bluuebunny/crossref_metadata_2025_split huggingface dataset:
Past Temperature Record From The Analysis of Melt Features In The Dye 3, Greenland, Ice Core
Authors: Langway Chester C. , Shoji Hitoshi 
Published: September 2017

The layered sequences of melt features preserved in inland polar ice sheets provide valuable proxy data on past variations in summer temperature. A continuous detailed light-table examination was made on the 2037 m-deep Dye 3 ice core immediately after core recovery. Melt features are products of high air temperatures or solar insolation which occur only at or near the snow surface during summer months. A correlation is made between these features and the extent and intensity of summer temperatures. Care must be exercised to identify and distinguish between all mm-thick radiation crusts and wind crusts contained in the record. The absence or presence of these discrete features serve respectively as indicators of total summer cloud cover and the extent of winter storm activity although they are difficult to differentiate from only light-table observations. In this analysis both thin radiation crusts and wind crusts are not in themselves significant indicators of long-term temperature trends, but may serve as incipient subsurface horizons or barrier crusts for the formation of thicker ice melt features caused by downward melt percolation during elevated surface temperature conditions.More than 10 000 individual melt features, including ice layers, ice lenses and ice wedges (but excluding ice glands) were measured down to a depth of 1278 m; below this depth transformation of air bubbles to transparent air hydrate inclusions occurs (Shoji and Langway, 1987) and the megascopic melt features become obscure. The melt-feature data extends back to 1883 B.c. or approximately 3900 years B.P., based on the accurate time scale of continuous δ18O measurements (Dansgaard and others, 1985) For the entire core profile investigated the annual melt percentage is 5.7. Individual melt features range in thickness from 1 mm to 100 mm. A mean value for melt-feature thickness was calculated for continuous 30-year time intervals to consider the general long-term summer temperature trends with corrections made for progressive annual accumulation layer thinning due to ice flow.Since the AMP parameter includes noise from radiation and wind crusts it appears that the simple average of melt-feature thickness per longer time-units is a better indication of air temperature paleodata. The average melt-feature thickness is 1.2 cm. The complete curve obtained shows a higher thickness value of about 1.5 cm for the period 1800 B.C. to 1300 B.C. A lower, almost constant thickness value of about 1cm is shown for the period 1000 B.c. to 1800 A.D., with a slight reduction in thickness recorded around 200 B.C., 400 A.D. and 1600 A.D. These long-term trends are coherent with those recorded in the δ18O profile for the same ice core.
Atmospheric Chemistry Changes Over The Last Climatic Cycle (180 000 Years) Inferred From The Vostok (Antarctica) Ice-Core Study
Authors: Legrand M. , Feniet-Saigne C. , Petit J.R. 
Published: September 2017

A 2 200 m-deep ice core from Vostok Station (East Antarctica) has been used for a comprehensive study of a series of ions (Na+ NH4+, K+, H+, Ca2+, Mg2+, C1−, F−, NO3− and SO42−) originating from impurities deposited over the whole last climatic cycle (180 000 years) as depicted from the isotopic composition of the ice.Concentration profiles confirm that both marine and terrestrial aerosol inputs were higher (up to five and 30 times the Holocene values respectively) during cold climatic conditions. Such large variations of marine and terrestrial aerosol concentrations measured in ice mainly reflect global (source strength and atmospheric transport efficiency) changes, and to a lesser extent local (deposition) changes.As opposed to these primary aerosols, secondary aerosols or gases (HNO3, HC1) exhibit more moderate variations. Finally, variations of other minor ions such as NH4+ provide information on the capacity of ammonia to neutralize the natural acidity of the past background atmosphere.Spectral analyses performed on our chemical profiles (200 samples) exhibit several specific periodicities (around 20 and 40 k year) close to the Earth's orbit tilt and precession frequencies which are discussed in terms of atmospheric response to climatic fluctuations.
Ice-Core Evidence For Weddell Sea Ice Extent During The Past 200 Years
Authors: Mulvaney R. , Reid A.P. , Peel D A. 
Published: September 2017

