DUST SOURCES AND WESTERLIES STORMS IN PATAGONIA: COMPARISON OF IN SITU MEASUREMENTS WITH REMOTE SENSING ESTIMATIONS

DIEGO GAIERO, BARBARA VILLOSLADA AND SANTIAGO GASSÓ

Rio Gallegos

Workshop; ICDP-Workshop PASADO: Potrok Aike Lake Sediment Archive Drilling Project; 2006

ICDP-Universitat Bremen

How much aerosol mass is transported from Patagonia to the South Atlantic Ocean (SAO) basin? What are the sources, the frequency and the extent of the delivery of those particles? Is the regional forcing directly or indirectly affected by the presence of aerosols in the region? Is the amount of iron present in those particles able to control biological processes of this oceanic region? To answer the above questions we have started in 2004 a two year-round program of in-situ and remote sensing dust flux measurements. Hence, four dust samplers equipped with weather stations were installed along 2200 km of Patagonian coast (Bahía Blanca, Trelew, San Julián and Río Grande).  Surface concentrations are compared with aerosol columnar concentrations derived from the MODIS detector onboard the Terra and Aqua satellites following the technique developed by Gassó and Hegg (2003). Global dust distributions usually are estimated based on global dust cycles models, which predict dust emissions, transport through the atmosphere and deposition. However, these models must be validated with available in situ observations. By means of both, remote sensing and ground observation, during June 2004 to April 2005 and according to the true color pictures and confirmed by the surface visibility observations we recorded at least 16 ocean-going dust events mainly triggered by strong westerlies winds. The horizontal flux measurements were compared with the same estimates derived from MODIS. The scale of the events varied from small (single dust plumes along the coast) to large (dust front extending ~600 km). One of the most important of these dust event was perceived at San Julian city on October 20th 2004, where it last almost four hours with average wind speed of 56 km h-1 and maximal gust of 93 km h-1. Satellite images detected small individuals dust plumes clearly transporting dust to the ocean in the San Julián city area. Although, satellite retrievals help to detect the extent and distribution of dust, the retrievals are uncertain due to optical properties of the aerosol under observation. Then, our study provides helpful information for validation of both in situ measurements and satellites estimations. Small-scale events like the squall lines observed in Patagonia cannot be easily represented in global models and are frequently ignored thus causing underestimation of dust emissions and an underestimate of long-distance transport. Such small-scale events like the October 20th should be taken into account in regional models to simulate specific dust storm events and to test parameterizations in global models. Finally, satellite images supported by ground observations indicate that at the Patagonian surface the occurrence of topographic depressions (ephemeral lakes or deflation holes) in dry, unvegetated areas are important sources for fine, loose sediment easily deflated under strong wind conditions. One important question to elucidate is how changes in the frequency and extent of natural inundation occurring on ephemeral lakes systems may lead to significant fluctuations in Patagonian dust loading.