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Ice Cap (ice + cap)
Selected AbstractsRate of late Quaternary ice-cap thinning on King George Island, South Shetland Islands, West Antarctica defined by cosmogenic 36Cl surface exposure datingBOREAS, Issue 2 2009YEONG BAE SEONG Glacial landforms on the Barton and Weaver peninsulas of King George Island in the South Shetland Islands, West Antarctica were mapped and dated using terrestrial cosmogenic 36Cl methods to provide the first quantitative terrestrial record for late Quaternary deglaciation in the South Shetland Islands. 36Cl ages on glacially eroded and striated bedrock surfaces range from 15.5±2.5 kyr to 1.0±0.7 kyr. The 36Cl ages are younger with decreasing altitude, indicating progressive downwasting of the southwestern part of the Collins Ice Cap at a rate of ,12 mm yr,1 since 15.5±2.5 kyr ago, supporting the previously published marine records for the timing and estimate of the rate of deglaciation in this region. [source] Ice caps existed throughout the Lateglacial Interstadial in northern Scotland,JOURNAL OF QUATERNARY SCIENCE, Issue 5 2008Tom Bradwell Abstract We constrain, in detail, fluctuations of two former ice caps in NW Scotland with multibeam seabed surveys, geomorphological mapping and cosmogenic 10Be isotope analyses. We map a continuous sequence of 40 recessional moraines stretching from ,10,km offshore to the Wester Ross mountains. Surface-exposure ages from boulders on moraine ridges in Assynt and the Summer Isles region show that substantial, dynamic, ice caps existed in NW Scotland between 13 and 14,ka BP. We interpret this as strong evidence that large active glaciers probably survived throughout the Lateglacial Interstadial, and that during the Older Dryas period (ca. 14,ka BP) ice caps in NW Scotland were thicker and considerably more extensive than in the subsequent Younger Dryas Stadial. By inference, we suggest that Lateglacial ice-cap oscillations in Scotland reflect the complex interplay between changing temperature and precipitation regimes during this climatically unstable period (ca. 15,11,ka BP). © Natural Environment Research Council (NERC) copyright 2008. Reproduced with the permission of NERC. Published by John Wiley & Sons, Ltd. [source] Evidence of genetic distinction and long-term population decline in wolves (Canis lupus) in the Italian ApenninesMOLECULAR ECOLOGY, Issue 3 2004V. Lucchini Abstract Historical information suggests the occurrence of an extensive human-caused contraction in the distribution range of wolves (Canis lupus) during the last few centuries in Europe. Wolves disappeared from the Alps in the 1920s, and thereafter continued to decline in peninsular Italy until the 1970s, when approximately 100 individuals survived, isolated in the central Apennines. In this study we performed a coalescent analysis of multilocus DNA markers to infer patterns and timing of historical population changes in wolves surviving in the Apennines. This population showed a unique mitochondrial DNA control-region haplotype, the absence of private alleles and lower heterozygosity at microsatellite loci, as compared to other wolf populations. Multivariate, clustering and Bayesian assignment procedures consistently assigned all the wolf genotypes sampled in Italy to a single group, supporting their genetic distinction. Bottleneck tests showed evidences of population decline in the Italian wolves, but not in other populations. Results of a Bayesian coalescent model indicate that wolves in Italy underwent a 100- to 1000-fold population contraction over the past 2000,10 000 years. The population decline was stronger and longer in peninsular Italy than elsewhere in Europe, suggesting that wolves have apparently been genetically isolated for thousands of generations south of the Alps. Ice caps covering the Alps at the Last Glacial Maximum (c. 18 000 years before present), and the wide expansion of the Po River, which cut the alluvial plains throughout the Holocene, might have provided effective geographical barriers to wolf dispersal. More recently, the admixture of Alpine and Apennine wolf populations could have been prevented by deforestation, which was already widespread in the fifteenth century in northern Italy. This study suggests that, despite the high potential rates of dispersal and gene flow, local wolf populations may not have mixed for long periods of time. [source] THE LAST GLACIATION OF SHETLAND, NORTH ATLANTICGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2008N.R. GOLLEDGE ABSTRACT. Evidence relating to the extent, dynamics, and relative chronology of the last glaciation of the Shetland Islands, North Atlantic, is presented