Retreat dynamics of the eastern sector of the British–Irish Ice Sheet during the last glaciation     

David J. A. Evans  David H. Roberts  Mark D. Bateman  Chris D. Clark  Alicia Medialdea  Louise Callard  Elena Grimoldi  Richard C. Chiverrell  Jeremy Ely  Dayton Dove  Colm Ó Cofaigh  Margot Saher  Tom Bradwell  Steven G. Moreton  Derek Fabel  Sarah L. Bradley 《第四纪科学杂志》2021,36(5):723-751

The findings of BRITICE-CHRONO Transect 2 through the North Sea Basin and eastern England are reported. We define ice-sheet marginal oscillation between ~31 and 16 ka, with seven distinctive former ice-sheet limits (L1–7) constrained by Bayesian statistical analysis. The southernmost limit of the North Sea Lobe is recorded by the Bolders Bank Formation (L1; 25.8–24.6 ka). L2 represents ice-sheet oscillation and early retreat to the northern edge of the Dogger Bank (23.5–22.2 ka), with the Garret Hill Moraine in north Norfolk recording a significant regional readvance to L3 at 21.5–20.8 ka. Ice-marginal oscillations at ~26–21 ka resulted in L1, L2 and L3 being partially to totally overprinted. Ice-dammed lakes related to L1–3, including Lake Humber, are dated at 24.1–22.3 ka. Ice-sheet oscillation and retreat from L4 to L5 occurred between 19.7 and 17.3 ka, with grounding zone wedges marking an important transition from terrestrial to marine tidewater conditions, triggered by the opening of the Dogger Lake spillway between 19.9 and 17.5 ka. L6 relates to ice retreat under glacimarine conditions and final ice retreat into the Firth of Forth by 15.8 ka. L7 (~15 ka) represents an ice retreat from Bosies Bank into the Moray Firth.  相似文献   

Snow accumulation and ablation response to changes in forest structure and snow surface albedo after attack by mountain pine beetle          下载免费PDF全文

Rita Winkler  Sarah Boon  Barbara Zimonick  Dave Spittlehouse 《水文研究》2014,28(2):197-209

This study quantified changes in snow accumulation and ablation with forest defoliation in a young pine stand attacked by mountain pine beetle, a mature mixed species stand, and a clearcut in south‐central British Columbia. From 2006 to 2012, as trees in the pine stand turned from green to grey, average canopy transmittance increased from 27% to 49%. In the mixed stand, transmittance remained constant at 19%. In 2009, the year of greatest needle loss, average snow surface litter cover in the pine stand was 29% (range 4 – 61%), compared to ≤9% in other years and over double that in the mixed stand. By 2012, litter accumulation in the now‐grey pine stand was only a sixth of that in the mixed stand. Inter‐annual variability in the weather had the greatest effect on snow accumulation and ablation, with the greatest differences between both forested stands and the clearcut occurring in 2010, the year of lowest SWE. Differences in snow accumulation between the pine and mixed stand increased in 2010 as a result of decreased snow interception in the young stand after needlefall. Average ablation rates in the attacked stand were most different from the mixed stand in 2009 and 2012, the years with the largest and smallest over‐winter needle loss, respectively. This study shows that grey, non‐pine, and understory trees moderate snow response to changes in the main canopy. It also highlights the complex interrelationships between ecohydrological processes key to assessing watershed response to forest cover loss in snow dominated hydrologic regimes. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

A multi‐species dendroclimatic reconstruction of Chilko River streamflow,British Columbia,Canada     

Sarah J. Hart  Dan J. Smith  John J. Clague 《水文研究》2010,24(19):2752-2761

Dendroclimatological data were used to reconstruct the discharge history of Chilko River, which drains a glacierized watershed in the Coast Mountains of British Columbia. We correlated ring‐width records from Engelmann spruce (ES) (Picea engelmanni) and mountain hemlock (MH) (Tsuga mertensiana) trees to historical hydroclimate data. Over the period of record, spruce and hemlock radial growth correlates significantly with temperature and snow depth, respectively. We found that a multi‐species approach provided a better model fit and reconstructive power. Using these relationships, we developed generalized linear models for mean June, July, and June‐July discharge. The proxy records provide insights into streamflow variability of a typical Coast Mountains river over the past 240 years and confirm the long‐term influence of the Pacific Decadal Oscillation (PDO) on hydroclimatic regimes in the region. A relationship also exists between the reconstructed June‐July discharge record and the North Pacific (NP) Index, suggesting that winter atmospheric patterns over the North Pacific influence the hydrology of coastal British Columbia. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Assessing the effects of post‐pine beetle forest litter on snow albedo     

Rita Winkler  Sarah Boon  Barbara Zimonick  Karen Baleshta 《水文研究》2010,24(6):803-812

