bluuebunny/crossref_metadata_2025 huggingface dataset:
Tunnel channel formation during the November 1996 jökulhlaup, Skeiðarárjökull, Iceland
Authors: Russell Andrew J. , Gregory Andrew R. , Large Andrew R.G. , Fleisher P. Jay , Harris Timothy D.
Published: December 2007

Despite the ubiquity of tunnel channels and valleys within formerly glaciated areas, their origin remains enigmatic. Few modern analogues exist for event-related subglacial erosion. This paper presents evidence of subglacial meltwater erosion and tunnel channel formation during the November 1996 jökulhlaup, Skeiðarárjökull, Iceland. The jökulhlaup reached a peak discharge of 45 000 to 50 000 m3s–1, with flood outbursts emanating from multiple outlets across the entire 23 km wide glacier snout. Subsequent retreat of the southeast margin of Skeiðarárjökull has revealed a tunnel channel excavated into the surrounding moraine sediment and ascending 11.5m over a distance of 160 m from a larger trough to join the apex of an ice-contact fan formed in November 1996. The tunnel channel formed via hydro-mechanical erosion of 14 000m3to 24 000 m3of unconsolidated glacier substrate, evidenced by copious rip-up clasts within the ice-contact fan. Flow reconstruction provides peak discharge estimates of 680±140m3s–1. The tunnel channel orientation, oblique to local ice flow direction and within a col, suggests that local jökulhlaup routing was controlled by (a) subglacial topography and (b) the presence of a nearby proglacial lake. We describe the first modern example of tunnel channel formation and illustrate the importance of pressurized subglacial jökulhlaup flow for tunnel channel formation.
Cauldron subsidence and subglacial floods
Authors: Evatt G.W. , Fowler A.C.
Published: December 2007

Ice cauldrons are depressions which form at the surface of ice sheets when an underlying subglacial lake empties, in particular when subglacial volcanic eruptions occur. Notable examples of such cauldrons occur on the surface of the Vatnajökull ice cap in Iceland. More generally, cauldrons will form when a subglacial lake empties during a jökulhlaup. The rate of subsidence of the ice surface is related to the rate at which the subglacial water empties from the lake. We use a viscous version of classical beam theory applied to the ice sheet to determine the relation between the subsidence rate and flood discharge. We use the results to make inferences concerning ring fracture spacings in cauldrons, the consequent effect on flood discharge dynamics and the likely nature of subsidence events in the Antarctic Ice Sheet.
Volcano–glacier interactions on composite cones and lahar generation: Nevado del Ruiz, Colombia, case study
Authors: Thouret J.C. , Ramírez C. J. , Gibert-Malengreau B. , Vargas C.A. , Naranjo J.L. , Vandemeulebrouck J. , Valla F. , Funk M.
Published: December 2007

The catastrophic lahars triggered by the 13 November 1985 eruption of the ice-clad Nevado del Ruiz volcano, Colombia, demonstrate that the interaction of hot pyroclasts with snow and ice can release 30–50 millionm3 of meltwater in 30–90 minutes. The 1985 eruption caused a 16% loss in area and a 9% loss in volume of snow, firn and ice. Turbulent pyroclastic density currents mechanically mixed with snow and produced meltwater at a rate of 0.5–1.6mms–1. Laboratory experiments suggest that turbulent, fluidized pyroclastic density currents exert mechanical and thermal scour, thereby efficiently transferring heat from hot pyroclasts to snow. Ice cap loss at Nevado del Ruiz continued between 1985 and 2000, representing a ∽52% decline in area and a ∽30% fall in volume. Ice 60–190m thick caps the east and southeast summit plateau, whereas an ice field < 30m thick and devoid of snow is retreating on the north, northeast and west edges. This asymmetrical distribution of ice reflects combined long-term effects of the 1985 eruption and of the post-1985 ice cap retreat. Should volcanic activity resume, steep-sided glaciers can fail and pyroclastic flows and surges can sweep the snowpack and generate mixed avalanches and lahars. Although the potential source of meltwater has decreased since 1985, extensive debris at the ice cap margins can be incorporated to future lahars.
Evolution of Rhonegletscher, Switzerland, over the past 125 years and in the future: application of an improved flowline model
Authors: Sugiyama Shin , Bauder Andreas , Zahno Conradin , Funk Martin
Published: December 2007

To study the past and future evolution of Rhonegletscher, Switzerland, a flowline model was developed to include valley shape effects more accurately than conventional flowband models. In the model, the ice flux at a gridpoint was computed by a two-dimensional ice-flow model applied to the valley cross-section. The results suggested the underestimation of the accumulation area, which seems to be a general problem of flowline modelling arising from the model’s one-dimensional nature. The corrected mass balance was coupled with the equilibrium-line altitude (ELA) change, which was reconstructed for the period 1878–2003 from temperature and precipitation records, to run the model for the past 125 years. The model satisfactorily reproduced both changes in the terminus position and the total ice volume derived from digital elevation models of the surface obtained by analyses of old maps and aerial photographs. This showed the model’s potential to simulate glacier evolution when an accurate mass balance could be determined. The future evolution of Rhonegletscher was evaluated with three mass-balance conditions: the mean for the period 1994–2003, and the most negative (2003) and positive (1978) mass-balance values for the past 50 years. The model predicted volume changes of –18%, –58% and +38% after 50 years for the three conditions, respectively.
Spatial and morphological change on Eliot Glacier, Mount Hood, Oregon, USA
Authors: Jackson Keith M. , Fountain Andrew G.
Published: December 2007

