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Observations of cryoconite hole system processes on an Antarctic glacier

Autores:

Macdonell, S. & Fitzsimons, S.

Resumen:

Los "cryoconite holes" son cavidades que contienen agua, formadas en las superficies de glaciares, donde la desigual distribución de sedimentos causa diferencias espaciales en el derretimiento. Los "cryoconite holes" son importantes componentes de los sistemas glaciares fríos, debido a que incrementan el derretimiento del hielo, permiten el desarrollo de complejos sistemas de drenajes y facilitan el crecimiento de comunidades microbianas en la superficie del glaciar. Este estudio describe el desarrollo de una red hidrológica de "cryoconite holes" en un glaciar de la Antártica y explora las implicancias para la reserva y entrega de nutrientes dentro del sistema del glaciar. Las mediciones de terreno incluyen dimensiones internas y mapeo de "cryoconite holes" a lo largo de la superficie del glaciar. El trabajo de laboratorio incluye análisis de cationes y aniones de hielo limpio y de los "cryoconite holes". Los resultados mostraron que la distribución de los "cryoconite holes" estaba determinada por la topografía y las tasas de erosión locales. Las superficies planas se caracterizaron por una alta densidad de "cryoconite holes". Los "cryoconite holes" fueron poco comunes dentro de canales sobre la superficie del glaciar y en superficies con altas tasas de erosión. La correlación negativa encontrada entre la densidad de "cryoconite holes" y la tasa de erosión sugiere que la superficie del glaciar necesita estar relativamente estable para el desarrollo y persistencia de los "cryoconite holes". Además, los "cryoconite holes" posiblemente contribuyan en 1/3 a la generación del derretimiento en superficies planas. Sin embargo, no toda esta agua es retenida en las cavidades. El agua puede ser drenada por canales, grietas o drenajes intergranulares, no obstante, la importancia relativa de cada uno no es conocida aún. Debido a que los "cryoconite holes" son relativamente ricos en nutrientes, comparados con el hielo limpio del glaciar, sería importante conocer la naturaleza de sus conexiones, a fin de determinar la entrega de nutrientes a lo largo del glaciar y a la región proglacial.

Año: 2012

Palabras claves: Agua de fusión, biogeoquímica, hidrología de glaciares, sistema de drenaje, sustancia disuelta.

Referencia APA: Macdonell, S. & Fitzsimons, S. (2012). Observations of cryoconite hole system processes on an Antarctic glacier. Rev. Chil. Hist. Nat., 85(4), 393-407.

Morphological variability of intertidal Eisenia arborea (Laminariales, Ochrophyta) at Punta Eugenia, Baja California Sur

Autores:

Parada, G., Riosmena-Rodriguez, R., Martinez, E., & Hernandez-Carmona, G.

Resumen:

Water motion is one of the main drivers in morphological variability in species within de order Laminariales, and most of our current knowledge is based on subtidal populations. is a dominant kelp species in the North Pacific, widely distributed along the Baja California Peninsula from mid intertidal down to subtidal areas. This species presents great variability in the intertidal zone but it has not been yet evaluated such variability according to wave exposure. The present work also identifies the spatial / temporal variation, particularly respect to the presence of stipes without medulla (hollow stipes) a feature common among other brown seaweeds. We evaluated the effects of wave action in morphological variation of intertidal (Laminariales, Ochrophyta) at Punta Eugenia. The spatial and temporal variation sampling was surveyed between February, May, July, and August 2004 in the intertidal of Punta Eugenia, Baja California Sur. Our results have shown that exposed sites correlate with increased length and width of stipes as compared to more protected sites. Hollow stipes frequency changed more in association with temporal variation than with spatial heterogeneity suggesting nutrient limitation for thalli development. Our results suggest that compensate by morphological modifications the stress of living in the intertidal zone by showing larger stipes. Hollow stipes might be are also a mechanical adaptation to increase survival in high energy environments.

Año: 2012

Palabras claves: Eisenia arborea;intertidal;Laminariales;morphological variability

Referencia APA: Parada, G., Riosmena-Rodriguez, R., Martinez, E., & Hernandez-Carmona, G. (2012). Morphological variability of intertidal Eisenia arborea (Laminariales, Ochrophyta) at Punta Eugenia, Baja California Sur. ALGAE, 27(2), 109-114.

Hydroclimate variability in the low-elevation Atacama Desert over the last 2500 yr.

Autores:

Gayo, E., Latorre, C., Santoro, C., Maldonado, A., & De Pol-Holz, R.

