Investigation of climate change in the southernmost South America and its impact on the local ecosystems
Creators: name: Soto-Rogel, Pamela
Publisher: name: Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
Year: 2024
Subjects: Southernmost South America
Climate Change
Ecosystems
Climate variability
Dendrochronology
Stable isotopes in tree rings

description: Recent changes in ecosystems across the globe are, in part, a direct response to the effect of climate change and the intensification of human activity. Despite being a situation of great importance, there are few studies on this topic in the area of southernmost South America (SSA, 50 - 56 °S). In SSA, recent trends in climate during the recent decades indicate a generalized warming trend, being more accentuated in the eastern parts of SSA. Analyses of Precipitation reveal different trends given by the complex ocean-atmosphere dynamics from the Atlantic and Pacific Ocean, and the complex orography of the Andes-Darwin mountain range. While the central area of SSA reveals a negative trend in precipitation, the western and eastern regions show positive trends. The precipitation increase in the easternmost zone can be associated with sources of water vapor from the Amazon and Atlantic basins induced by low-pressure anomalies in the middle troposphere. While in the westernmost area it is associated with the southward movement of the Westerly Wind Belt (WWB) driven the positive phase of the first extratropical atmospheric circulation pattern, the Antarctic Oscillation (AAO). The precipitation reduction in the central area of the SSA can be associated to a strengthening of the WWB (directly impacting on the mountain range), leading to an intensifying of Föhn effects. The WWB strengthening could be triggered by the strengthening of the South Pacific High (SPH) and deepening of the Amundsen Sea Low (ASL, located in the western sector of the Antarctic Peninsula) in the last decades. Nowadays, an increase in the occurrence and severity of extreme events (EE), such as, drought, flooding, heat, and cold wave are evident worldwide. In the SSA region, a lack long-term EE records based on the main meteorological station is evident. However, a series of EE are reported in literature. Also, the Chilean meteorological office has recently published a short-term time series of EE clearly indicating an increase in heat waves and droughts for the SSA. These EE are associated with a greater influx of warm subtropical air masses and a migration and strengthening to the south of the WWB. To date, only few studies exist for the SSA that evaluate the climatic effects (including extreme events - EE) on different ecosystems of Fuego-Patagonia. In this Ph.D. dissertation, I investigated these effects based on how recent climatic trends and EE in the SSA are affecting i) aboveground net primary productivity (ANPP), ii) socioeconomic impact on sheep production (SP), iii) tree growth by the analysis of tree-ring widths (TRW), and stable oxygen isotope variations in tree-ring cellulose (δ18OTRC) of the southernmost Nothofagus spp. forests in Punta Arenas, Yendegaia, and the Navarino Island. The main findings from this PhD thesis are as follows: 1. A decrease in Above-ground net primary productivity (ANPP) can be associated with regional droughts and cold wave episodes. 2. A decrease in sheep production (SP) can be related to EE, such as cold waves, drought, high precipitation amounts, and strong wind speed. 3. Analysis of tree-ring widths (TRW) revealed diverse tree growth patterns in response to strong climatic contrasts in the SSA and indicated intra-species differences. Nothofagus betuloides on the Navarino Island revealed a decrease in TRW since the mid-1980s in response to a predominant positive phase of the Antarctic Oscillation (AAO). 4. There is evidence of an abrupt decrease in the tree growth of Nothofagus pumilio. In the case of forests near Punta Arenas, growth depressions were associated withEE of drought-heat waves, while for Navarino Island, they are associated with EE´s caused by high wind speeds. 5. Oxygen isotopic enrichment in tree-ring cellulose (δ18OTRC) of N. betuloides and N. pumilio forests was detectable for episodes of reduced soil water, strong wind speeds, and high temperatures. In this Ph.D. dissertation, I additionally analyzed a potential if the southernmost forests of Nothofagus spp. are suitable proxies for the reconstruction of past climate variability. For the SSA, TRWs from N. pumilio forests of Punta Arenas showed that they have a high potential to reconstruct EE´s of drought-heat waves by using humidity datasets (February, r = 0.60), whereas δ18OTRC reveals significant relationships with soil water (December to February, r = 0.60) and precipitation (December to February, r = 0.56). The TRWs of N. pumilio from the Navarino Island have proven its high potential to reconstruct EE´s of strong wind speeds (October-November, r = 0.47). One of the best results of climate-proxy in this Ph.D. dissertation was that the δ18OTRC-N. betuloides forests of the Navarino Island. offering the highest guarantees for reconstructing past climate in the SSA, performing the highest correlations (1960 - 2019) with soil water (October to February, r = -0. 76), wind speed (November to February, r = 0.69), precipitation (November to January, r = -0.66), maximum temperature (October to December, r = 0.66), regional climate ASL (October to January, r = -0.80) and extratropical climate AAO (October to January, r = 0.77). Despite the reliable results, undoubtedly, further efforts are required to: 1. Deepen knowledge about the recent growth decline as recorded by an abrupt decrease in N. pumilio TRWs to investigate the occurrence, severity, and spatiality of EE in the past and reconstruct a long-term regional EE. 2. Further efforts are needed to understand the ecophysiology of the southernmost forests as an approach to study the resilience of Nothofagus tree forest against the impact of climate change in SSA. 3. Further extend existing δ18OTRC records from N. betuloides forests originating from the southern located Navarino Island to extent knowledge of the local, regional, and hemispheric climate variability for the last 400 - 500 years.