Problems associated with luminescence dating of Late Quaternary glacial sediments in the NW Scottish Highlands   总被引：2，自引：0，他引：2  

Sven Lukas  Joel Q.G. Spencer  Ruth A.J. Robinson  Douglas I. Benn   《Quaternary Geochronology》2007,2(1-4):243-248

Linking the timing of glacial episodes and behaviour to climatic shifts that are documented in ice and marine sedimentary archives is key to understanding ocean-land interactions. In the NW Scottish Highlands a large number of closely spaced (‘hummocky’) moraines formed at retreating glacier margins. Independent age control on one palaeo-glacier limit is consistent with the timing of Younger Dryas (YD) glaciation in the area, but adjacent glacier lobes have remained undated due to the lack of sites and material for ¹⁴C dating. Direct dating of ice-marginal moraines using optically stimulated luminescence (OSL) techniques has never been attempted before in Scotland, but if successful, they may be the most appropriate methods for constraining the age of sediment deposition in the absence of organic material. Coarse-grained quartz and K-feldspar minerals from supraglacial sheet flow deposits and glacilacustrine sediments within ice-marginal moraines were analysed using the single-aliquot regenerative-dose (SAR) protocol. Independent age control and clear geomorphological relationships indicate that all samples should yield YD or post-Last Glacial Maximum (LGM) ages. Quartz OSL shine down curves showed low luminescence sensitivity, significant medium-to-slow components, a weak fast component, and scattered SAR data; Linearly Modulated-OSL (LM-OSL) measurements confirmed that the fast component was weak or absent. In contrast, feldspar infrared stimulated luminescence (IRSL) was highly sensitive with excellent SAR data. However, SAR data from 3 mm diameter aliquots of feldspar (200 grains) give higher than expected equivalent doses (D_e) by an order of magnitude. SAR measurements of small clusters of feldspar grains (ranging from 1–8) considerably broaden the apparent D_e distribution, but even the lowest value is about 2–3 times the expected D_e. Two possibilities arise to explain the quartz and feldspar data: (1) that glacial sequences in the NW Highlands re-work inherited (older) glacial deposits and that some of the pre-Devensian existing glacial landforms have only been modified during Devensian glaciation; or (2) that the sedimentary processes operating in these ice-marginal environments are not conducive to adequate bleaching of quartz and feldspar grains. Our study implies that ice-proximal supraglacial sediments from this region in NW Scotland reflect older ages of deposition, but dating YD sediments has not been possible.  相似文献   

A sequential extraction to determine the distribution of apatite in granitoid soil mineral pools with application to weathering at the Hubbard Brook Experimental Forest,NH, USA     

Carmen A. Nezat  Joel D. Blum  Ruth D. Yanai  Steven P. Hamburg 《Applied Geochemistry》2007

Mineral weathering in soils is an important source of many nutrients to forest ecosystems. Apatite, a Ca phosphate mineral, occurs in trace amounts in virtually all igneous and metamorphic rocks and is often found as small mineral inclusions in more weathering-resistant silicate minerals. To better understand the distribution of apatite in soils and its exposure to soil solutions, a sequential extraction method was developed to selectively dissolve minerals from soils so that the amount of apatite in contact with soil solutions versus that armored by silicate minerals could be quantified. The use of three molarities of HNO₃ (0.01, 0.1 and 1 M) at three temperatures (0, 10, or 20 °C) was explored and it was found that apatite congruently dissolved in 1 M HNO₃ at all three temperatures, but did not completely dissolve in weaker HNO₃ solutions. Soil horizons, glacial till (i.e., soil parent material), and individual minerals separated from till collected from the Hubbard Brook Experimental Forest (HBEF), NH, were subjected to a 4-step sequential extraction. Chemical analyses of the extracts indicate that 1 M NH₄Cl (pH 7; 20 °C) removes exchangeable ions, 1 M HNO₃ at 20 °C primarily dissolves apatite in contact with solutions, 1 M HNO₃ at 200 °C primarily dissolves biotite and chlorite (and apatite armored by them), and a mixture of concentrated HNO₃, HCl, and HF at 200 °C dissolves the more refractory minerals including muscovite, alkali feldspar, plagioclase feldspar and quartz (and apatite armored by these minerals). This extraction method was applied to soil profiles from HBEF to demonstrate that it could be used to interpret the abundance of apatite and other minerals as a function of depth. Approximately 70% of the apatite in the HBEF soil parent material is exposed to soil solutions; the remaining 30% is armored in more weathering-resistant micas and feldspars. In the upper soil horizons, the only apatite that has not been weathered from the soil occurs as inclusions in micas and feldspars and thus the rate of dissolution of apatite in weathered soil horizons is controlled by silicate mineral dissolution.  相似文献   

Catchment contrasts: Comparing young people’s experiences and knowledge of a river environment     

