Tropical-extratropical rainfall systems interaction in the southern Atacama Desert since 17ka

MALDONADO, A.; DE PORRAS, M.E.; CARTAJENA, I.

Congreso; 20th Congress of the International Union for Quaternary Research (INQUA); 2019

The southernmost part of the Atacama Desert (24-27°S; SAD) lies in the transitional area between the tropical and extra-tropical rainfall systems linked to the South America Summer Monsoon (SASM) and the Southern Westerlies Wind Belt (SWWB), respectively, providing a unique chance to trace their interactions in the past. It has been largely hypothesized about the source of the rainfall associated to the different wet phases recorded in the SAD since 17ka, mainly based on the temporal and spatial patterns recorded in the different kind of archives and/or proxies. This led to some inconsistencies attributed to the different temporal and spatial scales in which palaeoclimatic archives/proxies capture the past climate variability. Furthermore, the geographic complexity of the regional climate such as variation in the sources and/or mechanisms delivering the precipitation in space over the entire SAD, made the picture in time even more complicated.In order to trace the past palaeoclimatic dynamics at the southern Atacama Desert and then, the interaction of tropical/extra-tropical interaction of the rainfall systems since the Late Pleistocene, this paper analyzed the changes in the fossil midden pollen assemblages (same archive/proxy) in time and space aided by a modern regional vegetation-pollen-climate calibration set. Rodent midden pollen series at 24.5°S show extremely humid conditions during the Late Pleistocene (14-10.8ka) coinciding with the Central Atacama Pluvial Event II (CAPE II) which gradually turned into extremely dry at 8.5ka which lasted until 2ka. Then, a climatic amelioration towards slightly wetter conditions occurred up to the present interrupted by a dry phase between 1.4-1.0ka. At 26-27°S, pollen assemblages preserved in fossil rodent middens reflect humid conditions between 17-13ka which gradually turned into extremely dry ones around 10ka peaking up to 9ka. During the Mid-Holocene and up to 3.3ka drier than present conditions prevailed followed by a wet phase up to 2.2ka and a dry period between 1.0-0.6ka. At 0.6ka, an increase in humidity was recorded followed by a trend to drier conditions similar to the present. Extremely humid conditions during the Late Pleistocene and early Holocene followed by severely arid phases prevailed both at 24.5°S and 26-27°S suggesting the intensification and posterior weakening of both, tropical and extra-tropical rainfall systems. Amelioration of dry conditions occurred into the Late Holocene which was characterized by alternating dry and wet phases at the centennial scale. The increase of humidity and occurrence of wet phases at 26-27°S indicate that the extra-tropical rainfall system intensified during the Late Holocene, particularly after 3.3ka and ca. 0.6ka whereas the tropical rainfall system behaved similar to the present. FONDECYT#11150089; 1181627