A continuous, detailed, 200-years record of the anionic species, chloride, nitrate and sulphate, has been measured on an ice core from Dolleman Island (70°35.2′ S, 60°55.5′ W), Antarctic Peninsula. The site lies on the east coast of the Peninsula, and the chemistry of the core is dominated by the changing pattern of sea-ice distribution and storm activity in the Wed dell Sea. Strong annual cycles in chloride and non sea salt sulphate reflect the dominance of the seasonal cycle in sea-ice distribution in the Weddell Sea, observed in time series derived from satellite imagery since the early 1970s. However, in the case of chloride there is also an exceptionally strong interannual variability, which in many parts of the core dominates the seasonal cycle.Secular variations in the sea-ice extent appear to have a strong influence on the climate of the region and may play a major role in determining how long-term climate change in the Antarctic Peninsula relates to global climate change. The paper examines documented evidence for sea-ice extent in the Weddell Sea sector, and evaluates the usefulness of ice-core data for reconstructing this parameter in the earlier period.
Late Pleistocene Glacier Dynamics and Paleoclimate Of South-Western Montana and North-Eastern Idaho. U.S.A.
Authors: Murray Donald R. 
Published: September 2017

Reliable reconstructions of paleoglaciers using topographic maps and aerial photographs allow calculation of effective basal shear stresses along the longitudinal profiles of these glaciers. Glacial flow theory applied to these shear stresses provides an estimate of the component of mass flux due to internal deformation. Assuming basal slip to be zero at the point where deformation mass flux is a maximum, minimum average accumulation gradients (above the equilibrium-line altitude (ELA)) and ablation gradients (below the ELA) can be calculated and minimum mass flux at the ELA can be estimated using the continuity equation. Average net winter accumulation can also be calculated by dividing the mass flux at the ELA by the accumulation area. Because local climate controls the mass balance of a glacier, and therefore the accumulation and ablation gradients, this model provides information on the climatic setting of these paleoglaciers.This model also allows estimation of basal slip as a factor in point estimates of glacial flow. Application of the continuity model above and below the ELA generates additional estimates of mass flux at discrete points along the glacier. The difference between deformation mass flux and continuity flux at these points yields a first approximation of basal slip, which is highly variable along the glacier.The model was tested on the Big Timber glacier of west-central Montana and applied to several other late Pleistocene glaciers in the northern Rocky Mountains of south-western Montana and north-eastern Idaho. Low ablation gradients (<4.0 mm m-1) suggest a climate during the late Pleistocene comparable to the present-day climate of the Brooks Range in Alaska. Calculated average net winter accumulation for the area is well below modern values, again indicating that the climate was much drier during the full glacial period. Basal sliding accounts for most (>90%) of the glacial flow near the terminus of each glacier but is variable along the rest of the glacier. While the mass-balance values are minima, they are assumed to be reasonable approximations of the actual values unless very high basal slip rates occurred along the entire length of each glacier.
200-Hundred Year Climate Record From Antarctic Peninsula
Authors: Peel D.A. , Mulvaney R. 
Published: September 2017

A stable isotope record extending back to 1795 is now available from Dolleman Island (70°35.2′S, 60°55.5′W), a small ice rise on the Weddell Sea coast of Antarctic Peninsula. An accurate chronology has been achieved by combined stratigraphic analysis of clear seasonal cycles in δ18O and excess SO4. Previous work (Peel and others, 1988) has shown that, since 1947, there is generally a satisfactory correlation between interannual variations in δ18O and air temperature (T) as recorded at weather stations in various parts of the region, suggesting that the derived δ18O/T ratio may be used to reconstruct air temperatures for the earlier period.Taken together with previously-reported data (Aristarain and others, 1986) for an ice core from James Ross Island it is now possible to propose a regional climatic signal for the Weddell Sea coastal sector of the region. The most striking feature is a broad maximum in δ18O for the mid-19th century, implying decadal average temperature at least as high as the present. This contrasts with available evidence from elsewhere in the southern hemisphere which suggest that this period was cooler than today. Tentative explanations for the anomaly are proposed based on evidence for a period (1974–80), where climatic shifts are clearly amplified in the isotopic records.
Changes In Glacier Length Induced By Climate Changes
Authors: Raymond C.F. , Waddington E.D. , Jøhannesson Tómas 
Published: September 2017

