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The last 7500 cal yr B.P. of westerly rainfall in Central Chile inferred from a high-resolution pollen record from Laguna Aculeo (34°S)
Abstract
We report multiproxy analyses of a sediment core obtained from Laguna Aculeo that spans the past 7500 years. Laguna Aculeo (33°50′S, 70°55′W) is one of the few natural inland lakes located in the Mediterranean zone of Central Chile, near the northern margin of the influence of the southern westerlies. The record shows elevated pollen counts of halophytes and seasonally drying of the lake basin prior to 5700 cal yr B.P., indicating severe aridity and warmer-than-present conditions. This was followed by the establishment of a fresh-water lake, along with an increase in arboreal and herbaceous plant diversity between 5700 and 3200 cal yr B.P. An intensification of this trend started at 3200 cal yr B.P., along with the abrupt decrease of halophytes until 100 cal yr B.P. Within this humid period, pollen accumulation rates show large-amplitude fluctuations, coeval with numerous turbidite layers, suggesting a highly variable and torrential rainfall pattern. This intense and variable precipitation regime is probably associated with the El Niño–Southern Oscillation (ENSO) phenomenon. We suggest that the modern Mediterranean climate of Central Chile was established at ∼3200 cal yr B.P. Paleovegetation and paleolimnological changes starting at 100 cal yr B.P. correlate with documented human activity surrounding the lake.
... However, the current absence of recurrent natural wildfires in central Chile is a recent phenomenon at a geological time-scale (Heusser, 1990;Villa-Martínez et al., 2003). Specifically, periods of frequent fires have been recorded in Laguna Tagua-Tagua (34°30′S) at the end of the Pleistocene (between 53,800 and 28,500 year BP), before the arrival of humans to the region, which dates back to 11,380 year BP (Heusser, 1990 and references therein). ...
... Specifically, periods of frequent fires have been recorded in Laguna Tagua-Tagua (34°30′S) at the end of the Pleistocene (between 53,800 and 28,500 year BP), before the arrival of humans to the region, which dates back to 11,380 year BP (Heusser, 1990 and references therein). Similarly, fires detected in Laguna Aculeo (33°S50′S) between 5500 and 2500 year BP are not necessarily attributable to human activity, considering that the oldest archaeological site in the Laguna Aculeo watershed dates from 2000 year BP (Villa-Martínez et al., 2003;Sanhueza et al., 2007). In both cases, the pollen record concomitant with fire occurrence indicates annual rainfall seasonality and warm conditions (Heusser, 1990;Villa-Martínez et al., 2003). ...
... Similarly, fires detected in Laguna Aculeo (33°S50′S) between 5500 and 2500 year BP are not necessarily attributable to human activity, considering that the oldest archaeological site in the Laguna Aculeo watershed dates from 2000 year BP (Villa-Martínez et al., 2003;Sanhueza et al., 2007). In both cases, the pollen record concomitant with fire occurrence indicates annual rainfall seasonality and warm conditions (Heusser, 1990;Villa-Martínez et al., 2003). ...
... This scenario is coincident with the severe aridity and warmer-than-present conditions inferred between 7500 and 5700 cal. yrs BP from the Aculeo lake pollen record (Villa-Martínez et al., 2003), and in others lakes in Central Chile, i.e. Tagua-Tagua (Valero-Garcés et al. 2005) and Laguna del Maule (Frugone-Álvarez et al., 2020). ...
... On the western side of the Andes belt (Chile), colder and wetter conditions have also been inferred between 5700 and 3200 yrs BP, i.e. Aculeo lake (Jenny et al. 2002;Villa-Martínez et al., 2003); these authors interpreted a progressive increase in precipitation in relation to a weakened South Pacific highpressure cell with intensified Westerlies in the subtropical region of Chile (Jenny et al. 2002). Accordingly, intensified westerlies would have been the main source of humidity at the El Peñón valley during the 5700-3700 cal. ...
... This contrasts with Jenny et al. (2002) who suggest higher influence of westerlies for the last 3200 yrs BP. Alternatively, in the El Peñon valley temperature would have played a more important role in the balance of humidity as suggested by Markgraf (1983), compared with sites in the western Andes slopes (Jenny et al. 2002;Villa-Martínez et al., 2003. The change in vegetation between 800 cal. ...
Wetlands in mountains are highly dynamic and provide ecosystem services to human wellbeing. Understanding temporal and spatial wetland dynamics is crucial for successful management. This paper presents the reconstruction of a mire evolution at a high-altitude Andean valley in central-western Argentina, in subtropical South America (30°-36° S), during the Mid- and Late Holocene. The research is based on sedimentological and pollen analysis from a sedimentary section of 3.2 m thick exposed at the El Peñón valley. The record begins with an outwash environment after ca. 5700 cal. yrs BP associated with Pteridophytes dominance, followed by the development of a mire environment after ca. 3700 cal. yrs BP associated with Cyperaceae dominance. The environmental and vegetation changes are hypothesised to have occurred in response to a shift from cold to warmer conditions. Colder environments may have occurred again between 800 until <600 cal. yrs BP, probably associated with the Little Ice Age. Tephra inputs are evidenced in the record from 1200 years BP onwards. However, the results do not show any conclusive evidence about the impact of volcanism in the dynamics of the wetland. High Amaranthaceae proportions would evidence human activities in the high-altitude valleys of the southern Andes, probably for the last 250 cal. yrs BP. This work permitted us to infer the evolution of the El Peñón wetland under multiple concurrent forcing factors from the Mid- Holocene onwards at different temporal scales, i.e. climate during the last 5700 yrs, and volcanism and anthropogenic impacts during the last millennium.
... It is located 50 km southwest of Santiago (33 • 50 S-70 • 54 W) at an altitude of~350 m.a.s.l. [2]. The lake is located between the inner foothills of La Costa mountain range in the Paine commune of the Metropolitan Administrative Region. ...
... According to paleoclimatological studies [2], the lagoon had dried between 9500 and 7500 cal yr. B.P. Rates of pollen accumulation allowed scientists to infer that the lagoon was a "dry environment" associated with more arid and warmer weather conditions. ...
... From a paleoclimatological perspective, it is also important to consider that the five years in which the lagoon was reduced from its historical levels to complete dryness-as shown in Figure 1-is a short period compared to the resolution of the paleoclimatological processes described by [2]. The authors suggested that the dry conditions persisted during the early-and mid-Holocene; therefore, the paleoclimatological fluctuation of the seasonal lagoon's water levels occurred over more protracted periods of time than the hundred years it took humans to transform the basin, or the ten years of climate drought that supposedly triggered the lagoon dry conditions. ...
Located southwest of the city of Santiago (Chile), the Aculeo Lagoon used to be an important body of water, providing environmental, social, and economic services to both locals (mostly drinking water and small-scale agricultural irrigation) and tourists who visited the area for fishing, sailing, and other recreational activities. The lagoon dried completely in May of 2018. The phenomenon has been attributed to the current climatic drought. We implemented and calibrated a surface-groundwater model to evaluate the hydrogeologic causes of the lagoon’s disappearance, and to develop feasible solutions. The lagoon’s recovery requires a series of urgent actions, including environmental education and significant investment in infrastructure to import water. Ultimately, there are two goals: bringing back historic water levels and ensuring the sustainability of water resources at the catchment scale.
... There is general consensus that the onset of the modern climate in Central Chile started about 3200 cal yrs BP (Frugone-Alvarez et al., 2017; Jenny et al., 2002b;2003;Villa-Martínez et al., 2003;Villagrán and Varela, 1990). Under this paleoclimatic scenario, regional pre-Columbian societies experienced significant changes in subsistence strategies, social organization, technologies and occupation patterns. ...
... The first event (3500-2400 cal yrs BP) is characterized by low population levels. Despite discrepancies in the paleoclimate conditions throughout this region, existing reconstructions concur that during this population phase cold but highly variable humid conditions prevailed (de Jong et al., 2013;Jenny et al., 2002b;Maldonado and Villagrán, 2002;Maldonado and Villagrán, 2006;Martel-Cea et al., 2016;Villa-Martínez et al., 2003). Since 2350 cal yrs BP human activities increased steadily, reaching a stationary phase between 1600 and 1250 cal yrs BP (Figure 4a). ...
... II . III between 3200-2500 cal yrs BP (Figure 4c, Heusser, 1990;Villa-Martínez et al., 2003). The same pattern is verified at the coast at 32°S, represented by an increment in charcoal at 3200 cal yrs BP that is coeval with the establishment of locally permanent human settlements (Maldonado and Villagrán, 2002). ...
The deep-time dynamics of coupled socio-ecological systems at different spatial scales is viewed as a key framework to understand trends and mechanisms that have led to the Anthropocene. By integrating archeological and paleoenvironmental records, we test the hypothesis that Chilean societies progressively escalated their capacity to shape national biophysical systems as socio-cultural complexity and pressures on natural resources increased over the last three millennia. We demonstrate that Pre-Columbian societies intentionally transformed Chile’s northern and central regions by continuously adjusting socio-cultural practices and/or incorporating technologies that guaranteed resource access and social wealth. The fact that past human activities led to cumulative impacts on diverse biophysical processes, not only contradicts the notion of pristine pre-Industrial Revolution landscapes, but suggests that the Anthropocene derives from long-term processes that have operated uninterruptedly since Pre-Columbian times. Moreover, our synthesis suggests that most of present-day symptoms that describe the Anthropocene are rooted in pre-Columbian processes that scaled up in intensity over the last 3000 years, accelerating after the Spanish colonization and, more intensely, in recent decades. The most striking trend is the observed coevolution between the intensity of metallurgy and heavy-metal anthropogenic emissions. This entails that the Anthropocene cannot be viewed as a universal imprint of human actions that has arisen as an exclusive consequence of modern industrial societies. In the Chilean case, this phenomenon is intrinsically tied to historically and geographically diverse configurations in society-environment feedback relationships. Taken collectively with other case studies, the patterns revealed here could contribute to the discussion about how the Anthropocene is defined globally, in terms of chronology, stratigraphic markers and attributes. Furthermore, this deep-time narrative can potentially become a science-based instrument to shape better-informed discourses about the socio-environmental history in Chile. More importantly, however, this research provides crucial “baselines” to delineate safe operating spaces for future socio-ecological systems.
... Esto generalmente se ha entendido como un evolución frente a cambios en la distribución y disponibilidad de los recursos (Binford 1980;Betinger 1991), lo que puede ser en ciertas situaciones una buena hipótesis, especialmente frente a cambios ambientales severos, cosa que al menos en nuestro caso no sería aplicable para el momento en que esto ocurre (Jenny et al. 2002a;Jenny et al. 2002b;Villa-Martínez et al. 2003). Más bien pareciera que esto se asocia a cuáles estrategias sociales son más adecuadas para explotar recursos que son esencialmente diferentes. ...
... Los estudios realizados en la laguna de Aculeo (Villa- Martínez et al. 2003;Jenny et al. 2002; proponen que a partir de los 3750 años a.C. (5700 años cal a.P.) ocurriría una fase de mayor humedad que la actual y el consecuente aumento de la cobertura vegetacional con respecto al presente. Por su parte, a partir de 1250 años a.C. (3200 años cal a.P.) se establecería el clima actual, caracterizado por eventos de El Niño y estacionalidad marcada por la presencia clara de cuatro estaciones con altas fluctuaciones en las lluvias de invierno, existiendo años secos y otros más lluviosos. ...
... que se caracterizaría por la dominancia de pastos (Chenopodiaceae), es decir con menor cobertura del bosque esclerófilo, y la presencia inusual de tormentas provenientes del oeste (Villa Martínez et al. 2003 La altitud que alcanza la Cordillera de los Andes en nuestra área de estudio es uno de los factores clave en la modelación del clima, ya que ella determina la alta incidencia de precipitaciones nivosas que se registran sobre los 1.800 m de altitud. De esta manera, el clima mediterráneo que caracteriza en términos generales a Chile central, adquiere gran complejidad debido a la incidencia de cuencas intermontañas y de los tres alineamientos cordilleranos que caracterizan el macizo Andino (Romero 1985). ...
... The cause of these anomalous conditions could be related to summer convective storm rains originating east of the Andes (Tiner et al., 2018). Other records, such as Laguna Aculeo, show an increase of humidity at 3000 cal a BP with an increase of storm events associated with El Niño since 1800 cal a BP (Jenny et al., 2002;Villa-Martínez et al., 2003). Different mechanisms have been proposed for the transition from humid to dry conditions at the Pleistocene-Holocene boundary, such as changes in the latitudinal position of the SWWB, variation in ENSO intensity and the influence of storm rains. ...
... Subsequently, the LDV record suggests periods of intercalation of wet and dry phases, with the driest period at around 6300 cal a BP (Phase 6). Extremely arid conditions have been reported for the coast and the semi-arid Andes during this period, even the so-called major dry pulse of the Holocene between 7800 and 5700 cal a BP (Villa-Martínez & Villagrán, 1997;Tiner et al., 2018;Maldonado and Villagrán, 2006;Méndez et al., 2015;Kim et al., 2002), while in the lowlands of central Chile more arid conditions than at present, not as intense as those during the early Holocene, are recorded (Jenny et al., 2002;Valero-Garcés et al., 2005;Villa-Martínez et al., 2003). ...
