Exploring possible connections between hydrological extreme events and climate change in central south Chile

Abstract

Motivated by recent extreme flow events in the Mataquito River located in the Mediterranean region of Chile, we performed a detailed trend analysis of critical hydroclimatic variables based on observed daily flow, precipitation and temperature within the basin. For the period 1976–2008, positive trends in temperature were observed, especially during spring and summer months. At the same time, we found negative trends in the frequency and intensity of precipitation, especially during spring months. We observed an increasing difference between average streamflow in the rainy season as compared to the snowmelt season. Part of this trend is caused by larger flows during autumn months, although no positive precipitation trends are observed for these months. Finally, significant reductions in minimum flow during spring/summer and a disproportionate concentration of high-flow events occurring in the last 10 years were also identified. These high-flow events tend to happen during autumn months, and are associated with high precipitation and high minimum temperatures. Based on a simple assessment of changes in irrigated agriculture and land use, we concluded that other non-climatic factors seem not to be as relevant to the detected flow trends. All these results are in accord with future climate change scenarios that show an increase in temperature, a reduction in average precipitation and a reduction in snow accumulation. Such future scenarios could seriously hamper the development of economic activities in this basin, exemplifying also a fate that may be shared by other similar basins in Chile and in other regions of the world.

Editor Z.W. Kundzewicz

Citation Vicuña, S., Gironás, J., Meza, F.J., Cruzat, M.L., Jelinek, M., Bustos, E., Poblete, D., and Bambach, N., 2013. Exploring possible connections between hydrological extreme events and climate change in central south Chile. Hydrological Sciences Journal, 58 (8), 1598–1619.     

Dynamic stresses in an elastic half-space

This paper deals with the problem of time-varying point loads applied onto the surface of an elastic half-space and the stresses that such loads elicit within that medium. The emphasis is on the evaluation of the isobaric contours for all six of the stress components at various frequencies of engineering interest and for a full range of Poisson’s ratios. The extensive set of pressure bulbs presented herein may be of help in predicting the severity of dynamic effects in common practical situations in engineering—or even the lack thereof.     

The Cretaceous sediment-hosted copper deposits of San Marcos (Coahuila,Northeastern Mexico): An approach to ore-forming processes

In the San Marcos ranges of Cuatrociénegas, NE Mexico, several sediment-hosted copper deposits occur within the boundary between the Coahuila Block, a basement high mostly granitic in composition and Late Paleozoic to Triassic in age, and the Mesozoic Sabinas rift basin. This boundary is outlined by the regional-scale synsedimentary San Marcos Fault. At the basin scale, the copper mineralization occurs at the top of a ～1000 m thick red-bed succession (San Marcos Formation, Berrisian), a few meters below a conformable, transitional contact with micritic limestones (Cupido Formation, Hauterivian to Aptian). It consists of successive decimeter-thick roughly stratiform copper-rich horizons placed just above the red-beds, in a transitional unit of carbonaceous grey-beds grading to micritic limestones. The host rocks are fine- to medium-grained arkoses, with poorly sorted and subangular to subrounded grains. The detrital grains are cemented by quartz and minor calcite; besides, late iron oxide grain-coating cement occurs at the footwall unmineralized red-beds. The source area of the sediments, indicated by their modal composition, is an uplifted basement. The contents of SiO₂ (40.70–87.50 wt.%), Al₂O₃ (5.91–22.00 wt.%), K₂O (3.68–12.50 wt.%), Na₂O (0.03–2.03 wt.%) and CaO (0.09–3.78 wt.%) are within the ranges expected for arkoses. Major oxide ratios indicate that the sedimentary-tectonic setting was a passive margin.The outcropping copper mineralization essentially consists in a supergene assemblage of chrysocolla, malachite and azurite. All that remains of the primary mineralization are micron-sized chalcocite grains shielded by quartz cement. In addition, pyrite subhedral grains occur scattered throughout the copper-mineralized horizons. In these weathered orebodies copper contents range between 4.24 and 7.72 wt.%, silver between 5 and 92 ppm, and cobalt from 8 to 91 ppm. Microthermometric measurements of fluid inclusions in quartz and calcite crystals from footwall barren veinlets gave temperatures of homogenization between 98 °C and 165 °C, and ice-melting temperatures between ?42.5 °C and ?26.1 °C.The primary copper mineralization formed during the early diagenesis, contemporary with the active life of the Sabinas Basin. The mineralizing fluids were dense, near neutral, moderately oxidized brines that originally formed from seawater that, driven by gravity, infiltrated to the deepest parts of the basin and dissolved evaporites. As a result, they became hydrothermal fluids of moderate temperature capable of leaching high amounts of copper. The source of this metal could be mafic detrital grains and iron oxides of the underlying Jurassic and Lower Cretaceous red-beds. Copper precipitation took place when the brines passed through the redox boundary marked by the transition from red- to grey-beds. The upward movement of the brines was promoted by a high heat flow that allowed their convective circulation and their ascent along the synsedimentary San Marcos Fault.     

