Oxygen and carbon isotope ratios of fresh-water carbonates as climatic indicators

Abstract

Carbonates and molluscs from sediments of four lakes in Maine, New York, Indiana, and South Dakota show increased 18O content during the hypsithermal interval. This increase suggests higher mean annual temperatures for this interval than found at present. The changes in 18O content not correlative with temperature changes are small, indicating stable atmospheric circulation patterns for the regions studied. The influence of seasonal variations in 18O content of atmospheric precipitation on the 18O content of carbonates is discussed for a small lake in Connecticut. The 13C content of fresh-water carbonates appears a less useful climatic indicator than 18O content.