Subtropical zones are crucial for understanding climate dynamics, as they strongly control the subtropical anticyclone system and serve as a bridge between the tropical and temperate regions of the planet. Therefore, understanding the long‐term dynamics of these areas is vital on a hemispheric scale. A continuous late Pleistocene climate record based on sedimentological proxies was reconstructed using a lacustrine core from the Chilean Subtropical Andes (~33°S). Since the late Pleistocene, high lake levels subjected to cold and wet conditions prevailed between ~15.4 and 14k cal a bp , followed by glacier retreat between 14 and 13.7k cal a bp . The Pleistocene–Holocene transition is marked by increasing sedimentological parameter values and organic matter content, recording a significant shift in the environmental conditions. Decreased lake levels and high‐energy events predominated until ~8.5k cal a bp , followed by warm and arid conditions with high‐energy/runoff events from 8.5 to 5.2k cal a bp , with the driest period occurring ~6.4k cal a bp . Turbiditic flows appear between 5.2 and 2.6k cal a bp , and cold conditions between 2.6 and 2.3k cal a bp . From 1720 to 960 cal a bp , cold and wet conditions predominated. Warm and wet conditions prevailed to the present, with a brief return to cold and dry conditions at 720 cal a bp . Important widely represented events such as the Last Glacial termination, early to mid‐Holocene Transition and Little Ice Age are present in the core record.
... However, in the long-term, paleoclimatic studies carried out along the north-central Chile margin indicate that dry conditions dominated during the early to mid-Holocene, while wet conditions developed since the mid-Holocene (e.g., Lamy et al., 1999;Kaiser et al., 2008), which became wetter in the late Holocene (e.g, Villa--Martinez and Villagrán, 1997;Jenny et al., 2002). These changes would be associated with the latitudinal migration of the northern margin of the SWW belt in response to SPSH changes (e.g., (Villa-Martínez et al., 2003); Lamy et al., 1999;Kaiser et al., 2008). This may be associated with the influence of ENSO along the eastern Pacific that intensified the frequency of El Niño events in the eastern Pacific from early to late Holocene (e.g., Sandweiss et al., 2007Sandweiss et al., , 2020. ...
... This likely reflects the onset of modern SWW and ENSO patterns that increased the frequency of El Niño events. A similar shift toward wetter conditions during the Late Holocene is also evident in other records of the semi-arid Andes (e.g., Martel-Cea et al., 2016), the central depression (e.g., Jenny et al., 2002;Villa-Martínez et al., 2003) and the coastal areas (e.g., Villagrán and Varela, 1990;Villa-Martinez and Villagrán, 1997;Maldonado and Villagrán, 2002;Frugone-Álvarez et al., 2017). Wetter conditions during the Late Holocene are associated with the strengthening and northward incursion of the SWW (e.g., Jenny et al., 2002). ...
... The relative high persistence and dominance of humid taxa throughout the pollen record of the Laguna El Calvario are consistent with the establishment of a wet Late Holocene inferred by several paleorecords in central Chile (30-35°S). Increased winter precipitation has been recorded from 4000 cal yrs BP on in the subtropical Andes (Veit, 1996;Grosjean et al., 1997;Espizua, 2005;Martel-Cea et al., 2016;Tiner et al., 2018;Frugone-Álvarez et al., 2020;Mayta and Maldonado, 2022), the lowlands (Jenny et al., 2002b;Jenny et al., 2003;Villa-Martıńez et al., 2003 andFrugone-Álvarez et al., 2017) and the coastal areas Villagrań, 2002 andVillagrań, 2006). Intense glacial activity in El Encierro valley (29°S; Figure 1A) located northwards of Laguna El Calvario was recorded before 2600 cal yrs BP (Grosjean et al., 1998;Zech et al., 2006). ...
... However, the Laguna Chepical record (33°S) reflects a decrease of moisture by this time but an extended ice cover season ( Figure 5G) (Martel-Cea et al., 2016). In the lowlands, the Laguna Aculeo (33°S; Figure 1A) record pinpoints wet conditions between 2500-700 cal yrs BP (Villa-Martıńez et al., 2003) while Palo Colorado (32°S; Figure 1A), a coastal record, displays a retraction of wet indicators around 700 cal yrs BP (Maldonado and Villagrań, 2006). ...
Mountain ecosystems located in the Andes cordillera of central Chile (29–35°S) have been strongly affected by the ongoing Mega Drought since 2010, impacting the snow cover, the surficial water resources (and thereby water storage), as well as the mountain biota and ecosystem services. Paleoenvironmental records in this part of the semiarid Andes are key to estimating the effects of past climate changes on local communities helping to forecast the ecological and biological responses under the aridification trend projected during the 21st century. Here we present a 2400-year multiproxy paleoenvironmental reconstruction based on pollen, diatoms, chironomids, sedimentological and geochemical data (XRF and ICP-MS data) of Laguna El Calvario (29°S; 3994 m a.s.l), a small and shallow Andean lake. Four main hydrological phases were established based on changes in the lithogenic and geochemical results associated with allochthonous runoff input and the subsequent response of the biological proxies. Between 2400 and 1400 cal yrs BP, wetter than present conditions occurred based on the intense weathering of the lake basin and the dominance of upper Andean vegetation. A decrease in moisture along with sub-centennial discrete wet pulses and lake-level changes occurred until ~800 cal yrs BP followed long-term stable climate conditions between 1850 and 1950 AD as suggested by a drop in vegetation productivity and low lake levels. From 1950 AD to the present, a decline in moisture with a severe trend to drier conditions occurring in the last decades occurred as reflected by an upward vegetation belt displacement around Laguna El Calvario along with a turnover of diatom assemblages and high productivity in the water column.
... A diferencia del área trasandina de Los Morrillos-Ansilta, en que es frecuente encontrar piedras tacitas en las entradas e interior de aleros rocosos o grutas (Gambier 1985), en Chile central, con escasas excepciones como el sitio Alero La Montera en el curso superior del valle de Aconcagua, se encuentran en sitios abiertos y, en general, es recurrente su ubicación en lugares próximos a cursos de agua. La mayoría de estos y las quebradas están secos en la actualidad, producto de las condiciones con intervalos de sequía que afectan esta región, condiciones que durante periodos anteriores pudieron ser distintas con aportes de mayor humedad, ya que los especialistas coinciden en que hacia el 3000 a. P. se habría establecido el clima mediterráneo en la región (Villagrán y Varela 1990;Villa-Martínez y Villagrán 1997;Maldonado 1999;Maldonado y Villagrán 2002;Villa-Martínez et al. 2003). Stehberg y Dillehay (1988) plantean, con relación a los numerosos sitios con piedras tacitas en el sector Chacabuco-Colina, que estos se encuentran en un alto porcentaje distribuidos en la zona de ecotono entre los 500 y 900 m s. n. m. que, como zona transicional, integra el acceso a una amplia base de recursos bióticos. ...
... It has a continuum of human occupation between ca. 10000 years bp (Martínez 2003) and present day. Starting on ca. ...
... A diferencia del área trasandina de Los Morrillos-Ansilta, en que es frecuente encontrar piedras tacitas en las entradas e interior de aleros rocosos o grutas (Gambier 1985), en Chile central, con escasas excepciones como el sitio Alero La Montera en el curso superior del valle de Aconcagua, se encuentran en sitios abiertos y, en general, es recurrente su ubicación en lugares próximos a cursos de agua. La mayoría de estos y las quebradas están secos en la actualidad, producto de las condiciones con intervalos de sequía que afectan esta región, condiciones que durante periodos anteriores pudieron ser distintas con aportes de mayor humedad, ya que los especialistas coinciden en que hacia el 3000 a. P. se habría establecido el clima mediterráneo en la región (Villagrán y Varela 1990;Villa-Martínez y Villagrán 1997;Maldonado 1999;Maldonado y Villagrán 2002;Villa-Martínez et al. 2003). Stehberg y Dillehay (1988) plantean, con relación a los numerosos sitios con piedras tacitas en el sector ...
... It has a continuum of human occupation between ca. 10000 years bp (Martínez 2003) and present day. Starting on ca. ...
... Several pollen records show that moisture and temperatures increased from 4000 cal yr. BP in central Chile (Heusser, 1990;Villa-Martínez and Villagrán, 1997;Villagrán, 2001;Maldonado and Villagrán, 2002;Villa-Martínez et al., 2003, 2004. However, most palynological studies do not have the appropriate resolution for understanding climatic variations on short (i.e., decadal to century) timescales during the Late Holocene. ...
... yrs BP in the Lake Laja basin could be related to the frequency of ENSO events, which are, in the study area, associated with average rainfall anomalies in late spring (Montecinos and Aceituno, 2003). Other investigations in central Chile have related the moisture changes with ENSO (Jenny et al., 2002;Villa-Martínez et al., 2003;Maldonado and Villagrán, 2006). ...
The objective of this research was to represent the spatial distribution of non-soluble sediment particles in the atmospheric basin of Lima and Callao. For this, a spatial interpolator that reproduces the surface distribution close to field values is used. Material collected during winter and summer in 33 sampling points was used (ASTM D-1739-98 norm). Gravimetric registers of non-soluble material were processed with ArcGIS software to obtain the surface distribution by using spatial interpolation methods known as Inverse Distance Weighting (IDW), and also the methods called Kriging and Spline. With the spline method, ranges of negative values for mass weight were obtained. With the Kriging method, the mass values were superior to those obtained in the field. In the case of the IDW method, the values were similar to those obtained in field work. Based on the results, the IDW method represents the best surface distribution method for non-soluble sediment particles in the atmospheric basin.
... Humid conditions returned between 31°S and 51°S at the end of the Holocene (5-0 ka) 11,48,53,54,56,57 , likely due to a northward expansion of the SWW 56 shifts. However, a minor effect of temperature on δD wax values cannot be completely ruled out. ...
Reconstructing rainfall variability and moisture sources is a critical aspect to understand past and future hydroclimate dynamics. Here, we use changes in the deuterium content of land-plant leaf waxes from two marine sediment cores located off Chile to reconstruct changes in rainfall amount and variation in moisture sources over the last ~50 ka. The records indicate increased moisture in central Chile during precession maxima, but an obliquity modulation is evident in southern Chile. While the southern westerly winds are the dominant factor of precipitation in southern Chile by bringing moisture and perturbations from the extratropics, the subtropics represent an additional moisture source during precession maxima due to a stronger subtropical jet increasing moisture transport from the tropics to the mid-latitudes. These findings imply that a combination of orbital modulation of moisture sources and rainfall amount explains the last glacial moisture maximum and early Holocene moisture minimum in south-central Chile.
... de extrema aridez registradas durante el Holoceno Medio las responsables en la deficiente conservación de los palinomorfos en los registros sedimentarios(Villa-Martínez et al. 2003). Esta suerte de sesgo o limitación del método palinológico, nos impulsa a tratar con otras técnicas a fin de reconstruir la vegetación terrestre, siendo el uso de técnicas de ADN sedimentario una alternativa para abordar el desafío de reconstruir la historia paleoambiental de los ecosistemas terrestres de Chile Central durante el Holoceno. ...
Este trabajo presenta nuevo registro sedimentológico y palinológico que reconstruye la historia ambiental durante la transición del Holoceno medio a tardío en el centro sur de Chile (34°-38°S). El sitio de estudio corresponde a un pequeño humedal llamado Laguna Verde (36º47’S, 73º09’W; 22 m s.n.m.; ~4 ha), el cual se emplaza en una micro-cuenca (136 ha) rodeada de vegetación nativa (i.e. bosque esclerófilo). Testigos de sedimentos obtenidos desde el humedal, permitieron reconstruir la evolución de este durante el Holoceno, dando cuenta que la formación del sitio ocurre alrededor de los 6.800 años cal AP, como resultado de un proceso de represamiento por parte de dunas. Posteriormente, se registra un aumento importante en la concentración de materiales líticos movilizados por el viento y la precipitación, dando como resultado la formación de un cuerpo de agua permanente en torno a los 4000 años cal AP. El registro palinológico muestra un predo-minio de taxa arbóreos y acuáticos durante este periodo, indicando el desarrollo ecosistemas de bosque en la cuenca en respuesta al incremento en las precipitaciones durante este periodo. Finalmente, se observa un cambio abrupto en el registro sedimentológico y palinológico hacia el año 1850AD, relacionado con una transformación en el paisaje vegetal y el régimen sedimentario debido a la actividad antropogénica. En resumen, este estudio proporciona información nueva y relevante para comprender la historia paleoambiental de los ecosistemas costeros del centro sur de Chile.