here, in an attempt to better illuminate some of the controversies that still surround the glacial history of the archipelago. We appraise previous interpretations and compare these earlier results with new evidence gleaned from the interpretation of a high resolution digital terrain model and from field reconnaissance. By employing a landsystems approach, we identify and describe three quite different assemblages of landscape features across the main islands of Mainland, Yell and Unst. Using the spatial interrelationship of these landsystems, an assessment of their constituent elements, and comparisons with similar features in other glaciated environments, we propose a simple model for the last glaciation of Shetland. During an early glacial phase, a coalescent British and Scandinavian ice sheet flowed approximately east to west across Shetland. The terrestrial land-forms created by this ice sheet in the north of Shetland suggest that it had corridors of relatively fast-flowing ice that were partially directed by bed topography, and that subsequent deglaciation was interrupted by at least one major stillstand. Evidence in the south of Shetland indicates the growth of a local ice cap of restricted extent that fed numerous radial outlet glaciers during, or after, ice-sheet deglaciation. Whilst the absolute age of these three landsystems remains uncertain, these new geo-morphological and palaeoglaciological insights reconcile many of the ideas of earlier workers, and allow wider speculation regarding the dynamics of the former British ice sheet. [source] Little ice age alluvial fan development in Langedalen, western NorwayGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 4 2001Simon G. Lewis This paper reports a preliminary investigation of the sedimentary succession in two alluvial fans in western Norway. Sedimentological information is supplemented by palaeoecological data from pollen analysis and the age of the sequence is constrained by six radiocarbon age estimates on woody fragments and peat. These data suggest that significant accumulation of fan sediments took place after AD 1637,1685. Before this, the fluvial landscape and the adjacent slopes may have been more stable with the development of Betula, Salix and Alnus woodland on the valley floor and sides. Although there is no indication of gradual climatic deterioration in the vegetation record from these sites, the radiocarbon chronology suggests that enhanced fan development was coincident with the climatic change associated with the ,Little Ice Age'. This was probably a response to glacier expansion and increased discharge and sediment supply to the alluvial fans from outlets of the Jostedalsbreen ice cap on the southern side of Langedalen. Initial response to climate change in this setting was therefore enhanced geomorphic activity and instability of the valley-side slopes. [source] Absolute S -velocity estimation from receiver functionsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2007L. Svenningsen SUMMARY We present a novel method to recover absolute S velocities from receiver functions. For a homogeneous half-space the S velocity can be calculated from the horizontal slowness and the angle of surface particle motion for an incident P wave. Generally, the calculated S velocity is an apparent half-space value which depends on model inhomogeneity and P -waveform. We therefore, suggest to calculate such apparent half-space S velocities from low-pass filtered (smoothed) receiver functions using a suite of filter-parameters, T. The use of receiver functions neutralize the influence of the P -waveform, and the successive low-pass filterings emphasize the variation of S velocity with depth. We apply this VS,app.(T) technique to teleseismic data from three stations: FUR, BFO and SUM, situated on thick sediments, bedrock and the Greenland ice cap, respectively. The observed VS,app.(T) curves indicate the absolute S velocities from the near surface to the uppermost mantle beneath each station, clearly revealing the different geological environments. Application of linearized, iterative inversion quantify these observations into VS(z) models, practically independent of the S -velocity starting model. The obtained models show high consistency with independent geoscientific results. These cases provide also a general validation of the VS,app.(T) method. We propose the computation of VS,app.