Browsing by Author "Contreras, Sergio"

Now showing 1 - 7 of 7
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    Cosmic web alignments with the shape, angular momentum and peculiar velocities of dark matter haloes
    (2014) Forero Romero, Jaime E.; Contreras, Sergio; Padilla, Nelson
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    Evaluating the isotopic composition of leaf organic compounds in fog-dependent Tillandsia landbeckii across the coastal Atacama Desert: Implications for hydroclimate reconstructions at the dry limit
    (2024) Jaeschke, Andrea; Boehm, Christoph; Schween, Jan H.; Schefuss, Enno; Koch, Marcus A.; Latorre, Claudio; Contreras, Sergio; Rethemeyer, Janet; Wissel, Holger; Luecke, Andreas
    Fog is an important component of the coastal climate of northern Chile and southern Peru. Moisture and nutrients from fog maintain highly endemic vegetation (lomas) as well as unique Tillandsia landbeckii ecosystems that thrive at elevations of ca. 900-1200 m asl. Although this epiphytic CAM bromeliad is well adapted to the extreme climate, declining Tillandsia stocks observed over the past decades question the long-term survival with ongoing climate change. Here, we aim at better understanding the hydroclimatic signal encoded in the leaf organic compounds of Tillandsia landbeckii across the Atacama Desert's coastal mountain range (ca. 18-21 degrees S). First, we investigate spatiotemporal patterns of fog occurrence and related moisture sources available for the plants applying a new satellite -based fog -detection approach. We then use stable carbon, oxygen and hydrogen ( delta 13 C, delta 18 O, delta D) isotope analysis of leaf wax n -alkanes and cellulose to identify photosynthetic pathway as well as environmental and physiological processes that shape the isotopic composition in Tillandsia landbeckii . We find that leaf wax n -alkanes and cellulose reflect the balance of climatic and physiological drivers differently. While n - alkane delta D values more closely follow changes in precipitation delta D, evaporative enrichment seems to have a dominant influence on cellulose delta 18 O values. Cellulose delta D values are highly enriched compared to n -alkane delta D values, likely reflecting a predominant metabolic imprint on delta D. delta 13 C signatures in the organic compounds are valid proxies for CAM activity. Our results prove the general applicability of the isotopic biomarkers for reconstructing environmental change in the coastal Atacama Desert. This approach can be extended globally to west -coast deserts that share fog as a major source of moisture.
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    Hydroclimate variations over the last 17,000 years as estimated by leaf waxes in rodent middens from the south-central Atacama Desert, Chile
    (2023) Frugone-Alvarez, Matias; Contreras, Sergio; Meseguer-Ruiz, Oliver; Tejos, Eduardo; Delgado-Huertas, Antonio; Valero-Garces, Blas; Diaz, Francisca P.; Briceno, Matias; Bustos-Morales, Manuel; Latorre, Claudio
    Leaf cuticular waxes are one of the most important environment-plant interaction structural systems that enable desert plants to withstand extreme climatic conditions. We present a long chain n-alkyl lipids study in fresh plant leaves and rodent palaeomiddens collected along an elevational gradient in the south-central Atacama Desert of Chile, covering six different vegetation belts: Steppe (4500-4000 m asl), Puna (4000-3300 m asl), pre-Puna (3300-2400 m asl), Absolute Desert (2400-1000 m asl) and Coastal Desert (1000-0 m asl). The 28 rodent palaeomiddens analyzed from Quebrada Incahuasi (25.6 & DEG;S, 3600 m asl) span the last 17,000 years. Modern-day distribution of long-chain n-alkanes and n-alkanoic acids varies among the dominant plant associations of the Atacama Desert. These plants show a species -specific chemotaxonomy linked to the climatic conditions. Furthermore, differences in average chain length (ACL) and carbon preference index (CPI) suggest that these plant communities are highly adapted to extreme environmental conditions. The sum of leaf wax n-alkanes was highest under wet conditions, while n-alkanoic acids (between n -C24 and n -C28) increased with hyperaridity. Similarly, analysis of n- alkane time series from palaeomiddens showed that the greatest changes in leaf wax n-alkane distri-butions (ACL and CPI) corresponded to the greatest increases in moisture during the Central Andean Pluvial Event (CAPE; between 18 and 9 ka cal BP) and the Late Holocene. The shift in the palaeomidden n- alkane distributions is corroborated by the relative abundance of rainfall-dependent extra-local taxa. This is the first study to report leaf wax content obtained from ancient rodent middens, and shows promising results as a robust hydroclimate proxy for the Atacama Desert region. & COPY; 2023 Published by Elsevier Ltd.
