Stable oxygen isotope ratios (delta O-18) of foraminifera are widely used to reconstruct the climatic history of Earth. It is well known that temperature reconstructions based on delta O-18 are complicated by factors such as the unknown isotopic composition of the ocean. In addition, recent experimental and theoretical work has shown that the seawater pH has a marked effect on the delta O-18 of foraminifera. Here I employ this effect to demonstrate that reconstructions based on delta O-18 of foraminifera may underestimate sea surface temperatures in the geological past. Ocean surface temperatures for the mid-Cretaceous are estimated to have been similar to2-3.5 degreesC higher than previously thought. (C) 2001 Elsevier Science B.V. All rights reserved.
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