Paleo-clamatology

There’s a new article at Nature News where they report on an amazing new paleoclimatology breakthrough with temperature reconstructions using clamshells. The Nature article reports on a  new paper in PNAS from William Patterson at the University of Saskachewan. Here’s a short excerpt:

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.

Unlike counting tree rings which have varying widths due to all sorts of external influences such as rainfall, sunlight, temperatures, available nutrients, and available CO2, this method looks at the levels of different oxygen isotopes in their shells that vary with the temperature of the water in which they live. One simple linear relationship.

The data resolution from isotope counts is incredible.

“What we’re getting to here is palaeoweather,” Patterson says. “We can reconstruct temperatures on a sub-weekly resolution, using these techniques. For larger clams we could do daily.”

The reconstruction is shown below. We see familiar features the little ice age, the medieval warm period and the  downturn which led to the extinction of Norse settlements on Greenland.

And the feature of this reconstruction to surely stick in the craw of many who think we are living in unprecedented times of warmth is the “Roman Warm Period”. Have a look:

From Nature: Shellfish could supplant tree-ring climate data

Temperature records gleaned from clamshells reveal accuracy of Norse sagas.

Richard A. Lovett

Oxygen isotopes in clamshells may provide the most detailed record yet of global climate change, according to a team of scientists who studied a haul of ancient Icelandic molluscs.

Most measures of palaeoclimate provide data on only average annual temperatures, says William Patterson, an isotope chemist at the University of Saskatchewan in Saskatoon, Canada, and lead author of the study¹. 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.

“What we’re getting to here is palaeoweather,” Patterson says. “We can reconstruct temperatures on a sub-weekly resolution, using these techniques. For larger clams we could do daily.”

It’s an important step in palaeoclimatic studies, he says, because it allows scientists to determine not only changes in average annual temperatures, but also how these changes affected individual summers and winters.

“We often make the mistake of saying that mean annual temperature is higher or lower at some period of time,” Patterson says. “But that is relatively meaningless in terms of the changes in seasonality.”

For example, in early Norse Iceland — part of the 2,000-year era spanned by the study — farmers were dependent on dairy farming and agriculture. “For a dairy culture, summer is by far the most important,” he says. “A one-degree decrease in summer temperatures in Iceland results in a 15% decrease in agricultural yield. If that happens two years in a row, your family’s wiped out.”

Technically, the molluscs record water temperatures, not air temperatures. But the two are closely linked — specially 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 says.

Read the complete article at Nature News