Climate variability and glacial processes in eastern Iceland during the past 700 years based on varved lake sediments     

JOHAN STRIBERGER  SVANTE BJÖRCK  ÓLAFUR INGÓLFSSON  KURT H. KJÆR  IAN SNOWBALL  CINTIA B. UVO 《Boreas: An International Journal of Quaternary Research》2011,40(1):28-45

Striberger, J., Björck, S., Ingólfsson, Ó., Kjær, K. H., Snowball, I. & Uvo, C. B. 2010: Climate variability and glacial processes in eastern Iceland during the past 700 years based on varved lake sediments. Boreas, 10.1111/j.1502‐3885.2010.00153.x. ISSN 0300‐9483. Properties of varved sediments from Lake Lögurinn in eastern Iceland and their link to climate and glacial processes of Eyjabakkajökull, an outlet glacier of the Vatnajökull icecap, were examined. A varve chronology, which covers the period AD 1262–2005, was constructed from visual observations, high‐resolution images, X‐ray density and geochemical properties determined from X‐radiography and X‐ray fluorescence scanning. Independent dating provided by ¹³⁷Cs analysis and eight historical tephras verify the varve chronology. The thickness of dark‐coloured seasonal laminae, formed mainly of coarser suspended matter from the non‐glacial river Grímsá, is positively correlated (r=0.70) with winter precipitation, and our 743‐year‐long varve series indicates that precipitation was higher and more varied during the later part of the Little Ice Age. Light‐coloured laminae thickness, controlled mainly by the amount of finer suspended matter from the glacial river Jökulsáí Fljótsdal, increased significantly during the AD 1972 surge of Eyjabakkajökull. As a consequence of the surge, the ice‐dammed Lake Háöldulón formed and recurrently drained and delivered significant amounts of rock flour to Lake Lögurinn. Based on these observations, and the recurring cyclic pattern of periods of thicker light‐coloured laminae in the sediment record, we suggest that Eyjabakkajökull has surged repeatedly during the past 743 years, but with an increased frequency during the later part of the Little Ice Age.  相似文献   

Generation of warps by accretion flows     

John E. Beckman  MartÍ n LÓpez-Corredoira  Juan Betancort-Rijo  Nieves Castro-RodrÍguez  Andrew Cardwell 《Astrophysics and Space Science》2003,284(2):747-751

We present ample evidence for the presence of continuing gaseous infall to the Galactic plane, and then show how interaction of this gas with the disc gas yields a warp of the observed amplitude and direction. The mechanism works for galaxies in general, predicting a small proportion of U-shaped warps, as observed. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Selective blackening of bioclasts via mixing‐zone aragonite neomorphism in Late Triassic limestone,Zlatibor Mountains,Serbia     

KINGA HIPS  JÁNOS HAAS  MÁRIA VIDÓ  ZSUZSANNA BARNA  DIVNA JOVANOVIĆ  MILAN N. SUDAR  ZOLTÁN SIKLÓSY 《Sedimentology》2011,58(4):854-877

A peculiar facies of the Norian–Rhaetian Dachstein‐type platform carbonates, which contains large amounts of blackened bioclasts and dissolutional cavities filled by cements and internal sediments, occurs in the Zlatibor Mountains, Serbia. Microfacies investigations revealed that the blackened bioclasts are predominantly Solenoporaceae, with a finely crystalline, originally aragonite skeleton of fine cellular structure. Blackening of other bioclasts also occurs subordinately. Solenoporacean‐dominated reefs, developed behind the platform margin patch‐reef tract, were the main source of sand‐sized detritus. The blackened and other non‐blackened bioclasts are incorporated in automicrite cement. Radiaxial fibrous calcite cements in the dissolutional cavities are also black, dark grey or white. Reworked black pebbles were reported from many occurrences of peritidal deposits; in those cases, the blackening took place under pedogenic, meteoric diagenetic conditions. In contrast, in the inner platform deposits of the Ilid?a Limestone, the blackening of bioclasts occurred in a marine–meteoric mixing‐zone, as indicated by petrographic features and geochemical data of the skeleton‐replacing calcite crystals. Attributes of mixing‐zone pore waters were controlled by mixing corrosion, different solubility of carbonate minerals and microbial decomposition of organic matter. In the moderate‐energy inner platform environment, large amounts of microbial organic tissue were accumulated and subsequently decomposed, triggering selective blackening in the course of early, shallow burial diagenesis. The δ¹⁸O and δ¹³C values of the mixing‐zone precipitates and replacive calcite do not produce a linear mixing trend. Variation mainly resulted from microbial decomposition of organic matter that occurred under mixing‐zone conditions. The paragenetic sequence implies cyclic diagenetic conditions that were determined by marine, meteoric and mixing‐zone pore fluids. The diagenetic cycles were controlled by sea‐level fluctuations of moderate amplitude under a semi‐arid to semi‐humid climate.  相似文献   