Resumen:

Paleoclimate reconstructions reveal that Earth system has experienced sub-millennial scale climate changes over the past two millennia in response to internal/external forcing. Although sub-millennial hydroclimate fluctuations have been detected in the central Andes during this interval, the timing, magnitude, extent and direction of change of these events remain poorly defined. Here, we present a reconstruction of hydroclimate variations on the Pacific slope of the central Andes based on exceptionally well-preserved plant macrofossils and associated archaeological remains from a hyperarid drainage (Quebrada Maní, ∼21° S, 1000 m a.s.l.) in the Atacama Desert. During the late Holocene, riparian ecosystems and farming social groups flourished in the hyperarid Atacama core as surface water availability increased throughout this presently sterile landscape. Twenty-six radiocarbon dates indicate that these events occurred between 1050–680, 1615–1350 and 2500–2040 cal yr BP. Regional comparisons with rodent middens and other records suggest that these events were synchronous with pluvial stages detected at higher-elevations in the central Andes over the last 2500 yr. These hydroclimate changes also coincide with periods of pronounced SST gradients in the Tropical Pacific (La Niña-like mode), conditions that are conducive to significantly increased rainfall in the central Andean highlands and flood events in the low-elevation watersheds at inter-annual timescales. Our findings indicate that the positive anomalies in the hyperarid Atacama over the past 2500 yr represent a regional response of the central Andean climate system to changes in the global hydrological cycle at centennial timescales. Furthermore, our results provide support for the role of tropical Pacific sea surface temperature gradient changes as the primary mechanism responsible for climate fluctuations in the central Andes. Finally, our results constitute independent evidence for comprehending the major trends in cultural evolution of prehistoric peoples that inhabited the region.

Año: 2012

Palabras claves:

Referencia APA: Gayo, E., Latorre, C., Santoro, C., Maldonado, A., & De Pol-Holz, R. (2012). Hydroclimate variability in the low-elevation Atacama Desert over the last 2500 yr. Climate Of The Past, 8(1), 287-306. http://dx.doi.org/10.5194/cp-8-287-2012

Inter-annual variability of southerly winds in a coastal area of the Atacama Desert: implications for the export of aeolian sediments to the adjacent marine environment.

Autores:

Flores-Aqueveque, V., Alfaro, S., Caquineau, S., Foret, G., Vargas, G., & Rutllant, J.

Resumen:

The analysis of the aeolian content of marine cores collected off the coast of the Atacama Desert (Mejillones Bay, Chile) suggests that marine sediments can record inter-annual to inter-decadal variations in the regional southerly winds responsible for particle entrainment at the surface of the nearby desert. However, the establishment of a simple and direct correlation between the sediment and wind records is complicated by the difference of time scales between the erosion and accumulation processes. The aim of this work is to: (i) assess the inter-annual variability of the surface winds responsible for the sand movements; and (ii) determine whether the integration over periods of several months completely smoothes the rapid changes in characteristics of the transported and deposited aeolian material. To accomplish this aim, 14 years of 10 m hourly wind speed, measured at the Cerro Moreno (Antofagasta) Airport between 1991 and 2003 and at the Orica Station between 2000 and 2004, were analyzed. For each year, the wind speed statistical distribution can be represented by a combination of two to three Weibull functions. Winds of the lowest Weibull mode are too weak to move the sand grains at the surface of the pampa; this is not the case for the intermediate mode and especially for the highest speed mode which are able to erode the arid surface and transport particles to the bay. In each individual year of the period of study, the highest speed mode only accounted for a limited number of strong erosion events. Quantitative analysis of the distribution of the friction velocities and of their impact on erosion using a saltation model suggests that, although all wind speeds above threshold produce erosion events, values around 0·45 m sec−1 contribute less to the erosion flux. This gap allows separation of the erosion events into low and high saltation modes. The correlation (r = 0·997) between the importance of the third Weibull mode and the extent of higher rate saltation indicates that the inter-annual variability of the erosion at the surface of the pampa, as well as the transport of coarse particles (>100 μm), are directly related to inter-annual variations in the prevalence of the strongest winds. Finally, a transport and deposition model is used to assess the possible impact of the wind inter-annual variability on the deposition flux of mineral particles in the bay. The results suggest that inter-annual differences in the wind speed distributions have a quantifiable effect on the intensity and size-distribution of this deposition flux. This observation suggests that a detailed analysis of the sediment cores collected from the bay could be used for reconstructing the inter-annual variability of past winds.

Año: 2012

Palabras claves: Atacama Desert; dust transport and deposition; wind erosion; wind variability.

