INTO THE TROPICAL-EXTRATROPICAL RAINFALL SYSTEMS INTERACTION IN THE SOUTHERN ATACAMA DESERT SINCE 17Ka

BOOM, A.; CARRÉ, M.; MUÑOZ, L.; MALDONADO, A.J.; DE PORRAS, M.E.

Congreso; ISOECOL 2018; 2018

The southernmost part of the Atacama Desert (24-27°S; AD) lies in the transitional area between the tropical (summer) and extra-tropical (winter) rainfall systems providing a unique chance to trace their interactions in the past. Even though the source of the rainfall associated to the different wet phases recorded since 17ka has been largely discussed, δ18O isotopic analysis were not applied to answer such issues even when both rainfall systems have different isotopic signature. Here we present the first results aiming to develop a calibration of plant cellulose oxygen isotopes as an indicator of rainfall oxygen isotopes along the southern AD to provide the basis for robust paleoclimatic interpretations of the fossil plant macro-remains cellulose isotopic record preserved in rodent middens. Thus, modern water from (winter 2016/winter 2016-2017) rainfall, ice, snow, rivers and salt lakes as well as plants (Jarava frigida) samples were collected at 32 sites at different altitude and latitude in the southern AD. Besides, a characterization of the synoptic conditions prevailing during rainy days was carried out to state the modern mechanisms delivering precipitation throughout the area during the sampling period. Winter and summer rain water isotopic values are clearly aligned along the meteoric line and could be easily distinguished based on their δ18O composition of -12(±1.1)? and -6.5(±2.5)? respectively. This significant isotopic difference confirms that winter and summer rainfall have different origin, extratropical vs. tropical, respectively. Ice and snow samples presented similar or more depleted δ18O values (~-14,7?) than winter precipitation which reflect the same source but solid precipitation. Rivers and salt lakes presented enriched δ18O values (-1,6?) which deviates from the meteoric line due to the high evaporation rates in these Altiplano basins. Summer (winter) precipitation δ18O composition shows a negative (positive) correlation with altitude which is consistent with the origin of precipitation. It is also probable that winter rain δ18O presents a latitudinal effect related to the distal location of the AD but also the synoptic mechanisms that delivered the precipitation. Once the plants (Jarava frigida) samples are isotopically (δ18O) analyzed, we will be jointly analyzed to complete the modern water-plants isotopic relationships. FONDECYT #11150089