Ruth Panelli  Gretchen Robertson 《Geoforum》2006,37(4):455-472

Early geographies focussed on children have recorded their environmental and spatial perceptions. Contemporary theoretical and methodological advances in, and beyond, children’s geographies have supported a more complex engagement with environmental topics. Complementing this work, a study of young people’s experience and knowledge of a river in southern New Zealand is presented. Data were gathered from four contrasting locations within one, 5650 sq. km, catchment, employing child-oriented, multi-method approaches. Data analysis confirms existing literature highlighting how young people are competent knowledge producers with varying experiences and understandings. Some of this variation can be appreciated by focussing on factors of age, gender and catchment location. Together these findings are relevant to both academic and planning circles and implications for young people’s participation in catchment management are noted as a key area for further development of work of this kind.  相似文献   

Towards fair local outcomes in adaptation to sea-level rise     

Sonia Graham  Jon Barnett  Ruth Fincher  Colette Mortreux  Anna Hurlimann 《Climatic change》2015,130(3):411-424

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Future changes in tropical cyclone genesis in fully dynamic ocean- and mixed layer ocean-coupled climate models: a low-resolution model study     

Joo-Hong Kim  Simon J. Brown  Ruth E. McDonald 《Climate Dynamics》2011,37(3-4):737-758

The global and regional projected changes in tropical cyclone (TC) genesis due to increased CO₂ concentrations has been investigated through a large-scale TC genesis parameter (convective seasonal genesis parameter, ConvGP) in two perturbed physics ensembles. The ensembles are based on the third generation Hadley Centre atmosphere?Cocean general circulation model with the first ensemble using a coupled fully dynamic ocean (HadCM3) and the second coupled to a simplified mixed layer thermodynamic ocean (HadSM3) both consisting of 17 members. In each ensemble, parameters are identically perturbed to provide a wide range of climate sensitivity whilst retaining a credible present-day climate simulation. It is found, by comparing the ConvGP climatology from reanalysis data with the best track genesis, that it is possible to reproduce the observed genesis distribution. Future changes in the spatial ConvGP distribution are explored with respect to each tropical ocean basin. Whilst there is a similarity in the gross pattern of the ensemble-mean projected ConvGP change between HadCM3 and HadSM3, there is a non-trivial difference in the tropical Pacific Ocean, arising from different patterns of tropical Pacific sea surface temperature change. This indicates that ocean representation can be important for regional scale projections. The quantitative contribution of individual constituent parameters (i.e. vorticity parameter, shear parameter and convective potential) to the projected ConvGP change is estimated. It is found that all three large-scale parameters generally contribute constructively, but with different magnitude, in the regions where a large doubled CO₂ response is found.  相似文献   

Understanding the impact of climate change on Northern Hemisphere extra-tropical cyclones   总被引：3，自引：2，他引：1  

Ruth E. McDonald 《Climate Dynamics》2011,37(7-8):1399-1425

Extra-tropical cyclones strongly influence weather and climate in mid-latitudes and any future changes may have large impacts on the local scale. In this study Northern Hemisphere storms are analysed in ensembles of time-slice experiments carried out with an atmosphere only model with present day and future anthropogenic emissions. The present day experiment is forced by observed sea-surface temperature and sea-ice. The sea-surface temperatures and sea-ice for the future experiment are derived by adding anomalies, from parallel but lower resolution coupled model experiments, to the observed data. The storms in the present day simulation compare fairly well with observations in all seasons but some errors remain. In the future simulations there is some evidence of a poleward shift in the storm tracks in some seasons and regions. There are fewer cyclones in the Northern Hemisphere in winter and spring. The northeast end of the North Atlantic storm track is shifted south in winter giving more storms and increased frequency of strong winds over the British Isles. This shift is related to an increase in baroclinicity and a southward shift of the jet that occurs as a response to a minimum in ocean warming in the central North Atlantic. An increase in the frequency of storms over the UK is likely to cause enhanced levels of wind and flood damage. These results concur with those from some other models, however, large uncertainties remain.  相似文献   

Inter-laboratory comparison of oxygen isotope compositions from biogenic silica     

Bernhard Chapligin  Melanie J. Leng  Anne Alexandre  Akira Ijiri  Aldo Shemesh  Ulrike Herzschuh  Hanno Meyer  Yusuke Okazaki  Zachary D. Sharp  Corinne Sonzogni  Florence Sylvestre  Ruth Yam 《Geochimica et cosmochimica acta》2011,75(22):7242-7256

Several techniques have been introduced in the last decades for the dehydration and release of O₂ from biogenic silica (opal-A) for oxygen-isotope analysis. However, only one silica standard is universally available: a quartz standard (NBS28) distributed by the IAEA, Vienna. Hence, there is a need for biogenic silica working standards. This paper compares the existing methods of oxygen-isotope analyses of opal-A and aims to characterize additional possible working standards to calibrate the δ¹⁸O values of biogenic silica. For this purpose, an inter-laboratory comparison was organized. Six potential working standard materials were analysed repeatedly against NBS28 by eight participating laboratories using their specific analytical methods. The materials cover a wide range of δ¹⁸O values (+23 to +43‰) and include diatoms (marine, lacustrine), phytoliths and synthetically-produced hydrous silica. To characterize the proposed standards, chemical analyses and imaging by scanning electron microscopy (SEM) were also performed. Despite procedural differences at each laboratory, all methods are in reasonable agreement with a standard deviation (SD) for δ¹⁸O values between 0.3‰ and 0.9‰ (1σ). Based on the results, we propose four additional biogenic silica working standards (PS1772-8: 42.8‰; BFC: 29.0‰; MSG60: 37.0‰; G95-25-CL leaves: 36.6‰) for δ¹⁸O analyses, available on request through the relevant laboratories.  相似文献   