Eliot Glacier is a small (1.6 km2) glacier on Mount Hood, Oregon, USA, and its ablation zone is largely covered with rock debris. We examine the interrelated processes of ablation rates, ice thickness and surface velocities to understand the retreat rate of this glacier. Since measurements began in 1901, the glacier has retreated 680 m, lost 19% of its area and thinned by about 50 m at the lower glacier profile before the terminus retreated past that point. The upper profile, 800m up-glacier, has shown thinning and thickening due to a kinematic wave resulting from a cool period during the 1940s–70s, and is currently about the same thickness as in 1940. Overall, the glacier has retreated at a slower rate than other glaciers on Mount Hood. We hypothesize that the rock debris covering the ablation zone reduces Eliot Glacier’s sensitivity to global warming and slows its retreat rate compared to other glaciers on Mount Hood. Spatial variations in debris thickness are the primary factor in controlling spatial variations in melt. A continuity model of debris thickness shows the rate of debris thickening down-glacier is roughly constant and is a result of the compensating effects of strain thickening and debris melt-out from the ice.
‘Calving laws’, ‘sliding laws’ and the stability of tidewater glaciers
Authors: Benn Douglas I. , Hulton Nicholas R.J. , Mottram Ruth H.
Published: December 2007

A new calving criterion is introduced, which predicts calving where the depth of surface crevasses equals ice height above sea level. Crevasse depth is calculated from strain rates, and terminus position and calving rate are therefore functions of ice velocity, strain rate, ice thickness and water depth. We couple the calving criterion with three ‘sliding laws’, in which velocity is controlled by (1) basal drag, (2) lateral drag and (3) a combination of the two. In model 1, velocities and strain rates are dependent on effective pressure, and hence ice thickness relative to water depth. Imposed thinning can lead to acceleration and terminus retreat, and ice shelves cannot form. In model 2, ice velocity is independent of changes in ice thickness unless accompanied by changes in surface gradient. Velocities are strongly dependent on channel width, and calving margins tend to stabilize at flow-unit widenings. Model 3 exhibits the combined characteristics of the other two models, and suggests that calving glaciers are sensitive to imposed thickness changes if basal drag provides most resistance to flow, but stable if most resistance is from lateral drag. Ice shelves can form if reduction of basal drag occurs over a sufficiently long spatial scale. In combination, the new calving criterion and the basal–lateral drag sliding function (model 3) can be used to simulate much of the observed spectrum of behaviour of calving glaciers, and present new opportunities to model ice-sheet response to climate change.
Long-term changes in the snow–firn pack stratigraphy on Ürümqi glacier No. 1, eastern Tien Shan, China
Authors: Wang Feiteng , Li Zhongqin , Edwards R. , Li Huilin
Published: December 2007

We report on changes to the snowpack of Ürümqi glacier No. 1, eastern Tien Shan, China, resulting from climate change between 1961 and 2005. Data from more than 120 snow pits were used to investigate temporal changes in the snow stratigraphy for three periods 1961–62, 1980–83 and 2002–05. Both the thickness and structure of the snow were found to be significantly altered by climatic warming. The proportion of coarse-grained firn, which is usually formed by infiltration water, was found to have increased from 40% to 65% over the period 1961–2005, and the distribution of the glacier zones also changed significantly, with all boundaries moving up-slope. The recrystallization–infiltration zone disappeared in 1989. The mean ablation rate over the melt season increased by ~26% from 1962 to 1980 at the west branch site and by ~75% from 1980 to 2004 at the east branch site.
Sea-ice mass-balance monitoring in an Arctic fjord
Authors: Gerland Sebastian , Renner Angelika H.H.
Published: December 2007

A sea-ice mass-balance monitoring study including ice extent and thickness observations was started at Kongsfjorden (79˚N, 12˚E), Svalbard, in 2003. The inner part of Kongsfjorden is usually covered by seasonal fast ice <1m thick, initially forming between December and March and persisting until June. Ice extent is visually observed from the mountain Zeppelinfjellet, and documented by ice maps and photographs several times a week. Ice and snow thickness is measured regularly at four sites from drillholes. Time series of ice extent in four areas east of Ny-Ålesund (total area 120 km2) were calculated for 2003–05. By combining extent with thickness data, ice-mass time series were calculated. As also observed earlier than 2003 in other studies, the fast ice varies interannually in extent and thickness. Among the factors which control the fast-ice evolution are physical and meteorological parameters, and the geographical setting of Kongsfjorden, with its coastline and a group of islands in its inner part having a protective effect. This study is ongoing and a major aim is to identify and quantify connections between the Kongsfjorden fast-ice evolution and climate parameters.
Reconstruction of mass balance of glaciers in southern Norway back to 1948
Authors: Rasmussen L.A. , Andreassen L.M. , Conway H.
Published: December 2007

