A statistical study of &amp;lt;i&amp;gt;Weinmannia&amp;lt;/i&amp;gt; pollen trajectories across the Andes

C F Pérez,M M Bianchi,M E Castañeda,M I Gassmann

doi:10.5194/adgeo-22-79-2009

Abstract

Abstract. Recent airborne pollen records data from Northern Patagonia (San Carlos de Bariloche, 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 of the Andes. However, the atmospheric characteristics responsible of this transport have not yet been studied. The aim of this paper is to assess potential source areas and to describe the involved atmospheric mechanisms of the trans-Andean pollen transport. Methodology relies on the analysis of backward trajectories of air masses calculated with the HYSPLIT 4.9 regional model for particular days where airborne pollen of Weinmannia trichosperma Cav. was detected east of the Andes. This pollen type was selected because it is found regularly at localities in eastern Patagonia beyond its present-day distribution. Weinmannia's substantial presence during early Holocene times would also benefit from better knowledge of its transport mechanisms. Correspondence between atmospheric trajectories and the position of sources was checked using GIS maps. Mode T, Principal Component Analysis (PCA) with Varimax rotation was used to identify the main spatial structure of geopotential height anomalies producing the calculated trajectories. Eighty-eight cases showed that the calculated directions of trajectories trended from the Northwest to Southwest passing over the Chilean region of W. trichosperma distribution. PCs results showed two patterns of negative anomalies over southern Patagonia. The prevailing circulation pattern which drives airborne transport is the presence of a trough located south of 37 to 40° S with its axis over western Patagonia. The synoptic situations for two cases highly correlated with principal component scores were described.

Highlights

How far pollen types are transported from their source region is an important question in Palynology
The aim of this paper is to study airborne pollen transport across the Andes applying the trajectory methodology in the case of Weinmannia trichosperma collected in San Carlos de Bariloche and to describe the synoptic mechanisms involved in the process
This pattern could be indicative that Weinmannia became airborne from pollen grains retained in the forest canopy being resuspended by gusty conditions on clear days

Summary

Introduction

How far pollen types are transported from their source region is an important question in Palynology. Long range transport of pollen grains is generally dominated by synoptic systems but local circulations induced by terrain in-homogeneities can affect it. Trajectories associated to regional and extra-regional pollen transport have been studied in Buenos Aires province (Argentina) showing that depending on the geographical location of the plant source in relation to the position of the sampling station, the transport of different pollen taxa was associated either to N-NE wind direction related to the South Atlantic Anticyclone or to a SW direction, related to the Westerlies circulation (Gassmann and Perez, 2006). 71.375◦ W, 800 m elevation), suggest that a significant pollen transport takes place from the western to the eastern slopes of the Andes. To evaluate this aspect of atmospheric transport mechanisms, we choose Weinmannia trichosperma Cav. Air masses trajectory calculation is a common methodology applied to pollution

Objectives

Methods

Results

Conclusion