Climate

Sources of Information about Paleoclimates: Clamshells

Clam Shells

The oxygen isotopes in clam shells provide a detailed view of climate history. The colder the water the higher the percentage of the oxygen isotope, O-18. A study was conducted of a core taken from an Icelandic bay. Mollusks grow continuously for two to nine years, providing an equivalent fine-grained water temperature profile. Twenty-six shells in all were analyzed in a mass spectrometer, yielding the result on the right.

Patterson, W. P. et al, PNAS

If the clams are large enough, resolution of water temperature by day is possible.  The purpose of this study was to determine the accuracy of  Icelandic historical sagas.  The authors found that during the eleventh century the summer water temperature averaged about 2 - 3 C degrees cooler than during the previous century.  This period was described in the "Book of Settlements" as  a period of severe famine.  Based on historical studies, for each one degree drop in temperature, harvests decrease by about 15%, so one can conclude that this record is broadly accurate.

This line of evidence conceivably can provide a continuous record of water temperature in the North Atlantic back to the end of the last ice age about 11,0000 years ago.  All it will take is time and money.  The time they have and the money is currently being sought by Patterson and his team.  It they are successful, this could provide much needed data for fine-tuning the global climate models.