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Abstract. During the early Pliocene, two major tectonic events triggered a profoundreorganization of ocean and atmospheric circulation in the eastern equatorialPacific (EEP), in the Caribbean Sea, and on adjacent land masses: theprogressive closure of the Central American Seaway (CAS) and the uplift ofthe Northern Andes. These affected, among other things, the mean latitudinalposition of the Intertropical Convergence Zone (ITCZ). The direction of anITCZ shift, however, is still debated, as numeric modeling results andpaleoceanographic data indicate shifts in opposite directions. To provide newinsights into this debate, an independent hydrological record of westernequatorial South America was generated. Vegetation and climate of this areawere reconstructed by pollen analysis of 46 samples from marine sediments ofOcean Drilling Program (ODP) Hole 1239A from the EEP comprising the interval between 4.7 and 4.2 Ma.The study site is sensitive to latitudinal ITCZ shifts insofar as a southward(northward) shift would result in increased (decreased) precipitation overEcuador. The presented pollen record comprises representatives from fiveecological groups: lowland rainforest, lower montane forest, upper montaneforest, páramo, and broad range taxa. A broad tropical rainforestcoverage persisted in the study area throughout the early Pliocene, withoutsignificant open vegetation beyond the páramo. Between 4.7 and 4.42 Ma,humidity increases, reaching its peak around 4.42 Ma and slightly decreasingagain afterwards. The stable, permanently humid conditions are rather inagreement with paleoceanographic data, indicating a southward shift of theITCZ, possibly in response to CAS closure. The presence of páramovegetation indicates that the Ecuadorian Andes had already reachedconsiderable elevation by the early Pliocene. Future studies could extend thehydrological record of the region further back into the late Miocene to seeif a more profound atmospheric response to tectonic changes occurred earlier.

Early Pliocene vegetation and hydrology changes in western equatorial South America