A model using upper-air meteorological variables in the US National Centers for Environmental Prediction and US National Center for Atmospheric Research (NCEP/NCAR) re-analysis database is used to extend net balance bn back to 1948 for seven glaciers in southern Norway. The observational record of another glacier, Storbreen, began in 1948. Over the observational record of each of the seven glaciers, correlation with Storbreen estimates bn more accurately than the upper-air model does for four of them and less accurately for three. In all seven cases, however, an average of the model and the Storbreen correlation is more accurate than either alone, so the average is used to reconstruct bn for years when it was not observed. For the seven glaciers other than Storbreen, a combined series is formed from observations during their period of record and from reconstructed values prior to then back to 1948. There are three distinct sections in all eight bn series: prior to 1989; 1989–1995, when the North Atlantic Oscillation index was strongly positive; and after 1995. The 1989–95 mean bn was anomalously positive because of both decreased ablation and especially increased accumulation. The mean bn since 1995 has been anomalously negative because of increased ablation, whilst accumulation has been nearly the same as over 1948–88. The first principal component of the eight 1949–2005 bn series explains 78% of the total variance, and the second explains 12%. Over 1949–88 there were no substantial shifts in bn or in either winter balance bw or summer balance bs at any of the seven glaciers where observations began after 1948, nor were there in the Storbreen record. There is a distinction between the three glaciers that gained mass over 1948–2005 and the five that lost mass. Each of the three that gained had accumulation-area ratio AAR ≥ 0.64 and <0.7% of its area δS in the lowest tenth of its altitude range, while the five that lost had AAR ≤ 0.46 and 1.9 ≤ δS ≤ 4.4%. Because of these hypsometries, the five glaciers that lost mass now have an especially large ablation area.
Contribution of glacier melt to stream runoff: if the climatically extreme summer of 2003 had happened in 1979…
Authors: Koboltschnig Gernot R. , Schöner Wolfgang , Zappa Massimiliano , Holzmann Hubert
Published: December 2007

This paper presents a comparative study at a small and highly glacierized catchment area in the Austrian Alps, where runoff under the extreme hot and dry conditions of summer 2003 was simulated based on two different glacier extents: the 2003 glacier extent and the 29% larger 1979 extent. Runoff was simulated applying the hydrological water balance model PREVAH at a high temporal resolution. For this purpose, the catchment area was subdivided into hydrological response units based on digital elevation model and land-cover data. The model was driven by meteorological data from the observatory at Hoher Sonnblick, situated at the highest point of the catchment area (3106ma.s.l.). We were interested in the effect the change in glacier extent would have on the annual and monthly water balance and the hydrograph of hourly discharges. Results of the 2003 and the hypothetical 1979 simulation show main differences in runoff for the period July–August depending on a higher ice-melt contribution. Due to the same meteorological input, both simulations calculate the same snow accumulation and snowmelt. Annual discharge in 1979 would have been 12% higher and hourly runoff up to 35% higher than in 2003.
The non-synchronous response of Rabots Glaciär and Storglaciären, northern Sweden, to recent climate change: a comparative study
Authors: Brugger Keith A.
Published: December 2007

Rabots Glaciär and Storglaciären, two small valley glaciers in the Swedish Arctic, have not behaved synchronously in response to recent climate change. Both glaciers advanced late in the 19th century and then began to retreat in response to a ~1˚C warming that occurred around 1910. By the mid-1980s the terminus and volume of Storglaciären had essentially stabilized, so it may have completed its response to the earlier warming. In contrast, ongoing thinning and retreat of Rabots Glaciär are substantial and suggest its response time is considerably longer. A time-dependent numerical model was used to investigate each glacier’s response to perturbations in mass balance. This modeling suggests that, for small perturbations, volume timescales for Storglaciären and Rabots Glaciär are ~125 and ~215 years, respectively. Another measure of response time (i.e. length response time) yields somewhat lower values for each glacier; however, what is significant is that by either measure and accounting for uncertainties, the response time for Rabots Glaciär is consistently about 1.5 times longer than that for Storglaciären. This implies that their non-synchronous behavior is likely due to differences in response times. The latter ultimately result from markedly different longitudinal geometries (particularly near the termini), velocity profiles and specific net balance gradients.
Response of glaciers in northwestern North America to future climate change: an atmosphere/glacier hierarchical modeling approach
Authors: Zhang Jing , Bhatt Uma S. , Tangborn Wendell V. , Lingle Craig S.
Published: December 2007

