A 106 ka paleoclimate record from drill core of the Salar de Atacama, northern Chile

Abstract

A 100 m long salt core (SQM #2005) from the Salar de Atacama, northern Chile (23°S, 68°W), a dry lake bed, contains a 106 kyr paleoclimate record of hydrologic balances on the western slopes of the central Andes of South America. Six U-series disequilibrium dates range sequentially from 106.1±6.4 to 5.4±2.7 ka. Based on sedimentary structures and petrographic textures of salts and associated siliciclastic sediments, interpretations of paleoenvironments and net hydrologic balance suggest that relatively wet periods (saline lakes and expanded mudflats) existed in the Salar de Atacama from 75.7 to 60.7 ka and from 53.4 to 15.3 ka, with the wettest perennial lake interval from 26.7 to 16.5 ka. Short relatively wet periods also occurred in the Holocene from 11.4 to 10.2 ka and from 6.2 to 3.5 ka. These wet periods at Salar de Atacama correspond well with other late Pleistocene climate records from the central Andes that are a function of the net hydrologic budget. The Minchin–Tauca lake sequence from Salar de Uyuni, Bolivia, is synchronous with the 53.4–15.3 ka saline lake wet period at Salar de Atacama. The Tauca phase coincided with the wettest perennial lake interval at Salar de Atacama from 26.7 to 16.5 ka. The Coipasa lake phase from Uyuni was probably contemporaneous with the early Holocene wet period at Salar de Atacama from 11.4 to 10.2 ka. The early Holocene wet interval at Salar de Atacama was also synchronous with the maximum Holocene lake levels of the Chilean Altiplano lakes to the east and with grass-rich rodent middens between 11.8 and 10.5 ka in age from the Atacama basin. The lake period at Salar de Atacama between 26.7 and 15.3 ka compares closely with low δ 18O values, low anion concentrations and high accumulation rates from the Sajama glacial ice core, southwestern Bolivia between 25 and 15.5 ka. It is concluded that wet and dry phases were synchronous in the central Andean plateau of southwestern Bolivia and along the western flank of the Andes of northern Chile over the past 50 kyr. This region, which today receives its moisture from the Amazon Basin to the east, probably also did so in the past. The wet periods at Salar de Atacama are in phase with January insolation maxima at 15°S at 70, 45, and 20 ka, which suggests that past changes in summer insolation influenced precipitation patterns in the central Andes. However, there are no major wet periods linked to the January insolation maximum at 93 ka and the present-day extremely dry climate in the Atacama Desert is associated with a peak in summer insolation. Therefore there must be other important influences over precipitation in the central Andes which modify the first order insolation controls.