Variation in test diameter of Orbulina universa in the paleoclimatology of the late Quaternary of the Gulf of Mexico

Abstract

Previous workers have shown that the mean diameter of the test of the planktonic foraminifer Orbulina universa d'Orbigny in Recent sediments of the Indian Ocean is related to water mass distribution and Late Quaternary paleoclimatic variation. In three Late Quaternary deep-sea cores from the Gulf of Mexico, studied here, variation in mean size of O. universa shows an inconsistent relationship with paleoclimatic changes. In two cores (K 97 and TR 126—29), mean size is significantly cross-correlated with paleoclimatic curves derived from principal-component analyses of planktonic foraminiferal frequencies ( r 0 = +0.46 and +0.37, respectively). In the third core (K 129), the variatilon in mean size is unrelated in a statistical basis to the paleoclimatic trends ( r 0 = +0.16). Oxygen-isotope records are statistically cross-related with the mean size of O. universa in K 97 ( r 0 = +0.51) but not in K 129 ( r 0 = +0.30). However, despite the occurrence of statistically significant relations in some cases and a general similarity in the trends, the mean diameter of O. universa and the paleoclimatic curves are very different in detail and magnitude. These inconsistencies preclude the use of the mean size of O. universa as a paleoclimatic index in Late Quaternary sequences from the Gulf of Mexico.