The effects of climate and landscape position on chemical denudation and mineral transformation in the Santa Catalina mountain critical zone observatory     

Rebecca Lybrand  Craig Rasmussen  Angie Jardine  Peter Troch  Jon Chorover 《Applied Geochemistry》2011

Understanding the interactions of climate, physical erosion, chemical weathering and pedogenic processes is essential when considering the evolution of critical zone systems. Interactions among these components are particularly important to predicting how semiarid landscapes will respond to forecasted changes in precipitation and temperature under future climate change. The primary goal of this study was to understand how climate and landscape structure interact to control chemical denudation and mineral transformation across a range of semiarid ecosystems in southern Arizona. The research was conducted along the steep environmental gradient encompassed by the Santa Catalina Mountains Critical Zone Observatory (SCM-CZO). The gradient is dominated by granitic parent materials and spans significant range in both mean annual temperature (>10 °C) and precipitation (>50 cm a^?1), with concomitant shift in vegetation communities from desert scrub to mixed conifer forest. Regolith profiles were sampled from divergent and convergent landscape positions in five different ecosystems to quantify how climate-landscape position interactions control regolith development. Regolith development was quantified as depth to paralithic contact and degree of chemical weathering and mineral transformation using a combination of quantitative and semi-quantitative X-ray diffraction (XRD) analyses of bulk soils and specific particle size classes. Depth to paralithic contact was found to increase systematically with elevation for divergent positions at approximately 28 cm per 1000 m elevation, but varied inconsistently for convergent positions. The relative differences in depth between convergent and divergent landscape positions was greatest at the low and high elevation sites and is hypothesized to be a product of changes in physical erosion rates across the gradient. Quartz/Plagioclase (Q/P) ratios were used as a general proxy for bulk regolith chemical denudation. Q/P was generally higher in divergent landscape positions compared to the adjacent convergent hollows. Convergent landscape positions appear to be collecting solute-rich soil–waters from divergent positions thereby inhibiting chemical denudation. Clay mineral assemblage of the low elevation sites was dominated by smectite and partially dehydrated halloysite whereas vermiculite and kaolinite were predominant in the high elevation sites. The increased depth to paralithic contact, chemical denudation and mineral transformation are likely functions of greater water availability and increased primary productivity. Landscape position within a given ecosystem exerts strong control on chemical denudation as a result of the redistribution of water and solutes across the landscape surface. The combined data from this research demonstrates a strong interactive control of climate, landscape position and erosion on the development of soil and regolith.  相似文献   

Upwelling in the Alaskan Beaufort Sea: Atmospheric forcing and local versus non-local response     

Robert S. Pickart  Michael A. Spall  G.W.K. Moore  Thomas J. Weingartner  Rebecca A. Woodgate  Knut Aagaard  Koji Shimada 《Progress in Oceanography》2011,88(1-4):78-100

The spin up and relaxation of an autumn upwelling event on the Beaufort slope is investigated using a combination of oceanic and atmospheric data and numerical models. The event occurred in November 2002 and was driven by an Aleutian low storm. The wind field was strongly influenced by the pack-ice distribution, resulting in enhanced winds over the open water of the Chukchi Sea. Flow distortion due to the Brooks mountain range was also evident. Mooring observations east of Barrow Canyon show that the Beaufort shelfbreak jet reversed to the west under strong easterly winds, followed by upwelling of Atlantic Water onto the shelf. After the winds subsided a deep eastward jet of Atlantic Water developed, centered at 250 m depth. An idealized numerical model reproduces these results and suggests that the oceanic response to the local winds is modulated by a propagating signal from the western edge of the storm. The disparity in wave speeds between the sea surface height signal—traveling at the fast barotropic shelf wave speed—versus the interior density signal—traveling at the slow baroclinic wave speed—leads to the deep eastward jet. The broad-scale response to the storm over the Chukchi Sea is investigated using a regional numerical model. The strong gradient in windspeed at the ice edge results in convergence of the offshore Ekman transport, leading to the establishment of an anti-cyclonic gyre in the northern Chukchi Sea. Accordingly, the Chukchi shelfbreak jet accelerates to the east into the wind during the storm, and no upwelling occurs west of Barrow Canyon. Hence the storm response is fundamentally different on the Beaufort slope (upwelling) versus the Chukchi slope (no upwelling). The regional numerical model results are supported by additional mooring data in the Chukchi Sea.  相似文献   