... Different paleoclimate records of the Subtropical Andes (Fig. 1a), particularly those of the western slope of the range, indicate the occurrence of humid conditions in the Late Holocene, associated with a high temporal and spatial variability since 2000 cal yrs BP (Jenny et al. 2002;Villa-Martínez et al. 2003;Maldonado and Villagrán 2006;Martel-Cea et al. 2016;Frugone-Álvarez et al. 2020). This increase in annual and inter-annual climate variability would have been associated with an increase in the frequency of El Niño events recorded at this time (Moy et al. 2002;Rein et al. 2005). ...
The most recent IPCC report indicated that the Subtropical Andes (32°–35° S) are one of the world areas undergoing a strong tendency towards more arid conditions due to current climate change. The winter precipitation that falls on the Andes, related to the Southern Westerlies System (SWS), is the main source of water for central Chile and west central Argentina, making it a fundamental socioeconomic resource. The few long-term records of the eastern slope of the Subtropical Andes do not permit establishing the long-term natural climate variability or determining if this trend does or does not respond to natural forcings. This study therefore presents a centennial and sub-centennial scale reconstruction of the paleoenvironmental dynamics of the eastern slope of the Subtropical Andes during the last 3000 cal yrs BP, based on the pollen record of the Laguna Corazón (LCO; 35.13° S; 2200 m a.s.l.), in order to establish the different regional paleoenvironmental scenarios. The sedimentary record (182 cm) is mostly composed of laminated dark brown clay, and includes a 21–24 cm layer preliminarily associated with the 1932 AD eruption of the Quizapú volcano. The LCO record shows the development of a grass steppe associated with high-Andean shrubs between 3000 and 2440 cal yrs BP, suggesting slightly more humid conditions than present. From 2440 to 1110 cal yrs BP, there was continuous presence of the grass steppe along with high-Andean and Patagonian low shrubs, indicating moderately more humid conditions than today. The development of a grass steppe with low high-Andean shrubs from 1110 to 320 cal yrs BP reflects conditions slightly more humid that at present, showing a progressive decrease in humidity between 900 and 320 cal yrs BP. Since then, environmental conditions were similar to present ones, associated with the climatic variability at sub-centennial timescale. In the last 320 cal yrs BP, the record shows the presence of introduced species as a consequence of the occupation of the valley to raise livestock, and more recently, tourist activities. These environmental/climatic patterns are similar to those recorded for the western slope of the Subtropical Andes for the Late Holocene, indicating a regional forcing related to the winter precipitation associated with the SWS.
... These conditions are due to the semi-permanent influence of the South Pacific Anticyclone (SPA) and winter storms that stem off the Southern Westerly Wind Belt (SWW), where in addition, the activity of the El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) are the main drivers of climate variability on interdecadal and decadal time scales (Montecinos and Aceituno, 2003). This modern climate variability has been established for around 4000-3000 cal yr BP and is characterized by wetter conditions compared to the Middle Holocene (Frugone-Álvarez et al., 2017(Frugone-Álvarez et al., , 2020Jenny et al., 2002Jenny et al., , 2003Maldonado and Villagrán, 2006;Martel-Cea et al., 2016;Villa-Martínez et al., 2003; Figure 1a). ...
Understanding socio-ecological systems over the long term can shed light on past adaptive strategies in environmentally sensitive regions. Central Chile is an emblematic case study for mediterranean ecosystems, where a progressive and sustained population increase began approximately 2000 years ago alongside significant landscape changes. In this work we analyzed regional paleo-demographic trends by compiling a new database of archaeological dates over the last 3000 years, and integrating population dynamics theory with an analysis of the spatio-temporal variation of regional cultural stages. Results show three moments of marked acceleration in population growth: just before agricultural adoption, during the Archaic Period (c. 700-300 BCE); during the second half of the ECP (500–900 CE); and during the Late Intermediate Period (1200–1400 CE). We also identified periods of deceleration in per capita growth rates, although population size continued to increase (300 BCE−500 CE, 900–1200 CE and after 1400 CE). These large shifts in the per capita growth rates coincide with major cultural changes associated with social and economic aspects. The pulses of major occupation show in general terms a more intensive use of the valleys as the population size increased, although the remaining ecosystems never ceased to be occupied with different economic and symbolic emphases.
... In contrast, at the western distribution, there are no natural records (i.e. not from anthropogenic or culture settlements collecting sites), even in locations where the species is abundant today [43][44][45]. All in all, from the above, we can conclude that there is more empirical support for a historical long-distance dispersal scenario than for a vicariant process for V. caven. ...
Vachellia caven has a disjunct distribution at the southern cone of South America, occupying two major ranges: west of Andes (Central Chile) and east of them (mainly the South American Gran Chaco). For decades, the species has been subject to various ecological and natural history studies across its distribution, but questions concerning its origin in the western range remain unresolved. Thus far, it is unclear whether Vachellia caven was always a natural component of the Chilean forests, and "how" and "when" the species arrived in the country. In this study, we revised the dispersal syndromes of the species and contrast the two main hypotheses of dispersion to the west of Andes that have been proposed in the 90's, namely animal versus human-mediated dispersal. For this, we reviewed all scientific literature on the species and explored the available information on morphology, genetics, fossil records and distribution patterns of closely related species. Here we illustrate how the collected evidence provides support for the human-mediated dispersal hypothesis, by including a conceptual synthesis that summarizes the outcomes of different dispersal scenarios. Lastly, and regarding the positive ecological effects this species has in the introduced area, we suggest reconsidering the (underappreciated) historical impacts of archae-ophytes and rethinking the role that indigenous human tribes may have had in the dispersion of different plants in South America.
... Central Chile is subject to a Mediterranean climate with dry summers and wet winters. The current climatic conditions have remained much the same for the last 3000 years with seasonal and inter-annual variations in rainfall influenced by El Niño Southern Oscillation fluctuations (Villagrán and Varela 1990;Jenny et al. 2002;Villa-Martínez et al. 2003). Inka control of Central Chile is generally held to have been via a system of indirect government (Silva 1978;Falabella 1994;Stehberg 1995;Uribe 2000;Sánchez Romero 2002;Hermosilla et al. 2005). ...
Estadio de Quillota (EDQ) is the largest known pre-Columbian cemetery site within the Aconcagua Valley of Central Chile. Despite its importance, existing chronological data for EDQ are limited and questions remain regarding the prehistory of the Valley, particularly around the adoption and intensification of maize agriculture, as well as the timing of Inka influence reaching the region. Seventeen new AMS radiocarbon dates presented here indicate two distinct phases of use at EDQ: An earlier phase (339–196 cal BC to cal AD 128–339), and a later phase (cal AD 1280–1387 to cal AD 1413–1458). Accompanying stable isotope (δ ¹³ C and δ ¹⁵ N) analyses of human bone collagen (n=22) demonstrate diachronic dietary changes corresponding to these phases, with a reliance on terrestrial C 3 resources during the earlier period, followed by a heavy dependence on C 4 -based (maize) resources during the later use. Bayesian modeling of the dates from Late Period contexts suggests Inka influence arrived in Central Chile by ca. cal AD 1400, decades before the date cited in traditional chronologies, AD 1471. Inka expansion likely occurred here with an initial phase of interaction and exchange preceding a later phase of integration. This finding supports growing evidence that the traditional chronology of the Inka Empire requires reconsideration.
... Around ca. 12,000 years BP the temperature began to increase gradually, remaining with a trend relatively constant from ca. 11,000 to 500 years BP (Abarzúa et al., 2014;de Porras, 2017;Llano et al., 2020;Markgraf et al., 2009;Marcott et al., 2013;Pedro et al., 2016;Petit et al., 1999;Thompson et al., 1998;Valero-Garcés et al., 2005;Villa-Martínez et al., 2003). Similarly, the archaeological evidence suggests the occurrence of important spatial and temporal variation at regional level in the exploitation of wild and domesticated resources and the use of different processing technologies -pottery and grinding tools-since the beginning of the occupation of the territory -ca. ...
Our goal is to study the spatio-temporal changes in human demographic density in Northwest Patagonia and central Chile throughout the Late Pleistocene-Holocene using geo-referenced absolute dates. Given the heterogeneous environmental and cultural characteristics of this region, differences in the demographic dynamics across geographic areas are expected. Using 1,284 absolute dates we explored different null and continuous piecewise linear (CPL) models of regional population change. We also estimated density curves along with a local geometric growth rate analysis. The best fit model was a flexible CPL model, showing an initial increase in population density between ca. 15,500–12,500 years BP, a second rise after 6,500 years BP and a third increase after 2,500 years BP, although disparate spatio-temporal changes in the relative density were found. These results were robust when the effect of potential biases was considered –e.g., dates with large errors, marine-reservoir and old-wood effects– and the frequency distribution of absolute dates and sites were estimated. We observed significant spatio-temporal changes in human population density, which might be related to the complex environmental and cultural changes: the megafaunal extinction, the incorporation of marine resources and the acquisition of techniques for cultivating and processing food. The results of this study remark that, compared to other types of data, the use of absolute dates allows paleo-demographic reconstructions at regional geographical scales with higher spatial and temporal resolution.
... Similar to the glacial advances/retreats, changes in vegetation have been associated with greater or lesser influence of the SWs (e.g., de Porras et al., 2012;Glasser et al., 2012;Kaplan et al., 2016;Davies et al., 2020;Villa-Martinez and Moreno, 2021). However, the changes recorded are very dissimilar throughout the latitudinal range of Southern Westerlies' influence, from subtropical to Antarctic zones (e.g., Villa-Martínez et al., 2003;Maldonado and Villagrán, 2006;Moreno et al., 2018;Nanavati et al., 2019;Davies et al., 2020;Kaplan et al., 2020). Particularly in Patagonia, the differences between records have been associated with latitudinal expansions or retractions of the SWs, greater or lesser strength of the SWs, and/or latitudinal displacement of this climatic belt (e.g., Villa-Martínez et al., 2012;de Porras et al., 2014;Quade and Kaplan, 2017;Moreno et al., 2019). ...
Deglaciation modeling of the Patagonian Ice Field since the Last Glacial Maximum has been a topic of intensive research in Central West Patagonia (44°–49°S). However, the chronology of deglaciation onset, acceleration, and the subsequent thinning and recession of the different ice lobes as well as the timing and extension of large proglacial systems are still a matter of discussion. The maximum eastward extension the Lago Cochrane/Pueyrredón ice lobe was around ∼20,000–27,000 cal yrs BP; its associated proglacial lake drained toward the Pacific between 12,600 and 8,000 cal yrs BP. This study presents the first two pollen and charcoal records from the Lago Cochrane/Pueyrredón valley, spanning the last 11,650 cal yrs BP. The Laguna Maldonado record spans between 11,650 and 8,500 cal yrs BP, while the Laguna Anónima record the last 8,500 cal yrs BP, thereby overlapping chronologically. The lithological record of Laguna Maldonado shows that organic sedimentation began at the onset of the Holocene (11,650 cal yrs BP), once the site was free of glacio-lacustrine influence. Between 11,650 and 10,500 cal yrs BP, an open Nothofagus forest developed associated with high fire occurrence/frequency, followed by a transitional phase to a closer forest associated with a shift from low to high fire activity up to 9,400 cal yrs BP. Between 9,400 and 8,500 cal yrs BP, the Laguna Maldonado record suggests the development of an open forest or probably scattered patches of forest of variable size in a steppe matrix, probably related to geomorphological and paraglacial dynamics as well as climatic forcings, while the Laguna Anónima record indicates the development of a closed Nothofagus forest and high to low fire occurrence/frequency from 8,200 to 3,800 cal yrs BP. Since 3,800 cal yrs BP, a highly dynamic open forest or forest patches scattered in a grass/shrub–grass steppe matrix occurred around Laguna Anónima associated with high fire occurrence/frequency synchronous with an important increase in the presence of hunter-gatherers during the last 3,000 years. The results from the Lago Cochrane/Pueyrredón valley are integrated and discussed at the regional scale alongside other records from Central West Patagonia.
... yr BP and an important increase in torrential rains associated with El Niño starting 1,800 cal. yr BP (Jenny et al., 2002;Villa-Martínez et al., 2003). Considering the beginning of the decrease of indicators of the low vegetation belt (sub-Andean) in LCO and LQP, there is some correspondence in the chronology of this humid phase, although at different times and intensity or maximum values from those found in the Laguna Chepical and Laguna Aculeo. ...
The effects of climate change may be more evident in mountainous areas. In these areas, an increase in temperature and a decrease in precipitation can reduce the amount of snow, which represents a source of water for human consumption and vegetation. To analyze the effects of climate change on vegetation, it is possible to examine the climate–vegetation relationship in the past and observe the influence of variation in temperature and precipitation on the dynamics of plant communities. The aim of the present work was to describe the climate–vegetation dynamics of the last 4,500 years in the high subtropical Andes of Chile (30°S). The paleoclimatic reconstruction was carried out through the analysis of fossil pollen and macroscopic carbon obtained from sediment cores from two high Andean lakes. The dynamics of the vegetation was analyzed taking into account the alpha and beta diversity. The pollen and carbon records showed three contrasting periods during the last 4,500 years. From the beginning of the sequences until ∼1900 cal. yr BP, relatively dry climatic conditions are suggested, with a slight trend toward more humid conditions after 2,700 cal. yr BP. Pollen records from ∼1900 to ∼600 cal. yr BP suggest wetter conditions than today. Finally, relatively arid conditions have reappeared in the last ∼600 years. The diversity analysis showed that the climate mainly influences the composition of taxa in the communities (beta diversity) and not the richness (alpha diversity). In periods of dry/wet transition and vice versa, beta diversity changes. On the other hand, richness remains relatively constant throughout the record.
