Neoproterozoic chemostratigraphy   总被引：3，自引：0，他引：3  

Galen P. Halverson  Benjamin P. Wade  Matthew T. Hurtgen  Karin M. Barovich 《Precambrian Research》2010

Chemostratigraphy has diverse applications to investigating the rock record, such as reconstructing paleoenvironments, determining the tectonic setting of sedimentary basins, indirect dating, and establishing regional or global correlations. Chemostratigraphy is thus an integral component of many investigations of the ancient sedimentary record. In this contribution, we review the principle inorganic geochemical methods that have been applied to the Neoproterozoic sedimentary record. Analysis of the traditional stable and radiogenic isotope systems, such as δ¹³C, δ¹⁸O, δ³⁴S, and ⁸⁷Sr/⁸⁶Sr, is routine, particularly in successions rich in carbonate. These mainstay applications have yielded invaluable data and information bearing on the chronology and evolution of this eventful era in Earth history. Alongside the growing database of traditional data, a series of novel geochemical techniques have given rise to important new models and constraints on Neoproterozoic biogeochemical change. In particular, a range of proxies for water column redox, mainly obtained from black shales, have shed light on the pace and tempo of Neoproterozoic oxygenation and its link to the appearance of early animal evolution. Increased integration of diverse geochemical, sedimentological, and paleontological datasets, and the gradual radiometric calibration of the stratigraphic record promise to bring the details of the evolution of the Neoproterozoic Earth system into ever greater focus.  相似文献   

Assessing the response of watersheds to catastrophic (logging) and possible secular (global temperature change) perturbations using sediment-chemical chronologies     

David T. Long  Matthew J. Parsons  Catherine H. Yansa  Sharon S. Yohn  Colleen E. McLean  Ryan G. Vannier 《Applied Geochemistry》2010

Geochemical profiles of sediment cores from two oligotrophic lakes (Elk and Mullett) in northern Lower Michigan were studied to examine the response and recovery of watersheds to large-scale logging that occurred between 1850 and 1920. Specific questions addressed were: can the impact of extensive clear-cutting of forests be recognized in the sediment-chemical chronologies, can states of system stability be identified prior to the logging, and are there indications that the systems are recovering and possibly returning to a stable state? To answer these questions, elements were put into four groups as proxies for watershed runoff or export (e.g., Al, Mg), pollution (e.g., Pb, Cu), redox (e.g., Fe, As), and productivity (e.g., Ca, P). It was observed that vertical patterns of all proxies were influenced by logging and the early increases in concentration of pollution proxies were due to increased watershed export, not pollution. System stability might be recognized by relatively symmetrical vertical patterns among all of the proxies or secular changes of slowly increasing or decreasing vertical concentration trajectories. Some pre-logging trajectories were punctuated by episodes of slightly elevated concentrations that appear to be related to comparatively warmer periods during the Little Ice Age. Iron and Mn enrichments caused by increased watershed runoff might be misinterpreted as paleo-redox horizons. Results are interpreted to indicate that (1) reference conditions may be better defined as the temporal trends among proxy groups and not individual concentrations, (2) simply assuming pre-1800 conditions as a reference may not be appropriate, (3) inter-proxy group comparisons are needed to help for interpretations of intra-proxy group patterns, (4) the possible regime shift identified here might be expected for other ecosystems because of the intensity of human disturbances and secular changes, and (5) without consideration of a possible regime shift, recovery from logging is estimated to be on the order of 75–130 a, but shorter if regime shifts are considered.  相似文献   

The impact of over 100 years of wildfires on mercury levels and accumulation rates in two lakes in southern California,USA     

Sarah E. Rothenberg  Matthew E. Kirby  Broxton W. Bird  Margie B. DeRose  Chu-Ching Lin  Xinbin Feng  Richard F. Ambrose  Jennifer A. Jay 《Environmental Earth Sciences》2010,60(5):993-1005

