Stability of massive ground ice bodies in University Valley,McMurdo Dry Valleys of Antarctica: Using stable O–H isotope as tracers of sublimation in hyper-arid regions     

Denis Lacelle  Alfonso F. Davila  Wayne H. Pollard  Dale Andersen  Jennifer Heldmann  Margarita Marinova  Christopher P. McKay 《Earth and Planetary Science Letters》2011,301(1-2):403-411

To date, studies of the stability of subsurface ice in the McMurdo Dry Valleys of Antarctica have been mainly based on climate-based vapor diffusion models. In University Valley (1800 m), a small glacier is found at the base of the head of the valley, and adjacent to the glacier, a buried body of massive ice was uncovered beneath 20–40 cm of loose cryotic sediments and sandstone boulders. This study assesses the origin and stability of the buried body of massive ice by measuring the geochemistry and stable O–H isotope composition of the ice and applies a sublimation and molecular diffusion model that accounts for the observed trends. The results indicate that the buried massive ice body represents an extension of the adjacent glacier that was buried by a rock avalanche during a cold climate period. The contrasting δ¹⁸O profiles and regression slope values between the uppermost 6 cm of the buried massive ice (upward convex δ¹⁸O profile and S_D-18O = 5.1) and that below it (progressive increase in δ¹⁸O and S_D-18O = 6.4) suggest independent post-depositional processes affected the isotope composition of the ice. The upward convex δ¹⁸O profile in the uppermost 6 cm is consistent with the ice undergoing sublimation. Using a sublimation and molecular diffusion model, and assuming that diffusion occurred through solid ice, the sublimation rate needed to fit the measured δ¹⁸O profile is 0.2 ? 10^? 3 mm yr^? 1, a value that is more similar to net ice removal rates derived from ³He data from cobbles in Beacon Valley till (7.0 ? 10^? 3 mm yr^? 1) than sublimation rates computed based on current climate (0.1–0.2 mm yr^?1). We suggest that the climate-based sublimation rates are offset due to potential ice recharge mechanisms or to missing parameters, particularly the nature and thermo-physical properties of the overlying sediments (i.e., temperature, humidity, pore structure and ice content, grain size).  相似文献   

Modeling aquifer�Criver interactions under the influence of groundwater abstraction in the Mancha Oriental System (SE Spain)     

David Sanz  Santiago Casta?o  Eduardo Cassiraga  Andr��s Sahuquillo  Juan Jos�� G��mez-Alday  Salvador Pe?a  Alfonso Calera 《Hydrogeology Journal》2011,19(2):475-487

The Mancha Oriental System (MOS, 7,260?km²) is one of the largest aquifers within Spain, and is encompassed by the Jucar River Basin. Over the past 30?years, socioeconomic development within the region has been largely due to intensive use of groundwater resources for irrigating crops (1,000?km²). Groundwater pumping (406 million m³/year) has provoked a steady drop in the groundwater level and a reduction of MOS discharge to the Jucar River. The study aims to characterize the river?Caquifer relationship, to determine the influence that groundwater abstraction has on the river discharge. This research has advanced a three-dimensional large-scale numerical groundwater-flow model (MODFLOW 2000) in order to spatially and temporally evaluate, quantify and predict the river?Caquifer interactions that are influenced by groundwater abstraction in MOS. It is demonstrated that although groundwater abstraction increased considerably from the early 1980s to 2000, the depletion of water stored in the aquifer was lower than might be expected. This is mainly due to aquifer recharge from the Jucar River, induced by groundwater abstraction. The area of disconnection between the river and the water table (i.e. where groundwater head is lower than the riverbed) is found to have spread 20?km downstream from its position before pumping started.  相似文献   

Preface to John W. Morse Special Issue of Aquatic Geochemistry     

Fred T. Mackenzie  Alfonso Mucci  George W. Luther III 《Aquatic Geochemistry》2011,17(4-5):307-310

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Waiting Time Distribution of Emissions in Complex Coronal Mass Ejections     

