Ice Masses (ice + mass)

Distribution by Scientific Domains

Selected Abstracts

Depositional environment of Sirius Group sediments, Table Mountain, Dry Valleys area, Antarctica

James R. Goff
Outcrops and cores of the Sirius Group sediments were studied at Table Mountain, Dry Valleys area, Antarctica. These sediments form a surficial veneer at least 9.5 m thick. Three facies , a gravelly sandstone, a sandstone, and a sandy conglomerate , are mapped and described from 13 outcrops and three cores. The gravelly sandstone, constituting 13%of all cored material, is bimodal with matrix-supported clasts comprising 5,33%of the facies. Fabric analysis indicates that it was deposited primarily by lodgment from glacial ice but with minor elements of meltout and flow. The sandstone facies, constituting 77%of all cored material, is a well-sorted, fine- to medium-grained sand, which commonly has laminated bedding. It is predominantly a glaciofluvial deposit but has some glaciolacustrine elements. The sandy conglomerate, constituting 10%of all cored material, is a minor facies. It is massive and clast-supported. It was deposited in a high-energy environment suggestive of subglacial meltwater channels. Sirius Group sediments at Table Mountain are the result of wet-based ice advancing and retreating over waterlain deposits. This is consistent with an advancing ice mass in climatic conditions that were warmer than present. The majority of the sediments were deposited by alpine ice following a similar pathway to the present-day Ferrar Glacier and as such the depositional environment is one that concurs with evidence of a stable East Antarctic Ice Sheet approach. At Table Mountain, the predominantly glaciofluvial and glaciolacustrine facies is inferred to represent a more distal part of the Sirius Group environment than that seen at other outcrops in the Dry Valleys. [source]

Microphysical structure of a developing convective snow cloud simulated by an improved version of the multi-dimensional bin model

Ryohei Misumi
Abstract A new version of the multi-dimensional bin-microphysics model, which employs four dimensions to represent ice-particle properties (ice mass, solute mass, aspect ratio and volume), was developed. The model was incorporated into an adiabatic parcel model to simulate the developing stage of a convective snow cloud observed over the Sea of Japan. The results suggest that crystals originating from deposition/condensation,freezing nuclei grow the fastest in the cloud, and isometric crystals among them effectively act as embryos of graupels. Copyright © 2010 Royal Meteorological Society [source]

The Keiva ice marginal zone on the Kola Peninsula, northwest Russia: a key component for reconstructing the palaeoglaciology of the northeastern Fennoscandian Ice Sheet

BOREAS, Issue 4 2007
Clas H, ttestrand
One of the key elements in reconstructing the palaeoglaciology of the northeastern sector of the Fennoscandian Ice Sheet is the Keiva ice marginal zone (KIZ) along the southern and eastern coast of Kola Peninsula, including the Keiva I and II moraines. From detailed geomorphological mapping of the KIZ, primarily using aerial photographs and satellite images, combined with fieldwork, we observed the following. (1) The moraines display ice contact features on both the Kola side and the White Sea side along its entire length. (2) The Keiva II moraine is sloping along its length from c. 100 m a.s.l. in the west (Varzuga River) to c. 250 m a.s.l. in the east (Ponoy River). (3) The KIZ was partly overrun and fragmented by erosive White Sea-based ice after formation. From these observations we conclude that the KIZ is not a synchronous feature formed along the lateral side of a White Sea-based ice lobe. If it was, the moraines should have a reversed slope. Rather, we interpret it to be time transgressive, formed at a northeastward-migrating junction between a warm-based Fennoscandian Ice Sheet expanding from the west and southwest into the White Sea depression, and a sluggish cold-based ice mass centred over eastern Kola Peninsula. In contrast to earlier reconstructions, we find it unlikely that an ice expansion of this magnitude was a mere re-advance during the deglaciation. Instead, we propose that the KIZ was formed during a major expansion of a Fennoscandian Ice Sheet at a time pre-dating the Last Glacial Maximum. [source]