Neoarchean suprasubduction zone arc magmatism in southern India: Geochemistry,zircon U-Pb geochronology and Hf isotopes of the Sittampundi Anorthosite Complex     

M. Ram Mohan  M. Satyanarayanan  M. Santosh  Paul J. Sylvester  Mike Tubrett  Rebecca Lam 《Gondwana Research》2013,23(2):539-557

The Sittampundi Anorthosite Complex (SAC) in southern India is one of the well exposed Archean layered anorthosite-gabbro-ultramafic rock associations. Here we present high precision geochemical data for the various units of SAC, coupled with zircon U-Pb geochronology and Hf isotopic data for the anorthosite. The zircon ages define two populations, the older yield a concordia age of 2541 ± 13 Ma, which is interpreted as the best estimate of the magmatic crystallization age for the Sittampundi anorthosite. A high-grade metamorphic event at 2461 ± 15 Ma is suggested by the upper intercept age of the younger zircon population. A Neoproterozoic event at 715 ± 180 Ma resulted in Pb loss from some of the metamorphic zircons. The magmatic age of the anorthosite correlates well with the timing of crystallization of the arc-related ~ 2530 Ma magmatic charnockites in the adjacent Salem Block, while the metamorphic age is synchronous with the regional metamorphic event. The geochemical data suggest that the rocks were derived from a depleted mantle source. Sub-arc mantle metasomatism of slab derived fluids and subsequent partial melting produced hydrous, aluminous basalt magma. The magma fractionated at depth to produce a variety of high-alumina basalt compositions, from which the anorthositic complex with its chromite-rich and amphibole-rich layers formed as cumulates within the magma chamber of a supra-subduction zone arc. The coherent initial¹⁷⁶Hf/¹⁷⁷Hf ratios and positive εHf values (1.7 – 4.5) of the magmatic zircons in the anorthosite are consistent with derivation of a rather homogeneous juvenile parent magma from a depleted mantle source. Our study further confirms that the southern part of the Dharwar Craton was an active convergent margin during the Neoarchean with the generation and emplacement of suprasubduction zone arc magmas which played a significant role in continental growth.  相似文献   

Marine debris surveys at Volunteer Beach, Falkland Islands, during the summer of 2001/02     

Otley H  Ingham R 《Marine pollution bulletin》2003,46(12):1534-1539

This survey evaluated the monthly accumulation rate of marine debris and the types of objects washed ashore at Volunteer Beach on East Falkland between October 2001 and March 2002. The mean (±SD) accumulation rate of marine debris was 77 ± 25 items/km/month, of a mean weight of 17.3 ± 12 kg. Forty different objects were collected and the five most frequent items were cotton fabric, string, polystyrene packing sheet, plastic packing tape and broken plastic pieces. The debris on Volunteer Beach was dominated by fishing debris; 42% of the items were discarded fishing equipment, while 39% of the items were of a packaging or associated nature. The mostly likely source of this household waste was fishing vessels, with Falkland Islands Government (FIG) fisheries observers seeing 27 of the 40 items of debris collected from Volunteer Beach being discarded from fishing vessels. It is suggested that, although further marine debris research is warranted, more effective at-sea ship waste disposal regulations are required in Falkland waters to reduce environmental and economic threats both at the local and international level.  相似文献   

How good is good? Human values and Europe's proposed Marine Strategy Directive   总被引：2，自引：0，他引：2  

Mee LD  Jefferson RL  Laffoley Dd  Elliott M 《Marine pollution bulletin》2008,56(2):187-204