(T) curves for individual three-component broad-band stations, both for direct indication of the S velocities and for inverse modelling. [source] Climate change-driven forest fires marginalize the impact of ice cap wasting on KilimanjaroGLOBAL CHANGE BIOLOGY, Issue 7 2005Andreas Hemp Abstract The disappearing glaciers of Kilimanjaro are attracting broad interest. Less conspicuous but ecologically far more significant is the associated increase of frequency and intensity of fires on the slopes of Kilimanjaro, which leads to a downward shift of the upper forest line by several hundred meters as a result of a drier (warmer) climate since the last century. In contrast to common belief, global warming does not necessarily cause upward migration of plants and animals. Here, it is shown that on Kilimanjaro the opposite trend is under way, with consequences more harmful than those due to the loss of the showy ice cap of Africa's highest mountain. [source] The influence of large-scale atmospheric circulation on the surface energy balance of the King George Island ice capINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2001Matthias Braun Abstract During the austral summer 1997,1998 three automatic weather stations were operated at different altitudes on the sub-Antarctic ice cap of King George Island (South Shetland Islands). Snowmelt was derived from energy balance computations. Turbulent heat fluxes were calculated from meteorological measurements using the bulk aerodynamic approach, with net radiation being measured directly. Modelled ablation rates were compared with readings at ablation stakes and continuously measured snow height at a reference site. Snow depletion and daily snowmelt cycles could be well reproduced by the model. Generally, radiation balance provided the major energy input for snowmelt at all altitudes, whereas sensible heat flux was a second heat source only in lower elevations. The average latent heat flux was negligible over the entire measuring period. A strong altitudinal gradient of available energy for snowmelt was observed. Sensible heat flux as well as latent heat flux decreased with altitude. The measurements showed a strong dependence of surface energy fluxes and ablation rates on large-scale atmospheric conditions. Synoptic weather situations were analysed based on AVH RR infrared quicklook composite images and surface pressure charts. Maximum melt rates of up to 20 mm per day were recorded during a northwesterly advection event with meridional air mass transport. During this northwesterly advection, the contribution of turbulent heat fluxes to the energy available for snowmelt exceeded that of the radiation balance. For easterly and southerly flows, continentally toned, cold dry air masses dominated surface energy balance terms and did not significantly contribute to ablation. The link between synoptic situations and ablation is especially valuable, as observed climatic changes along the Antarctic Peninsula are attributed to changes in the atmospheric circulation. Therefore, the combination of energy balance calculations and the analysis of synoptic-scale weather patterns could improve the prediction of ablation rates for climate change scenarios. Copyright © 2001 Royal Meteorological Society [source] Isozyme variation and recent biogeographical history of the long-lived conifer Fitzroya cupressoidesJOURNAL OF BIOGEOGRAPHY, Issue 2 2000A. C. Premoli Abstract Aim Palaeoenvironmental records of Pleistocene glaciation and associated vegetation changes in Patagonia have led to the hypothesis that during the last glacial maximum (LGM) tree species survived locally in favourable habitats. If present populations originated from spread from only one refugium, such as an ice-free area of coastal Chile (Single Refugium hypothesis), we would expect that eastern populations would be genetically depauperate and highly similar to western populations. In contrast, if the ice cap was not complete and tree species persisted in forest patches on both slopes of the Andes (Multiple Refugia hypothesis), we would expect a greater degree of genetic divergence between populations either on opposite sides of the Cordillera (Cordillera Effect scenario) or towards its present-day southern distributional limit where the ice sheet reached its maximum coverage (Extent-of-the-Ice scenario). Location We tested this refugia hypothesis using patterns of isozyme variation in populations sampled over the entire modern range of the endemic conifer Fitzroya cupressoides (Mol.) Johnst. (Cupressaceae) in temperate South America. Methods Fresh foliage was collected from twenty-four populations and analysed by horizontal electrophoresis on starch gels. Results Twenty-one putative loci were reliably scored and 52% were polymorphic in at least one population. Populations from the eastern slope of the Andes were genetically more variable than those from the western slope; the former had a greater mean number of alleles per