MAPPING AND INTERPRETATION OF FIELD PHENOMENA FOR GROUNDWATER RECONNAISSANCE IN A PRAIRIE ENVIRONMENT,ALBERTA, CANADA     

J. TÓTH 《水文科学杂志》2013,58(2):20-68

ABSTRACT

Theoretically, a small drainage basin may be divided into equal areas of downward flow and upward flow of groundwater. In regions where surface water does not obscure the phenomena produced by groundwater, these areas can be differentiated by mapping springs, seepages, groundwater levels, flowing wells, chemical quality of water, natural vegetation, salt precipitates, quality of crops, soap holes, and moist and dry depressions.

Mapping and interpretation of field phenomena have been carried out in a section of the Ghostpine Creek valley in a Prairie environment. The relief is gently rolling, the geology is simple, and the climate is cold, humid, and continental. The area of the “north flow-systems” is apportioned as follows: 26 per cent underlain by downward flow; 42 per cent underlain by a mid-line area; and 32 per cent underlain by upward flow.

Noting that groundwater flow is nearly parallel to the water table in the vicinity of the mid-line these results comply with the above-mentioned theory of groundwater flow distribution in small drainage basins. Thus, the method is suggested for: 1. A reconnaissance study of the groundwater regime in certain areas, and 2. Specific problems related to groundwater in a Prairie environment, such as: finding suitable locations for dug-out type water supplies, estimating prospects for slough-draining and irrigation, and explanation of the development of certain soil types. For such purposes, the method appears to be competitive with test drilling.  相似文献   

River flow forecasting system with data management,graphical river network control and interactive operation     

LÁSZLÓ IRITZ 《水文科学杂志》2013,58(6):637-651

Abstract

The feasibility and success of a forecasting system depend on many factors. Although the models may be of the highest accuracy, they cannot make a forecasting system effective without a well organized database and interpretable output. The interaction between the processes of data management, computation and output presentation should be dynamic. A complete river forecasting system for IBM (or compatible) personal computers aimed at meeting the above demands has been developed at the Department of Hydrology of Uppsala University. The program package sets up the river network, stores a database for it, supplies the appropriate data for a wide choice of forecasting models, and gives interpretable output. The functions are supported by screen graphics. The paper presents this system, the most important points of the algorithms, and an example application.  相似文献   

Formational history of the Wicklow Trough: a marine-transgressed tunnel valley revealing ice flow velocity and retreat rates for the largest ice stream draining the late-Devensian British–Irish Ice Sheet     

Mark Coughlan  Zsuzsanna TÓth  Katrien J. J. Van Landeghem  Stephen Mccarron  Andrew J. Wheeler 《第四纪科学杂志》2020,35(7):907-919

The Wicklow Trough is one of several Irish Sea bathymetric deeps, yet unusually isolated from the main depression, the Western Trough. Its formation has been described as proglacial or subglacial, linked to the Irish Sea Ice Stream (ISIS) during the Last Glacial Maximum. The evolution of the Wicklow Trough and neighbouring deeps, therefore, help us to understand ISIS dynamics, when it was the main ice stream draining the former British–Irish Ice Sheet. The morphology and sub-seabed stratigraphy of the 18 km long and 2 km wide Wicklow Trough is described here from new multibeam echosounder data, 60 km of sparker seismic profiles and five sediment cores. At a maximum water depth of 82 m, the deep consists of four overdeepened sections. The heterogeneous glacial sediments in the Trough overlay bedrock, with indications of flank mass-wasting and subglacial bedforms on its floor. The evidence strongly suggests that the Wicklow Trough is a tunnel valley formed by time-transgressive erosional processes, with pressurised meltwater as the dominant agent during gradual or slow ice sheet retreat. Its location may be fault-controlled, and the northern end of the Wicklow Trough could mark a transition from rapid to slow grounded ice margin retreat, which could be tested with modelling.  相似文献   