The adoption of the proposed European Marine Strategy Directive is an opportunity for a comprehensive policy for protecting, improving and sustainably using Europe's environmentally degraded seas. It calls for an ecosystem-based approach to management where humans are regarded as a key system component. Although the proposed wording has been the subject of fierce debate, the central policy goal remains achieving "Good Environmental Status". The interpretation of "good" is key to implementation and relates to human values and worldviews. We demonstrate how these vary widely across Europe. Solution of fundamental considerations such as the assignation of reference states, the balance between precautionary and evidence-based action, the degree of subsidiarity, and conservation strategies including marine protected areas, will ultimately depend upon public understanding, involvement in and support for the Directive. The social element, critical to effective adaptive management, requires greater attention within the context of a regional seas geographical framework.  相似文献   

Using housing estates as conservation tools: A case study in KwaZulu-Natal, South Africa     

Rebecca Grey-Ross  Colleen T. Downs  Kevin Kirkman 《Applied geography (Sevenoaks, England)》2009,29(3):371-376

Increasing transformation and fragmentation of rural landscapes for economic reasons is causing concern to conservationists worldwide. With this trend likely to continue, perhaps conservation agencies and development corporations need to co-operate and plan housing developments that are environmentally and ecologically sustainable and can serve as refuges for endangered species. In KwaZulu-Natal, South Africa, grasslands are particularly threatened by land transformation for housing developments. A case study is presented of a housing development, Wedgewood Estate in KwaZulu-Natal that has been developed and managed for conserving grassland habitat and associated species, particularly the endangered oribi (Ourebia ourebi). Feedback from the Estate's managers about the development and ecological impact were obtained. Wedgewood is an example of the viability of housing estates as refuges for endangered species and shows that the density and placement of housing and management of the natural habitat are important. It emphasizes the need for reviewing the types and amount of housing development, management of natural habitat, and the rules and regulations they put in place to assure the integrity of the conservancy is preserved. This case study also shows the potential of such ecologically sensitive housing developments as sources of surplus game for translocation, especially in the case of endangered species such as oribi.  相似文献   

A sediment budget for a grazed semi-arid catchment in the Burdekin basin, Australia   总被引：2，自引：2，他引：0  

Rebecca Bartley  Aaron Hawdon  David A. Post  Christian H. Roth 《Geomorphology》2007,87(4):302-321

In catchments adjacent to the Great Barrier Reef World Heritage Area in Queensland, Australia, there is a growing concern that sediments and nutrients being exported from the land are having a detrimental effect on coral reef communities. There is a need to determine the processes and rates of erosion from the major land use types, so that management intervention can be initiated to reduce sediment yields where required. This paper presents a sediment budget for Weany Creek, a 13.5 km² grazed semi-arid sub-catchment of the Burdekin River catchment, Australia. A range of field methods was used to measure erosion from hillslopes, gullies and stream banks, as well as identify the amount of sediment being deposited and remobilised on the bed of gullies and the stream network. The data suggests that at least during drought conditions, the primary erosion source in this catchment is gully erosion. However, the largest source of sediment in the budget is actually associated with the remobilisation of in-channel sediment stores. Overall, the sediment budget is comprised of  81% coarse material and 19% fine sediment and an agreement between the fine sediment yield estimated in the sediment budget and the yield measured at the catchment outlet is within 10%. The total sediment yield estimated for this catchment is  4205 t yr^− 1 and is much lower than expected for a catchment of this size. This may reflect the drought conditions during the measurement period; however, there is also the possibility that the primary erosion sources have been exhausted, and the rates of sediment loss may be much lower now than they may have been in the past. Nonetheless, the results show that stored sediment, which may have been deposited in the channel many decades ago, is an important contributor to end of catchment sediment yields and warrants further investigation.  相似文献   

Resident Attitudes Toward Timber Rattlesnakes (Crotalus horridus)     

Lindsay S. Keener-Eck  Rebecca A. Christoffel 《社会与自然资源》2020,33(9):1073-1091

Abstract

Timber rattlesnakes (Crotalus horridus) are endangered throughout the northeastern United States where multiple factors contribute to population declines. Challenges exist to managing rattlesnake populations because there is little information about human dimensions of this species or other small predators that are venomous or perceived as hazardous. Our objective was to evaluate relationships between resident attitudes and behavioral intentions toward timber rattlesnakes. A mail survey (n?=?593) was used to collect data from residents who live near a rattlesnake population in central Connecticut. Two variables defined resident attitudes toward rattlesnakes: coexistence with the species and perceived threats from the species. Rattlesnake-related factors and situational factors appeared to contribute more heavily to behavioral intentions toward rattlesnakes than general wildlife value orientations. Attitudes predicted behavioral intentions toward rattlesnakes. Results will help wildlife managers incorporate human factors into appropriate management and public outreach strategies.  相似文献   