locus, a larger total number of alleles and rare alleles, and higher polymorphism. Genetic identities within western populations were greater than within eastern populations. Discriminant analyses using allelic frequencies of different grouping schedules of populations were non significant when testing for the Single Refugium hypothesis whereas significant results were obtained for the Multiple Refugia hypothesis. Main conclusions Our results indicate that present Fitzroya populations are the result of spreading from at least two, but possibly more, glacial refugia located in Coastal Chile and on the southern flanks of the Andes in Argentina. [source] Climate change and its impact on the forests of KilimanjaroAFRICAN JOURNAL OF ECOLOGY, Issue 2009Andreas Hemp Abstract Cloud forests are of great importance in the hydrological functioning of watersheds in subhumid East Africa. However, the montane forests of Mt. Kilimanjaro are heavily threatened by global change impacts. Based on an evaluation of over 1500 vegetation plots and interpretation of satellite imagery from 1976 and 2000, land-cover changes on Kilimanjaro were evaluated and their impact on the water balance estimated. While the vanishing glaciers of Kilimanjaro attract broad interest, the associated increase of frequency and intensity of fires on the slopes of Kilimanjaro is less conspicuous but ecologically far more significant. These climate change-induced fires have lead to changes in species composition and structure of the forests and to a downward shift of the upper forest line by several hundred metres. During the last 70 years, Kilimanjaro has lost nearly one-third of its forest cover, in the upper areas caused by fire, on the lower forest border mainly caused by clearing. The loss of 150 km2 of cloud forest , the most effective source in the upper montane and subalpine fog interception zone , caused by fire during the last three decades means a considerable reduction in water yield. In contrast to common belief, global warming does not necessarily cause upward migration of plants and animals. On Kilimanjaro the opposite trend is under way, with consequences more harmful than those due to the loss of the showy ice cap of Africa's highest mountain. [source] Micrometeorites from the northern ice cap of the Novaya Zemlya archipelago, Russia: The first occurrenceMETEORITICS & PLANETARY SCIENCE, Issue 3 2003Dmitry D. BADJUKOV The 1 Kyr old glacier has decreased in volume and coverage during the last 40 years, leaving the spherules contained in the ice at the margins of the glacier where they can be easily collected. The spherules are similar in their appearance, texture, and mineralogy to cosmic spherules found in deep-sea sediments in Greenland and Antarctica. Silicate spherules have typical bar-like textures (75%) or porphyritic textures (15%), while other spherules are glassy (7%). The spherules from Novaya Zemlya are altered only slightly. There are spherules consisting of iron oxides, metal cores with iron oxide rims, a continuous network of iron oxide dendrites in a glass matrix, and particles rich in chromite (3%). Some spherules contain metal droplets and relict forsterite and low-Ca pyroxene. Silicate spherule compositions match compositions of other cosmic spherules. Both Nova Zemlya and other cosmic spherules are close to carbonaceous chondrite matrices in patterns of variations for Ca, Mg, Si, and Al, which might suggest that their predecessor was similar to carbonaceous chondrite matrices. Unmelted micrometeorites are generally depleted in Ca and Mg and enriched in Al relative to cosmic spherules. The depletion of the micrometeorites in Ca and Mg can be connected with their terrestrial alteration (Kurat et al. 1994), while the Al enrichment seems to be primary. [source] Chronology of deglaciation based on 10Be dates of glacial erosional features in the Grimsel Pass region, central Swiss AlpsBOREAS, Issue 4 2006MEREDITH A. KELLY Surface exposure dating, using in situ produced cosmogenic 10Be, is applied to determine the time since deglaciation of bedrock surfaces in the Grimsel Pass region. Nine 10Be dates from bedrock surfaces corrected for cover by snow are minimum ages for deglaciation of the pass. Four 10Be dates from surfaces below 2500 meters above sea level (m a.s.l.) on Nägelisgrätli, east of Grimsel Pass, yield ages that range from about 14 000 to 11 300 years. Three 10Be dates from locations above 2600 m a.s.l. on Nägelisgrätli are between about 11 700 and 10 400 years. Two 10Be dates from locations at 2560 m a.s.l. below Juchlistock are about 12 100 and 11 000 years. The geographical distribution of 10Be dates on Nägelisgrätli either may show