European summer temperature response to annually dated volcanic eruptions over the past nine centuries

The drop in temperature following large volcanic eruptions has been identified as an important component of natural climate variability. However, due to the limited number of large eruptions that occurred during the period of instrumental observations, the precise amplitude of post-volcanic cooling is not well constrained. Here we present new evidence on summer temperature cooling over Europe in years following volcanic eruptions. We compile and analyze an updated network of tree-ring maximum latewood density chronologies, spanning the past nine centuries, and compare cooling signatures in this network with exceptionally long instrumental station records and state-of-the-art general circulation models. Results indicate post-volcanic June–August cooling is strongest in Northern Europe 2 years after an eruption (?0.52?±?0.05 °C), whereas in Central Europe the temperature response is smaller and occurs 1 year after an eruption (?0.18?±?0.07 °C). We validate these estimates by comparison with the shorter instrumental network and evaluate the statistical significance of post-volcanic summer temperature cooling in the context of natural climate variability over the past nine centuries. Finding no significant post-volcanic temperature cooling lasting longer than 2 years, our results question the ability of large eruptions to initiate long-term temperature changes through feedback mechanisms in the climate system. We discuss the implications of these findings with respect to the response seen in general circulation models and emphasize the importance of considering well-documented, annually dated eruptions when assessing the significance of volcanic forcing on continental-scale temperature variations.     

Decreasing precipitation extremes at higher temperatures in tropical regions

It has been often accepted that rising troposphere temperatures will lead to higher precipitation intensities. This argument is based on the Clausius?CClapeyron (C?CC) relation, which indicates an increase in atmospheric moisture storage capacity of approximately 7?% K^?1. However, recent studies carried out in mid-latitude regions indicate that changes in precipitation intensity as a function of temperature do not necessarily follow the C?CC relation. This study aimed to evaluate the correlation between precipitation extremes and temperature in tropical regions, using measured data obtained at low latitude ranges over Brazil. The results indicate that, at daily timescale, the C?CC relation alone is unlikely to explain the relation between precipitation extremes and temperatures in tropical regions. Additional aspects, such as moisture availability and the duration of precipitation events, should be further analyzed to allow a comprehensive understanding of the relationship between temperature and precipitation intensity. Moreover, we show that in tropical regions, higher temperatures may reduce the magnitude of extreme precipitation events at daily timescales, independent of the season of the year.     

Mesoscale and Nutrient Conditions Associated with the Massive 2008 Cochlodinium polykrikoides Bloom in the Sea of Oman/Arabian Gulf

Cochlodinium polykrikoides formed large blooms in the coastal waters of Oman from October 2008 through mid-January 2009, and satellite images from Aqua-MODIS and region-wide reports suggest that this bloom was found throughout the Arabian Gulf and Sea of Oman for more than 10 months. The unusual occurrence of this species appears to have supplanted the more regularly occurring bloom species, Noctiluca scintillans, in 2008–2009. For the first 2 weeks of the coastal Omani bloom, C. polykrikoides abundance was near monospecific proportions, with cell densities ranging from 4.6?×?10³ to 9?×?10⁶ cells L^?1 and very high levels of chlorophyll a (78.0 μg L^?1) were also recorded. The regional progression of the bloom likely began with stronger than normal upwelling along the Iranian and northern Omani coasts during the southwest monsoon in late summer, followed by discharge of unusually warm coastal plume water along the coast of Oman with the reversal of monsoonal winds in late October. The occurrence and persistence of high densities of C. polykrikoides in Oman coastal water were also significantly influenced by an elevated nutrient load and warmer than normal temperatures. Concentrations of nutrients, especially NH₄ ⁺, urea, PO₄ ^3?, and organic nitrogen and phosphorus, were manyfold higher than observed in the year prior or since. These findings suggest that mesoscale features were important in bloom dynamics more regionally, but locally the bloom was sustained by nutrient enrichment supplemented by its mixotrophic capabilities.     