Time scales for adjustment in the length of a glacier to changing climate may be described in terms of a relatively short time scale, TS and a longer memory time, Tm. The memory Tm represents the time scale needed for asymptotic approach of the glacier to a steady state following a climate change event. Tm is determined by simple continuity considerations concerning the total volume change that must occur to reach steady state and the balance rate that drives the change. We show that Tm is relatively independent of the size of the climate change or to details of how ice flow is related to the geometry of the glacier. The time scale TS represents the time between a climate event and the occurrence of substantial changes in the glacier length. We show that, in contrast to Tm, Ts is highly dependent on the size of the climate change and on details of ice dynamics. This dependence is investigated by several ice-flow models including a simple one in which ice transport is determined by local thickness and slope, as in the analysis of kinematic waves, and a finite element representation that fully includes longitudinal stress gradients. The ice-flow models are subjected to mass-balance perturbations of varying size — from small, for which linearization approximations are valid, to large, for which linearization breaks down.The following behavior may be identified. Increasing the size of a mass-balance rate change causes a more rapid initial response of a glacier terminus, which tends to shorten Ts. Longitudinal stress gradients damp local variations in velocity and thereby slow the propagation and diffusion of kinematic waves and retard the response of the terminus, which tends to lengthen Ts. Longitudinal stress gradients transmit forces to the terminus region and influence the terminus motion without the necessity of redistributing mass from the glacier length into the terminus zone, which tends to shorten Ts. These various results indicate that accurate modeling of the short term responses of glaciers to climate change requires fairly sophisticated ice-flow models, However, for purposes of tracking glacier lengths (or areas) over time scales considerably great than Ts, fairly simple ice-flow models may suffice.
A Detailed Oxygen-18 Profile From The Greenland Ice-Sheet Margin Through The Wisconsinan-Holocene Transition
Authors: Reeh Niels , Letréguilly Anne , Oerter Hans 
Published: September 2017

About 1500 surface-ice samples for δ18O analysis were collected in the 1988 field season along a 750 m profile perpendicular to the margin of the Greenland ice sheet at Pakitsoq, ca 40 km north-east of Jakobshavn, central West Greenland. The purpose of the study was to evaluate how well the continuity of the layer sequence is preserved in ice-margin records, a question of crucial importance for evaluating the potential yield of using ice margins as “mining areas” for easily accessible old ice for climate and environmental studies.More than half of the 1500 samples were taken continuously as 20 cm samples along a 170 m section through the Wisconsinan-Holocene transition which, previously, had been located at the surface of the ice margin. Along this transition section δ18O values decrease by about 6‰ from −31.5 to 37.5‰ on an average. Detailed studies were made of surface elevations and surface structures (e.g. blue bands) along the “horizontal core” profile which, moreover, was photographed section by section, thus enabling the δ-record to be correlated with surface features.Results of the δ18O analyses are promising. Even though ice from the blue bands has δ-values that are 7–8‰ higher than those of the surrounding white ice, there seems to be no discontinuity in the white-ice δ-record across the blue bands.
Can Milankovitch Variations Initiate The Growth Of Ice Sheets In A Global Circulation Model?
Authors: Rind David 
Published: September 2017

The GISS climate model is used to investigate whether the growth of ice sheets could have been initiated by solar insolation variations. Three different orbital configurations are used, corresponding to 116 000 yr B.P., 106 000 yr B.P., and a modified insolation field with greater reductions in summer insolation at high northern latitudes. The time periods chosen are those in which geophysical evidence implies that ice sheets were growing rapidly.The results show that the model fails to maintain snow cover through the summer at locations of suspected initiation of the major ice sheets, despite the reduced summer insolation. When 10 m-thick ice was inserted in all locations where continental ice sheets existed during the last glacial maximum, the model failed to maintain it as well: the ice would melt away in less than five years. Only cooling the ocean to its full ice-age value allowed the model to keep any of the additional ice, and then only in a very restricted region in northern Baffin Island.The experiments indicate there is a wide discrepancy between the model’s response to Milankovitch variations and the geophysical evidence of ice sheet initiation. As the model failed to grow or sustain low-elevation ice during the time of high latitude maximum solar radiation reduction (120 000–100 000 yr B.P.), it is unlikely it could have done so at any time within the last several hundred thousand years. Either the model is not nearly sensitive enough, or we do not understand the connection between Milankovitch variations and the growth of ice sheets.
A 3500-Year Ice Chemistry Record From The Dominion Range, Antarctica: Linkages Between Climatic Variations and Precipitation Chemistry
Authors: Jo Spencer Mary , Mayewski Paul A. , Berry Lyons W. , Twickler Mark S. , Grootes Pieter 
Published: September 2017

