Dendrochronological Techniques and Glacier Mapping Based on Satellite Images Applied in Patagonia, Argentina

MASIOKAS, M.; LUCKMAN, B.; VILLALBA, R.; DELGADO, S.; SVARKA, P.; RIPALTA, A.

San Carlos, Mendoza, Argentina

Taller; Second Science Meeting, IAI CRN 2047, Documenting, understanding and projecting changes in the hydrological cycle in the American Cordillera; 2008

IAI

The glaciers of the Patagonian Andes in southern South America have an enormous potential as indicators of past and present climatic changes. However, past glacier fluctuations and glacier-climate relationships in the Patagonian Andes are still not well known. Current knowledge about late Holocene glacier fluctuations in the south Patagonian Andes is mainly based on evidence from large outlet glaciers of the North and South Patagonian Icefields, and few data exist for the smaller glaciers elsewhere in the region. Here we provide dendrogeomorphological evidence for Little Ice Age (LIA) and post-LIA activity for several small glaciers located near the northeast margin of the South Patagonian Icefield. At these sites the LIA maximum position was identified by massive moraines with mature trees dating to the late 1500s-early 1600s. Several older moraines were observed beyond these limits but could not be precisely dated. Relatively synchronous advances occurred at most glaciers in the early 1700s and were dated using living trees and in situ, subfossil material. All glaciers show three to five subsequent advances mostly concentrated between the mid 19th and early 20th centuries. These results provide important new information on the glacier history of this area but additional, more precisely-dated records are needed from many more sites before we can fully elucidate the complex late Holocene glacial history of this region.   Using the dating and location of LIA moraines as a reference, estimates based on Landsat TM imagery indicate these glaciers lost between 15 and 46% of their LIA areas by 1984 and a further 5-18% by 2005, with the smallest glaciers showing the greatest proportional loss. Paired comparisons of contemporary and historical photography for the glaciers confirm this mass loss. The drastic, widespread glacier recession observed at the study sites indicates that, over the past several decades, the overall conditions in this region have clearly favored glacier ice ablation over accumulation at high elevation sites across the mountains. Despite the lack of long, good quality climate records in the vicinity of these study sites, the large-scale pattern of warming identified in instrumental climate records from the south Patagonian region provides support for a primary role of temperature in this regional phenomenon.   A research project is currently underway that will develop the first comprehensive glacier inventory for Argentina. Given the large-scale nature of this project, the mapping of glaciers and monitoring of changes will rely heavily on remote sensing. The preliminary analysis presented here, in which tree-ring dating and mapping of moraines is used in combination with satellite imagery to extend the analysis of glacier areal changes over the past few centuries, appears to be an interesting and useful approach for Patagonian conditions because it would allow the evaluation of the most recent glacier and climate changes in a longer term context.