Why we're still arguing about the Pleistocene occupation of the Americas

Nicole M. Waguespack
Abstract Although empirical issues surround the when, how, and who questions of New World colonization, much of current debate hinges on theoretical problems because it has become clear that our understanding of New World colonization is not resolute.1 In fact, the central issues of debate have remained essentially unchanged for the last eighty years. The now classic and probably incorrect story of New World colonization begins in Late Pleistocene Siberia, with small a population of foragers migrating across Beringia (,13,500 calendar years before present (CYBP) (Box 1) through an ice-free corridor and traveling through the interior of North America. High mobility and rapid population growth spurred southward expansion into increasingly distant unoccupied regions, culminating in the settlement of the Southern Cone of South America. Armed with the skills and weapons needed to maintain a megafauna-based subsistence strategy, early colonists necessarily had the adaptive flexibility to colonize a diverse array of Pleistocene landscapes. For a time, this scenario seemed well substantiated. The earliest sites in South America were younger than their northern counterparts, fluted artifacts were found across the Americas within a brief temporal window, and projectile points capable of wounding elephant-sized prey were commonly found in association with proboscidean remains. The Bering Land Bridge connecting Asia to Alaska and an ice-free corridor providing passage between the Pleistocene ice masses of Canada seemed to provide a clear route of entry for Clovis colonists. However, recent archeological, paleoenvironmental, biological, and theoretical work largely questions the plausibility of these events. [source]

Talus Instability in a Recent Deglaciation Area and Its Relationship to Buried Ice and Snow Cover Evolution (Picacho Del Veleta, Sierra Nevada, Spain)

Antonio Gómez
The southernmost glacier in Europe formed during the Little Ice Age at the foot of the north wall of Picacho del Veleta (3 398 m) in Sierra Nevada, in the southeast region of the Iberian Peninsula (lat. 37,03,N, long. 3,22,W). The glacier gradually retreated during the last century, leaving a large talus slope at the base of the wall. The unconsolidated material covering the ice masses acted as a thermal insulator. Recent bottom temperature of snow (BTS) analyses and drillings indicate that the ice still exists within the talus. Evidence from field observations made during the period 1995,2001, revealed that large mass movements occurred during the driest summers (1998 and especially, 1999 and 2000) when the talus was snow free. These conditions suggest a direct relationship between talus stability and thermal insulation from the snow cover in areas where buried ice or decaying marginal permafrost exists. [source]

The Donegal ice dome, northwest Ireland: dimensions and chronology,

Colin K. Ballantyne
Abstract Geomorphological evidence indicates that Donegal was formerly occupied by an ice dome that extended offshore to the west, northwest and north and was confluent with adjacent ice masses to the east and south. Erosive warm-based ice over-rode almost all the highest mountains, implying an ice-divide altitude greater than 700,m. Only six peripheral summits escaped glacial modification, implying either that they remained above the ice surface as nunataks or supported a thin cover of protective cold-based ice. Gibbsite, a pre-last glacial weathering product, is preferentially represented on summits that escaped glacial modification. Cosmogenic 10Be exposure ages of 18.6,±,1.4 to 15.9,±,1.0,k yr for coastal sites confirm that Donegal ice extended offshore at the last glacial maximum. Reconstruction of the form of the Donegal ice dome suggests a former minimum ice thickness of ,500,m close to the present coastline in the west and northwest, and ,400,m near the coast of the Inishowen Peninsula in the north, with the ice extending at least 20,km across the adjacent shelf to the west and northwest. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Ice-wedge pseudomorphs and frost-cracking structures in Weichselian sediments, central-west Poland

Marek Ewertowski
Abstract Wedge-shaped structures are described from three sites in the central Wielkopolska region (central-west Poland) in two main positions: (1) within fluvioglacial deposits below the Weichselian subglacial till and (2) within recessional deposits above this subglacial till. The wedges are interpreted as ice-wedge pseudomorphs (Rensko site), relict frost cracks (Tomice site) and thermokarst-affected ice-wedge pseudomorphs (Annowo-Kiszkowo area). The pseudomorphs suggest that thermal-contraction cracking occurred in the region in front of the advancing Weichselian ice sheet, as well as following its recession. Frost structures, which are interpreted as having degraded slowly, were much more affected by thermokarst processes (Annowo-Kiszkowo area) than those in the Rensko and Tomice sites which probably thawed rapidly, due to an insulating and warming effect of the overlying ice masses. The development of ice wedges was influenced by wet conditions in former depressions between ice-cored ridges or by large amounts of meltwater in the proglacial environment. These periglacial features support previous hypotheses that climatic conditions in the Wielkopolska region after the last ice-sheet recession changed gradually from glacial to periglacial. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Intercomparison of model simulations of mixed-phase clouds observed during the ARM Mixed-Phase Arctic Cloud Experiment.

