Universita "G. D'Annunzio", Italy

This study presents a new alkenone-derived Sea Surface Temperature (SST) record and delta (super 18) O (sub Noelaerhabdaceae) data of the 2-5mu m carbonate fractions from the IODP site U1338 located in the Eastern Equatorial Pacific (EEP), over the Miocene-Pliocene. Our data and those available from other sites of the same area show the establishment of a cold tongue during the early Pliocene (4.4-3.6 Ma). SST and delta (super 18) O (sub Noelaerhabdaceae) time-series indicate periods of significant salinity variations. Comparison with the delta (super 18) O (sub benthic) curve from sediment cores of the Equatorial Pacific Ocean allows us to distinguish between global changes and local surface salinity variations in the EEP. Ice sheet growth and evaporation-precipitation are then discussed as possible drivers of such changes, along with the role of Central American and the Indonesian seaway restriction. Our data suggest a shallowing of the thermocline in the EEP, between 6.8 and 6 Ma, and its shoaling between 4.8 and 4.0 Ma, suggesting the appearance of the cold tongue (Steph et al., 2010). The Pliocene climate transition would therefore not be primarily driven by Northern hemisphere glaciation. Abstract Copyright (2013) Elsevier, B.V.