Abstract
The extent and behaviour of glaciers during the mid-Piacenzian warm period illustrate the sensitivity of the cryosphere to atmospheric CO2 concentrations above pre-industrial levels. Knowledge of glaciation during this period is restricted to globally or regionally averaged records from marine sediments and to sparse terrestrial glacial deposits in mid-to-high latitudes. Here we expand the Pliocene glacial record to the tropics by reporting recurrent large-scale glaciation in the Bolivian Andes based on stratigraphic and paleomagnetic analysis of a 95-m sequence of glacial sediments underlying the 2.74-Ma Chijini Tuff. Paleosols and polarity reversals separate eight glacial diamictons, which we link to cold periods in the benthic oxygen isotope record. The glaciations appear to coincide with the earliest glacial activity at high northern latitudes and with events in Antarctica, including the strong M2 cold peak and terminal Pliocene climate deterioration. This concordance suggests inter-hemispheric climate linkages during the late Pliocene and requires that the Central Andes were at least as high in the late Pliocene as today. Our record fills a critical gap in knowledge of Earth systems during the globally warm mid-Piacenzian and suggests a possible driver of faunal migration preceding the large-scale biotic interchange in the Americas during the earliest Pleistocene.
Highlights
The extent and behaviour of glaciers during the mid-Piacenzian warm period illustrate the sensitivity of the cryosphere to atmospheric CO2 concentrations above pre-industrial levels
Outside the Cordillera Real, the earliest known evidence of tropical Cenozoic glaciation is on Mount Kenya where glacial diamictons date to the Olduvai subchron and earlier Matuyama Chron[42] and in the Andes of Colombia where glaciofluvial sediments have been reported from the earliest Pleistocene[43]
The continuous glacial sequence at La Paz, Bolivia contains the only known record of low-latitude late Pliocene glaciation on Earth. This sequence is probably the best terrestrial archive of Earth’s cryosphere during the mid-Piacenzian climatic optimum and subsequent end-Pliocene climatic deterioration. This record reveals that high-mountain ice caps formed repeatedly in the tropical Andes throughout the late Pliocene – before, during, and after the mid-Piacenzian warm period
Summary
The extent and behaviour of glaciers during the mid-Piacenzian warm period illustrate the sensitivity of the cryosphere to atmospheric CO2 concentrations above pre-industrial levels. Knowledge of glaciation during this period is restricted to globally or regionally averaged records from marine sediments and to sparse terrestrial glacial deposits in mid-to-high latitudes. Existing late Pliocene glacial records are regional or global averages derived from elemental and isotopic compositions of marine microorganisms[2,3,10], ice-rafted detritus in sub-polar seas[11,12], global ice volumes[10,13], sea level[10,14], or atmospheric CO2 concentrations[5,6]. Their K-Ar23 and 40Ar/39Ar24 ages on potassium feldspar in the Chijini Tuff, which www.nature.com/scientificreports/
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