II: Multilayer cloud
Abstract Results are presented from an intercomparison of single-column and cloud-resolving model simulations of a deep, multilayered, mixed-phase cloud system observed during the Atmospheric Radiation Measurement (ARM) Mixed-Phase Arctic Cloud Experiment. This cloud system was associated with strong surface turbulent sensible and latent heat fluxes as cold air flowed over the open Arctic Ocean, combined with a low pressure system that supplied moisture at mid-levels. The simulations, performed by 13 single-column and 4 cloud-resolving models, generally overestimate liquid water path and strongly underestimate ice water path, although there is a large spread among models. This finding is in contrast with results for the single-layer, low-level mixed-phase stratocumulus case in Part I, as well as previous studies of shallow mixed-phase Arctic clouds, that showed an underprediction of liquid water path. These results suggest important differences in the ability of models to simulate deeper Arctic mixed-phase clouds versus the shallow, single-layered mixed-phase clouds in Part I. The observed liquid-ice mass ratios were much smaller than in Part I, despite the similarity of cloud temperatures. Thus, models employing microphysics schemes with temperature-based partitioning of cloud liquid and ice masses are not able to produce results consistent with observations for both cases. Models with more sophisticated, two-moment treatment of cloud microphysics produce a somewhat smaller liquid water path closer to observations. Cloud-resolving models tend to produce a larger cloud fraction than single-column models. The liquid water path and cloud fraction have a large impact on the cloud radiative forcing at the surface, which is dominated by long-wave flux. Copyright © 2009 Royal Meteorological Society [source]

Depositional environments and chronology of Late Weichselian glaciation and deglaciation in the central North Sea

BOREAS, Issue 3 2010
Graham, A.G.C., Lonergan, L. & Stoker, M.S. 2010: Depositional environments and chronology of Late Weichselian glaciation and deglaciation in the central North Sea. Boreas, Vol. 39, pp. 471,491. 10.1111/j.1502-3885.2010.00144.x. ISSN 0300-9483. Geological constraints on ice-sheet deglaciation are essential for improving the modelling of ice masses and understanding their potential for future change. Here, we present a detailed interpretation of depositional environments from a new 30-m-long borehole in the central North Sea, with the aim of improving constraints on the history of the marine Late Pleistocene British,Fennoscandian Ice Sheet. Seven units characterize a sequence of compacted and distorted glaciomarine diamictons, which are overlain by interbedded glaciomarine diamictons and soft, bedded to homogeneous marine muds. Through correlation of borehole and 2D/3D seismic observations, we identify three palaeoregimes. These are: a period of advance and ice-sheet overriding; a phase of deglaciation; and a phase of postglacial glaciomarine-to-marine sedimentation. Deformed subglacial sediments correlate with a buried suite of streamlined subglacial bedforms, and indicate overriding by the SE,NW-flowing Witch Ground ice stream. AMS 14C dating confirms ice-stream activity and extensive glaciation of the North Sea during the Last Glacial Maximum, between c. 30 and 16.2 14C ka BP. Sediments overlying the ice-compacted deposits have been reworked, but can be used to constrain initial deglaciation to no later than 16.2 14C ka BP. A re-advance of British ice during the last deglaciation, dated at 13.9 14C ka BP, delivered ice-proximal deposits to the core site and deposited glaciomarine sediments rapidly during the subsequent retreat. A transition to more temperate marine conditions is clear in lithostratigraphic and seismic records, marked by a regionally pervasive iceberg-ploughmarked erosion surface. The iceberg discharges that formed this horizon are dated to between 13.9 and 12 14C ka BP, and may correspond to oscillating ice-sheet margins during final, dynamic ice-sheet decay. [source]