The response of glaciers to changing climate is explored with an atmosphere/glacier hierarchical modeling approach, in which global simulations are downscaled with an Arctic MM5 regional model which provides temperature and precipitation inputs to a glacier mass-balance model. The mass balances of Hubbard and Bering Glaciers, south-central Alaska, USA, are simulated for October 1994–September 2004. The comparisons of the mass-balance simulations using dynamically-downscaled vs observed temperature and precipitation data are in reasonably good agreement, when calibration is used to minimize systematic biases in the MM5 downscalings. The responses of the Hubbard (a large tidewater glacier) and Bering (a large surge-type glacier) mass balances to the future climate scenario CCSM3 A1B, a ‘middle-of-the-road’ future climate in which fossil and non-fossil fuels are assumed to be used in balance, are also investigated for the period October 2010–September 2018. Hubbard and Bering Glaciers are projected to have increased accumulation, particularly on the upper glaciers, and greater ablation, particularly on the lower glaciers. The annual net balance for the entire Bering Glacier is projected to be significantly more negative, on average (–2.0ma–1w.e., compared to –1.3ma–1w.e. during the hindcast), and for the entire Hubbard Glacier somewhat less positive (0.3ma–1w.e. compared to 0.4 ma–1w.e. during the hindcast). The Hubbard Glacier mass balances include an estimated iceberg calving flux of 6.5 km3 a–1, which is assumed to remain constant.
Observed changes of cryosphere in China over the second half of the 20th century: an overview
Authors: Xiao Cunde , Liu Shiyin , Zhao Lin , Wu Qingbai , Li Peiji , Liu Chunzhen , Zhang Qiwen , Ding Yongjian , Yao Tandong , Li Zhongqin , Pu Jiancheng
Published: December 2007

During approximately the past five decades, changes in snow cover, mountain glaciers, frozen ground (including permafrost), sea ice and river ice have been observed in China. However, most data were published in Chinese and thus unknown to the international communities. Here we review these published results to show an overview of cryospheric changes in China for the last ~50 years. Long-term variability of snow cover over the Qinghai–Xizang (Tibetan) Plateau (QXP) is characterized by large interannual variability superimposed on a continuously increasing trend. Glacier changes in western China vary remarkably in different regions. Although in most mountains the glaciers display a retreating trend (~80%) or have even vanished, some glaciers (~20%) are still advancing. Frozen ground (including permafrost) has experienced a rapid decay since the 1980s, and these changes are occurring both in the QXP and in the cold regions of north China. Sea-ice areas in the Bohai and north Yellow Seas have been shrinking since the 1970s. Interannual variations possibly relate to the solar cyles, and sea-ice extent extremes relate to El Niño–Southern Oscillation (ENSO) events. The freeze-up and break-up dates of river ice in north China in the 1990s are, on average, 1–6 days later and 1–3 days earlier, respectively, than the 1950s–1990 mean. Frozen duration and the maximum thickness of river ice are, respectively, 4–10 days shorter and 0.06–0.21cm thinner in the 1990s than the average.
Proxy data reconstructions of the Storglaciären (Sweden) mass-balance record back to AD 1500 on annual to decadal timescales
Authors: Linderholm Hans W. , Jansson Peter
Published: December 2007

Regional summer temperatures (TS), derived from tree rings, and large-scale atmospheric circulation indices (North Atlantic Oscillation (NAO)) were used to infer the mass balance of Storglaciären, Sweden, on annual and decadal timescales back to AD 1500. Winter (January–March) NAO was not a suitable proxy for interannual winter balance variability, but seemed to have substantial influence on decadal timescales. TS were highly correlated to the summer balance, but also to the annual net balance. This association was much weaker on decadal timescales, mainly because of the increased maritime climate around 1980. Storglaciären net balance was modelled back to AD 1500 with annual resolution (using TS as a predictor), and AD 1664 with decadal resolution (using TS and NAO as predictors). Both reconstructions displayed similar evolution. Negative mass balances dominated most of the 16th century, followed by a longer period of predominantly positive mass-balance years culminating in about 1750. This is in agreement with previous suggestions of Holocene maximum expansion of Storglaciären at that time. Subsequently, the mass balance is highly variable, with an increased number of negative years. The build-up to the well-documented early-20th-century advance is evident as mass balance becomes progressively more positive towards the early 20th century.
Satellite-derived surface type and melt area of the Greenland ice sheet using MODIS data from 2000 to 2005
Authors: Fausto Robert S. , Mayer Christoph , Ahlstrøm Andreas P.
Published: December 2007

A new surface classification algorithm for monitoring snow and ice masses based on data from the moderate-resolution imaging spectroradiometer (MODIS) is presented. The algorithm is applied to the Greenland ice sheet for the period 2000–05 and exploits the spectral variability of ice and snow reflectance to determine the surface classes dry snow, wet snow and glacier ice. The result is a monthly glacier surface type (GST) product on a 1 km resolution grid. The GST product is based on a grouped criteria technique with spectral thresholds and normalized indices for the classification on a pixel-by-pixel basis. The GST shows the changing surface classes, revealing the impact of climate variations on the Greenland ice sheet over time. The area of wet snow and glacier ice is combined into the glacier melt area (GMA) product. The GMA is analyzed in relation to the different surface classes in the GST product. The results are validated with data from weather stations and similar types of satellite-derived products. The validation shows that the automated algorithm successfully distinguishes between the different surface types, implying that the product is a promising indicator of climate change impact on the Greenland ice sheet.
Glacier geometry and elevation changes on Svalbard (1936–90): a baseline dataset
Authors: Nuth C. , Kohler J. , Aas H.F. , Brandt O. , Hagen J.O.
Published: December 2007

