L’expansion des déserts andins aux moyennes latitudes de l’Amérique du Sud ˸ une approximation paléoclimatique
Year: 2025
Type: dissertation
Abstract: Environmental changes such as more frequent and severe droughts, resulting from anthropogenic, natural or combined factors, have been recorded throughout the temperate Andean region of South America. Water availability is crucial for the functioning of ecosystems, societies and economies in this region. Moreover, climate projections for the region indicate trends of sustained increases in tropospheric warming and decreases in river flows. However, the lack of long-term climate observations complicates the contextualization of these changes and generates uncertainty about the new climatic normality in the future.Climate variability in the temperate Andean region is modulated by different forcing factors on seasonal, annual, decadal and even longer time scales. Teleconnections with tropical sea surface temperature driven by El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) or high-latitude circulation such as the Southern Annular Mode (SAM), have a strong effect on precipitation patterns at different time scales in South America. Beyond these natural drivers of climate variability, some of the temperature and precipitation trends in the Andean region of South America could be related to changes in larger-scale atmospheric circulation patterns caused by anthropogenic global warming. The Hadley Cell is the large-scale atmospheric circulation that connects the tropical and subtropical regions, spanning half the globe. The descending branch of this circulation largely determines the subtropical climate and is considered the "edge of the tropics". In response to natural and anthropogenic global changes, the Hadley Cell has expanded poleward, changing rainfall patterns and expanding the extent of subtropical dry zones to higher latitudes in both hemispheres.Tree ring width provides information on regional variations in temperature and precipitation in Central Chile, northern Patagonia and other regions of South America. The composition of stable isotopes (carbon and oxygen) in tree cellulose is a useful paleoenvironmental indicator for deciphering and reconstructing past climate variations. Isotopic records have been used in reconstructions of temperature, precipitation and relative humidity. However, this information from tree rings represents an unexplored resource for deepening key aspects of past climate variability and change in Andean regions of South America. One of the endemic species of the Andean forests of Chile and Argentina is Austrocedrus chilensis ("Patagonian cypress"). The information contained in its growth rings is a key record of past environmental changes.The general objective of this work was to develop long-term perspectives of the dynamics of the Hadley Cell along the western sector of South America, extending the analysis of past variations in precipitation and temperature beyond the relatively short period provided by instrumental data through paleoenvironmental records.The information obtained provides an updated overview of the variability of tree-ring width and stable isotope chronologies of Austrocedrus chilensis and their relationships with climate variables (temperature, precipitation and vapor pressure deficit) and forcings of regional (ENSO, PDO, SAM) and hemispheric (Hadley Cell) climate circulation. This information is the basis for advancing the development of climate reconstructions at different spatiotemporal scales, which allow contextualizing present environmental changes and hypothesizing about their future behaviour.
Source: theses.fr (ABES)
Author: Vega, Leticia
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Climate action
Open Access status: green
OpenAlex ID: W7030016695
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