The effect of forest litter on snow surface albedo has been subject to limited study, mainly in the hardwood‐dominated forests of the northeastern United States. Given the recent pine beetle infestation in Western North America and associated increases in litter production, this study examines the effects of forest litter on snow surface albedo in the coniferous forests of south‐central British Columbia. Measured changes in canopy transmittance provide an indication of canopy loss or total litterfall over the winter of 2007–2008. Relationships between percent litter cover, an index of albedo, snow depth, and snow ablation during the 2008 melt season are compared between a mature, young, and clearcut coniferous stand. Results indicate a strong feedback effect between canopy loss and subsequent enhanced shortwave transmittance, and litter accumulation on the snow surface from that canopy loss. However, this relationship is confounded by other variables concurrently affecting albedo. While results suggest that a relatively small percent litter cover can have a significant effect on albedo and ablation, further research is underway to extract the litter signal from that of other factors affecting albedo, particularly snow depth. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Developing a systematic “science of the past” to create our future     

Sarah Cornell  Robert Costanza  Sverker Sörlin  Sander van der Leeuw 《Global Environmental Change》2010,20(3):426-427

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Flame and fortune in California: The material and political dimensions of vulnerability     

Gregory L. Simon  Sarah Dooling 《Global Environmental Change》2013,23(6):1410-1423

This paper seeks to clarify and refine the assertion that vulnerability exists as both a material, condition and discursive construct. Building off of previous scholarship analyzing the production of, vulnerabilities, we present a conceptual framework that illuminates how material vulnerabilities are translated into political vulnerabilities and ossified in the policy realm. We argue that specifying components of, and relationships between, the material and political aspects of vulnerability will result in a more sophisticated articulation of vulnerability as a recursive process. In order to achieve this level of analysis we propose a spatial–historical analytic approach that blends point-in-time and, empirically driven analysis with robust historical and political economic analysis. We use the largest urban wildfire – in terms of dwellings lost – in California's history to show how the persistent disconnection between material and political forms of vulnerability has, over time, resulted in contradictory landscapes where homes are intentionally placed in landscapes vulnerable to wildfires with reduced fire protection. Spatial historical analysis of the Tunnel Fire reveals how representations of vulnerability oftentimes deviate from lived experiences, engendering responses of exploitation, ignorance, mobilization and resistance. This framework also recognizes how these responses can create new vulnerabilities while also maintaining, deepening and diminishing existing material conditions. Finally, relational analysis illuminates how factors generating vulnerability in fire areas also contribute to and reinforce vulnerabilities within other parts of cities like Oakland, California.  相似文献   

Last glacial ice‐rafted debris off southwestern Europe: the role of the British–Irish Ice Sheet     

Grant R. Bigg  Richard C. Levine  Chris D. Clark  Sarah L. Greenwood  Haflidi Haflidason  Anna L. C. Hughes  Atlé Nygård  Hans Petter Sejrup 《第四纪科学杂志》2010,25(5):689-699

Ice‐rafted debris (IRD) seeded into the ocean from Northern Hemisphere ice sheets is found in ocean cores along the southwestern European margin through the last glacial period. It is known that the origin of this IRD, especially off Iberia, can vary between North America and western Europe during short‐lived episodes of greatly enhanced iceberg flux, known as Heinrich events, although in most Heinrich events the IRD has a North American source. During the longer times of much lower IRD fluxes between Heinrich events, use of an intermediate complexity climate model, coupled to an iceberg dynamic and thermodynamic model, shows that background levels of IRD most likely originate from western Europe, particularly the British–Irish Ice Sheet. Combining modelling with palaeoceanographic evidence supports reconstructions of a short‐lived, but substantial, Celtic and Irish Sea Ice Stream around 23 ka. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

The High Resolution Imaging Science Experiment (HiRISE) during MRO’s Primary Science Phase (PSP)     

Alfred S. McEwen  Maria E. Banks  Kris Becker  James W. Bergstrom  Edward Bortolini  Shane Byrne  Frank C. Chuang  Ingrid Daubar  Donald G. Deardorff  W. Alan Delamere  Colin M. Dundas  Yisrael Espinoza  Kathryn E. Fishbaugh  Paul E. Geissler  Jennifer L. Griffes  Virginia C. Gulick  Kenneth E. Herkenhoff  Windy L. Jaeger  Bob Kanefsky  Robert King  Kelly J. Kolb  Alexandra Lefort  Kevin W. Lewis  Sarah Mattson  Michael T. Mellon  Moses P. Milazzo  Tahirih Motazedian  Albert Ortiz  Joseph Plassmann  Patrick S. Russell  Mindi L. Searls  Steven W. Squyres  Nicolas Thomas  Livio L. Tornabene  Circe Verba  James J. Wray 《Icarus》2010,205(1):2-216