This study uses older topographic maps made from high-oblique aerial photographs for glacier elevation change studies. We compare the 1936/38 topographic map series of Svalbard (Norwegian Polar Institute) to a modern digital elevation model from 1990. Both systematic and random components of elevation error are examined by analyzing non-glacier elevation difference points. The 1936/38 photographic aerial survey is examined to identify areas with poor data coverage over glaciers. Elevation changes are analyzed for seven regions in Svalbard (~5000 km2), where significant thinning was found at glacier fronts, and elevation increases in the upper parts of the accumulation areas. All regions experience volume losses and negative geodetic balances, although regional variability exists relating to both climate and topography. Many surges are apparent within the elevation change maps. Estimated volume change for the regions is –1.59±0.07km3 a–1 (ice equivalent) for a geodetic annual balance of –0.30ma–1w.e., and the glaciated area has decreased by 16% in the 54 year time interval. The 1936–90 data are compared to modern elevation change estimates in the southern regions, to show that the rate of thinning has increased dramatically since 1990.
Climate sensitivity of Storglaciären, Sweden: an intercomparison of mass-balance models using ERA-40 re-analysis and regional climate model data
Authors: Hock Regine , Radić Valentina , De Woul Mattias
Published: December 2007

Estimates of glacier contributions to future sea-level rise are often computed from mass-balance sensitivities derived for a set of representative glaciers. Our purpose is to investigate how mass-balance projections and sensitivities vary when using different approaches to compute the glacier mass balance. We choose Storglaciären, Sweden, as a test site and apply five different models including temperature-index and energy-balance approaches further varying in spatial discretization. The models are calibrated using daily European Centre for Medium-Range Weather Forecasts re-analysis (ERA-40) data. We compute static mass-balance sensitivities and cumulative mass balances until 2100 based on daily temperatures predicted by a regional climate model. Net mass-balance sensitivities to a +1 K perturbation and a 10% increase in precipitation spanned from –0.41 to –0.61 and from 0.19 to 0.22ma–1, respectively. The cumulative mass balance for the period 2002–2100 in response to the climate-model predicted temperature changes varied between –81 and –92m for four models, but was –121m for the fully distributed detailed energy-balance model. This indicates that mass losses may be underestimated if temperature-index methods are used instead of detailed energy-balance approaches that account for the effects of temperature changes on all energy-balance components individually. Our results suggest that future glacier predictions are sensitive to the choice of the mass-balance model broadening the spectrum in uncertainties.
Investigation of the impact of Antarctic ice-shelf melting in a global ice–ocean model (ORCA2-LIM)
Authors: Wang Caixin , Beckmann Aike
Published: December 2007

Ice-shelf melting (ISM) removes heat from and injects fresh water into the adjacent ocean and contributes significantly to the freshwater balance and water mass formation in the Antarctic marginal seas. The thermodynamic interaction between ocean and ice shelf is a complicated process and usually not adequately included in the ocean–ice climate models. In this paper, the ISM from all major ice-shelf areas around Antarctica is added to a global coupled ice–ocean model ORCA2-LIM following the parameterization proposed by Beckmann and Goosse (2003). Using interannual forcing data from 1958 through 2000, the impact of ISM on Southern Ocean hydrography and sea-ice distribution is investigated. The model also shows global signatures of the Antarctic ISM.
A statistical mass-balance model for reconstruction of LIA ice mass for glaciers in the European Alps
Authors: Schöner Wolfgang , Böhm Reinhard
Published: December 2007

Stepwise linear regression models were calibrated against the measured mass balance of glaciers in the Austrian Alps for the prediction of specific annual net balance and summer balance from climatological and topographical input data. For estimation of winter mass balance, a simple ratio between the amount of winter precipitation and the measured winter balance was used. A ratio with a mean value of 2.0 and a standard deviation of 0.44 was derived from the sample of measured winter balances. Climate input data were taken from the HISTALP database which offers a homogenized data source that is outstanding in terms of its spatial and temporal coverage. Data from the Austrian glacier inventory were used as topographical input data. From the group of possible predictors summer air temperature, winter precipitation, summer snow precipitation and continentality (as defined from seasonal temperature variation) were selected as climatological driving forces in addition to lowest glacier elevation and area-weighted mean glacier elevation as topographical driving forces. Summer temperature explains 60% of the variance of summer mass balance and 39% of the variance of annual mass balance. Additional factors increase the explained variance by 22% for summer and 31% for annual net balance. The calibrated mass-balance model was used to reconstruct the mass balance of Hintereisferner and Vernagtferner back to 1800. Whereas the model performs well for Hintereisferner, it fails for some sub-periods for Vernagtferner due to the complicated flow dynamics of the glacier.
Soluble ionic and oxygen isotopic compositions of a shallow firn profile, Baishui glacier No. 1, southeastern Tibetan Plateau
Authors: Pang Hongxi , He Yuanqing , Theakstone Wilfred H. , Zhang David D.
Published: December 2007

