In-stream wetland deposits, megadroughts, and cultural change in the northern Atacama Desert, Chile

Abstract

A key concern regarding current and future climate change is the possibility of sustained droughts that can have profound impacts on societies. As such, multiple paleoclimatic proxies are needed to identify megadroughts, the synoptic climatology responsible for these droughts, and their impacts on past and future societies. In the hyperarid Atacama Desert of northern Chile, many streams are characterized by perennial flow and support dense in-stream wetlands. These streams possess sequences of wetland deposits as fluvial terraces that record past changes in the water table. We mapped and radiocarbon dated a well-preserved sequence of in-stream wetland deposits along a 4.3-km reach of the Río San Salvador in the Calama basin to determine the relationship between regional climate change and the incision of in-stream wetlands. The Río San Salvador supported dense wetlands from 11.1 to 9.8, 6.4 to 3.5, 2.8 to 1.3, and 1.0 to 0.5 ka and incised at the end of each of these intervals. Comparison with other in-stream wetland sequences in the Atacama Desert, and with regional paleoclimatic archives, indicates that in-stream wetlands responded similarly to climatic changes by incising during periods of extended drought at ~9.8, 3.5, 1.3, and 0.5 ka.

Did Modern Precipitation Drivers Influence Centennial Trends in the Highlands of the Atacama Desert During the Most Recent Millennium?

“…For instance, dry conditions at Toconce are punctuated by more humid pollen assemblages at 790 and 730 BP, which could be associated with wetland terraces above modern elevations at 700 BP at Tilomonte springs, in the hyperarid core of the desert (Rech et al, 2002, Figure 1a). Similarly, peak aridity around 550 BP at Toconce could be linked to the documented onset of hyperaridity by ∼500 BP inferred from the incision of elevated wetland deposits at Rio San Salvador (Tully et al, 2019, Figure 1a). While we acknowledge the discontinuous nature of our midden series, the prevalence of dry assemblages during the first part of the last millennium is inconsistent with an extended pluvial event in the Atacama Desert.…”

Tributary-junction alluvial fan response to an ENSO rainfall event in the El Huasco watershed, northern Chile

“…Relatively more arid periods in the mid-Holocene (e.g. within 8 ka BP to *4 ka BP) (Grosjean et al, 1997(Grosjean et al, , 2007Ortega et al, 2012;Tiner et al, 2018;Tully et al, 2019) would have provided the necessary conditions to form and preserve regolith in inter-storm periods, and the short-lived rains would have been responsible for presenting similar stratigraphic arrangements to the observed March 2015 event. Spatially and temporally, distribution of these records suggests that the El Niñ o Southern Oscillation (ENSO) signature and its temporal variability may account for the landscape evolution of these valleys during the Holocene (e.g.…”

Late Pleistocene–Early Holocene human settlement and environmental dynamics in the southern Atacama Desert highlands (24.0°S–24.5°S, Northern Chile)

“…The observed trend in population growth in the inland Atacama Desert reversed sharply around 9,500 cal years BP (Gayó et al, 2015) in association with the end of CAPE II and the onset of a sustained period of drought around 9,800 cal years BP, as recorded in numerous paleoclimate archives (summarized in Grosjean et al, 2003;Latorre et al, 2007;Workman et al, 2020). This dry period was recently characterized as a megadrought based on studies of several in-stream Atacama Desert wetlands (Tully et al, 2019). Although widespread wet conditions prevailed in the central and southern Atacama during CAPE II, their timing and magnitude differed in these two areas, with records showing that wet phases lasted longer in southern than in central Atacama (de Porras et al, 2017;Sáez et al, 2016).…”