... [45], Aculeo lies at the northern boundary of the Southern Westerly Wind Belt (SWWB) and, therefore, it is dominated by a steep precipitation gradient [9]. Previous palaeoclimatological investigations indicate an arid early-to-mid Holocene period (about 9500-5700 cal yr B.P.) with an increase in annual rainfall after 5700 cal yr B.P., increasing even more (to modern conditions) to around 3200 cal yr B.P. [9][10][11][12]. Scientific evidence shows that this body of water has not naturally disappeared for thousands of years [9,10] (a fact confirmed by one of the authors from the former study, as they always found lake-related diatoms in the sediment core extracted from the bottom of the lagoon), making it hard to believe that a decade of below-normal precipitation (including a few wet years, as detailed further down) under modern humid conditions would be the main variable leading to the complete disappearance of the lagoon, as concluded by Barría et al. [17]. ...
Several studies have focused on why the Aculeo Lagoon in central Chile disappeared, with a recent one concluding that a lack of precipitation was the main cause, bringing tremendous political consequences as it supported the argument that the government is not responsible for this environmental, economic, and social disaster. In this study, we evaluated in detail the socio-economic history of the watershed, the past climate and its effects on the lagoon’s water levels (including precipitation recycling effects), anthropogenic modifications to the lagoon’s water balance, the evolution of water rights and demands, and inaccurate estimates of sustainable groundwater extraction volumes from regional aquifers. This analysis has revealed novel and undisputable evidence that this natural body of water disappeared primarily because of anthropogenic factors that, combined with the effects of less than a decade with below-normal precipitation, had a severe impact on this natural lagoon-–aquifer system.
... Las tormentas eléctricas son muy raras y han sido responsables sólo del 0,2% de los casi 70.000 incendios ocurridos entre 2003 y 2017 entre la región de Valparaíso y del Bío-Bío (CONAF, 2017a). Los estudios paleoecológicos relacionan la aparición de incendios frecuentes con los primeros asentamientos humanos entre 9.000 y 14.000 años atrás (Aravena et al., 2003;Villa-Martínez et al., 2003). Se ha planteado que la elevación de los Andes durante el Pleistoceno redujo la frecuencia de tormentas eléctricas en la zona central de Chile y con ello los incendios naturales (Keeley et al., 2012). ...
Resumen El fuego no parece haber sido un factor evolutivo relevante en la formación de los caracteres de las plantas en el matorral mediteráneo de Chile central. Aunque mu-chas de sus especies leñosas pueden rebrotar, la germinación estimulada por fuego es menos frecuente que en otros ecosistemas mediterráneos. Las señales del fuego (humo y/o calor) inhiben la germinación en casi el 40% de las especies nativas evaluadas hasta ahora, muchas de ellas endémicas y de gran valor para la conservación. Por otro lado, los espacios abiertos del matorral están dominados por especies herbáceas exóticas, que son muy favorecidas por el fuego. Los incendios frecuentes causan gran mortalidad en el banco de semillas nativo y van generando nuevos espacios abiertos que, a su vez, son colonizados por exóticas. Los herbívoros podrían determinar el patrón de reclutamiento tras los incendios, dado que afectan de forma diferencial a especies nativas y exóticas. Por otro lado, el cultivo de plantaciones forestales extensivas ha cambiado la inflama-bilidad del paisaje de Chile central, suponiendo un mayor riesgo de incendios para los bosques nativos aledaños. Las evidencias sugieren que el matorral requiere medidas de restauración activas para poder recuperarse del fuego. Chile central requiere diversificar el uso del suelo y recuperar parte de sus bosques nativos para diseñar nuevos paisajes más resilientes a los incendios en el contexto de cambio climático que se está haciendo presente.
... Archaeological investigations, together with paleoclimatic, geomorphological, pollen, paleofauna and archaeobotanical studies, have made it possible to determine the coexistence of human groups with extinct species of fauna, especially herbivores, from the end of the Pleistocene (Núñez et al., 1994;Jackson et al., 2007) and with plant species from different local environments that show signs of human activity (Heusser, 1990;Gajardo, 1994;Valero-Garcés et al., 2005;Maldonado, 2007;Planella and McRostie, 2008;Maldonado, 2010). The presence of Chenopodiaceae in plant contexts deposited during warm, dry climatic episodes is also evident in sediment samples from pollen columns in strata from the early, middle and late Holocene, dating from 11,000-9000 years BP onwards (Heusser, 1983;Villagrán and Varela, 1990;Rojas, 1991;Villa-Martínez et al., 2003;Villagrán, 2002, 2006). Climate fluctuations allowed the development of Chenopodiaceae-Amaranthaceae; this finding suggests that they were available in the herbaceous flora for gathering by human groups in the region. ...
... It is located at 33°50 0 S and 70°54 0 W at an elevation of 350 m within the Chilean Mediterranean biodiversity hotspot (Alaniz et al. 2016). The lake has a Holocene origin from c. 11 000 ybp (Villa-Martínez et al. 2003); it was created by natural damming by sediments transported via the Pintué River and a series of ravines from the Altos de Cantillana range. Aculeo Lake is very important to the inhabitants of Paine, a small commune with a subsistence agricultural tradition that greatly depends on the availability of water for cropland irrigation (Valencia 2018). ...
The environmental destruction generated by human activities, driven mainly by changes in land use, has generated several extinctions around the world (Pimm et al. 2014). Collapse of whole ecosystems has been reported in 37 marine pelagic cases and 48 temperate forests but not in fresh water (Bland et al. 2018). One of the most iconic is the case of the Aral Sea in Middle Asia (Keith et al. 2013). This ecosystem, which was the fourth largest water body in the world, was transformed into a desert due to the overuse of its water for cropland irrigation and human consumption (Keith et al. 2013). Ecosystem collapse changes both the biotic and abiotic original characteristics of the system (Bland et al. 2017, 2018). Here we explore the political and environmental causes of the recent collapse of the largest natural freshwater body in the central metropolitan zone of Chile.
... Condiciones más cálidas y secas pudieron generar este incremento en la bioproductividad y el ingreso de detritos de mayor tamaño, debido a un descenso en el nivel del Lago, desarrollo de ambientes litorales más productivos y mayor erosión de la cuenca. Estas condiciones climáticas coinciden con otros registros lacustres de Chile central 19,11,20 , que sugieren condiciones cálidas y secas durante la ACM. Justamente esta condición se invierte durante la PEH, con condiciones generalmente más frías y húmedas. ...
Los ecosistemas litorales se encuentran en un delicado equilibrio entre la influencia marina y terrestre, albergan una alta biodiversidad y ejercen un importante control sobre los ciclos y flujos biogeoquímicos entre los continentes y los océanos. Las proyecciones de cambio climático para los próximos 100 años señalan a estos ambientes como altamente vulnerables. Las costas mediterráneas y templadas, como las de España y Chile, han sufrido una fuerte modificación durante el último siglo debido al aumento de la población y las alteraciones concomitantes generadas por la industrialización y cambios en el uso del suelo. El lago Vichuquén, en la costa centro-sur de Chile, proporciona un ejemplo de cómo estos ecosistemas han variado desde el Holoceno medio a raíz de las sinergias entre cambio climático e impacto humano, lo que establece un reto para su manejo y conservación. El estudio de sedimentos acumulados en el último milenio revela los cambios que experimentó la cuenca desde épocas prehispánicas (siglo XVI) hasta la actualidad y cómo la modificación reciente de la cobertura vegetal por plantaciones de pinos y eucaliptos ha impactado en la dinámica natural de la cuenca. Los cambios más recientes están asociados a la creciente presión antrópica resultado de la intensa urbanización del litoral, a lo que se suman variaciones climáticas como las de la Anomalía Climática Medieval (siglos X al XIII), la Pequeña Edad de Hielo (siglos XIV al XIX) y el reciente calentamiento global. El ejemplo de Vichuquén ilustra la necesidad de conocer la dinámica y evolución de los ecosistemas lacustre costeros con una perspectiva histórica milenial para comprender las características y magnitud de las respuestas de estos ambientes a crecientes impacto antrópico locales y cambios climático globales.
... Alluvial deposits from the arid (23°S) and semiarid (32°50′S) coast of Chile show that these kinds of events occurred sporadically since the Middle Holocene (Vargas et al., 2006;Ortega et al., 2012Ortega et al., , 2013, when a scenario of intense and persistent aridity prevailed in the central and northern coast of Chile (Villagrán and Varela, 1990;Villagrán, 2002, 2006;Villa-Martínez et al., 2003). An increased frequency in heavy rainfall events that generated major debris flows occurred beginning 5300-5700 yr BP and continuing over the last millennium. ...
Extreme precipitation events and multi-annual droughts, especially in arid to semi-arid subtropical regions, are among the most critical El Niño Southern Oscillation (ENSO) and global climate change impacts. Here, we assess the variability of torrential rainfall during the Late Holocene and its projection into the 21st century at the southern edge of the hyperarid Atacama Desert.
The analysis of historical data since the beginning of the 20th century reveals that most (76.5%) alluvial disasters in the southern Atacama Desert (26–30°S) have resulted from extreme rainfall events occurring between March and September under El Niño conditions, and more frequently during the warm phase of the Pacific Decadal Oscillation. Particular rainfall events under these ocean-climate conditions are associated with the convective phase of the Madden-Julian Oscillation (MJO) near the central-equatorial Pacific, resulting in warmer sea surface temperature (SST) there and in the triggering of persistent/intense Pacific South America (PSA) tropical-extratropical teleconnection patterns which result in blocking of the westerly flow at high latitudes and the subsequent deviation of storm tracks towards central-northern Chile.
On a longer timescale, marine sediments from Tongoy Bay (30°S) reveal an increasing trend of stronger runoff by torrential coastal rain since ca. 3500 cal yr BP and even stronger heavy rainfall since ca. 1700 cal yr BP. Highly variable coastal sea surface temperatures in the same time span deduced from the sedimentary record can be explained by intensified southerly winds in connection with stronger alongshore pressure gradients and reduced coastal low-cloud cover. Both storm intensification and increased intensity of upwelling-favorable winds point to a variable climate conditioned by strengthened interannual ENSO and interdecadal ENSO-like variability during the Late Holocene.
Climate projections from the Coupled Model Intercomparison Project Phase 5 (CMIP5) indicate a reduction in annual precipitation of 15–30% during the current century, together with an intensification of the storms, such as the alluvial disaster on March 25, 2015 in Atacama.
... BP with strengthened and poleward shifted SHW (Varma et al., 2012). This agrees with more pronounced ENSO frequencies in response to increased insolation (Clement et al., 2000) and reached the highest intensity during the past 3500 years (Moy et al., 2002;Villa-Martínez et al., 2003). ...
Multiproxy investigations of lacustrine sediments from Laguna Azul (52 °S) document multi-millennial Holocene influences of Southern Hemispheric Westerlies (SHW) on the hydroclimatic variability of south-eastern Patagonia. During the last 4000 years, this hydroclimatic variability is overprinted by centennial warm/dry periods. A cool/wet period from 11,600 to 10,100 cal. BP is succeeded by an early Holocene dry period (10,100–8300 cal. BP) with a shallow lake, strong anoxia, methanogenesis and high salinity. Between 8300 and 4000 cal. BP the influence of SHW weakened, resulting in a freshwater lake considered to be related to less arid conditions. Since 4000 cal. BP, regional temperature decreased accompanied by re-intensification of SHW reaching full strength since 3000 cal. BP. Centred around 2200, 1000 cal. BP and in the 20th century, Laguna Azul experienced century-long warm/dry spells. Between these dry periods, two pronounced moist periods are suggested to be contemporaneous to the ‘Dark Age Cold Period’ and the ‘Little Ice Age’. Different from millennial SHW variations, centennial fluctuations appear to be synchronous for South America and the Northern Hemisphere. Changes in solar activity, large volcanic eruptions and/or modulations of ocean circulation are potential triggers for this synchronicity.
... Pollen reconstructions from Laguna de Tagua Tagua 34.5 • S 71.16 • W (Heusser, 1990;Valero-Garcés et al., 2005) indicate the presence of extensive temperate woodlands at the LGM that match the simulated mesic woodland biome for this location in our simulations (Fig. 4a). Multiple lake sediment records of the region indicate dry and warm condi- tions in the MH and the onset of more humid, but strongly seasonal, conditions (winter rainfall) in the late Holocene (Heusser, 1990;Villa-Martínez et al., 2003;Valero-Garcés et al., 2005). While LPJ-GUESS simulates Mediterranean vegetation types (matorral and sclerophyllous woodland) for the MH and a shift to denser xeric woodlands in the late Holocene for this region, substantial variations in the precipi- tation regime as suggested by the lake records are not present in the TraCE-21ka data used. ...
