Climatic and environmental controls on the occurrence and distributions of long chain alkenones in lakes of the interior United States   总被引：1，自引：0，他引：1  

Jaime L. Toney  Yongsong Huang  Sherilyn C. Fritz  Eric Grimm 《Geochimica et cosmochimica acta》2010,74(5):1563-7565

Long chain alkenones (LCA) are temperature-sensitive lipids with great potential for quantitative reconstruction of past continental climate. We conducted the first survey for alkenone biomarkers from 55 different lakes in the Northern Great Plains and Nebraska Sand Hills of the United States. Among those surveyed, we found 13 lakes that contain LCAs in the surface sediments. The highest concentrations of alkenones in sediments are found in cold (mean annual air temperature ∼11 °C versus 17 °C in our warmest sites), brackish to mesosaline (salinity = 8.5-9.7 g/L), and alkaline (pH = 8.4-9.0) lakes with high concentrations of sodium and sulfate. The dynamics of stratification and nutrient availability also appear to play a role in LCA abundance, as early spring mixing promotes a bloom of alkenone-producing haptophytes. Four of the alkenone-containing sites contain the C_37:4 alkenone; however, we discovered an unprecedented lacustrine alkenone distribution in a cluster of lakes, with a total absence of C_37:4 alkenone. We attribute this unusual composition to a different haptophyte species and show that the sulfate:carbonate ratio may control the occurrence of these two distinct populations. We created a new in-situ temperature calibration for lacustrine sites that contain C_37:4 using a water-column calibration from Lake George, ND and show that is linearly correlated to lake water temperature (R² = 0.74), but is not. A number of lakes contain an unidentified compound series that elutes close to the LCAs, highlighting the importance of routine GC-MS examination prior to using lacustrine LCAs for paleotemperature reconstructions.  相似文献   

Assessing the vulnerability of over-exploited volcanic aquifer systems using multi-parameter analysis,Toluca Basin,Mexico   总被引：1，自引：0，他引：1  

J. Hancox  Jaime Gárfias  R. Aravena  D. Rudolph 《Environmental Earth Sciences》2010,59(8):1643-1660

The potential for contamination of groundwater in an over-exploited system led to this investigation on aspects of aquifer vulnerability in the Toluca Basin, Mexico. This study involved the use of various hydrogeological, geochemical and isotopic tools to better understand the susceptibility to contamination where heavy groundwater extraction along with industrial extensive development is concentrated. Geochemical and isotopic analyses of groundwater from production wells along the mountain boundary show little evidence of contamination at present time. Radiocarbon and tritium data collected in piezometers and wells penetrating the Lower basalt aquifer indicate that the groundwater is of varying age and quality. These data, in addition to stable isotope and chemical data also indicate evidence of contamination in the Lower aquifer; which could be associated with fast recharge in the mountains or injection of waste water by illegal wells. Evidence found in this study of low downward gradients in the valley fill sediments and the presence of low permeability aquitard deposits suggest that the aquifer system is currently not highly threatened by surface sources of contamination. However, where urban and industrial development occurs, in the centre of the valley and along the flanks of the Basin, the vulnerability of the aquifer system increases significantly.  相似文献   

Multi-platform model assessment in the Western Mediterranean Sea: impact of downscaling on the surface circulation and mesoscale activity     

Aguiar  Eva  Mourre  Baptiste  Juza  Mélanie  Reyes  Emma  Hernández-Lasheras  Jaime  Cutolo  Eugenio  Mason  Evan  Tintoré  Joaquín 《Ocean Dynamics》2020,70(2):273-288

Ocean Dynamics - In numerical ocean modeling, dynamical downscaling is the approach consisting in generating high-resolution regional simulations exploiting the information from coarser resolution...  相似文献   

Robert N. Farvolden − Pioneering contributions in Mexican hydrogeology     

Alejandra Cortes  Jaime Durazo 《Hydrogeology Journal》2000,8(2):251-253

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Foreword to Special Issue: Modeling Subsurface Flow     

J. Jaime Gómez-Hernández  Clayton V. Deutsch 《Mathematical Geology》1999,31(7):747-748

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Simulation of Non-Gaussian Transmissivity Fields Honoring Piezometric Data and Integrating Soft and Secondary Information   总被引：1，自引：0，他引：1  

José E. Capilla  Javier Rodrigo  J. Jaime Gómez-Hernández 《Mathematical Geology》1999,31(7):907-927