Ecotoxicological approach for assessing the contamination of a Hawaiian coral reef ecosystem (Honolua Bay, Maui) by metals and a metalloid     

Hédouin L  Metian M  Gates RD 《Marine environmental research》2011,71(3):149-161

The goal of this study was to assess the contamination of Honolua Bay using an ecotoxicological approach. First, the concentrations of 9 contaminants (metals and metalloid) were assessed in sediments and tropical marine organisms (alga Halimeda kanaloana, goatfish Parupeneus multifasciatus and urchin Tripneustes gratilla) sampled from Honolua and surrounding Bays. Then, the ecological parameters characterizing coral health (e.g. coral cover) were evaluated in Honolua Bay in the context of these contaminants. High concentrations of Co, Cr, Mn, Ni, and V in sediments from Honolua and Honokohau Bay were measured, but these concentrations were not mirrored in the organisms examined, except for Mn, suggesting that the metals are generally bound in chemically inert forms in these sediments. Moreover, few anthropogenic activities impact these bays and so the elevated Co, Cr, Mn, Ni and V concentrations in sediments appear to stem from their high natural background in Honolua and Honokohau watersheds. An analysis of the relationship between the ecological parameters and metal concentrations in Honolua Bay revealed a significant correlation between coral cover and Co, Cr, Mn, Ni, V, Zn concentrations in sediments, with coral cover decreasing with increasing metal concentration. Collectively, however, the data suggest that a complex mixture of land-based stressors (e.g. sediment, metals, nutrients) affect the coral health in Honolua Bay, rather than metal stress alone.  相似文献   

Observations of the Hubble Deep Field South with the Infrared Space Observatory– II. Associations and star formation rates     

Robert G. Mann  Seb Oliver  Ruth Carballo  Alberto Franceschini  Michael Rowan-Robinson  Alan F. Heavens  Maria Kontizas  David Elbaz  Anastasios Dapergolas  Evanghelos Kontizas  Gian Luigi Granato  Laura Silva  Dimitra Rigopoulou  J. Ignacio Gonzalez-Serrano  Aprajita Verma  Steve Serjeant  reas Efstathiou  Paul P. van der Werf 《Monthly notices of the Royal Astronomical Society》2002,332(3):549-574

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Sediment‐rich meltwater plumes and ice‐proximal fans at the margins of modern and ancient tidewater glaciers: Observations and modelling          下载免费PDF全文

Julian A. Dowdeswell  Kelly A. Hogan  Neil S. Arnold  Ruth I. Mugford  Martin Wells  J. Philip P. Hirst  Carole Decalf 《Sedimentology》2015,62(6):1665-1692

Turbid meltwater plumes and ice‐proximal fans occur where subglacial streams reach the grounded marine margins of modern and ancient tidewater glaciers. However, the spacing and temporal stability of these subglacial channels is poorly understood. This has significant implications for understanding the geometry and distribution of Quaternary and ancient ice‐proximal fans that can form important aquifers and hydrocarbon reservoirs. Remote‐sensing and numerical‐modelling techniques are applied to the 200 km long marine margin of a Svalbard ice cap, Austfonna, to quantify turbid meltwater‐plume distribution and predict its temporal stability. Results are combined with observations from geophysical data close to the modern ice front to refine existing depositional models for ice‐proximal fans. Plumes are spaced ca 3 km apart and their distribution along the ice front is stable over decades. Numerical modelling also predicts the drainage pattern and meltwater discharge beneath the ice cap; modelled water‐routing patterns are in reasonable agreement with satellite‐mapped plume locations. However, glacial retreat of several kilometres over the past 40 years has limited build‐up of significant ice‐proximal fans. A single fan and moraine ridge is noted from marine‐geophysical surveys. Closer to the ice front there are smaller recessional moraines and polygonal sediment lobes but no identifiable fans. Schematic models of ice‐proximal deposits represent varying glacier‐terminus stability: (i) stable terminus where meltwater sedimentation produces an ice‐proximal fan; (ii) quasi‐stable terminus, where glacier readvance pushes or thrusts up ice‐proximal deposits into a morainal bank; and (iii) retreating terminus, with short still‐stands, allowing only small sediment lobes to build up at melt‐stream portals. These modern investigations are complemented with outcrop and subsurface observations and numerical modelling of an ancient, Ordovician glacial system. Thick turbidite successions and large fans in the Late Ordovician suggest either high‐magnitude events or sustained high discharge, consistent with a relatively mild palaeo‐glacial setting for the former North African ice sheet.  相似文献