Experimental impact cratering: A summary of the major results of the MEMIN research unit     

Thomas Kenkmann  Alex Deutsch  Klaus Thoma  Matthias Ebert  Michael H. Poelchau  Elmar Buhl  Eva-Regine Carl  Andreas N. Danilewsky  Georg Dresen  Anja Dufresne  Nathanaël Durr  Lars Ehm  Christian Grosse  Max Gulde  Nicole Güldemeister  Christopher Hamann  Lutz Hecht  Stefan Hiermaier  Tobias Hoerth  Astrid Kowitz  Falko Langenhorst  Bernd Lexow  Hanns-Peter Liermann  Robert Luther  Ulrich Mansfeld  Dorothee Moser  Manuel Raith  Wolf Uwe Reimold  Martin Sauer  Frank Schäfer  Ralf Thomas Schmitt  Frank Sommer  Jakob Wilk  Rebecca Winkler  Kai Wünnemann 《Meteoritics & planetary science》2018,53(8):1543-1568

This paper reviews major findings of the Multidisciplinary Experimental and Modeling Impact Crater Research Network (MEMIN). MEMIN is a consortium, funded from 2009 till 2017 by the German Research Foundation, and is aimed at investigating impact cratering processes by experimental and modeling approaches. The vision of this network has been to comprehensively quantify impact processes by conducting a strictly controlled experimental campaign at the laboratory scale, together with a multidisciplinary analytical approach. Central to MEMIN has been the use of powerful two-stage light-gas accelerators capable of producing impact craters in the decimeter size range in solid rocks that allowed detailed spatial analyses of petrophysical, structural, and geochemical changes in target rocks and ejecta. In addition, explosive setups, membrane-driven diamond anvil cells, as well as laser irradiation and split Hopkinson pressure bar technologies have been used to study the response of minerals and rocks to shock and dynamic loading as well as high-temperature conditions. We used Seeberger sandstone, Taunus quartzite, Carrara marble, and Weibern tuff as major target rock types. In concert with the experiments we conducted mesoscale numerical simulations of shock wave propagation in heterogeneous rocks resolving the complex response of grains and pores to compressive, shear, and tensile loading and macroscale modeling of crater formation and fracturing. Major results comprise (1) projectile–target interaction, (2) various aspects of shock metamorphism with special focus on low shock pressures and effects of target porosity and water saturation, (3) crater morphologies and cratering efficiencies in various nonporous and porous lithologies, (4) in situ target damage, (5) ejecta dynamics, and (6) geophysical survey of experimental craters.  相似文献   

On the occurrence and origin of anthropogenic radionuclides found in a fragment of the Chelyabinsk (LL5) meteorite          下载免费PDF全文

Rebecca Querfeld  Mohammad R. Tanha  Lars Heyer  Franz Renz  Georg Guggenberger  Franz Brandstätter  Ludovic Ferrière  Christian Koeberl  Georg Steinhauser 《Meteoritics & planetary science》2017,52(6):1244-1250

A piece of the 2013 Chelyabinsk meteorite was investigated for its content of anthropogenic radionuclides. In addition to traces of cesium‐137 that had been previously reported for this particular fragment, we found an unusually high amount of strontium‐90, which indicates that the source of this contamination was the Kyshtym accident (1957). A high Sr‐90/Cs‐137 activity ratio is characteristic for Kyshtym‐derived contaminations. Based on the cesium‐137 content in the soil from the finding site, it is estimated that the fragment was contaminated with soil particles in the milligram range upon impact. Investigation of the soil revealed very unusual ferromagnetic characteristics and an iron‐rich chemical composition. Mössbauer spectroscopy indicated the presence of steel components in this soil, suggesting that the investigated meteorite fragment was found in an industrial dumping site rather than natural soil.  相似文献