Referencia APA: Flores-Aqueveque, V., Alfaro, S., Caquineau, S., Foret, G., Vargas, G., & Rutllant, J. (2012). Inter-annual variability of southerly winds in a coastal area of the Atacama Desert: implications for the export of aeolian sediments to the adjacent marine environment. Sedimentology, 59(3), 990-1000.

Functional identity and functional structure change through succession in a rocky intertidal marine herbivore assemblage.

Autores:

Aguilera, M. & Navarrete, S.

Resumen:

Despite the great interest in characterizing the functional structure and resilience of functional groups in natural communities, few studies have examined in which way the roles and relationships of coexisting species change during community succession, a fundamental and natural process that follows the release of new resources in terrestrial and aquatic ecosystems. Variation in algal traits that characterize different phases and stages of community succession on rocky shores are likely to influence the magnitude, direction of effects, and the level of redundancy and complementarity in the diverse assemblage of herbivores. Two separate field experiments were conducted to quantify per capita and population effects and the functional relationship (i.e., redundancy or complementarity) of four herbivore species found in central Chile during early and late algal succession. The first experiment examined grazer effects on the colonization and establishment of early-succession algal species. The second experiment examined effects on the late-successional, dominant corticated alga Mazzaella laminarioides. Complementary laboratory experiments with all species and under natural environmental conditions allowed us to further characterize the collective effects of these species. We found that, during early community succession, all herbivore species had similar effects on the ephemeral algae, ulvoids, but only during the phase of colonization. Once these algae were established, only a subset of the species was able to control their abundance. During late succession, only the keyhole limpet Fissurella crassa could control corticated Mazzaella. The functional relationships among these species changed dramatically from redundant effects on ephemeral algae during early colonization, to a more complementary role on established early-successional algae, to a dominant (i.e., keystone) effect on late succession. This study highlights that functional relationship within consumer assemblages can vary at different phases and times of community succession. Differentiation in herbivore roles emphasizes the need to evaluate consumer's impacts through different times of community succession, and through experimental manipulations to make even broad predictions about the resilience or vulnerability of diverse intertidal assemblages to human disturbances.

Año: 2012

Palabras claves: Chile; ephemeral algae; functional redundancy; functional roles; grazing; herbivores; human impact; interaction strength; keystone species; rocky shore

Referencia APA: Aguilera, M. & Navarrete, S. (2012). Functional identity and functional structure change through succession in a rocky intertidal marine herbivore assemblage. Ecology, 93(1), 75-89. http://dx.doi.org/10.1890/11-0434.1

Recent melt rates of Canadian arctic ice caps are the highest in four millennia. Global And Planetary Change

Autores:

Fisher, D., Zheng, J., Burgess, D., Zdanowicz, C., Kinnard, C., Sharp, M., & Bourgeois, J.

Resumen:

There has been a rapid acceleration in ice-cap melt rates over the last few decades across the entire Canadian Arctic. Present melt rates exceed the past rates for many millennia. New shallow cores at old sites bring their melt series up-to-date. The melt-percentage series from the Devon Island and Agassiz (Ellesmere Island) ice caps are well correlated with the Devon net mass balance and show a large increase in melt since the middle 1990s. Arctic ice core melt series (latitude range of 67 to 81 N) show the last quarter century has had the highest melt in two millennia and The Holocene-long Agassiz melt record shows that the last 25 years has the highest melt in 4200 years. The Agassiz melt rates since the middle 1990s resemble those of the early Holocene thermal maximum over 9000 years ago.

Año: 2012

Palabras claves: Ice core; Melt layers; Holocene; Warming; Ice caps

Referencia APA: Fisher, D., Zheng, J., Burgess, D., Zdanowicz, C., Kinnard, C., Sharp, M., & Bourgeois, J. (2012). Recent melt rates of Canadian arctic ice caps are the highest in four millennia. Global And Planetary Change, 84-85, 3-7.

Nutritional Aspects of Six Quinoa (Chenopodium quinoa Willd.) Ecotypes from three Geographical Areas of Chile. Chilean

Autores:

Miranda, M., Vega-Gálvez, A., Quispe-Fuentes, I., Rodríguez, M., Maureira, H., & Martínez, E.