In 1984 a 200-m ice core was collected from a local accumulation basin in the Dominion Range, Transantarctic Mountains, Antarctica. A complete oxygen isotope record has been obtained and a considerable portion of the core has been analyzed in detail for chloride, nitrate, sulfate, and sodium. About half of the chloride is due to sea salt with the remainder originating as gaseous HCl. Nitrate levels have increased markedly over the last 1000 years whereas the levels of the other constituents have remained fairly constant.The oxygen isotope results suggest that this region of Antarctica is responding to long-term global climate forcing as well as to shorter-term climatic variations. This data will be compared with the anion and sodium records in order to determine the effects of climatic forcing on these other records. In particular, nitrate appears to vary in concert with fluctuations in long-term climate. Additionally, variations in each constituent over the 3500 year period will be examined in detail to determine the influence of other processes which affect their concentrations.
Internal Freezing of Snow Cover due to its Own Cold Heat Sources (Abstract)
Authors: Yamada Y. , Ikarashi T. 
Published: September 2017

This report discusses the one-dimensional freezing of dry snow/ wet snow systems for the condition first examined by Stefan: the problem of heat conduction with phase change. There are two systems of internal freezing: one is a closed system of temperature rise in a dry snow layer sandwiched between upper and lower wet snow layers; the other an open system of freezing of a thin wet layer provoked mainly by an upper dry snow layer facing the atmosphere at its surface. The latter negatively concerns the release of some avalanches, because the weak layers of surface avalanches in districts where the melt-freeze metamorphism prevails (as in the Horuriku district of Japan) may be the thin wet granular snow layers.Numerical results are given for different conditions of internal freezing. A comparison with field observations reveals the fundamental aspect of this phenomenon and the possibility of avalanche release.
Thinning and retreat of Glaciar Upsala, and an estimate of annual ablation changes in southern Patagonia
Authors: Naruse Renji , Skvarca Pedro , Takeuchi Yukari 
Published: September 2017

Glaciar Upsala, a freshwater calving glacier in southern Patagonia, has been retreating since 1978, and after a drastic recession of about 700 m a−1 in 1994 the retreat seems to have stopped in 1995. A large ice-thinning rate of 11 m a−1 was obtained between 1990 and 1993, by surveying surface elevations near the terminus of Glaciar Upsala. In 1993–94, the thinning was estimated at about 20 m a−1 near the lateral margin. Some possible causes of the thinning behavior are considered.In the ablation area of Glaciar Perito Moreno, 50 km south of Glaciar Upsala, ablation rates were measured during 110 d in summer 1993–94, and air temperature was continuously recorded throughout 1994. Using a degree-day method with temperature data at the nearest meteorological station, Calafate, annual ablation during the last 30 years was estimated to fluctuate from about 12 ± 2 to 16 ± 2 m a−1 in ice thickness, with a mean of 14 ± 2 m a−1. Thus, the temperature anomaly alone cannot elucidate the thinning of 11 m a−1 at Glaciar Upsala. As a possible mechanism of the ice-thinning, it is suggested that the considerable retreat due to calving may have resulted in reduction of longitudinal compressive stress exerted from bedrock rises and islands near the glacier front, causing a considerable decrease in the emergence flow. Thus, the ice may have thinned at a rate close to the annual ablation rate.
Glacial variations on a meso-scale: examples from glaciers in the Aurland Mountains, southern Norway
Authors: Tvede Arve M. , Laumann Tron 
Published: September 2017