Forecasting wind gusts in complex terrain   总被引：1，自引：1，他引：0  

H. Ágústsson  H. Ólafsson 《Meteorology and Atmospheric Physics》2009,103(1-4):173-185

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Gravity wave breaking in easterly flow over Greenland and associated low level barrier- and reverse tip-jets     

Haraldur Ólafsson  Hálfdán Ágústsson 《Meteorology and Atmospheric Physics》2009,104(3-4):191-197

A first evidence of severe turbulence in the lower stratosphere during easterly tropospheric flow over Greenland is presented. A numerical simulation shows the turbulence to be associated with gravity wave breaking and that simulating with a horizontal resolution of 3 km gives substantially greater and more realistic turbulence than at a 9 km horizontal resolution. It is concluded that real-time simulations at high resolutions would improve aviation forecasts. As the atmospheric flow impinges on South-Greenland a barrier jet, a reverse tip jet and amplified mountain waves with secondary wave breaking are generated at the same time.  相似文献   

Oxygen and Hydrogen Isotopic Signatures of Large Atmospheric Ice Conglomerations     

J. Martinez-FrÍAs  A. Delgado  M. MillÁN  E. Reyes  F. Rull  D. Travis  R. Garcia  F. LÓPez-Vera  J. A. RodrÍGuez-Losada  J. A. Martin-Rubi  J. Raya  E. Santoyo 《Journal of Atmospheric Chemistry》2005,52(2):185-202

Specific studies about the stable isotope composition (¹⁸O/¹⁶O and D/H) of atmospheric icy conglomerations are still scarce. The present work offers, for the first time, a very detailed analysis of oxygen and hydrogen isotopic signatures of unusually large ice conglomerations, or “megacryometeors”, that fell to the ground in Spain during January 2000. The hydrochemical analysis is based on the bulk isotopic composition and systematic selective sampling (deuterium isotopic mapping) of eleven selected specimens. δ¹⁸O and δD (V-SMOW) of all samples fall into the Meteoric Water Line matching well with typical tropospheric values. The distribution of the samples on Craig's line suggests either a variation in condensation temperature and/or different residual fractions of water vapour (Rayleigh processes). Three of the largest megacryometeors exhibited unequivocally distinctive negative values (δ¹⁸O = −17.2%₀ and δD = −127 %₀ V-SMOW), (δ¹⁸O = −15.6%₀ and δD = −112%₀ V-SMOW) and (δ¹⁸O = −14.4%₀ and δD = −100%₀ V-SMOW), suggesting an atmospheric origin typical of the upper troposphere. Theoretical calculations indicate that the vertical trajectory of growth was lower than 3.2 km. During the period in which the fall of megacryometeors occurred, anomalous atmospheric conditions were observed to exist: a substantial lowering of the tropopause with a deep layer of saturated air below, ozone depression and strong wind shear. Moreover, these large ice conglomerations occurred during non-thunderstorm conditions, suggesting an alternative process of ice growth was responsible for their formation.  相似文献   

Map and GIS database of glacial landforms and features related to the last British Ice Sheet   总被引：1，自引：0，他引：1  

CHRIS D. CLARK  DAVID J. A. EVANS  ANJANA KHATWA  TOM BRADWELL  COLM J. JORDAN  STUART H. MARSH  WISHART A. MITCHELL  MARK D. BATEMAN 《Boreas: An International Journal of Quaternary Research》2004,33(4):359-375

A review of the academic literature and British Geological Survey mapping is employed to produce a 'Glacial Map', and accompanying geographic information system (GIS) database, of features related to the last (Devensian) British Ice Sheet. The map (1:625 000) is included in a folder and GIS data are freely available by web download (http://www.shef.ac.uk/geography/staff/clark_chris/britice.html). Emphasis is on information that constrains the last ice sheet. The following are included: moraines, eskers, drumlins, meltwater channels, tunnel valleys, trimlines, limit of key glacigenic deposits, glaciolacustrine deposits, ice-dammed lakes, erratic dispersal patterns, shelf-edge fans and the Loch Lomond Readvance limit of the main ice cap. The GIS contains over 20 000 features split into thematic layers (as above). Individual features are attributed such that they can be traced back to their published sources. Given that the published sources of information that underpin this work were derived by piecemeal effort over 150 years, then our main caveat is of data consistency and reliability. It is hoped that this compilation will stimulate greater scrutiny of published data, assist in palaeoglaciological reconstructions and facilitate use of field evidence in numerical ice-sheet modelling. It may also help direct field workers in their future investigations.  相似文献