18O for Site 1241 reveal the development of east Pacific surface hydrography for the time interval from 4.8 to 2.4 Ma.
High-resolution analyses of the mixed-layer dwelling planktonic foraminifer G. sacculifer for Mg/Ca and 18O for Site 1241 reveal the development of east Pacific surface hydrography for the time interval from 4.8 to 2.4 Ma.
An increase in average SSTMg/Ca (24.5°–25.5°C) between 4.8 and 3.7 Ma interrupted by short-term cooler periods, can be explained by a general southward shift of the ITCZ, increasing the influence of the warmer NECC.
The general global cooling trend, a response to intensification of NHG started at ~3.2 Ma, shown by the 18Obenthic record, is paralleled by tropical east Pacific cooling, indicated by SSTMg/Ca. Tropical east Pacific cooling, however, had already commenced around 3.7 Ma, suggesting that global cooling, probably related to decreasing atmospheric CO2 concentrations, might have started well before intensification of NHG.
Relative variations in local SSS indicated by 18Osalinity show a decoupling from the global, high-latitude processes shown by the 18Obenthic record. Long-term regional freshening started with decreasing SSTMg/Ca at ~3.7 Ma, suggesting that changes in the tropical wind field in combination with latitudinal shifts of the tropical rainbelt related with general decrease in tropical east Pacific SST–controlled 18Osalinity.
Pliocene SSTMg/Ca for G. sacculifer for Site 1241 close to modern SSTs in the tropical east Pacific, in combination with the early Pliocene development of a shallow thermocline, give no direct support to the idea that a permanent El Niņo-like Pliocene climate might have existed during the early Pliocene.