In the summer of 2004, a firn profile, 18.3 m long, extending down to glacier ice, was recovered in the accumulation area of the largest glacier, Baishui No. 1, on Yulong mountain, the southernmost glacier-covered area in mainland Eurasia. Multivariate empirical orthogonal function (EOF) and statistical correlation analyses of major-ion data from the profile demonstrate that three distinct types of ionic material contribute to the chemical characteristics of firn in this monsoonal region: material of marine origin, which is transported by the Indian southwest monsoon; crustal materials, which come from local sources; and anthropogenic pollutants, which are produced by industrial and agricultural activities in South Asia. Although the influence of post-depositional processes on the seasonal isotopic and soluble ionic compositions is significant, dust layers in the firn profile are clearly visible. Due to the effects of meltwater percolation, the dust layers generally coincide with late-summer snow surfaces. We therefore use the dust layers, combined with the seasonal variations of electrical conductivity (EC), Ca2+ and Mg2+, to establish a depth/age scale for the firn profile. The reconstructed net accumulation has a significant negative correlation with the temperature at Lijiang, whereas the correlation between the net accumulation and the precipitation amount at Lijiang is weak. Although the δ18O time series of the firn profile was modified significantly by meltwater percolation, the correlation between annual mean δ18O values and the Indian southwest monsoon index (WSI1) is significant. This result suggests that δ18O records from monsoon-influenced temperate glaciers can provide a valuable record of past variations of the Indian southwest monsoon.
Recent glacier variations in Mongolia
Authors: Tsutomu Kadota , Gombo Davaa
Published: December 2007

Glacier monitoring enables us to detect influences of global warming in high mountain regions. To initiate the establishment of a glacier-monitoring network in northern Eurasia, we studied recent glacier variations in Mongolia using topographical maps, aerial photographs and satellite images (Corona and Landsat). Glaciers in Mongolia exist in the Altai mountains which span approximately 1400 km within Russia, China and Mongolia. Four regions were selected to form the study area: Tavan Bogd region, Turgen massif, Kharkhiraa massif and Tsambagarav massif. During the period from the 1940s to 2000 or from 1968 to 2000, the glaciers in these regions lost 10.2%, 19.3%, 28.0% and 28.8% of their area respectively. The glaciers in the Tavan Bogd, Kharkhiraa and Turgen regions were found to have been almost stationary since 1987/88, while those in Tsambagarav massif showed no significant change in area since 1963. Shrinkage of the glaciers occurred between 1945/68 and 1987/88 in the former regions and between 1948 and 1963 in the latter. Mongolian glaciers seem to behave differently from other glaciers which have been experiencing steady shrinkage recently.
The impact of global change on low-elevation blue-ice areas in Antarctica: a thermo-hydrodynamic modelling study
Authors: Rasmus Kai , Beckmann Aike
Published: December 2007

In Antarctica, low-elevation (<1000 m) blue-ice areas (LEBIAs) may experience melt–freeze cycles due to absorbed solar radiation and the small heat conductivity in the ice. In some cases, LEBIAs can contain significant amounts of subsurface liquid water. Since the spatial extent of blue-ice areas depends on climatic conditions, they have been seen as good indicators of warming in Antarctica. A two-dimensional (x-z) model has been developed to simulate the formation and water circulation in the subsurface ponds. The model results show that for a reasonable parameter set, the formation of liquid water within the ice can be reproduced. Vertical convection and a weak overturning circulation is generated which acts to stratify the fluid and transport warmer water downward, thereby causing additional melting at the base of the pond. In a multi-year integration, a global warming scenario mimicked by a decadal-scale increase (3˚C per 100 years) in air temperature, leads to a general increase in subsurface water volume and changes in pond shape and depth. Even before melting at the surface is reached, heat that accumulates below a certain depth can no longer be removed during winter and leads to disintegration of the ice.
The impact of jökulhlaups on basal sliding observed by SAR interferometry on Vatnajökull, Iceland
Authors: Magnússon Eyjólfur , Rott Helmut , Björnsson Helgi , Pálsson Finnur
Published: December 2007

We have analyzed InSAR data from the ERS-1/ERS-2 tandem mission, to study the ice dynamics of Vatnajökull, Iceland, during jökulhlaups from the Skaftá cauldrons and the Grímsvötn geothermal area, which drained under the Tungnaárjökull and Skeiðarárjökull outlets, respectively. During the initial phase of a Grímsvötn jökulhlaup in March 1996, the velocity of Skeiðarárjökull increased up to three-fold (relative to observed velocities in December 1995) over an area up to 8 km wide around the subglacial flood path. Accumulation of water was observed at one location in the flood path. During a small jökulhlaup from the Skaftá cauldrons in October 1995 the velocity on Tungnaárjökull increased up to four-fold over a 9 km wide area. The velocity increase was observed 1.5 days before the floodwater was detected in the river Skaftá. A reduced glacier speed as the flood peaked in Skaftá indicates evolution of the subglacial drainage system from sheet to tunnel flow. The glacier acceleration and local uplift, observed in the early phase of both jökulhlaups, supports the concept that increased water inflow in a narrow tunnel system causes water pressure to rise and forces water into areas outside the channels, thus reducing the coupling of ice with the glacier bed.
Reversal of ice motion during the outburst of a glacier-dammed lake on Gornergletscher, Switzerland
Authors: Sugiyama Shin , Bauder Andreas , Weiss Patrik , Funk Martin
Published: December 2007