Resumen:

This study explored the diversity of the quinoa crop in Chile from a nutritional perspective. Nutritional properties, minerals, vitamins, and saponin content were assessed in seeds of six Chilean quinoa (Chenopodium quinoa Willd.) ecotypes grown in three main production areas with distinctive climatic and edaphic conditions: Ancovinto and Cancosa in the North-Altiplano or High Plateau, Cáhuil and Faro in the central coastal area, and Regalona and Villarrica in the south of the country. There were significant differences (P < 0.05) in all the nutritional properties of the quinoa seeds in all three areas. Quinoa of the Villarrica ecotype showed the highest protein content (16.10 g 100 g-1 DM) and the highest content of vitamins E and C (4.644 ± 0.240 and 23.065 ± 1.119 mg 100 g-1 DM, respectively). The highest content of vitamins B1 (0.648 ± 0.006 mg 100 g-1 DM) and B3 (1.569 ± 0.026 mg 100 g-1 DM) was found in the Regalona ecotype, while the highest value of vitamin B2 (0.081 ± 0.002 mg 100 g-1 DM) occurred in the Ancovinto ecotype. Potassium was the most abundant mineral with a maximum value of 2325.56 mg 100 g-1 DM in the Cancosa ecotype. Saponin content varied from 0.84 g 100 g-1 DM in the Villarrica ecotype to 3.91 g 100 g-1 DM in the Cáhuil ecotype. Significant differences were found among the Chilean quinoa ecotypes grown under different climatic conditions; however, all the quinoa seeds exhibited a high nutritional value. These results are compatible with the genetic differences previously observed in the three geographical areas under study. Thus, if more studies are conducted to show the particular properties of quinoa from specific areas, it would be possible in the future to coin the term "controlled designation of origin" (appellation d'origine contrólée) and add commercial value to Chilean quinoa seeds in the domestic and international markets.

Año: 2012

Palabras claves: Quinoa, vitamins, minerals, saponin content, nutritional properties.

Referencia APA: Miranda, M., Vega-Gálvez, A., Quispe-Fuentes, I., Rodríguez, M., Maureira, H., & Martínez, E. (2012). Nutritional Aspects of Six Quinoa (Chenopodium quinoa Willd.) Ecotypes from three Geographical Areas of Chile. Chilean. J. Agric. Res., 72(2), 175-181.

The trade-off between cold resistance and growth determines the Nothofagus pumilio treeline.

Autores:

Molina-Montenegro, M., Gallardo-Cerda, J., Flores, T., & Atala, C.

Resumen:

The upper and poleward limit of tree distribution are usually determined by abiotic factors such as low temperature and strong winds. Thus, cold resistance is a key element for survival in high altitudes and latitudes where conditions can reduce plant growth. A trade-off between resource allocation to cold resistance and growth could emerge in populations frequently exposed to low temperatures like those in the treeline zone. We studied annual height growth and ice nucleation temperature in Nothofagus pumilio (Nothofagaceae) populations growing in its extremes of altitudinal distribution and in 3 sites situated on a latitudinal gradient in the Chilean Andes. Additionally, gas exchange, water and nitrogen use efficiency and total soluble sugar (TSS) were also measured as possible mechanisms for survival in high altitudes. Individuals from the treeline populations showed lower annual height growth and lower ice nucleation temperatures compared with those from lower populations. In the same way, individuals from more poleward populations showed lower annual height growth and lower ice nucleation temperatures. Gas exchange, water and nitrogen use efficiency and TSS were also higher in the high altitude populations. The results obtained support the hypothesis of trade-off, because the upper and poleward populations showed more cold resistance but a lower height growth. Additionally, we show that cold resistance mechanisms do not impact the physiological performance, suggesting possible adaptation of the high altitude populations. Low temperatures may be affecting cellular growth instead of photosynthesis, creating a pool of carbohydrates that could participate in cold tolerance. Other abiotic and biotic factors should be also assessed to fully understand the distributional range of Nothofagus species.

Año: 2012

Palabras claves: Height growth, Los Andes, Photosynthesis, Treeline, Environmental gradients, Ice nucleation.

Referencia APA: Molina-Montenegro, M., Gallardo-Cerda, J., Flores, T., & Atala, C. (2012). The trade-off between cold resistance and growth determines the Nothofagus pumilio treeline. Plant Ecol, 213(1), 133-142.

Upwelling response to atmospheric coastal jets off central Chile: A modeling study of the October 2000 event.

Autores:

Renault, L., Dewitte, B., Marchesiello, P., Illig, S., Echevin, V., & Cambon, G., Ramos, M., Astudillo, O., Minnis, P., Ayers, J.K.