the timing of progressive deglaciation of Grimsel Pass or may reflect differences in subglacial erosion of bedrock in the pass region. All dates are discussed in the context of deglaciation of the late Würmian Alpine ice cap and deglaciation from Last Glacial Maximum (LGM) ice extents in other regions. [source] Late Pleistocene glacial and lake history of northwestern RussiaBOREAS, Issue 3 2006EILIV LARSEN Five regionally significant Weichselian glacial events, each separated by terrestrial and marine interstadial conditions, are described from northwestern Russia. The first glacial event took place in the Early Weichselian. An ice sheet centred in the Kara Sea area dammed up a large lake in the Pechora lowland. Water was discharged across a threshold on the Timan Ridge and via an ice-free corridor between the Scandinavian Ice Sheet and the Kara Sea Ice Sheet to the west and north into the Barents Sea. The next glaciation occurred around 75,70 kyr BP after an interstadial episode that lasted c. 15 kyr. A local ice cap developed over the Timan Ridge at the transition to the Middle Weichselian. Shortly after deglaciation of the Timan ice cap, an ice sheet centred in the Barents Sea reached the area. The configuration of this ice sheet suggests that it was confluent with the Scandinavian Ice Sheet. Consequently, around 70,65 kyr BP a huge ice-dammed lake formed in the White Sea basin (the ,White Sea Lake'), only now the outlet across the Timan Ridge discharged water eastward into the Pechora area. The Barents Sea Ice Sheet likely suffered marine down-draw that led to its rapid collapse. The White Sea Lake drained into the Barents Sea, and marine inundation and interstadial conditions followed between 65 and 55 kyr BP. The glaciation that followed was centred in the Kara Sea area around 55,45 kyr BP. Northward directed fluvial runoff in the Arkhangelsk region indicates that the Kara Sea Ice Sheet was independent of the Scandinavian Ice Sheet and that the Barents Sea remained ice free. This glaciation was succeeded by a c. 20-kyr-long ice-free and periglacial period before the Scandinavian Ice Sheet invaded from the west, and joined with the Barents Sea Ice Sheet in the northernmost areas of northwestern Russia. The study area seems to be the only region that was invaded by all three ice sheets during the Weichselian. A general increase in ice-sheet size and the westwards migrating ice-sheet dominance with time was reversed in Middle Weichselian time to an easterly dominated ice-sheet configuration. This sequence of events resulted in a complex lake history with spillways being re-used and ice-dammed lakes appearing at different places along the ice margins at different times. [source] Climate change and ,anomalous' glacier fluctuations: the southwest outlets of Mrdalsjökull, IcelandBOREAS, Issue 2 2004ANDREW F. CASELY Evidence of past glacier fluctuations is valuable palaeoenvironmental data, but determining their relationship to climatic change is sometimes complex because of differing glacier sensitivities and patterns of response. In Iceland, a diverse range of glaciation creates changing geographical patterns of response to climatic changes. The outlet glaciers of the Márdalsjökull ice cap in southern Iceland have produced detailed, but differing, records of change. For a key southwestern sector of the ice cap, we specifically searched for evidence equivalent to the c. 4500 BP, c. 3100 BP and c. 1200 BP advances of Sólheimajökull reported earlier. A combination of geomorphological mapping and dating by tephrochronology and lichenometry was used to constrain the glacier advances and determine the relative magnitude of Neoglacial glacier episodes. This is a key step towards creating a record of the changes for the entire ice cap. Major glacier advances c. 4500,1000 BP previously identified on the southern margin of Márdalsjökull are shown not to have occurred in this sector, where Neoglacial maxima occur post-1755 AD. [source] Ages and inferred causes of Late Pleistocene glaciations on Mauna Kea, Hawai'i,JOURNAL OF QUATERNARY SCIENCE, Issue 6-7 2008Jeffrey S. Pigati Abstract Glacial landforms on Mauna Kea, Hawai'i, show that the summit area of the volcano was covered intermittently by ice caps during the Late Pleistocene. Cosmogenic 36Cl dating of terminal moraines and other glacial landforms indicates that the last two ice caps, called Older Makanaka and Younger Makanaka, retreated from their maximum positions approximately 23,ka and 13,ka, respectively. The margins and equilibrium line altitudes of these ice caps on the remote, tropical Pacific island were nearly identical, which would seem to imply the same mechanism for ice