During the outburst flood of a glacier-dammed lake on Gornergletscher, Switzerland, in July 2004, the drained lake water triggered anomalous glacier motion. At the onset of the outburst, the ice-flow direction in the vicinity of the lake became closer to the central flowline. When the lake discharge magnitude decreased, the flow direction altered such that the ice moved back to the azimuth of the initial motion. At one of the survey points, where the ice flows parallel to the central flowline, the ice accelerated along the pre-event flow direction followed by a 180° backward motion that lasted over 2 days. These observations indicate the impact of the lake outburst on the subglacial and englacial stress conditions; however, the reversal in the flow direction is difficult to explain by drawing on our current understanding of glacier mechanics. The timing and the timescale of the flow-direction changes suggest that the elastic glacier motion and its rebound played a role under the rapidly changing stress conditions, but the Young’s modulus of ice is too large to cause the observed ice motion. Other processes, including basal separation and subglacial sediment deformation, are discussed as possible mechanisms for the reversal of the ice motion.
Laminar flow and mass transport in a twice–folded microchannel
Authors: Barz Dominik P. J. , Zadeh Hamid Farangis , Ehrhard Peter
Published: December 2007

The flow and mass transport within a twice–folded microchannel is investigated. For the measurement of the concentration field the microlaser–induced fluorescence technique (μLIF) is engaged. Microparticle image velocimetry (μPIV) is further employed to obtain the velocity field. Deviation from standard μPIV by seeding a partial stream of the flow only, results in partial velocity profiles. This procedure allows for the observation of the contact interface between the seeded and the unseeded liquid. Distorted contact interfaces is recognized within and after each bend, indicating strong secondary flows. The measurements are compared to numerical simulations, solving for both the flow, and the mass‐transport equations, and, subsequently, performing particle tracking. The results are, on one hand, in reasonable agreement with the experiments. On the other hand, the differences between the contact interface from the mass‐transport equation and from particle tracking clarifies the effect of diffusion. © 2007 American Institute of Chemical Engineers AIChE J, 2008
Wetting dynamics in multiscale porous media. Porous pore‐doublet model, experiment and theory
Authors: Lundström T. Staffan , Gustavsson L. Håkan , Jēkabsons Normunds , Jakovics Andris
Published: December 2007

Fiber reinforced composite materials often consist of fibers gathered in bundles. Thus, during manufacturing, a liquid resin impregnates a multiscale porous medium. For wetting systems the capillary pressure jump becomes much higher in the smaller pores, i.e., within the bundles, and in addition to any applied pressure gradient there will be a local driving pressure gradient between the small‐ and large‐scale areas. Such gradients will influence mechanisms, such as void formation and particle filtration. Hence, it is of interest to clarify the mechanisms for the wetting in general and the influence from the detailed geometry of the fiber network in particular. In this article, a porous pore‐doublet model is studied in order to determine if an overflow of liquid can explain a leading flow in the smaller capillaries, and at which conditions it takes place. Experiments, as well as theoretical calculations on this generic geometry show that the leading front can be in the smaller capillary, as well as in the larger one. The outcome is dependent on the actual permeability of the porous material being a parameter that determines to what extent the larger capillary feeds the smaller one. © 2007 American Institute of Chemical Engineers AIChE J, 2008
Active ghrelin levels across time and associations with leptin and anthropometrics in healthy ache Amerindian women of Paraguay
Authors: Bribiescas Richard G. , Betancourt Jaime , Torres Angélica M. , Reiches Meredith
Published: December 2007

Active (acylated) ghrelin is a peptide hormone secreted primarily by the stomach, positively associated with fasting, orexigenic, and promotes growth hormone secretion. It is therefore important to energy intake management. The objective of this pilot research was to (1) compare active ghrelin with previous measurements of leptin and anthropometrics; (2) assess the consistency of active ghrelin across time in this population; (3) extend our understanding of potential population variation in active ghrelin. Two serum samples separated by 10 days at the same time between meals were collected from healthy Ache women (n = 12, mean age 32.2 ± 14.0 SD) to determine consistency over time, associations with leptin, and anthropmetric values. Mean active ghrelin was 72.9 ± 23.0 pg/ml, highly correlated (r2 = 0.95, P < 0.0001) between collections, and showed no paired mean differences (P < 0.18). There was no significant correlation with leptin, age, or anthropometric measures. Active ghrelin appears to be consistent over time in this population, perhaps reflecting regimented meal schedules and less interpopulation variation compared to leptin. Am. J. Hum. Biol., 2008. © 2007 Wiley‐Liss, Inc.
Higher levels of central adiposity in healthy premenopausal women with family histories of premenopausal breast cancer
Authors: Dettenborn Lucia , James Gary D. , Britton Julie A. , Bovbjerg Dana H.
Published: December 2007

