Quaternary palaeoceanography of the Eastern Equatorial Pacific: Planktonic foraminiferal evidence for dual upwelling mechanism and high latitude influence

High-resolution planktonic foraminiferal assemblage data from ODP Hole 846B provide new insights into Quaternary palaeoceanographic variability in the Eastern Equatorial Pacific (EEP). The record reveals that the EEP was a highly dynamic system characterised by recurrent shifts in water column structure, upwelling strength, and faunal composition in response to both tropical and high latitude climatic forcing. The repeated appearance of the temperate species Globorotalia (Globoconella) inflata identifies distinct episodes of cold water incursions into the equatorial zone, reflecting enhanced eastern boundary currents and strong teleconnections with Antarctic climate processes. The long-term dominance of Neogloboquadrina dutertrei indicates the persistent influence of the wind driven equatorial cold tongue, although its asynchronous relationship with coastal upwelling taxa points to a decoupling between equatorial and Peruvian margin upwelling systems. Variations in mixed-layer and thermocline dwellers document alternating El Niño and La Niña like conditions, tracking changes in upper ocean stratification and thermocline depth. A marked reorganisation of faunal patterns after the Mid-Pleistocene Transition (MPT) signals a fundamental shift in the dominant controls on EEP oceanography, coinciding with intensified glacial interglacial cycles. Overall, this study refines the understanding of the EEP as a climatically sensitive region governed by the complex interaction of high-latitude forcing, tropical atmospheric variability, and boundary current dynamics.