Vegetation is crucial for modulating rates of denudation and landscape evolution, as it stabilizes and protects hillslopes and intercepts rainfall. Climate conditions and the atmospheric CO2 concentration, hereafter [CO2], influence the establishment and performance of plants; thus, these factors have a direct influence on vegetation cover. In addition, vegetation dynamics (competition for space, light, nutrients, and water) and stochastic events (mortality and fires) determine the state of vegetation, response times to environmental perturbations and successional development. In spite of this, state-of-the-art reconstructions of past transient vegetation changes have not been accounted for in landscape evolution models. Here, a widely used dynamic vegetation model (LPJ-GUESS) was used to simulate vegetation composition/cover and surface runoff in Chile for the Last Glacial Maximum (LGM), the mid-Holocene (MH) and the present day (PD). In addition, transient vegetation simulations were carried out from the LGM to PD for four sites in the Coastal Cordillera of Chile at a spatial and temporal resolution adequate for coupling with landscape evolution models.
A new landform mode was introduced to LPJ-GUESS to enable a better simulation of vegetation dynamics and state at a sub-pixel resolution and to allow for future coupling with landscape evolution models operating at different spatial scales. Using a regionally adapted parameterization, LPJ-GUESS was capable of reproducing PD potential natural vegetation along the strong climatic gradients of Chile, and simulated vegetation cover was also in line with satellite-based observations. Simulated vegetation during the LGM differed markedly from PD conditions. Coastal cold temperate rainforests were displaced northward by about 5∘ and the tree line and vegetation zones were at lower elevations than PD. Transient vegetation simulations indicate a marked shift in vegetation composition starting with the past glacial warming that coincides with a rise in [CO2]. Vegetation cover between the sites ranged from 13 % (LGM: 8 %) to 81 % (LGM: 73 %) for the northern Pan de Azúcar and southern Nahuelbuta sites, respectively, but did not vary by more than 10 % over the 21 000 year simulation. A sensitivity study suggests that [CO2] is an important driver of vegetation changes and, thereby, potentially landscape evolution. Comparisons with other paleoclimate model drivers highlight the importance of model input on simulated vegetation.
In the near future, we will directly couple LPJ-GUESS to a landscape evolution model (see companion paper) to build a fully coupled dynamic-vegetation/landscape evolution model that is forced with paleoclimate data from atmospheric general circulation models.
... Ellos indican aridez en el Holoceno temprano a medio, entre alrededor de 9500-5700 cal. años AP 20 (Jenny et al. 2002;Villa-Martínez et al. 2003, 2004. Estos autores concluyen que: 19 Proxy: indicador paleo-ecológico. ...
This work emphasizes the heuristic role of some pioneering hypotheses for understanding the complex biogeographic and evolutionary history of southern South American forests. First, I document the mixed structure of subtropical and temperate rain forests of Chile, considering the geographic distribution and phylogenetic relationships of the main components of the flora. Based on this evidence, I acknowledge the archaic character of the flora, with many lineages dating back to the Cretaceous- Paleogene, a period marked by profound geological, oceanographic, and climatic changes, coeval with the breakup of the supercontinent of Gondwana. In second place, I review the effects of fragmentation and isolation of extra-tropical forests within South America, which is related primarily to the development of the Arid Diagonal (AD) and the maximum Andean uplift during the Neogene. Finally, I review the changes in the position and intensity of the AD through the glacial-interglacial cycles of the Quaternary period, using geologic, paleoclimatic, palynologic and phylogeographic evidence.
... El aporte hídrico depende de napas subterráneas y cursos superficiales como esteros y quebradas que se activan durante la estación invernal, convirtiéndola en un área vulnerable a sequías durante años de escasa pluviosidad. Diversos estudios paleoclimáticos coinciden que hacia el 3000 A.P. se habría establecido este clima mediterráneo en la región (Villagrán y Varela 1990;Villa-Martínez y Villagrán 1997;Maldonado 1999;Maldonado y Villagrán 2002;Villa-Martínez et al. 2003). ...
Frente a la necesidad de abordar el estudio de las piedras tacitas en la totalidad de sus dimensiones posibles, surge esta primera e inédita compilación de trabajos sobre este recurso cultural inmueble. Este libro es el resultado de las presentaciones y discusiones del primer encuentro organizado específicamente para discutir este tema, en el Taller Piedras Tacitas, realizado en Santiago de Chile durante el mes de agosto del 2014.
La propuesta apuntó a una puesta en común de dichos aspectos, los cuales se debaten y resuelven, por lo general, a nivel local o al interior de los grupos de investigación, siendo escasamente planteados en encuentros académicos. Bajo esta modalidad, se crearon las condiciones apropiadas para un diálogo abierto, con exposiciones que permitieron intercambio de experiencias, opiniones y saberes.
Los objetivos de este encuentro fueron 1) sistematización y puesta al día de la información disponible sobre investigaciones relativas a las piedras tacitas, 2) organizar los resultados de estos tipos de contextos arqueológicos inmuebles, por medio de estudios interdisciplinarios, 3) conocer casos de estudios que abordan diversas temáticas como la determinación de funcionalidad de las piedras tacitas, distribución espacial e interpretación de los contextos arqueológicos asociados, además de 4) dar a conocer los sitios arqueológicos excavados y los resultados obtenidos de los análisis arqueológicos de los sitios enmarcados en el Proyecto Desarrollo Los Bronces.
... Es de trascendental importancia analizar la funcionalidad de las piedras tacitas y por qué se asociarían tan marcadamente con las serranías del cordón de Chacabuco, lo que ocurriría al establecerse completamente las condiciones climáticas actuales (Jenny et al. 2002;Villa-Martínez et al 2003;Villa-Martinezet al. 2004;Valero-Garcés etal. 2005). ...
... Mediterranean-type ecosystems of Central Chile (the matorral) stand out among the other MTE because their current fire regime is recent (Holocene) and mainly driven by human activities [27][28]. Although natural fires were relatively common through the Miocene [29], the Andean uplift in the late-Miocene formed an effective barrier to westward storms. ...
Fire is a selective agent shaping plant traits and community assembly in fire-prone ecosystems. However, in ecosystems with no fire history, it can be a cause of land degradation when it is suddenly introduced by humans, as plant species may not be able to respond to such novel disturbance. Unlike other Mediterranean-type ecosystems (MTE) of the world, natural fires have not been frequent during the Quaternary in the matorral of Central Chile, and thus, plant adaptive responses are expected to be uncommon. We evaluated the effect of heat shock on seed survival and germination of 21 native woody plants of the Chilean matorral and compiled information on smoke-stimulation and resprouting, to evaluate the importance of fire-adaptive responses in the context of the other MTE. We found that in the Chilean woody flora negative seed responses to fire cues were more frequent than positive responses. Although resprouting is a relatively widespread trait, fire-stimulated germination is not as common in the Chilean matorral as in other MTE. The seeds of seven endemic species were strongly damaged by fire cues and this should be considered in post-fire restoration planning. However, our results also showed that many species were resistant to elevated doses of heat shock and in some, germination was even stimulated. Thus, future research should focus on the evolutionary causes of these responses. These findings could help to develop strategies for fire management in the Chilean matorral. In addition, they will improve our understanding of the evolutionary forces that shaped this plant community and to better frame this region among the other MTE worldwide.
... Poaceae ($10-55%) and Amaranthaceae (20-80%) dominate the Matanzas Lake pollen record (33.7˚S) (Villa-Martínez, 2002). The Aculeo record (Fig. 7c) shows the establishment of modern moisture conditions associated with frequent/intense El Niño-like activity around 3.2 cal ka BP (Jenny et al., 2002;Villa-Martínez et al., 2003). ...
We present a 7-ka environmental reconstruction based on sedimentological and geochemical data from Lago Vichuquén, a coastal eutrophic lake in central Chile (34°48′S, 72°03′ W, 4 m a.s.l.). A relatively shallow and restricted marine environment with low productivity, high detrital input and dominant anoxic conditions in the Vichuquén Basin occurred from 7.0 to 6.5 cal ka BP. Rapid onset of a Holocene marine transgression at 6.5 cal ka BP favoured deeper and more biologically productive environments that existed until 2.8 cal ka BP. Bioproductivity changes during the mid-Holocene (6.5–4.2 cal ka BP) were related to upwelling dynamics controlled by the intensity of the South-east Pacific Anticyclone (SPA). Periods with lower organic productivity and dominant anoxic conditions reflect an increased intensity of SPA (increased upwelling) and decreased precipitation. A shift at ∼4.0 cal ka BP reflects the onset of modern Southern Westerly Winds and El Niño-Southern Oscillation patterns. Tectonic uplifting and geormorphological activity (dune advancement) are possible reasons behind the Vichuquén Basin closure at ∼1.2 cal ka BP, leading to a low bioproductivity lacustrine environment which has developed until the present.
... Laguna Chepical shows relatively wet conditions during the late Holocene, which is coherent with other paleoclimatological records between 27°S and 34°S located in coastal areas (such as Quintero and Palo Colorado; Maldonado and Villagrán, 2006;Villagrán and Varela, 1990), in the lowlands (Laguna Aculeo, 33°50′S; 350 m a.s.l.; Jenny et al., 2003;Villa-Martínez et al., 2003), in marine records of Central Chile (Lamy et al., 1999), and in Andean areas between 27°-33°S (Grosjean et al., 1997;Veit, 1996). These moist conditions were associated with an equatorward expansion of the Southern Westerlies Wind Belt (SWWB) relative to patterns during the early and mid-Holocene (Lamy et al., 2010). ...
Paleoclimate reconstructions are essential for understanding the dynamics of the climate system and its past variations. By utilizing climate-dependent proxies, these reconstructions provide a comprehensive perspective on climatic variations that extend far beyond the limited scope of instrumental records, spanning centuries to millennia. Particularly, proxy-based reconstructions for the last two millennia provide valuable insights into natural climate variability during the preindustrial era and the anthropogenic influence on current climate change. As a result, paleoclimate studies are also critical for interpreting climate projections in the context of anthropogenic forcing. South America, with its vast and diverse climate conditions, is a region rich in high-resolution paleoclimate records, including marine, lacustrine, and fjord sediments, speleothems, ice cores, tree rings, glacial and aeolian deposits, archaeological evidence, and historical documents, among others, all of which capture past climate changes. However, despite numerous paleoclimate reconstructions conducted across the continent and significant advances in understanding its past climate, substantial research gaps remain. These gaps are particularly evident in understudied regions and poorly understood phenomena, hindering a comprehensive understanding of climate variability at both regional and continental scales. To advance paleoclimatic research in South America, future efforts should prioritize (a) the collection of high-resolution records from key locations, (b) the integration of diverse proxies and innovative methodologies, (c) enhancing our understanding of climate-proxy relationships, and (d) developing new proxy calibrations. Collaboration with local communities and indigenous peoples and adopting interdisciplinary approaches will be vital in driving the field forward.
The Toro and Tastil Quebradas (river valleys) present different terrace-like geoforms made up of deposits of coarse-grained clastic materials. These terraces display convex-upward surfaces, a highly variable distribution, have a small lateral extension and depend on the lithology of the geological basement, which differs significantly along the quebradas . The number of terraces between one area and another indicates that these terraced geoforms should not be ascribed to one single cause, but rather to a variety of factors, i.e. local variations at base-level. The coarse-grained materials of the terraces are usually arranged in roughly horizontal layers that characterize the outcrops. These are interfingered with fine-grained mud-rich materials. The freshwater gastropod remains in the mud-rich materials indicate that they accumulated in lacustrine-like sedimentary environments. These developed from alluvial fans that spread out from the lateral quebradas to occupy the entire main valley (q uebrada) , giving rise to natural dams and temporary lakes upstream. Absolute dates obtained by radiocarbon ( ¹⁴ C) methods strongly suggest that the alluvial fans were coeval with the temporary lakes in the Upper Pleistocene - Middle Holocene. The ENSO effects could have brought about the local variations in base-level that generated the younger temporary lakes, whereas the older ones were probably controlled by precession cycles (at about 21,000 y). The large number of temporary lakes scattered across the region suggests the overlapping of forcing factors at local and regional scales.
Disjunct distributions in species lead to questions about population separation events and their consequences, affecting traits and functions depending on the disjunction time. While niche and morphology are essential, research on functional differences in disjunct populations is limited.
Acacia caven, found in South America, has a disjunct distribution between Central Chile (west) and the South American Gran Chaco (east of Andes). Chapter 1 explores its origin, supporting a human-mediated dispersal from Argentina to Chile in the early Holocene.
Chapter 2 examines morphological variability in Acacia caven, comparing traits divergence between western and eastern populations, confirming varieties' validity and identifying identification challenges. Of six varieties growing in the eastern range, only one has a closer affinity to the western populations, agreeing with an introduction event.
