A statistical study of iWeinmannia/i pollen trajectories across the Andes

摘要

Recent airborne pollen records data from Northern Patagonia (San Carlos deBariloche, Argentina, Lat. 41.1435° S, Long. 71.375° W, 800 m elevation)suggest that pollen transport takes place from the west to the east slope ofthe Andes. However, the atmospheric characteristics responsible of thistransport have not yet been studied. The aim of this paper is to assesspotential source areas and to describe the involved atmospheric mechanismsof the trans-Andean pollen transport. Methodology relies on the analysis ofbackward trajectories of air masses calculated with the HYSPLIT 4.9 regionalmodel for particular days where airborne pollen of Weinmannia trichosperma Cav. was detected eastof the Andes. This pollen type was selected because it is found regularly atlocalities in eastern Patagonia beyond its present-day distribution.Weinmannia's substantial presence during early Holocene times would also benefit frombetter knowledge of its transport mechanisms. Correspondence betweenatmospheric trajectories and the position of sources was checked using GISmaps. Mode T, Principal Component Analysis (PCA) with Varimax rotation wasused to identify the main spatial structure of geopotential height anomaliesproducing the calculated trajectories. Eighty-eight cases showed that thecalculated directions of trajectories trended from the Northwest toSouthwest passing over the Chilean region of W. trichosperma distribution. PCs resultsshowed two patterns of negative anomalies over southern Patagonia. Theprevailing circulation pattern which drives airborne transport is thepresence of a trough located south of 37 to 40° S with its axis overwestern Patagonia. The synoptic situations for two cases highly correlatedwith principal component scores were described.