Mass-balance measurements carried out since 1963 on six glaciers in southern Norway indicate that glaciers to the west of the main water divide have increased their mass, whereas glaciers further east have decreased. However, when small glaciers within the same mountain area are studied, the picture is more complicated. Different exposures, the terrain forms on the upwind side and area distribution of the glaciers are important factors with regard to the effect of the wind-driven snow.The three glaciers studied in this paper are located within a 10 km radius in the Aurland Mountains, but differ in size, exposure and dynamic condition. Volume changes were calculated from two repeated mappings of two glaciers. Svartavassbreen increased in volume in all areas; Storskavlen decreased over most of its area and increased in some parts. Vargebreen has lost nearly all its ice mass in the eastern part, but has changed little in the western part. It is concluded that the volume changes found on these glaciers mainly reflect changes in local snow accumulation. Analysis of air-pressure data from the period 1952–94 is presented and supports the hypothesis that there has been a change to stronger westerly winds from the mid-1960s onwards.It is recommended that glaciers chosen for long-term studies of volume changes should represent different exposures. The topography of the surrounding terrain is also important.
A synthesis of remote sensing data on Wilkins Ice Shelf, Antarctica
Authors: Vaughan D.G. , Mantripp D.R. , Sievers J. , Doake C.S.M. 
Published: September 2017

Wilkins Ice Shelf has an area of 16000 km2 and lies off the west coast of the Antarctic Peninsula bounded by Alexander, Latady, Charcot and Rothschild islands. Several ice shelves, including Wilkins, exist close to a climatic limit of viability. The recent disintegration of the neighbouring Wordie Ice Shelf has been linked to atmopsheric warming observed on the Antarctic Peninsula. The limit of ice-shelf viability thus appears to have migrated south. Should this continue, the question arises; how long will Wilkins Ice Shelf survive?Compared with the other ice shelves on the Antarctic Peninsula, few surface glaciological data have been collected on Wilkins Ice Shelf. We compare, contrast and combine a variety of remotely sensed data: the recently declassified GEOSAT Geodetic Mission altimetry, Landsat MSS and TM imagery, and radio-echo sounding data (RES), to study its structure and mass balance regime.We find that this shelf has an unusual mass balance regime and relies heavily for sustenance on in situ accumulation. Its response to a continued atmospheric warming may be significantly different from that of Wordie Ice Shelf. Wordie Ice Shelf was fed by several dynamic outlet glaciers which accelerated the disintegration process when the ice shelf fractured. Wilkins Ice Shelf by contrast is almost stagnant and is expected to respond by normal calving at the ice front. Changes in the accumulation rate or basal melt-rate may, however, dominate any dynamic effect. Over the last two decades the ice front positions have remained stable.
Relief and decay of flow stripes on Byrd Glacier, Antarctica
Authors: Casassa G. , Brecher H. H. 
Published: September 2017

Curvilinear flow stripes appear on aerial photographs and satellite imagery of polar ice. On Byrd Glacier, Antarctica, flow stripes are especially prominent and can be detected on AVHRR imagery down to the ice shelf margin.Aerial photographs of Byrd Glacier (Brecher, 1986) are used to determine photogrammetrically the relief associated with flow stripes on two transverse profiles separated by a distance of 65 km. Two kinds of stripes are found, topographic and textural flow stripes. Topographic flow stripes are associated with a ridge-trough topography with double amplitudes of 7 m to 45 m and slopes of 1–7 %. The valleys of the topographic flow stripes appear bright in the photographs and correspond to snow-covered areas, while ridges appear in general as dark stripes that correspond to bare ice areas with abundant crevasses. Textural flow stripes correspond to bands of distinct crevasse pattern which are not associated with topography.The photogrammetric information is correlated with the brightness pattern across flow stripes that appears on Advanced Very High Resolution Radiometer (AVHRR) data. Flow stripes decay rapidly on the AVHRR imagery over the first 40 km downstream from Byrd Glacier and some persist for nearly 400 km to the front of the Ross Ice Shelf.Velocity was measured across a transect on the upstream photogrammetric profile. There are no velocity discontinuities across the boundaries of flow stripes, which shows that lateral shear between flow stripes is not a valid mechanism for explaining their persistence.