures. But the two are closely linked - especially close to the shore, where most people lived.

“So, when the water temperatures are up, air temperatures are up. When water temperatures are down, air temperatures are down,” Patterson said.

One of Patterson’s goals was to verify assertions in historical Icelandic sagas describing the weather.

Because these sagas include dispatches to the king back in Norway, there was an incentive to exaggerate.

The study’s findings suggest that the sagas are reasonably accurate.

In the 1000s, for example, the ‘Book of Settlements’ - a medieval manuscript containing details of Iceland’s settlements - reports a famine so severe “men ate foxes and ravens” and “the old and helpless were killed and thrown over cliffs”, Patterson said.

According to his shells, it was indeed a difficult era, with summer water temperatures peaking at only 5-6 degree Celsius, down from as high as 7.5-9.5 degree C around 100 years earlier.

Patterson’s data also reveal a number of climate changes recorded by historians, including a Roman-era warming period, a cold snap in the Dark Ages and a subsequent period of warming, during which the Vikings discovered Iceland.

“The new data will help climate modellers to improve their understanding of seasonal effects in the North Atlantic,” Patterson said. (ANI)

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