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      Early Pliocene vegetation and hydrology changes in western equatorial South America

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      Climate of the Past
      Copernicus GmbH

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          Abstract

          Abstract. During the early Pliocene, two major tectonic events triggered a profound reorganization of ocean and atmospheric circulation in the eastern equatorial Pacific (EEP), in 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, among other things, the mean latitudinal position of the Intertropical Convergence Zone (ITCZ). The direction of an ITCZ shift, however, is still debated, as numeric modeling 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 sediments of Ocean 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 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 beyond the páramo. Between 4.7 and 4.42 Ma, humidity increases, reaching its peak around 4.42 Ma 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 Ecuadorian 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.

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          A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records

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            Migrations and dynamics of the intertropical convergence zone.

            Rainfall on Earth is most intense in the intertropical convergence zone (ITCZ), a narrow belt of clouds centred on average around six degrees north of the Equator. The mean position of the ITCZ north of the Equator arises primarily because the Atlantic Ocean transports energy northward across the Equator, rendering the Northern Hemisphere warmer than the Southern Hemisphere. On seasonal and longer timescales, the ITCZ migrates, typically towards a warming hemisphere but with exceptions, such as during El Niño events. An emerging framework links the ITCZ to the atmospheric energy balance and may account for ITCZ variations on timescales from years to geological epochs.
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              Amazonia through time: Andean uplift, climate change, landscape evolution, and biodiversity.

              The Amazonian rainforest is arguably the most species-rich terrestrial ecosystem in the world, yet the timing of the origin and evolutionary causes of this diversity are a matter of debate. We review the geologic and phylogenetic evidence from Amazonia and compare it with uplift records from the Andes. This uplift and its effect on regional climate fundamentally changed the Amazonian landscape by reconfiguring drainage patterns and creating a vast influx of sediments into the basin. On this "Andean" substrate, a region-wide edaphic mosaic developed that became extremely rich in species, particularly in Western Amazonia. We show that Andean uplift was crucial for the evolution of Amazonian landscapes and ecosystems, and that current biodiversity patterns are rooted deep in the pre-Quaternary.
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                Author and article information

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                Journal
                Climate of the Past
                Clim. Past
                Copernicus GmbH
                1814-9332
                2018
                November 14 2018
                : 14
                : 11
                : 1739-1754
                Article
                10.5194/cp-14-1739-2018
                238e5e8b-970b-4944-b332-bfee1c09c16d
                © 2018

                https://creativecommons.org/licenses/by/4.0/

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