Adolfo L. Méndez Berhondo  Ramón E. Rodríguez Taboada  Liliana Alfonso Larralde 《Astrophysics and Space Science》2006,302(1-4):213-216

The waiting time distribution of emissions in Coronal Mass Ejections (CMEs) with several emissions is examined. We define the waiting time as the time interval between the commencement of an emission and the commencement of the next emission considered as parts of a unique CME. The distribution seems to follow a power-law. Two classes of CMEs several emissions are considered: “close” and “separate” depending on angular distance between emissions.  相似文献   

Near-IR Integral Field Spectroscopy of High-z Galaxies     

Andrew Bunker  Annette Ferguson  Rachel Johnson  Richard McMahon  Ian Parry  Max Pettini  Alfonso Aragón-Salamanca  Rachel Somerville  Nicole Vogt 《Astrophysics and Space Science》2002,281(1-2):529-529

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On gravitational instability of the interstellar gas     

Bruno Bertotti  Alfonso Cavaliere 《Astrophysics and Space Science》1969,5(1):78-91

In the galaxy, Jeans' critical length for the interstellar gas is appreciably smaller than the critical length for the stars, a necessary condition for the gravitational instability of the former to have a local character. An accurate discussion of the orders of magnitude involved leads to the establishment of a well defined limiting procedure and to simplified equations in which the effect of stars occurs only through the equilibrium, but disappears from the perturbations. The equations are spatially local, but their coefficients are time-dependent, in that they describe the evolution of a small wave packet dragged along by the supersonic gas motion. They have been solved in several interesting cases by the introduction of an effective, time-dependent wave vector, which describes the deformation of a wave profile due to the velocity gradients. The ordinary Jeans' instability is recovered only when the velocity gradient is a skew tensor; otherwise we find a stabilizing effect in accelerated and sheared flows, a destabilizing effect in a decelerated flow. Possible connections of this model with the observed turbulent structure of the interstellar gas are discussed.  相似文献   

The density of Red Sea brines     

Frank J. Millero  Alfonso Mucci  James Zullig  Peter Chetirkin 《Marine Chemistry》1982,11(5):463-475

The densities of artificial and real Red Sea brines have been measured at 25°C with a vibrating tube densimeter. Measurements were also made on mixtures of Red Sea brines with seawater and pure water. The results have been used to characterize the density—composition relations of waters across the interface of brine and average Red Sea waters. The results for the real and artificial brines are in reasonable agreement.The composition of the brines and mixtures with seawater have been characterized by conductivity measurements of weight diluted samples. The conductivity salinities were found to be conservative to within $\text{±0.07‰}$ for the mixtures.The densities of brines and mixtures of brines and seawater were estimated from apparent molal volume data using Young's rule. The calculated densities for all of the solutions were found to be in good agreement with the measured values, demonstrating the applicability of Young's rule to concentrated natural waters.  相似文献   

Diffuse Baryons in Cosmic Structures     

Alfonso Cavaliere 《Astrophysics and Space Science》2004,294(1-2):109-124

I review the processes that govern the amount and the thermal state of the hot plasma pervading clusters and groups of galaxies: the gravitational heating driven by the DM merging histories, the radiative cooling of baryons, and the energy fed back by SNe and by AGNs or quasars. I argue that the X-ray emissions and the entropy levels now observed from clusters to groups require the AGNs to contribute substantially to preheat the gas before it falls into clusters, and the quasars to blow some plasma out of groups and galaxies.  相似文献   

Undrained instability detection under general stress conditions     

Leguizamón-Barreto  Luis C.  Ramos-Cañón  Alfonso M.  Andrade  José E. 《Acta Geotechnica》2021,16(10):3041-3059

Acta Geotechnica - This work proposes a criterion for the detection of undrained instability under multiaxial stress conditions at elemental level. To do so, it develops the application of the...  相似文献   

Editorial to the topical collection in Environmental Earth Sciences “Stone in the architectural heritage: from quarry to monuments—environment,exploitation, properties and durability”     

Siegfried Siegesmund  Luís Sousa  Rubén Alfonso López-Doncel 《Environmental Earth Sciences》2018,77(21):730

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