growth. But modelling of glacier mass balance, combined with palaeotemperature proxy data from the subtropical North Pacific, suggests that the causes of the two glacial expansions may have been different. Older Makanaka air atop Mauna Kea was likely wetter than today and cold, whereas Younger Makanaka times were slightly warmer but significantly wetter than the previous glaciation. The modelled increase in precipitation rates atop Mauna Kea during the Late Pleistocene is consistent with that near sea level inferred from pollen data, which suggests that the additional precipitation was due to more frequent and/or intense tropical storms associated with eastward-moving cold fronts. These conditions were similar to modern La Niña (weak ENSO) conditions, but persisted for millennia rather than years. Increased precipitation rates and the resulting steeper temperature lapse rates created glacial conditions atop Mauna Kea in the absence of sufficient cooling at sea level, suggesting that if similar correlations existed elsewhere in the tropics, the precipitation-dependent lapse rates could reconcile the apparent difference between glacial-time cooling of the tropics at low and high altitudes. Copyright © 2008 John Wiley & Sons, Ltd. [source] Ice caps existed throughout the Lateglacial Interstadial in northern Scotland,JOURNAL OF QUATERNARY SCIENCE, Issue 5 2008Tom Bradwell Abstract We constrain, in detail, fluctuations of two former ice caps in NW Scotland with multibeam seabed surveys, geomorphological mapping and cosmogenic 10Be isotope analyses. We map a continuous sequence of 40 recessional moraines stretching from ,10,km offshore to the Wester Ross mountains. Surface-exposure ages from boulders on moraine ridges in Assynt and the Summer Isles region show that substantial, dynamic, ice caps existed in NW Scotland between 13 and 14,ka BP. We interpret this as strong evidence that large active glaciers probably survived throughout the Lateglacial Interstadial, and that during the Older Dryas period (ca. 14,ka BP) ice caps in NW Scotland were thicker and considerably more extensive than in the subsequent Younger Dryas Stadial. By inference, we suggest that Lateglacial ice-cap oscillations in Scotland reflect the complex interplay between changing temperature and precipitation regimes during this climatically unstable period (ca. 15,11,ka BP). © Natural Environment Research Council (NERC) copyright 2008. Reproduced with the permission of NERC. Published by John Wiley & Sons, Ltd. [source] Late Quaternary terrestrial tephrochronology of Iceland,frequency of explosive eruptions, type and volume of tephra deposits,JOURNAL OF QUATERNARY SCIENCE, Issue 2 2008Gudrún Larsen Abstract Close to 100 silicic tephra layers have been identified in Icelandic terrestrial soils of Holocene age. The majority of these tephras were erupted at the Hekla, Torfajökull, Öræfajökull, Askja, Snæfellsjökull, Eyjafjallajökull and Katla central volcanoes. By far the most active is Hekla with close to 50 identified silicic tephra layers in ,8000 years, showing an inverse relationship between eruption frequency and volume of erupted tephra. Volumes of uncompacted silicic tephra layers range from <0.01,km3 to >10,km3, with nearly 50% of known tephra volumes lying between 0.1 and 0.5,km3. Seven closely spaced Hekla eruptions in the period 950,550 BC with identical major element composition illustrate the need of stratigraphic control in short and long distance correlations. A 2600 year old tephra geochemically indistinguishable from the Borrobol tephra is a reminder that no tephra is geochemically unique. The major producers of basaltic tephra are the volcanic systems that are partly covered by ice, or partly lying within areas of high groundwater or extending offshore, i.e. the Grímsvötn, Katla, Veidivötn-Bárdarbunga, Reykjanes, Kverkfjöll and Vestmannaeyjar volcanic systems. The best known eruption record is that of the Katla system with over 170 identified basaltic tephra layers and more than 300 estimated in 8400 years. The Grímsvötn system is currently the most active volcanic system with over 70 eruptions during the last 1100 years. Volumes of uncompacted basaltic tephra layers range from <0.01,km3 to >20,km3, the majority of known tephra volumes lying between 0.1 and 1,km3. The most voluminous basaltic tephra deposit, the ,10,200,yr old Saksunarvatn tephra, may however represent more than one eruption on the Grímsvötn system. Deposition of approximately 800 basaltic tephra layers during the last 9000 14C years is estimated but many of those erupted from volcanoes within ice caps have not been preserved. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||||||||