In southern California, USA, wildfires may be an important source of mercury (Hg) to local watersheds. Hg levels and Hg accumulation rates were investigated in dated sediment cores from two southern California lakes, Big Bear Lake and Crystal Lake, located approximately 40-km apart. Between 1895 and 2006, fires were routinely minimized or suppressed around Big Bear Lake, while fires regularly subsumed the forest surrounding Crystal Lake. Mean Hg concentrations and mean Hg accumulation rates were significantly higher in Crystal Lake sediments compared to Big Bear Lake sediments (Hg levels: Crystal Lake 220 ± 93 ng g⁻¹, Big Bear Lake 92 ± 26 ng g⁻¹; Hg accumulation: Crystal Lake 790 ± 1,200 μg m⁻² year⁻¹, Big Bear 240 ± 54 μg m⁻² year⁻¹). In Crystal Lake, the ratio between post-1965 and pre-1865 Hg concentrations was 1.1, and several spikes in Hg levels occurred between 1910 and 1985. Given the remote location of the lake, the proximity of fires, and the lack of point sources within the region, these results suggested wildfires (rather than industrial sources) were a continuous source of Hg to Crystal Lake over the last 150 years.  相似文献   

Multi-zone fusion crust formation and classification of the 2004 Auckland meteorite (L6, S5, and W0)     

James M. Scott  Marianne Negrini  Kevin Faure  Marshall C. Palmer  Derek R. Knaack  Matthew I. Leybourne 《Meteoritics & planetary science》2023,58(3):328-340

On June 12, 2004, a meteorite passed through Earth's atmosphere and landed under the television in the living room of a house in Auckland, New Zealand. Textural characteristics, the chemistry of olivine (Fa_23–24) and orthopyroxene (Fs_20.7), and the bulk rock triple oxygen isotopes (δ¹⁷O + 3.1; δ¹⁸O + 4.2‰) from the interior of the completely unweathered (W0) 1.3 kg meteorite, hereafter referred to as Auckland, suggest it to be a strongly metamorphosed fragment from the interior of a low iron ordinary chondrite (L6) parent asteroid. The occurrence of maskelynite but shock fracturing of olivine and pyroxene indicates Auckland experienced extreme shock metamorphism (S5), likely during Ordovician fragmentation of the asteroid parent. The fusion crust consists of three zones: (1) an innermost zone containing narrow Fe-Ni-S-bearing veins that migrated along pre-existing shock fractures in olivine and pyroxene; (2) a middle zone in which the meteorite partially melted to form a silicate glass and immiscible blebs of metal and troilite, and is accompanied by unmelted silicate minerals; and (3) an approximately 0.1 mm wide vesicular-rich outermost layer that largely melted, volatilizing sulfides, before quenching to form glass and olivine. Oxygen isotope values of the bulk rock and/or maskelynite of melted rim and modified substrate are 2–3‰ greater than the meteorite interior and indicate that up to 19% of terrestrial atmospheric O₂ was incorporated into the fusion crust during the formation. The fusion crust migrated inwards as ablation occurred, enabling melting, migration, and re-precipitation ± loss of sulfide and metal components, with the prominent glassy rim therefore forming from an already chemically modified zone.  相似文献   

Ecological Modernization or Aristocratic Conservation? Exploring the Impact of Affluence on Carbon Emissions at the Local Level     

Andrew Pattison  Robert Habans  Matthew Thomas Clement 《社会与自然资源》2014,27(8):850-866

Social scientists have debated how affluence impacts carbon emissions at the national level. We conduct an exploratory study at the subnational level to expose another dimension of the affluence–emissions debate. Based on the notion of aristocratic conservation, we hypothesize that affluence is positively related to carbon emissions from consumption activities but negatively related to emissions from production activities. We test these hypotheses using county-level data in the United States for the year 2002. A spatial regression analysis demonstrates that median household income is positively associated with consumption-based emissions; nevertheless, we find evidence of an environmental inequality Kuznets curve in the relationship between median household income and production-based emissions. This finding suggests that the wealthiest counties are able to displace certain types of emissions, specifically those related to energy and industrial production. We discuss the theoretical and political implications of these results.  相似文献   

Tropical and extratropical cyclone damages under climate change     

Matthew Ranson  Carolyn Kousky  Matthias Ruth  Lesley Jantarasami  Allison Crimmins  Lisa Tarquinio 《Climatic change》2014,127(2):227-241