Research strongly suggests that lower overall adiposity and higher central adiposity are independent risk factors for premenopausal breast cancer in the general population. We aimed to test the possibility that these factors may contribute to familial risk of premenopausal breast cancer. A convenience sample of healthy women, ages 25–49, was recruited to yield three study groups: (1) Women with first‐degree family histories of premenopausal breast cancer, operationally defined as being diagnosed prior to age 50 (Group FH < 50, n = 39); (2) Women with first‐degree family histories of postmenopausal breast cancer, operationally defined as being diagnosed at age 50 or after (Group FH ≥ 50, n = 33); and (3) Women without a history of breast cancer in first‐degree relatives (Group FH−, n = 132). Multinomial logistic regression analyses, including possible confounders, waist circumference, and BMI, revealed a lower BMI among FH < 50 compared to either FH− (OR = 0.72; 95% CI = 0.59–0.87), or FH ≥ 50 women (OR = 0.75; 95% CI = 0.60–0.95), and higher waist circumferences in FH < 50 compared to either FH− (OR = 1.15; 95% CI = 1.06–1.25), or FH ≥ 50 women (OR = 1.16; 95% CI = 1.05–1.28). No group differences were seen for waist skinfold measures. These results support the possibility that differences in patterns of adiposity may contribute to familial risk of premenopausal breast cancer, and suggest the importance of conducting large scale, population‐based studies of the link between body size characteristics and familial breast cancer risk. Am. J. Hum. Biol., 2008. © 2007 Wiley‐Liss, Inc.
Y‐STR analysis in Brazilian and South Amerindian populations
Authors: Leite Fabio P. N. , Callegari‐Jacques Sidia M. , Carvalho Bianca A. , Kommers Trícia , Matte Cecília H. F. , Raimann Paulo E. , Schwengber Solange P. , Sortica Vinicius A. , Tsuneto Luiza T. , Petzl‐Erler M. Luiza , Salzano Francisco M. , Hutz Mara H.
Published: December 2007

A sample of 203 Brazilian males from Rio Grande do Sul (RS), the Brazilian southernmost state, was typed for 11 Y‐STR markers (DYS19, DYS389I/II, DYS390, DYS391, DYS392, DYS393, DYS385, DYS437, DYS438, and DYS439). We also typed 42 individuals from two South Amerindian tribes (Kaingang and Guarani) to use the data as parental Amerindian contribution to our analyses. Gene and haplotypic diversities were estimated, with the South Amerindian samples showing smaller values for these parameters than Brazilians. To obtain a more comprehensive picture of the genetic structure of the Brazilian population as a whole, the Y‐STR data from the RS sample was compared with those already published. No genetic substructuring was observed in the comparisons performed. Multidimensional scaling confirmed the proposed European source of most Y‐chromosome Brazilian patrilineages. Am. J. Hum. Biol., 2008. © 2007 Wiley‐Liss, Inc.
Computational models of ethanol‐induced neurodevelopmental toxicity across species: Implications for risk assessment
Authors: Gohlke Julia M. , Griffith William C. , Faustman Elaine M.
Published: December 2007

Computational, systems‐based approaches can provide a quantitative construct for evaluating risk in the context of mechanistic data. Previously, we developed computational models for the rat, mouse, rhesus monkey, and human, describing the acquisition of adult neuron number in the neocortex during the key neurodevelopmental processes of neurogenesis and synaptogenesis. Here we apply mechanistic data from the rat describing ethanol‐induced toxicity in the developing neocortex to evaluate the utility of these models for analyzing neurodevelopmental toxicity across species. Our model can explain long‐term neocortical neuronal loss in the rodent model after in utero exposure to ethanol based on inhibition of proliferation during neurogenesis. Our human model predicts a significant neuronal deficit after daily peak BECs reaching 10–20 mg/dl, which is the approximate BEC reached after drinking one standard drink within one hour. In contrast, peak daily BECs of 100 mg/dl are necessary to predict similar deficits in the rat. Our model prediction of increased sensitivity of primate species to ethanol‐induced inhibition of proliferation is based on application of in vivo experimental data from primates showing a prolonged rapid growth period in the primate versus rodent neuronal progenitor population. To place our predictions into a broader context, we evaluate the evidence for functional low‐dose effects across rats, monkeys, and humans. Results from this critical evaluation suggest subtle effects are evident at doses causing peak BECs of approximately 20 mg/dl daily, corroborating our model predictions. Our example highlights the utility of a systems‐based modeling approach in risk assessment. Birth Defects Res (Part B) © 2007 Wiley‐Liss, Inc.
Improved correction for population stratification in genome‐wide association studies by identifying hidden population structures
Authors: Li Qizhai , Yu Kai
Published: December 2007

Hidden population substructure can cause population stratification and lead to false‐positive findings in population‐based genome‐wide association (GWA) studies. Given a large panel of markers scanned in a GWA study, it becomes increasingly feasible to uncover the hidden population substructure within the study sample based on measured genotypes across the genome. Recognizing that population substructure can be displayed as clustered and/or continuous patterns of genetic variation, we propose a method that aims at the detection and correction of the confounding effect resulting from both patterns of population substructure. The proposed method is an extension of the EIGENSTRAT method (Price et al. [2006] Nat Genet 38:904–909). This approach is computationally feasible and easily applied to large‐scale GWA studies. We show through simulation studies that, compared with the EIGENSTRAT method, the new method requires a smaller number of markers and yields a more appropriate correction for population stratification. Genet. Epidemiol. 2007. Published 2007 Wiley‐Liss, Inc.