Chapter 3 uses climatic niche modelling to study Acacia caven's distribution, revealing significant overlap in climatic spaces, supporting niche conservatism. A common area of occupancy is suggested in southern Bolivia and northwest Argentina since the late Pleistocene.
Lastly, chapter 4 investigates Acacia caven's ecological effects as a nurse plant at a continental scale. Geographical differences in its impacts on neighbouring plant communities are emphasized, showing large-scale context dependence but suggesting substantial positive effects on both ranges.
These studies provide insights into Acacia caven's origin, dispersal, morphology, ecological role, and distribution patterns in South America, contributing to its ecological significance in diverse ecosystems.
The hydroclimate of South America is characterized by the South American summer monsoon (SASM), a tropical atmospheric circulation that induces a summer precipitation regime, and the Southern Hemisphere Westerlies (SHW), an extratropical atmospheric circulation that induces a winter precipitation regime. Stretched between these two systems is a NW-SE-oriented region dominated by descending air masses, resulting in the South American subtropical dry zone (SASDZ), also known as the arid diagonal. We investigated the Cerro Tuzgle cushion peatland (CTP) located on the Argentine Altiplano, north of the present-day SASDZ. Previous work revealed that the CTP was consistently in the SASM regime during the last 2900 cal yr BP. Here, we extend the CTP record to the middle Holocene covering the last 7200 cal yr BP to gain further knowledge of the Holocene development of the SASM and potential modulations of the SASDZ. The prominent feature of the entire record is a distinct and lasting transition centred around 3100 cal yr BP characterized by declining minerogenic content, increasing organic carbon content, rising stable carbon isotope values of organic matter and cellulose, and increasing stable oxygen isotope values of cellulose. We interpret this specific proxy pattern as a hydroclimatic transition towards less arid conditions at the CTP after 3100 cal yr BP. The transition corresponds with the end of the continuous Holocene strengthening of the SASM between 3500 cal yr BP and 3000 cal yr BP indicated by proxy records from north and east of the CTP. The CTP does not reflect this strengthening of the SASM and rather exhibits a threshold response indicating the effective establishment of the SASM summer precipitation regime at 24°S. This suggests that moisture supply during a more arid middle Holocene was provided by isotopically depleted precipitation, while moisture supply after the transition originated from isotopically enriched SASM summer precipitation. Concurrent hydroclimatic changes in the SHW winter precipitation regime south of the SASDZ are documented in a distinct lake level rise of Laguna Aculeo (33°50´S) around 3200 cal yr BP. These coinciding hydrological changes of the SASM and the SHW precipitation regimes indicate larger scale reorganisations of atmospheric circulation components, potentially connected to major modulations of the SASDZ. Thus, our CTP record sheds light on the middle to late Holocene development of the SASM at its southern limit and corroborates connections between the tropical and extratropical hydroclimate of South America.
Quaternary lake systems have developed in many Andean intermontane valleys in northwestern Argentina in association with landslides, rock avalanches, and the development of large alluvial fans, caused either by tectonics, climate change, and/or increased rainfall. At the El Candado location, in the narrow, southern sector of the Quebrada del Toro (Salta Province, Argentina), fine-grained sedimentary deposits are recognized, which, based on their sedimentological and paleontological characteristics, are interpreted as the sedimentary infill of shallow lakes-marshes that were generated by the development of large alluvial fans that dammed the Río Toro. Based on AMS 14C dating of gastropod shells and organic matter (ca. 8-4.8 ka), this region experienced multiple lacustrine-marsh paleoenvironments during the middle Holocene. Pollen analysis and paleobotanical investigations of these deposits suggest that the accumulation of the lake sediments occurred under relatively humid conditions that alternated with semi-arid periods as is typical for the Andean Holocene.
Paleoclimate studies in Patagonia show a high Holocene climate variability, strongly controlled by the intensity and latitudinal position of the Southern Westerly Winds. In this study, environmental and climate variability, and in particular winter precipitation, was reconstructed over the last centuries through sedimentological and geochemical analyses of a core from Lake Jeinimeni in North East Patagonia. Visual description, X-ray radiographies and thin section observations point to finely laminated sediments, made by fine sands and light brown clayey silts forming an annual deposition (varves) occasionally interrupted by two Hudson volcano-related tephras and 15 pluri-millimetre to pluri-centimetre coarser sandy to gravely layers. Varve counting confirmed by ²¹⁰Pb and ¹³⁷Cs indicates a detrital sequence of at least 750 yr. Based on a correlation with local meteorological data for the 1930–1988AD interval, varve thickness and statistical treatment of XRF geochemical data give information on transport pathway and sedimentary deposit conditions. The sandy laminae correspond to the deposition of high sedimentary load delivered by austral spring snowmelt whereas the clayey silt laminae result of particle settling in the water column during low hydrodynamical conditions. Thicker varves observed in dry conditions underline the importance of aeolian transport in sedimentary deposition. During locally dry and windy summer, the wind may erode and remobilise the sedimentary deposits along the lake margins. The sandy and gravely layers record massive erosional events due to proximal watershed perturbation driven by climatic or tectonic mechanisms. The clastic varves of Lake Jeinimeni document environmental decadal to multidecadal variability in East Patagonia over the last centuries. The more pronounced sediment transition around 1750 CE is consistent with the inception of the Little Ice Age-type event, in agreement with North Patagonian paleoclimate reconstructions derived from glacier advances, lacustrine varve thickness and tree-ring records.
Quaternary lake systems have developed in many Andean intermontane valleys in northwestern Argentina in association with landslides, rock avalanches, and the development of large alluvial fans, caused either by tectonics, climate change, and/or increased rainfall. At the El Candado location, in the narrow, southern sector of the Quebrada del Toro (Salta Province, Argentina), fine-grained sedimentary deposits are recognized, which, based on their sedimentological and paleontological characteristics, are interpreted as the sedimentary infill of shallow lakes-marshes that were generated by the development of large alluvial fans that dammed the Río Toro. Based on AMS 14 C dating of gastropod shells and organic matter (ca. 8-4.8 ka), this region experienced multiple lacustrine-marsh paleoenvironments during the middle Holocene. Pollen analysis and paleobotanical investigations of these deposits suggest that the accumulation of the lake sediments occurred under relatively humid conditions that alternated with semi-arid periods as is typical for the Andean Holocene.
This paper presents the results of a study of the composition of lithic raw materials from the contexts of archaeological sites of hunter-gatherers of Central Chile (latitudes 33° to 34.5° S) between 5000 to 1000 years BP. This territory is characterized by a wide distribution of certain coarse and medium-grained lithic raw materials (andesite, basalt and granite), preferably used in low formatted tools, and the specific location of those of fine grain (obsidian and siliceous rocks), suitable for bifacial reduction, only in some localities. In this analysis, 22 sites have been included, each of which presents different proportions of these raw materials in their context, a set that, when analysed in terms of the diversity of each case, generated clear spatial groupings which were ratified by means of a principle component analysis. These groupings of sites are located in direct association with the lithic landscape of different localities within the region, although we propose that the simple cost-benefit explanation would not account for their formation. According to the authors, these groups would be marked by behaviours that can only result from social restrictions on access to certain sources of these raw materials, especially considering that the distances between their location and the position of the different sources in several cases is not too large to be considered a factor in itself. These restrictions could be interpreted as the existence of socially different groups within the study area, a question that is compared with ethnographic data currently available on the size of the territories of different groups of hunter-gatherers and their annual mobility ranges.
This paper presents the results of a study of the composition of lithic raw materials from the contexts of archaeological sites of hunter-gatherers of Central Chile (latitudes 33° to 34.5° S) between 5000 to 1000 years BP. This territory is characterized by a wide distribution of certain coarse and medium-grained lithic raw materials (andesite, basalt and granite), preferably used in low formatted tools, and the specific location of those of fine grain (obsidian and siliceous rocks), suitable for bifacial reduction, only in some localities. In this analysis, 22 sites have been included, each of which presents different proportions of these raw materials in their context, a set that, when analysed in terms of the diversity of each case, generated clear spatial groupings which were ratified by means of a principle component analysis. These groupings of sites are located in direct association with the lithic landscape of different localities within the region, although we propose that the simple cost-benefit explanation would not account for their formation. According to the authors, these groups would be marked by behaviours that can only result from social restrictions on access to certain sources of these raw materials, especially considering that the distances between their location and the position of the different sources in several cases is not too large to be considered a factor in itself. These restrictions could be interpreted as the existence of socially different groups within the study area, a question that is compared with ethnographic data currently available on the size of the territories of different groups of hunter-gatherers and their annual mobility ranges.
The Southern Hemisphere Westerlies (SHW) are an important driver of climate in the mid-latitudes of the Southern Hemisphere. Abrupt latitudinal migration of this coupled atmospheric-oceanic system is thought to be linked to the onset of the Termination at the end of the last ice age and to subsequent climatic variation through the late-glacial period and Holocene. However, the timing and spatial extent of these shifts, as well as variations in wind intensity, are poorly constrained, hindering our understanding of abrupt climate change in the Southern Hemisphere. In addition, future changes in the position and intensity of the SHW are a critical part of model projections, because the SHW affect Southern Ocean upwelling and CO2 sequestration. Insight into the future behavior of the SHW can come from examination of past fluctuations. My focus is the South Atlantic region, thought to be a key area for interactions between the SHW and other components of the climate system. However, there are few terrestrial datasets constraining past variations in the SHW in this region and many of these appear contradictory. This study is comprised of two alpine lake sediment cores extracted from tarns occupied by alpine glaciers during the last ice age on Mount Usborne of East Falkland (51oS). This terrestrial record, which spans the last 23 ka, uses stratigraphy, organic content, biomarkers (with a focus on plant wax), isotopic composition of plant waxes, and a preliminary pollen record to identify relative wind intensity, wetness, precipitation source, and temperature of the site. Moisture source is particularly useful as it can be tied to the average position of the SHW over time, with enriched precipitation reflecting a southerly location and depleted precipitation indicating a northerly shifted wind belt. My data suggest climate at Mount Usborne was cold and windy until 16.4 ka, when the SHW moved south and the area may have warmed. This shift represents the local expression of the onset of the Termination. Following a brief period at 13.6-14 ka when the SHW returned to a northern position during the Antarctic Cold Reversal, climate became wetter at 12.5-13.6 ka, associated with a southward migration of the SHW. At 11.2-12.5 ka, the westerlies again moved north and climate in the Falkland Islands became more humid. The start of the Holocene was marked by increasingly warmer and wetter conditions, with the SHW migrating south between 9-11 ka. Southward migration from 6-9 ka resulted in drier, windier conditions over the Falkland Islands. A brief event in the mid-Holocene (5.5-6 ka) is wet and less windy. A distinct reversal in the southward trend occurred at 5.5 ka. During the rest of the Holocene, the SHW have slowly migrated to the north. Climate was windy and dry from 3-5.5 ka and less windy and wet from 0-3 ka. My dataset suggests a highly variable position of the SHW over the past 23 ka, with multiple north-south migrations, including 1) southward migration during the Termination 2) periodic northward shifts in the late-glacial period, 3) a southerly position during the early Holocene, and 4) northward movement in the mid to late Holocene, particularly after 5.5 ka. The relative position of the SHW calculated in this study combined with other climate records at 51-54oS suggest that variations in the position of the SHW correspond closely with temperature, wind intensity, and precipitation variations, as well as to well-known climate events, regionally. The correspondence between changes in the SHW and periods of abrupt climate change support the hypothesis that the SHW are linked to much of the climatic variation in the South Atlantic region.
Late Quaternary volcanic basins are active landscapes from which detailed archives of past climate and seismic and volcanic activity can be obtained. A multidisciplinary study performed on a transect of sediment cores was used to reconstruct the depositional evolution of the high-elevation Laguna del Maule (LdM) (36∘ S, 2180 m a.s.l., Chilean Andes). The recovered 5 m composite sediment sequence includes two thick turbidite units (LT1 and LT2) and numerous tephra layers (23 ash and 6 lapilli). We produced an age model based on nine new 14C AMS dates, existing 210Pb and 137Cs data, and the Quizapú ash horizon (1932 CE). According to this age model, the relatively drier Early Holocene was followed by a phase of increased productivity during the mid-Holocene and higher lake levels after 4.0 ka cal BP. Major hydroclimate transitions occurred at ca. 11, 8.0, 4.0 and 0.5 ka cal BP. Decreased summer insolation and winter precipitation due to a southward shift in the southern westerly winds and a strengthened Pacific Subtropical High could explain Early Holocene lower lake levels. Increased biological productivity during the mid-Holocene (∼8.0 to 6.0 ka cal BP) is coeval with a warm–dry phase described for much of southern South America. Periods of higher lake productivity are synchronous to a higher frequency of volcanic events. During the Late Holocene, the tephra layers show compositional changes suggesting a transition from silica-rich to silica-poor magmas at around 4.0 ka cal BP. This transition was synchronous with increased variability of sedimentary facies and geochemical proxies, indicating higher lake levels and increased moisture at LdM after 4.0 ka cal BP, most likely caused by the inception of current El Niño–Southern Oscillation and Pacific Decadal Oscillation (ENSO–PDO) dynamics in central Chile.