The Rhyacian E1 Cortijo suture zone： Aeromagnetic signature and insights for the geodynamic evolution of the southwestern Rio de la Plata craton,Argentina

The amalgamation of the southern Río de la Plata craton involves two possibly coeval Rhyacian sutures associated with the Transamazonian orogeny,rather than a single one as previously envisaged,i.e.the El Cortijo suture zone and the Salado suture.We circumscribe the Tandilia terrane to the region between these two sutures.The El Cortijo suture zone runs along a roughly WNW oriented magnetic low aligned along the southern boundary of the Tandilia terrane,i.e.boundary between the Tandilia and Balcarce terranes.This extensive magnetic low,ca.300 km long,and ca.90 km wide,would be caused by demagnetization associated with shearing.At a more local scale,the trend of the El Cortijo suture zone often turns toward the EeW.At this scale,WNW trending tholeiitic dykes of Statherian age are seen to cut the Rhyacian El Cortijo suture zone.Spatially associated with the El Cortijo suture zone,there are small magnetic highs interpreted to be related to unexposed basic bodies of ophiolitic nature related to those forming part of the El Cortijo Formation.We envisage the pre-Neoproterozoic evolution of the Tandilia belt to have been initiated by the extension of Neoarchean(w2650 Ma)crust occurred during Siderian times(2500e2300 Ma),causing the separation between the Balcarce,Tandilia and Buenos Aires terranes,and the development of narrow oceans at both north and south sides of the Tandilia terrane,accompanied by w2300e2200 Ma sedimentation over transitional econtinental to oceanice crust,and arc magmatism developed in the Tandilia terrane.The island arc represented by the El Cortijo Formation was also developed at this time.At late Rhyacian times,it occurred in both the closure of the narrow oceans developed previously,the entrapment of the El Cortijo island arc,as well as anatectic magmatism in the Balcarce terrane.     

http://www.sciencedirect.com/science/article/pii/S1674987113000571

The amalgamation of the southern Río de la Plata craton involves two possibly coeval Rhyacian sutures associated with the Transamazonian orogeny,rather than a single one as previously envisaged,i.e.the El Cortijo suture zone and the Salado suture.We circumscribe the Tandilia terrane to the region between these two sutures.The El Cortijo suture zone runs along a roughly WNW oriented magnetic low aligned along the southern boundary of the Tandilia terrane,i.e.boundary between the Tandilia and Balcarce terranes.This extensive magnetic low,ca.300 km long,and ca.90 km wide,would be caused by demagnetization associated with shearing.At a more local scale,the trend of the El Cortijo suture zone often turns toward the EeW.At this scale,WNW trending tholeiitic dykes of Statherian age are seen to cut the Rhyacian El Cortijo suture zone.Spatially associated with the El Cortijo suture zone,there are small magnetic highs interpreted to be related to unexposed basic bodies of ophiolitic nature related to those forming part of the El Cortijo Formation.We envisage the pre-Neoproterozoic evolution of the Tandilia belt to have been initiated by the extension of Neoarchean(w2650 Ma)crust occurred during Siderian times(2500e2300 Ma),causing the separation between the Balcarce,Tandilia and Buenos Aires terranes,and the development of narrow oceans at both north and south sides of the Tandilia terrane,accompanied by w2300e2200 Ma sedimentation over transitional econtinental to oceanice crust,and arc magmatism developed in the Tandilia terrane.The island arc represented by the El Cortijo Formation was also developed at this time.At late Rhyacian times,it occurred in both the closure of the narrow oceans developed previously,the entrapment of the El Cortijo island arc,as well as anatectic magmatism in the Balcarce terrane.