This paper provides the first quantitative synthesis of the rapidly growing literature on future tropical and extratropical cyclone damages under climate change. We estimate a probability distribution for the predicted impact of changes in global surface air temperatures on future storm damages, using an ensemble of 478 estimates of the temperature-damage relationship from nineteen studies. Our analysis produces three main empirical results. First, we find strong but not conclusive support for the hypothesis that climate change will cause damages from tropical cyclones and wind storms to increase, with most models predicting higher future storm damages due to climate change. Second, there is substantial variation in projected changes in losses across regions. Potential changes in damages are greatest in the North Atlantic basin, where the multi-model average predicts that a 2.5 °C increase in global surface air temperature would cause hurricane damages to increase by 63 %. The ensemble predictions for Western North Pacific tropical cyclones and European wind storms (extratropical cyclones) are +28 % and +23 %, respectively. Finally, our analysis shows that existing models of storm damages under climate change generate a wide range of predictions, ranging from moderate decreases to very large increases in losses.  相似文献   

Downscaling reveals diverse effects of anthropogenic climate warming on the potential for local environments to support malaria transmission     

Krijn P. Paaijmans  Justine I. Blanford  Robert G. Crane  Michael E. Mann  Liang Ning  Kathleen V. Schreiber  Matthew B. Thomas 《Climatic change》2014,125(3-4):479-488

The potential impact of climate warming on patterns of malaria transmission has been the subject of keen scientific and policy debate. Standard climate models (GCMs) characterize climate change at relatively coarse spatial and temporal scales. However, malaria parasites and the mosquito vectors respond to diurnal variations in conditions at very local scales. Here we bridge this gap by downscaling a series of GCMs to provide high-resolution temperature data for four different sites and show that although outputs from both the GCM and the downscaled models predict diverse but qualitatively similar effects of warming on the potential for adult mosquitoes to transmit malaria, the predicted magnitude of change differs markedly between the different model approaches. Raw GCM model outputs underestimate the effects of climate warming at both hot (3-fold) and cold (8–12 fold) extremes, and overestimate (3-fold) the change under intermediate conditions. Thus, downscaling could add important insights to the standard application of coarse-scale GCMs for biophysical processes driven strongly by local microclimatic conditions.  相似文献   

Estimating present day extreme water level exceedance probabilities around the coastline of Australia: tropical cyclone-induced storm surges   总被引：2，自引：0，他引：2  

Ivan D. Haigh  Leigh R. MacPherson  Matthew S. Mason  E. M. S. Wijeratne  Charitha B. Pattiaratchi  Ryan P. Crompton  Steve George 《Climate Dynamics》2014,42(1-2):139-157

The incidence of major storm surges in the last decade have dramatically emphasized the immense destructive capabilities of extreme water level events, particularly when driven by severe tropical cyclones. Given this risk, it is vitally important that the exceedance probabilities of extreme water levels are accurately evaluated to inform risk-based flood and erosion management, engineering and for future land-use planning and to ensure the risk of catastrophic structural failures due to under-design or expensive wastes due to over-design are minimised. Australia has a long history of coastal flooding from tropical cyclones. Using a novel integration of two modeling techniques, this paper provides the first estimates of present day extreme water level exceedance probabilities around the whole coastline of Australia, and the first estimates that combine the influence of astronomical tides, storm surges generated by both extra-tropical and tropical cyclones, and seasonal and inter-annual variations in mean sea level. Initially, an analysis of tide gauge records has been used to assess the characteristics of tropical cyclone-induced surges around Australia. However, given the dearth (temporal and spatial) of information around much of the coastline, and therefore the inability of these gauge records to adequately describe the regional climatology, an observationally based stochastic tropical cyclone model has been developed to synthetically extend the tropical cyclone record to 10,000 years. Wind and pressure fields derived for these synthetically generated events have then been used to drive a hydrodynamic model of the Australian continental shelf region with annual maximum water levels extracted to estimate exceedance probabilities around the coastline. To validate this methodology, selected historic storm surge events have been simulated and resultant storm surges compared with gauge records. Tropical cyclone induced exceedance probabilities have been combined with estimates derived from a 61-year water level hindcast described in a companion paper to give a single estimate of present day extreme water level probabilities around the whole coastline of Australia. Results of this work are freely available to coastal engineers, managers and researchers via a web-based tool (www.sealevelrise.info). The described methodology could be applied to other regions of the world, like the US east coast, that are subject to both extra-tropical and tropical cyclones.  相似文献   

Mega-scale groundwater quality challenges and the need for an inter-disciplinary approach     

Matthew Currell 《Hydrogeology Journal》2014,22(4):745-748

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Editors’ Message: The 2013 Editors’ Choice articles,a new editor,and the 2013 ‘Coolest Paper’ award     

Clifford Voss  Matthew Currell  Tom Gleeson 《Hydrogeology Journal》2014,22(2):293-294

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