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    Leaf wax composition and distribution of Tillandsia landbeckii reflects moisture gradient across the hyperarid Atacama Desert
    (2022) Contreras, Sergio; Landahur, Manlio; Garcia, Karla; Latorre, Claudio; Reyers, Mark; Rethemeyer, Janet; Jaeschke, Andrea
    In the hyperarid Atacama Desert, water availability plays a crucial role in allowing plant survival. Along with scant rainfall, marine advective fog frequently occurs along the coastal escarpment fueling isolated mono-specific patches of Tillandsia vegetation. In this study, we investigate the lipid biomarker composition of the bromeliad Tillandsia landbeckii (CAM plant) to assess structural adaptations at the molecular level as a response to extremely arid conditions. We analyzed long-chain n-alkanes and fatty acids in living specimens (n = 59) collected from the main Tillandsia dune ecosystems across a 350 km coastal transect. We found that the leaf wax composition was dominated by n-alkanes with concentrations (total average 160.8 +/- 91.4 mu g/g) up to three times higher than fatty acids (66.7 +/- 40.7 mu g/g), likely as an adaptation to the hyperarid environment. Significant differences were found in leaf wax distribution (Average Chain Length [ACL] and Carbon Preference Index [CPI]) in the northern zone relative to the central and southern zones. We found strong negative correlations between fatty acid CPI and n-alkane ACL with precipitation and surface evaporation pointing at fine-scale adaptations to low moisture availability along the coastal transect. Moreover, our data indicate that the predominance of n-alkanes is reflecting the function of the wax in preventing water loss from the leaves. The hyperarid conditions and good preservation potential of both n-alkanes and fatty acids make them ideal tracers to study late Holocene climate change in the Atacama Desert.
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    The assembly bias of emission-line galaxies
    (2021) Jimenez, Esteban; Padilla, Nelson; Contreras, Sergio; Zehavi, Idit; Baugh, Carlton M.; Orsi, Alvaro
    The next generation of spectroscopic surveys will target emission-line galaxies (ELGs) to produce constraints on cosmological parameters. We study the large-scale structure traced by ELGs using a combination of a semi-analytical model of galaxy formation, a code that computes the nebular emission from H II regions using the properties of the interstellar medium, and a large-volume, high-resolution N-body simulation. We consider fixed number density samples where galaxies are selected by their H alpha, [O III] lambda 5007, or [O II] lambda lambda 3727-3729 emission-line luminosities. We investigate the assembly bias signatures of these samples, and compare them to those of stellar mass- and star formation rate-selected samples. Interestingly, we find that the [O III]- and [O II]-selected samples display scale-dependent bias on large scales and that their assembly bias signatures are also scale dependent. Both these effects are more pronounced for lower number density samples. The [O III] and [O II] emitters that contribute most to the scale dependence tend to have a low gas-phase metallicity and are preferentially found in low-density regions. We also measure the baryon acoustic oscillation (BAO) feature and the beta parameter related to the growth rate of overdensities. We find that the scale of the BAO peak is roughly the same for all selections and that beta is scale dependent at large scales. Our results suggest that ELG samples include environmental effects that should be modelled in order to remove potential systematic errors that could affect the estimation of cosmological parameters.
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    The impact of assembly bias on the galaxy content of dark matter halos
    (2018) Zehavi, Idit; Contreras, Sergio; Padilla, Nelson; Smith, Nicholas J.; Baugh, Carlton M.; Norberg, Peder
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    The origin of the atomic and molecular gas contents of early-type galaxies – II. Misaligned gas accretion
    (2015) Lagos, C.; Padilla, Nelson; Davis, Timothy A.; Lacey, C.; Baugh, Carlton M.; González, Violeta F.; Zwaan, M. A.; Contreras, Sergio