The High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO) acquired 8 terapixels of data in 9137 images of Mars between October 2006 and December 2008, covering ∼0.55% of the surface. Images are typically 5-6 km wide with 3-color coverage over the central 20% of the swath, and their scales usually range from 25 to 60 cm/pixel. Nine hundred and sixty stereo pairs were acquired and more than 50 digital terrain models (DTMs) completed; these data have led to some of the most significant science results. New methods to measure and correct distortions due to pointing jitter facilitate topographic and change-detection studies at sub-meter scales. Recent results address Noachian bedrock stratigraphy, fluvially deposited fans in craters and in or near Valles Marineris, groundwater flow in fractures and porous media, quasi-periodic layering in polar and non-polar deposits, tectonic history of west Candor Chasma, geometry of clay-rich deposits near and within Mawrth Vallis, dynamics of flood lavas in the Cerberus Palus region, evidence for pyroclastic deposits, columnar jointing in lava flows, recent collapse pits, evidence for water in well-preserved impact craters, newly discovered large rayed craters, and glacial and periglacial processes. Of particular interest are ongoing processes such as those driven by the wind, impact cratering, avalanches of dust and/or frost, relatively bright deposits on steep gullied slopes, and the dynamic seasonal processes over polar regions. HiRISE has acquired hundreds of large images of past, present and potential future landing sites and has contributed to scientific and engineering studies of those sites. Warming the focal-plane electronics prior to imaging has mitigated an instrument anomaly that produces bad data under cold operating conditions.  相似文献   

Radiometric and stratigraphic constraints on terminal Ediacaran (post-Gaskiers) glaciation and metazoan evolution     

Craig L. Hebert  Alan J. Kaufman  Sarah C. Penniston-Dorland  Aaron J. Martin 《Precambrian Research》2010

Radiometric constraints on mid-Ediacaran Period glaciation (Gaskiers) in Newfoundland narrowed the known temporal gap between widespread ice ages and the evolution of complex metazoans to several million years. To further evaluate this claim we studied an Ediacaran glacial diamictite at the base of the Fauquier Formation of northern Virginia, and discovered a conformable relationship between the post-glacial cap carbonate and overlying volcanic rocks of the Catoctin Formation. U/Pb zircon age constraints for the rift-related volcanic flows suggest initial emplacement around 571 million years ago. Application of the Catoctin age to the Fauquier succession indicates the occurrence of an ice age about 10 million years younger than the 582 Ma Gaskiers event, supporting the view of multiple Ediacaran Period glaciations. Furthermore, the age constraint from eastern Laurentia falls within radiometric uncertainty of fossiliferous strata in Avalonia, indicating that the Fauquier glaciation was coincident with early metazoan evolution.  相似文献   

Hydrous partial melting in the sheeted dike complex at fast spreading ridges: experimental and natural observations   总被引：5，自引：1，他引：4  

Lydéric France  Juergen Koepke  Benoit Ildefonse  Sarah B. Cichy  Fabien Deschamps 《Contributions to Mineralogy and Petrology》2010,160(5):683-704

In ophiolites and in present-day oceanic crust formed at fast spreading ridges, oceanic plagiogranites are commonly observed at, or close to the base of the sheeted dike complex. They can be produced either by differentiation of mafic melts, or by hydrous partial melting of the hydrothermally altered sheeted dikes. In addition, the hydrothermally altered base of the sheeted dike complex, which is often infiltrated by plagiogranitic veins, is usually recrystallized into granoblastic dikes that are commonly interpreted as a result of prograde granulitic metamorphism. To test the anatectic origin of oceanic plagiogranites, we performed melting experiments on a natural hydrothermally altered dike, under conditions that match those prevailing at the base of the sheeted dike complex. All generated melts are water saturated, transitional between tholeiitic and calc-alkaline, and match the compositions of oceanic plagiogranites observed close to the base of the sheeted dike complex. Newly crystallized clinopyroxene and plagioclase have compositions that are characteristic of the same minerals in granoblastic dikes. Published silicic melt compositions obtained in classical MORB fractionation experiments also broadly match the compositions of oceanic plagiogranites; however, the compositions of the coexisting experimental minerals significantly deviate from those of the granoblastic dikes. Our results demonstrate that hydrous partial melting is a likely common process in the root zone of the sheeted dike complex, starting at temperatures exceeding 850°C. The newly formed melt can either crystallize to form oceanic plagiogranites or may be recycled within the melt lens resulting in hybridized and contaminated MORB melts. It represents the main MORB crustal contamination process. The residue after the partial melting event is represented by the granoblastic dikes. Our results support a model with a dynamic melt lens that has the potential to trigger hydrous partial melting reactions in the previously hydrothermally altered sheeted dikes. A new thermometer using the Al content of clinopyroxene is also elaborated.  相似文献