Resumen:

The spatial and temporal variability of nearshore winds in eastern boundary current systems affect the oceanic heat balance that drives sea surface temperature changes. In this study, regional atmospheric and oceanic simulations are used to document such processes during an atmospheric coastal jet event off central Chile. The event is well reproduced by the atmospheric model and is associated with the migration of an anomalous anticyclone in the southeastern Pacific region during October 2000. A robust feature of the simulation is a sharp coastal wind dropoff, which is insensitive to model resolution. As expected, the simulated oceanic response is a significant sea surface cooling. A surface heat budget analysis shows that vertical mixing is a major contributor to the cooling tendency both in the jet core area and in the nearshore zone where the magnitude of this term is comparable to the magnitude of vertical advection. Sensitivity experiments show that the oceanic response in the coastal area is sensitive to wind dropoff representation. This is because total upwelling, i.e., the sum of coastal upwelling and Ekman pumping, depends on the scale of wind dropoff. Because the latter is much larger than the upwelling scale, coastal wind dropoff has only a weak positive effect on vertical velocities driven by Ekman pumping but has a strong negative effect on coastal upwelling. Interestingly though, the weakening of coastal winds in the dropoff zone has a larger effect on vertical mixing than on vertical advection, with both effects contributing to a reduction of cooling.

Año: 2012

Palabras claves: atmospheric coastal jets; eastern boundary current systems; numerical simulation; ocean/atmosphere interactions; upwelling; wind dropoff

Referencia APA: Renault, L., Dewitte, B., Marchesiello, P., Illig, S., Echevin, V., & Cambon, G., Ramos, M., Astudillo, O., Minnis, P., Ayers, J.K. (2012). Upwelling response to atmospheric coastal jets off central Chile: A modeling study of the October 2000 event. J. Geophys. Res., 117(C2), n/a-n/a.

Interspecific Competition for Shelters in Territorial and Gregarious Intertidal Grazers: Consequences for Individual Behaviour.

Autores:

Aguilera, M. & Navarrete, S.

Resumen:

Experiments have shown that interspecific interactions within consumer guilds can alter patterns of distribution, abundance and size of species. Plastic behavioural responses can be modulated by agonistic interactions. In many cases, consumers compete for space and shelters, and these interactions change the manner in which they exploit food. This study investigates the consequences of competition in the spatial and temporal organization of behaviour of intertidal grazers, which share algal resources and the use of rock crevices while resting, but exhibit different body sizes, spatial behaviour and foraging modes. We evaluate interaction strength between small gregarious Siphonaria lessoni and the larger territorial keyhole limpet Fissurella crassa and between S. lessoni and the medium-size gregarious chiton Chiton granosus. Using field manipulations and artificial arenas in the laboratory, we tested whether the use of crevices, micro-spatial distribution and activity are modified by the density of conspecifics and the presence of heterospecifics. Our results show that small-scale spatial segregation observed in the field between S. lessoni and C. granosus result from species-specific differences in habitat use. In turn, we found evidence that spatial segregation between F. crassa and S. lessoni results from highly asymmetric interference competition in the use of shelters. The presence of F. crassa reduced the use of crevices and growth rates of S. lessoni. Effects on growth rates are assumed to result from exposure to harsh environmental conditions rather than food limitation. Thus, neither gregarious behaviour nor differences in activity were sufficient to prevent competition with the larger grazer. Our study illustrates the importance of competition for shelters, which results in behavioural changes of the smaller-sized species, and how these plastic responses can translate into differences in growth rates. Use of shelters can thus be modulated by environmental conditions in a species-specific as well as an interactive manner within consumers’ guilds.

Año: 2012

Palabras claves: Foraging, Shelters, Herbivory, Physiological parameters, Species interactions, Trophic interactions, Food, Predation.

Referencia APA: Aguilera, M. & Navarrete, S. (2012). Interspecific Competition for Shelters in Territorial and Gregarious Intertidal Grazers: Consequences for Individual Behaviour. Plos ONE, 7(9), e46205.

What do we know about high-altitude precipitation in the semi-arid Andes of Chile?

Autores:

Bourgin P, Andreassian V, Gascoin S, Valery A.

Resumen:

Mapping precipitations on a regular grid is often required for hydrological and ecological modelling. The spatial interpolation methods are generally used to estimate such a distribution from ground-based measurements. In the case of mountainous areas, the estimation of precipitation amounts is still a challenging task and the results of spatial interpolation should be verified as much as possible. Here we describe a three-steps method for the validation of a precipitation map. This is used in the context of a mountainous semi-arid region, the Norte Chico in Chile (26°S-32°S). The implementation of this validation method showed the benefits of an interpolation method developed by Valéry [2010] for mountainous areas. The hydrological balance of the high-altitude watersheds is now more realistic.

Año: 2012

Palabras claves: Precipitation, spatial interpolation method, extrapolation, altitude, altitudinal corrections, validation, water equivalent, water balance.

Referencia APA: Bourgin P, Andreassian V, Gascoin S, Valery A. (2012). Que sait-on des précipitations en altitude dans les Andes semi-arides du Chili?. La Houille Blanche. 2012;(2):12-17.