Background and aims:
The Mediterranean-type forest of central Chile is considered a "biodiversity hotspot" and a relic of a wider ancient distribution produced by past climatic oscillations. Nothofagus macrocarpa, commonly known as 'roble de Santiago', is a threatened palaeoendemism of this forest, poorly represented in the protected area system. This tree has been repeatedly misidentified as the sister species N. obliqua, which has affected its recognition and protection. Only a few populations of N. macrocarpa remain within a matrix of intensive land use that has been affected by recent forest fires. We tested the hypothesis that current populations of N. macrocarpa are a relic state of a previously widespread range, with the aim of contributing to its identification, biogeographic history, and the design of conservation measures using genetic information.
Methods:
We analysed remnant N. macrocarpa forests using nuclear (nDNA) and chloroplast (cpDNA) DNA sequences, conducted phylogenetic and phylogeographic analyses to reconstruct its biogeographic history, and assessed microsatellites (SSRs) to determine contemporary patters of diversity within and among all remnant populations. We also examined the degree of past, current, and potential future isolation of N. macrocarpa populations using ecological niche models (ENMs).
Key results:
The N. macrocarpa species was confirmed by chromosomal nDNA sequences, as previously suggested. Small isolated populations of N. macrocarpa exhibited moderate to high genetic diversity according to SSRs. cpDNA analysis revealed a marked past latitudinal geographic structure, whereas SSRs analysis did not find such current structure. ENM analyses show local expansion-contraction of the N. macrocarpa range during warmer climates, particularly in the northern and central ranges where basal-most cpDNA haplotypes were detected, and recent expansion to the south of the distribution.
Conclusions:
Genetic patterns confirm that N. macrocarpa is a distinct species and suggest a marked latitudinal relic structure in at least two evolutionarily significant units (ESUs), despite contemporary gene flow among the population. This information must be considered when choosing individuals (seeds and/or propagules) for restoration purposes, to thus avoid the admixture of divergent genetic stocks.
La pesca desempeña funciones fundamentales en el suministro
de alimentos a la humanidad, en la seguridad alimentaria y en
la generación de ingresos. Según las proyecciones, los cambios
globales repercutirán importantemente en los ecosistemas
marinos, afectando las comunidades y las economías costeras.
Existen abundantes y diferentes factores de cambio global que
influyen sobre los océanos y, por supuesto, la extracción de
recursos del mar es en sí mismo un agente de cambio global.
En este capítulo se revisan estresores y desafíos claves de
cambio global que son relevantes para la actividad pesquera.
Comenzamos haciendo hincapié en alteraciones físico-químicas
como el aumento de la temperatura y la acidificación del océano
y sus repercusiones en los recursos marinos de importancia
comercial, para posteriormente focalizarnos en aspectos
relacionados con las dimensiones humanas de cambio global
que afectan a las pesquerías, como lo son la sobreexplotación
y las fuerzas de mercado. Finalizamos estableciendo la
importancia de comprender la vulnerabilidad de comunidades
costeras frente a diferentes estresores de cambio global como
una forma de potenciar esfuerzos de adaptación de individuos y
comunidades para enfrentar los problemas que se advierten en
el ámbito de la pesca.
The denudation history of active orogens is often interpreted in the context of modern climate gradients. Here we address the validity of this approach and ask what are the spatial and temporal variations in palaeoclimate for a latitudinally diverse range of active orogens? We do this using high-resolution (T159, ca. 80 × 80 km at the Equator) palaeoclimate simulations from the ECHAM5 global atmospheric general circulation model and a statistical cluster analysis of climate over different orogens (Andes, Himalayas, SE Alaska, Pacific NW USA). Time periods and boundary conditions considered include the Pliocene (PLIO, ∼ 3 Ma), the Last Glacial Maximum (LGM, ∼ 21 ka), mid-Holocene (MH, ∼ 6 ka), and pre-industrial (PI, reference year 1850). The regional simulated climates of each orogen are described by means of cluster analyses based on the variability in precipitation, 2 m air temperature, the intra-annual amplitude of these values, and monsoonal wind speeds where appropriate. Results indicate the largest differences in the PI climate existed for the LGM and PLIO climates in the form of widespread cooling and reduced precipitation in the LGM and warming and enhanced precipitation during the PLIO. The LGM climate shows the largest deviation in annual precipitation from the PI climate and shows enhanced precipitation in the temperate Andes and coastal regions for both SE Alaska and the US Pacific Northwest. Furthermore, LGM precipitation is reduced in the western Himalayas and enhanced in the eastern Himalayas, resulting in a shift of the wettest regional climates eastward along the orogen. The cluster-analysis results also suggest more climatic variability across latitudes east of the Andes in the PLIO climate than in other time slice experiments conducted here. Taken together, these results highlight significant changes in late Cenozoic regional climatology over the last ∼ 3 Myr. Comparison of simulated climate with proxy-based reconstructions for the MH and LGM reveal satisfactory to good performance of the model in reproducing precipitation changes, although in some cases discrepancies between neighbouring proxy observations highlight contradictions between proxy observations themselves. Finally, we document regions where the largest magnitudes of late Cenozoic changes in precipitation and temperature occur and offer the highest potential for future observational studies that quantify the impact of climate change on denudation and weathering rates.
Fossil Pediastrum is frequently found in Quaternary lacustrine deposits and has attracted much attention because it can be well preserved and easily identified. However its palaeoenvironmental significance is unclear. Several studies suggest that the occurrence of a large amount of Pediastrum indicates a gradually decreasing lake-level, while others point out that Pediastrum mainly occurs in the deep areas of lakes. Thus clarifying the relationship between Pediastrum and lake levels is of great importance for improving the reliability of palaeoenviromental reconstruction. In this study, we investigated the occurrence of
Pediastrum in Xingyun Lake, a semi-enclosed shallow fault and eutrophic lake located in central Yunnan Province, southwest China. We obtained 4 lake surface water samples at water depths of 4, 4.5, 5.2 and 6.5 m; 16 water samples collected at various depths within the water column at the deepest part of the lake; and 10 lake surface sediment samples taken at different water depths from the lake shore to the deepest part using a Grab sampler. We present the results of Pediastrum analysis of samples of both the lake water and surface sediments of Xingyun Lake and discuss the relationship between the Pediastrum distribution and the lake-level/water depth. The variation of the fossil records during the past 3000 years is also reported. The results show that two types of Pediastrum were identified in the water and lake sediment samples, including Pediastrum boryanum and Pediastrum simplex. The concentration of Pediastrum in the water samples is extremely low, varying from 2 to 6 grains mL1. Spatially, the concentrations of Pediastrum in the surface lake water samples exhibit little change with increasing water depth. In terms of the depth variation within the water column in the deepest part of the lake, the Pediastrum concentration of the bottom sample is the highest, which may be related to the effects of resuspension and redeposition of lake sediments caused by
wind-induced turbulence in shallow water. With respect to the lake surface sediment samples, the Pediastrum content is relatively high. The concentration of Pediastrum varies from 60700 to 104000 grains g1, with an average of 81000 grains g1; and the relative percentage abundance ranges from 66%–80%, averaging around 76%. Interestingly, both the concentration and percentage content of Pediastrum in these samples exhibit no significant relationship with water depth. Based on comparison of the results from Xingyun Lake with those of other workers, we conclude that the relationship between the Pediastrum distribution and water depth inferred from the lake sediments of several relatively larger lakes mentioned in previous studies
may be caused by depositional processes: turbulence resulting from wave activity in these larger lakes could result in the resuspension of Pediastrum in shallow water and its focusing into deeper areas. However, whether or not there is a large quantity of Pediastrum living in the lake water may be related to the physicochemical status of the lake water, determined by factors such as the river input, nutrient level, temperature, pH and salinity. In addition, these factors may vary between different lakes in different regions. Therefore, the variation of Pediastrum content cannot be used as an indicator of water depth or
lake-level without careful consideration of these factors. In addition, it needs to be used in the context of multi-proxy studies. Both the percentage and the concentration of fossil Pediastrum in the sediments of Xingyun Lake exhibit distinct features over the last 3000 years: very low values before 2000 cal a BP followed by a rising trend, and then an abrupt increase after 1500 cal a BP. This is consistent with variations in the intensity of human activity revealed by frequent high-amplitude fluctuations in mean grain-size and by an abrupt increase in magnetic susceptibility. In addition, the abrupt changes in fossil Pediastrum in Xingyun Lake precede those of mean grain-size and magnetic susceptibility, suggesting that the Pediastrum from the Xingyun Lake sediments may be a sensitive indicator of the process of lake water eutrophication caused by human activities.
Paleoclimatic records from equatorial East Africa, Antarctica, and Greenland reveal that atmospheric circulation changed abruptly
at the early to mid-Holocene transition to full postglacial conditions. A climatic reorganization occurred at all three sites
between 8200 and 7800 years ago that lasted 200 years or less and appears to have been related to abrupt transitions in both
marine and terrestrial records around the world.
We examined energy flow and nitrogen turnover in a highly eutrophic lake in Chile. Carbon fixation varied seasonally between 25–450 mg C m–2 h–1 in the photic zone, andca. 6.25106 kg C were fixed in the lake during 1980. Nitrogen turnover in the phytomas wasca. 1.04106 kg N yr–1 based on an arbitrary CN ratio of 6.0.En un lago muy eutrofizado en Chile se estudiaron el flujo de energa y la tasa de recambio de nitrgeno. La fijacin de carbono mostr variaciones estacionales entre 25 y 450 mg C m–2 h–1 en la zona ftica; cerca de 6,25106 kg C fueron fijados durante 1980. El recambio de nitrgeno, calculado asumiendo una relacin arbitraria CN=6,0, fue de 1,04106 kg N ao.
Pollen analysis of two sediment records from a coastal swamp forest site in the Chilean semiarid region (31°50′S; 71°28′W) shows an alternation of dry and wet phases during the past ∼6100 cal yr B.P. The most prominent vegetation changes occur at ∼4200 cal yr B.P., with the expansion of the swamp forest taxa Luma chequen and Escallonia sp., followed by a regression of the forest beginning at ∼3200 cal yr B.P. and ending with its replacement by a xerophytic scrub, between ∼1800 and 1300 cal yr B.P. The swamp forest reexpanded after ∼1300 cal yr B.P. and persisted, with minor variation, until the present. We interpret the establishment of the swamp forest at the study site to be the result of a rising watertable in response to increased rainfalls from ∼4200 cal yr B.P. onward. Our results indicate that in north-central Chile the second half of the Holocene was climatically more variable than previously thought, suggesting significant changes in the position and/or intensity of the westerlies wind belt and possibly in the frequency of El Niño–Southern Oscillation events.
Central Chile (32–35°S) lies at the northern border of strong Westerly influence and thus exhibits a steep precipitation gradient. Therefore, the palaeoclimatic archives in the region are suitable for detecting past moisture changes. The study of Laguna Aculeo (33°50'S, 70°54'W) presents a multiproxy Holocene lake record including sedimentology, geochemistry, mineralogy, pollen, diatoms, and radiocarbon dating (17 dates). Results indicate an arid early to mid-Holocene period (about 9500–5700 cal yr B.P.). After 5700 cal yr B.P. effective moisture increased progressively and, around 3200 cal yr B.P., modern humid conditions were established. Numerous intercalated clastic layers reflect flood deposition during rainy winters. A fluvial unit was deposited shortly before 9000 cal yr B.P. Subsequently, flood events were absent until 5700 but have become frequent since 3200 cal yr B.P. The frequency of flood layers possibly points to weak or no El Niño activity during the early and mid-Holocene, with a subsequent increase during the late Holocene. During the early and mid-Holocene, the Westerlies were probably blocked and hence deflected southward by the subtropical high-pressure cell. Higher precipitation during the last 3200 yr seems strongly related to a weakened subtropical high-pressure cell with intensified Westerlies and possibly increased El Niño activity.
Stratigraphically constrained cluster analysis is a multivariate method for quantitative definition of stratigraphic zones. As opposed to ordinary, unconstrained cluster analysis, only stratigraphically adjacent clusters are considered for merging. The method of incremental sum of squares has been used widely for unconstrained analyses and has proved particularly satisfactory for pollen frequency data. CONISS is a FORTRAN 77 program for stratigraphically constrained cluster analysis by this method. Several data transformations lead to different implicit dissimilarity coefficients. As an option, the program also will perform an unconstrained analysis, which can be useful for comparison with the constrained analysis.
