Scientists who are researching Icelandic clams state in a new report that oxygen isotopes inside the clams may prove the best source on global climate change that has been found so far.

An ancient Icelandic manuscript on display at the Culture House. Photo by Páll Stefánsson.

Moreover, the clams show that the ancient Icelandic manuscripts were quite accurate in their description of the climate while most ancient climate measurements only show the average temperature, mbl.is reports.

Isotope specialists William Patterson at the University of Saskatchewan, Saskatoon, Canada, who is the report’s main author, said in an interview with Nature News that the strength of various oxygen isotopes in the clams changes depending on the water’s temperature.

The colder the water, the higher the strength level of the isotope oxygen-18, Patterson explained. The water and ocean temperature in shallow waters is in close connection with the air temperature.

Twenty-six clams that were found in sediment in an Icelandic bay were investigated. They usually live for two to nine years and the isotope percentage in each clam contains information on the situation of the environment while the clam lived.

One of Patterson’s goals was to find out whether there was some truth in ancient written sources on the weather in Iceland.

For example, Landnáma (The Book of Settlement) describes an exceptionally cold period, during which people fed on ravens and foxes and old and weak people were thrown off cliffs.

Patterson’s study of clams confirm that such a period of cold had indeed occurred, when the ocean temperature in summer only measured 5-6°C (41-43°F) compared to 7.5-9.5°C (45.5-49°F) one century earlier.