Reassessment of CLIMAP Methods for Estimating Quaternary SeaSurface Temperatures:Examination Using Pacific Coretop Data Sets

Abstract

Quantitative analyses of planktonic foraminifer faunal data have been applied to reconstruct the past conditions of surface oceans and to verify the results of climate modeling. In the present study, planktonic foraminifer faunal SST (sea-surface temperature) estimates were evaluated using a calibration set and a test set of newly compiled coretop data from the low-latitude Pacific. A standard CLIMAP-type transfer function based on the IKM (Imbrie-Kipp Method) was developed in estimating SST. Comparisons between the SST function and the depth of thermocline (DOT) transfer function developed on the basis of the same calibration coretop data indicated that the correlation between the planktonic foraminiferal abundance distribution and DOT is more significant than that with SST. This comparison suggests that the DOT effect is a more important environmental control on faunal distributions and abundances. After evaluating the functions with a test set of coretop data, the residuals of SST estimates (¡µSST = estimated ¡V observed SST) were compared with two surface ocean modes which were derived statistically using a principle component analysis of seasonal SST and DOT data of the low-latitude Pacific, as well as an index of carbonate preservation (CPI). The analyses of residuals clearly indicated that the patterns of estimation bias are correlated significantly with the two ocean modes, with a tendency to yield colder estimates for high SST values, and warmer estimates for low SST values, and with a maximum uncertainty around 3 degree to 4 degree. These results also revealed that the carbonate preservation effect may not produce systematic biases. This reevaluation raises questions about the accuracy of faunal SST estimates that are based on the commonly used quantitative techniques, and implies that the CLIMAP low-latitude Pacific SST pattern should be reexamined. From these analyses we suggest that reconstructing DOT or surface ocean modes form planktonic foraminifer faunal data would be more appropriate in future paleoceanographic studies.

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