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Discussion papers | Copyright
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 03 Nov 2017

Research article | 03 Nov 2017

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Climate of the Past (CP).

Early Pliocene vegetation and hydrology changes in western equatorial South America

Friederike Grimmer1, Lydie Dupont1, Frank Lamy2, Gerlinde Jung1, Catalina González3, and Gerold Wefer1 Friederike Grimmer et al.
  • 1MARUM – Center for Marine Environmental Sciences, University of Bremen, Leobener Str. 8, 28359 Bremen, Germany
  • 2Alfred-Wegener-Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany
  • 3Department of Biological Sciences, Universidad de los Andes, Cra. 1 #18a-12, Bogotá, Colombia

Abstract. During the early Pliocene, two major tectonic events triggered a profound reorganization of ocean and atmospheric circulation in the Eastern Equatorial Pacific (EEP), the Caribbean Sea, and on adjacent land masses: the progressive closure of the Central American Seaway (CAS) and the uplift of the northern Andes. These affected amongst others the mean latitudinal position of the Intertropical Convergence Zone (ITCZ). The direction of an ITCZ shift however is still debated, as numeric modelling results and paleoceanographic data indicate shifts in opposite directions. To provide new insights into this debate, an independent hydrological record of western equatorial South America was generated. Vegetation and climate of this area were reconstructed by pollen analysis of 46 samples from marine sediment core ODP 1239A from the EEP comprising the interval between 4.7 and 4.2Ma. The study site is sensitive to latitudinal ITCZ shifts insofar as a southward (northward) shift would result in increased (decreased) precipitation over Ecuador. The presented pollen record comprises representatives from five ecological groups: lowland rainforest, lower montane forest, upper montane forest, páramo, and broad range taxa. A broad tropical rainforest coverage persisted in the study area throughout the early Pliocene, without significant open vegetation below the forest line. Between 4.7 and 4.42Ma, humidity increases, reaching its peak around 4.42Ma, and slightly decreasing again afterwards. The stable, permanently humid conditions are rather in agreement with paleoceanographic data indicating a southward shift of the ITCZ, possibly in response to CAS closure. The presence of páramo vegetation indicates that the Western Cordillera of the northern Andes had already reached considerable elevation by the early Pliocene. Future studies could extend the hydrological record of the region further back into the late Miocene to see if a more profound atmospheric response to tectonic changes occurred earlier.

Friederike Grimmer et al.
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Friederike Grimmer et al.
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Short summary
We present the first pollen record of the early Pliocene from western equatorial South America. Our reconstruction of the vegetation aims at providing insights into hydrological changes related to tectonic events (Central American Seaway closure, uplift of the Northern Andes). We find stable humid conditions, suggesting a southern location of the Intertropical Convergence Zone. The presence of high montane vegetation indicates an early uplift of the Western Cordillera of the northern Andes.
We present the first pollen record of the early Pliocene from western equatorial South America....