The multi-proxy study of lacustrine sediments from Laguna Aculeo (33°50′S) provides detailed information about moisture changes in the lowlands of Mediterranean Central Chile during the last 2000 years. The lake lies just at the northern border of the strong Westerlies influence with dry summers and humid winters. Geochemical, sedimentological and diatom analyses provide evidence for an arid period between cal 200 BC and AD 200 and a subsequent increase in moisture after cal AD 200. Abundant clastic layers in the core represent flood events. Periods with a higher frequency of flood events indicate an increased intensity of the Westerlies, more winter frontal system activity and possibly ENSO-related variability, probably comparable to modern conditions in Mediterranean Central Chile. Periods of high clastic input occur around cal AD 200–400, 500–700, especially around cal AD 1300–1700, and around AD 1850–1998. During the last 50 years, at least eight flood events were detected, correlating mainly with El Niño years. A very short drier period also occurred in the late 1960s. In recent decades, human impact has resulted in a eutrophication of the lake.
Debris flows have deposited inorganic laminae in an alpine lake that is 75 kilometers east of the Pacific Ocean, in Ecuador.
These storm-induced events were dated by radiocarbon, and the age of laminae that are less than 200 years old matches the
historic record of El Niño events. From about 15,000 to about 7000 calendar years before the present, the periodicity of clastic
deposition is greater than or equal to 15 years; thereafter, there is a progressive increase in frequency to periodicities
of 2 to 8.5 years. This is the modern El Niño periodicity, which was established about 5000 calendar years before the present.
This may reflect the onset of a steeper zonal sea surface temperature gradient, which was driven by enhanced trade winds.
The El Niño-Southern Oscillation (ENSO) is the most potent source of interannual climate variability. Uncertainty surrounding the impact of greenhouse warming on ENSO strength and frequency has stimulated efforts to develop a better understanding of the sensitivity of ENSO to climate change. Here we use annually banded corals from Papua New Guinea to show that ENSO has existed for the past 130,000 years, operating even during "glacial" times of substantially reduced regional and global temperature and changed solar forcing. However, we also find that during the 20th century ENSO has been strong compared with ENSO of previous cool (glacial) and warm (interglacial) times. The observed pattern of change in amplitude may be due to the combined effects of ENSO dampening during cool glacial conditions and ENSO forcing by precessional orbital variations.
The applicability of ecological principles, as they are discernible in pelagic systems, to the functioning of ecosystems generally, is re-examined: there are obvious similarities, most especially the base of photosynthetic plants, the array of consumers, the microbial returns and the intermediate trophic linkages. The reactions to environmental variability seem more conclusive in the pelagic but the observation makes no allowance for the differences in organismic temporal and spatial scaling: generation for generation, the plankton year is equivalent to the terrestrial interstadial. If the correct scaling factor is applied, the observable traits in the population and community ecology of the plankton may well provide appropriate models for the analogous high-order processes in terrestrial ecosystems but whose time scales are often much too extended relative to the life spans of ecologists to be verified. Ecosystem variability and resource fluctuation determine that biotic responses alternate between progressive expansion into the capacity of the resources and rapid contraction when the base is constrained. The deductions strongly support the themes of the 'new ecology' (Price et al. 1984) and oppose the retention of theories relating to steady states. The ability to determine the state ecosystem from the difference in its productive yield and the rate of its exploitative dissipation (the 'exergy flux' of Jorgensen 1992) is applied to suppositions about the impact of human activities on the providence of Planet Earth. World population is suggested to be closer to the thermodynamic supportive capacity than has been indicated previously. The mechanisms that promote high species diversity in the plankton are argued to be equally important on land. Patch diversity and separation, together with the stochastic frequencies and strength of structural setbacks (disturbances), are critical in both instances but there is great disparity in the spatial and temporal scaling, and in the contiguity of patches. The roles of disturbance frequency, the spectrum of patch ages, their interconnectedness and the transfer of propagules among patches are highlighted on the basis of planktonic biodiversities. The impact of planktonic-plant growth is considered in relation to the quality of water and, in particular, to its ability to constitute unacceptable and excessive biomass levels in lakes and rivers enriched with plant nutrients (chiefly phosphorus and nitrogen). The quantitative description of this eutrophication and the choice of methods available for its remediation are briefly reviewed. The steps necessary to secure effective nutrient-load reductions are not always the most practical compared to the application of physical mixing and biological control. Criteria for the successful application of these alternatives are rehearsed; the framework of a decision-support model is outlined. Special consideration is given to overcoming the problems caused by potentially-toxic cyanobacterial blooms and by the impacts of acid precipitation in base-poor catchments. Approaches towards striking sustainability in the management of the world's resources are identified. These call for greater management of demand, the application of low-energy, low-tech methods of waste-water recovery and a much more 'ecocentric' resolve to protect water quality for its own sake. The challenge to return all abstracted water to the hydrological cycle in at least as good or better quality requires us to care for the terrestrial environment too. This 'ecosystem approach' to water management is thus sympathetic to the properties of ecosystems generally. By placing these to the fore and seeking always to enhance them, good quality water and attractive habitat are no longer ruined by exploitation but, rather, are augmented by it. The techniques of managing ecosystems are most readily learned from the observation of systems dominated by aquatic microbes.
Outlines the physiography, climate and soil with which matorral is associated in Central Chile, and notes the human impact on the vegetation through fire, livestock grazing and other agricultural practices. Coastal matorral dominates the coastal terraces north of Zapallar; true matorral occurs on slopes of the coast range and foothills of the Andean Cordillera. Typical matorral communities consist of evergreen shrubs of 1-3 m height, with small sclerophyllous leaves; Lithraea caustica and Quillaja saponaria characterize the dominant vegetation, but communities are extremely variable in content. Stem-photosynthetic, drought-deciduous shrubs comprise an important sub-unit. Matorral communities of xeric slopes, mesic slopes and canyons, coastal areas, and montane regions are described. Espinal (Acacia caven-dominated open savanna) is especially found as a climax vegetation type in the central valley; on the coast, such vegetation may be an anthropogenically degraded form of matorral. Hygrophilous forest occurs on the western slopes of the coast range. Life forms of matorral dominants are discussed: evergreen sclerophylls; malacophyllous shrubs (whose non-sclerophyllous leaves last for a single year or less); deciduous phreatophytes (A. caven, Prosopis chilensis); evergreen phreatophytes (Jubaea chilensis); and succulents. The flora includes a high proportion of endemics. Evolutionary history is indicated, and the importance of relictual vegetation suggested.-P.J.Jarvis
The Age Calibration Program, CALIB, published in 1986 and amended in 1987 is here amended anew. The program is available on a floppy disk in this publication. The new calibration data set covers nearly 22 000 Cal yr (approx 18 400 14C yr) and represents a 6 yr timescale calibration effort by several laboratories. The data are described and the program outlined. -K.Clayton
Climate records from over much of the world show variability on both Milankovitch and millennial timescales. However, mechanisms in the climate system that have a global scale are lacking. In this two-part paper, we turn attention to a part of the system that is known from the modern climate record to be capable of organizing global scale climate events: the tropics. In the first part, we isolate this system using a coupled ocean-atmosphere model of the tropical Pacific. The model results demonstrate a tropical mechanism which can amplify Milankovitch forcing and generate a mean climate response. The model is also run for 150,000 years with no forcing. The results raise the possibility that millennial timescale variability can be generated within the tropics through non-linear interactions. In that case, power is to be expected over a range of frequencies, rather than in any particular narrow band. The second part of our study, presented in the following paper, will discuss the potential impact on the global climate of these mechanisms of tropical climate variability.
We offer the hypothesis that global scale millennial and glacial cycles may be initiated from the tropical Pacific. Part I used model results to illustrate how nonlinear ocean-atmosphere interactions in the tropical Pacific could generate variations in the field of sea surface temperature (SST) on both orbital and millennial timescales. The physics underlying these variations is essentially the same as that causing ENSO (El Niño - Southern Oscillation) variability in the modern climate. Here we argue that, as with ENSO but on paleoclimatic timescales, these changes in SST distribution will be accompanied by changes in the location of atmospheric convection, which will alter the global climate via atmospheric teleconnections. By analogy with ENSO, it is hypothesized that the cold phase will increase the glaciation over North America, increase low cloud cover, and reduce atmospheric water vapor. All tend to cool the earth either by increasing the planetary albedo or reducing greenhouse trapping. The warm phase has the opposite tendencies. We also critique the hypothesis that millennial changes are triggered by changes in the production of North Atlantic Deep Water.
A pollen record is presented from Laguna de Aculeo (33°50'S, 70°55'W, 360m a.s.l.) that documents important vegetation changes over the last 2500cal. yr in Central Chile. Grasses, composites, trees, paludal and aquatic taxa dominated the Aculeo watershed between 2500 and 100cal. yr BP under a humid climate. Large amplitude fluctuations of pollen and microalgal accumulation rates and numerous turbidite layers during this interval, however, suggest high precipitation variability probably linked to El Niño-Southern Oscillation (ENSO) events. Although the expansion of warm sclerophyllous forest taxa over the last 100 years could be interpreted as an onset of a drier and warmer climate, this trend was more likely linked to human activities in the watershed. High accumulation rates of microscopic charcoal particles, exotic pollen taxa, and a shift from oligo-mesotrophic to hypereutrophic indicators would seem to back the latter hypothesis.
The functioning of the Southern Oscillation (SO) over South America and the surrounding tropical Atlantic and eastern Pacific Oceans is studied through analyses of bimonthly patterns of correlation between an SO index and the fields of pressure, wind, temperature and rainfall; hydrometeorological anomalies being further ascertained from river discharge and lake level records and measurements of outgoing longwave radiation. -from Author
Analysis of mollusks from archaeological sites on the north and central
coasts of Peru indicates that between ca. 5800 and 3200 2800 cal yr
B.P., El Niño events were less frequent than today, with modern,
rapid recurrence intervals achieved only after that time. For several
millennia prior to 5.8 ka, El Niño events had been absent or very
different from today. The phenomena called El Niño have had
severe consequences for the modern and colonial (historically recorded)
inhabitants of Peru, and El Niño events also influenced
prehistoric cultural development: the onset of El Niño events at
5.8 ka correlates temporally with the beginning of monumental temple
construction on the Peruvian coast, and the increase in El Niño
frequency after 3.2 2.8 ka correlates with the abandonment of monumental
temples in the same region.
The dominant effect of El Nino/Southern Oscillation (ENSO) on amphi-South Pacific climates is to increase the variability of precipitation. The characteristic climate pattterns which accompany the alternating phases of ENSO are opposed in the eastern and western Pacific. Broadly speaking, in Australasia droughts accompany El Nino events, and wetter than average conditions accompany La Nina events, whereas in western South America south of the equator, wet conditions characterize El Nino and drier conditions characterize La Nina events. New Zealand and southern South American climates are somewhat cooler during El Nino events. The generally more stable climates of the early Holocene period and lack of comparable precipitation patterns in the amphi-South Pacific land areas point to either a much reduced amplitude of the ENSO fluctuations, or to a change in the extratropical expression of ENSO due to different climatic boundary conditions. -from Authors
Between about 8000 and 3000 years ago, climate worldwide underwent substantial changes. At the same time, human cultures experienced
a period of substantial progress toward more complex societies, as exemplified by the first temple mounds in South America,
the Egyptian pyramids, and the rise and fall of civilizations in East Asia. Archeologists and paleoclimotologists alike are
now investigating possible causal connections between these simultaneous developments and are finding a complex pattern of
cultural responses to climatic change.
The late Quaternary vegetation of the semiarid coast of central Chile is inferred from the palynological analysis of profiles from Quereo (31°55′S) and Quintero (32°47′S). Prior to 11,400 yr B.P., wet conditions are suggested by the abundance of pollen indicators of swamp and aquatic taxa, such as Cyperaceae and Myriophyllum, and by the presence of traces of arboreal pollen. Since ca. 10,000 yr B.P., a trend toward increasingly drier conditions is implied by the almost complete absence of arboreal and aquatic taxa, and a general decrease in the diversity of the semiarid shrubland indicators. From 3000 yr B.P. onward, the pollen records show the reappearance of swamp and aquatic taxa, presumably associated with wetter conditions, which led to recolonization by forest taxa at 1720 yr B.P. in Quintero. The drier climate detected along the semiarid coast of central Chile during most of the Holocene extended inland to the Andean foot-hills, within the present mediterranean-type climate zone of Chile, and also affected the distribution of the winter-deciduous Nothofagus forests and the northern boundary of the temperate rain forests.
In the Norte Chico precipitation is controlled by atmospheric perturbations and frontal systems associated with the belt of westerly wind circulation. The Holocene climatic history of the region can be reconstructed from geomorphic and pedologic investigations. In comparison to modern climatic conditions, increased influence of the westerlies is deduced for the time periods prior to 7300 yr B.P., between 5000-3700 yr B.P., 3000-1800 yr B.P. and around 270 yr B.P. It remains uncertain whether the increased influence of the westerlies was the consequence of northward shifts of the westerlies as a whole, of a meridional expansion of the westerly belt, or only of intensity changes of the atmospheric dynamics. Almost synchronous with changes in the westerlies the coastal fogs in the region were apparently reduced or the fog belt in the coastal range was elevated, probably due to a weakened upwelling and warmer water conditions in the eastern Pacific. In general, the climate of the Norte Chico has become more variable since 5000 yr B.P., especially since 3000 yr B.P., with frequent changes of the geoecological conditions.