The conditional probabilities (CP) method implements a new procedure for the generation of transmissivity fields conditional to piezometric head data capable to sample nonmulti-Gaussian random functions and to integrate soft and secondary information. The CP method combines the advantages of the self-calibrated (SC) method with probability fields to circumvent some of the drawbacks of the SC method—namely, its difficulty to integrate soft and secondary information or to generate non-Gaussian fields. The SC method is based on the perturbation of a seed transmissivity field already conditional to transmissivity and secondary data, with the perturbation being function of the transmissivity variogram. The CP method is also based on the perturbation of a seed field; however, the perturbation is made function of the full transmissivity bivariate distribution and of the correlation to the secondary data. The two methods are applied to a sample of an exhaustive non-Gaussian data set of natural origin to demonstrate the interest of using a simulation method that is capable to model the spatial patterns of transmissivity variability beyond the variogram. A comparison of the probabilistic predictions of convective transport derived from a Monte Carlo exercise using both methods demonstrates the superiority of the CP method when the underlying spatial variability is non-Gaussian.  相似文献   

New evidence of sea‐level lowstands and paleoenvironment during MIS 6 and 4 in the Cantabrian coastal karst: the Cobiheru cave (North Iberia)          下载免费PDF全文

Daniel Ballesteros  Laura Rodríguez‐Rodríguez  Saúl González‐Lemos  Santiago Giralt  Diego Jaime Álvarez‐Lao  Luna Adrados  Montserrat Jiménez‐Sánchez 《地球表面变化过程与地形》2017,42(11):1704-1716

The geomorphological evolution of the Cobiheru Cave shows the influence of the non‐carbonate coastal mountain ranges on coastal karst evolution, as well as the temporal distribution of the cold‐adapted fauna sites in the Cantabrian Coast. Geomorphological observation and uranium/thorium (U/Th) dating lead to the construction of an evolution model. The model comprises two episodes of cave deposition occurring at c. 60–70 and 130–150 ka, linked to cold climate conditions, global sea‐level lowstands and the erosion of alluvial fans that covered the karst. Moreover, the comparison between the Cobiheru record and some raised beaches identified in previous studies sets the beginning of the sea‐level lowering in the Cantabrian Sea during the marine isotope stages (MIS) 5–4 transition. Two palaeoenvironments are inferred based on finding Equus ferus and Elona quimperiana. A wet deciduous forest would have developed on the emerged marine terrace of the Cobiheru Cave since at least the Middle Pleistocene, and an open landscape with scarce vegetation would have been present at c. 65 ka. The erosional event identified in the Cobiheru Cave helps to understand the temporal distribution of cold‐adapted mammals located in the Asturias region. The probable sites of cold‐adapted fauna developed in caves and alluvial fans would have disappeared after 65 ka. Therefore, palaeontological and palaeoclimate research based on cold‐adapted mammals suggests the occurrence of an hiatus in the palaeontological record prior to 50 ka. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Measurement and modelling evaporation for irrigated crops in north-west Mexico     

Jaime Garatuza-Payan  W. James Shuttleworth  David Encinas  David D. McNeil  John B. Stewart  Henk deBruin  Christopher Watts 《水文研究》1998,12(9):1397-1418

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Regional analysis of indirect factors affecting the recovery,degradation and deforestation in the tropical dry forests of Oaxaca,Mexico     

Francisco Guerra‐Martínez  Arturo García‐Romero  Andrea Cruz‐Mendoza  Laura Osorio‐Olvera 《Singapore journal of tropical geography》2019,40(3):387-409

This study evaluates the dynamics and identifies the indirect biophysical and socio‐economic factors related to the recovery, degradation and deforestation of the tropical dry forest (TDF) cover in the municipality of Tehuantepec, Oaxaca, Mexico. Annual rates and transition matrices were determined to identify indirect factors; the cartographic information of 25 variables with shift points were overlaid and Generalized Linear Models (GLM) were applied. The change process with the greatest impact in TDF during the study period (1993–2011) was degradation, with 10468 ha degraded (12 per cent of the initial tropical cover); recovery of coverage was the second most important change process, with 4808 ha (5.5 per cent); and deforestation was the change process with the lowest impact, with a loss of 2800 ha (3.23 per cent). The net balance was negative, with a decrease (through land degradation and deforestation) of 8460 ha (9.75 per cent). The recovery of coverage was mainly associated with biophysical factors such as land suitability and accessibility to natural vegetation. On the other hand, deforestation and degradation of coverage were associated with both biophysical and socioeconomic factors such as land suitability, accessibility to natural vegetation, migration, marginalization, population pressure, economy, education and health. The findings of this study determined the spatial distribution of forest recovery, deforestation and degradation processes at a regional level, allowing for future researchers to focus their efforts at local and landscape levels. Also, the work allows for an approximation of the factors associated with the change processes studied, hence supporting the allocation of resources for the establishment of management, conservation, development and restoration strategies of tropical dry forests at the regional level.  相似文献