“Climatic fluctuations in the hyperarid core of the Atacama Desert during the past 215 ka”

www.nature.com/scientificreports OPEN Received: 2 October 2018 Accepted: 8 March 2019 Published: xx xx xxxx “Climatic fluctuations in the hyperarid core of the Atacama Desert during the past 215 ka” Benedikt Ritter1, Volker Wennrich 1, Alicia Medialdea 2, Dominik Brill2, Georgina King3, Sascha Schneiderwind4, Karin Niemann4, Emma Fernández-Galego1, Julia Diederich1, Christian Rolf5, Roberto Bao 6, Martin Melles1 & Tibor J. Dunai1 Paleoclimate records from the Atacama Desert are rare and mostly discontinuous, mainly recording runoff from the Precordillera to the east, rather than local precipitation. Until now, paleoclimate records have not been reported from the hyperarid core of the Atacama Desert (<2 mm/yr). Here we report the results from multi-disciplinary investigation of a 6.2 m drill core retrieved from an endorheic basin within the Coastal Cordillera. The record spans the last 215 ka and indicates that the long-term hyperarid climate in the Central Atacama witnessed small but significant changes in precipitation since the penultimate interglacial. Somewhat ‘wetter’ climate with enhanced erosion and transport of material into the investigated basin, commenced during interglacial times (MIS 7, MIS 5), whereas during glacial times (MIS 6, MIS 4–1) sediment transport into the catchment was reduced or even absent. Pelagic diatom assemblages even suggest the existence of ephemeral lakes in the basin. The reconstructed wetter phases are asynchronous with wet phases in the Altiplano but synchronous with increased seasurface temperatures off the coasts of Chile and Peru, i.e. resembling modern El Niño-like conditions. The Atacama Desert of northern Chile is one of the driest places on Earth; its extreme hyperarid core receives less than 2 mm/yr of precipitation1. These hyperarid conditions are the consequence of subtropical atmospheric subsidence2 and temperature inversion due to coastal upwelling of the cold Peru-Chile Current (PCC) (or Humboldt Current1). Furthermore, a continental effect (distance to the Atlantic) and rainshadow effect at the eastern flank of the Andes (Fig. 1A) effectively harvests sparse moisture arriving from the Atlantic3–6. High evaporation rates in most areas of the Atacama Desert additionally intensify the hyperarid conditions3,7. Although the main factors causing aridity are known, the onset of predominantly hyperarid conditions and variability in the degree of aridity in this area remain disputed8–18. Presently the core of the hyperarid Atacama Desert covers parts of the Coastal Cordillera and Central Depression between 22–19°S (Fig. 1A). Water availability increases, albeit moderately, away from this core. The Mean Annual Precipitation (MAP) increases rapidly from less than 20 mm/yr at 2300 m to over 300 mm/yr at 5000 m elevation3. At the southern edge of the hyperarid core, moisture sources are connected to south-westerly airflows that allow extratropical cyclone systems to migrate northwards bringing moisture to areas south of 24°S during austral winter1. These northward migrating cut-off low systems can penetrate further north, as occurred during recent flood events such as in March 201519,20. Similar rain events in the (sub-) recent past may be reflected by widespread traces of fluvial erosion and transport in the southernmost region of the dry core (i.e. south of 21°30′S), whereas comparable features are largely absent further to the north. Regional climate records from the Coastal Cordillera and the Central Depression are scarce and where available mostly cover only the Holocene and the Last Glacial Maximum (LGM)6,16,18,21–25. Climate records spanning the mid to late Pleistocene, exist from lake sediment sequences in the Bolivian Altiplano26 and from near-shore marine sediment-cores27,28, all of which are >400 km away from the desert interior, and cross steep climatic gradients1,3 (Fig. 1B). In this paper, we present a first mid to late Pleistocene record of precipitation changes close to 1 Institute of Geology & Mineralogy, University of Cologne, Cologne, Germany. 2Institute of Geography, University of Cologne, Cologne, Germany. 3Institute of Earth Surface Dynamics, University of Lausanne, Lausanne, Switzerland. 4 Institute of Neotectonics and Natural Hazards, RWTH Aachen University, Aachen, Germany. 5Leibniz Institute for Applied Geophysics (LIAG), Hannover, Germany. 6Centro de Investigacións Científicas Avanzadas (CICA), Facultade de Ciencias, Universidade da Coruña, Coruña, Spain. Correspondence and requests for materials should be addressed to B.R. (email: ) Scientific Reports | (2019) 9:5270 | https://doi.org/10.1038/s41598-019-41743-8 1 www.nature.com/scientificreports/ www.nature.com/scientificreports Figure 1. (A) Colour shaded digital elevation model (derived from SRTM-data, created using ArcGIS 10.5.1) with isohyets1 after Ritter, et al.31. Dashed white line indicates the border between winter-rain dominated areas in the SW and summer-rain dominated areas in the1. Sites from the literature are: rodent midden sites23,64, earliest archaeological sites65, stable isotope studies66, sedimentological studies14,25,67,68, cosmogenic nuclide exposure ages and erosion rates determined with cosmogenic nuclides9–12,68–74. The stippled yellow outline for Miocene relict surfaces is derived from studies yielding Miocene exposure ages (M) for sediment surfaces11,12,70,71 and sedimentological studies67. Studies yielding Pliocene ages for the onset of aridity are marked with P. The study area is marked with a black rectangle and drainage catchment of the sediment record is encircled with a black line. (B) Overview map of South America with positions of reference studies marked with coloured circles and the location of the Atacama Desert marked with a red rectangle. (C) Hillshade image based on Aster GDEM data (30 m resolution, produced using ArcGIS 10.5.1). Red lines indicate major tectonic fault systems (AFS = Atacama Fault System). The coring site (orange circle) is located in the mud pan in the northern part of an endorheic basin, whose drainage catchment is indicated with the black line. (D) View from the North onto the mud pan with the drilling location indicated by a star (Photo made by V. Wennrich). the driest part of the Atacama as preserved in lacustrine clay pan sediments of a tectonically blocked endorheic basin within the Coastal Cordillera. Site Information The study site is situated in the Coastal Cordillera, which forms a 1000–1800 m high and 50–70 km wide structural high that is restricted to the west by a 1000 m coastal cliff and bounded to the east by the Central Depression (Fig. 1A,C). The studied clay pan (21° 32.5″S, 69° 54.8″W) is located at the northern end of an endorheic basin (Fig. 1C), which was formed by tectonic drainage displacement by reverse faulting (Adamito or Auguire fault)29–31. The clay pan at its terminus has a maximum surface area of 640 by 1000 m, and a catchment area of 560 km2 (Fig. 1A (...truncated)