bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of the Sea-ice thickness distribution in the Lincoln Sea and adjacent Arctic Ocean in 2004 and 2005
Authors: Haas C. , Hendricks S. , Doble M. 
Published: December 2007

AbstractResults of helicopter-borne electromagnetic measurements of total (ice plus Snow) Sea-ice thickness performed in May 2004 and 2005 in the Lincoln Sea and adjacent Arctic Ocean up to 86˚N are presented. Thickness distributions South of 84˚N are dominated by multi-year ice with modal thicknesses of 3.9 m in 2004 and 4.2 m in 2005 (mean thicknesses 4.67 and 5.18 m, respectively). Modal and mean Snow thickness on multi-year ice amounted to 0.18 and 0.30 m in 2004, and 0.28 and 0.35 m in 2005. There are also considerable amounts of 0.9–2.2m thick first-year ice (modal thickness), mostly representing ice formed in the recurring, refrozen Lincoln Polynya. Results are in good agreement with ground-based electromagnetic thickness measurements and with ice types demarcated in Satellite Synthetic aperture radar imagery. Four drifting buoys deployed in 2004 between 86˚N and 84.5˚N Show a Similar pattern of a mean Southward drift of the ice pack of 83 ±18km between May 2004 and April 2005, towards the coast of Ellesmere Island and Nares Strait. The resulting area decrease of 26% between the buoys and the coast is larger than the observed thickness increase South of 84˚ N. This points to the importance of Shear in a narrow band along the coast, and of ice export through Nares Strait in removing ice from the Study region.
Bridging perspectives from remote Sensing and Inuit communities on changing Sea-ice cover in the Baffin Bay region
Authors: Meier Walter N. , Stroeve Julienne , Gearheard Shari 
Published: December 2007

AbstractPassive microwave imagery indicates a decreasing trend in Arctic Summer Sea-ice extent Since 1979. The Summers of 2002–05 have exhibited particularly reduced extent and have reinforced the downward trend. Even the winter periods have now Shown decreasing trends. At the local level, Arctic residents are also noticing changes in Sea ice. In particular, indigenous elders and hunters report changes Such as earlier break-up, later freeze-up and thinner ice. The changing conditions have profound implications for Arctic-wide climate, but there is also regional variability in the extent trends. These can have important ramifications for wildlife and indigenous communities in the affected regions. Here we bring together observations from remote Sensing with observations and knowledge of Inuit who live in the Baffin Bay region. Weaving the complementary perspectives of Science and Inuit knowledge, we investigate the processes driving changes in Baffin Bay Sea-ice extent and discuss the present and potential future effects of changing Sea ice on local activities.
The sea-ice compactness in the Greenland and Barents Seas during 1979–2003: changes and links to the surface air flow
Authors: Kern Stefan , Chen Youmin , Stammer Detlef , Spreen Gunnar 
Published: December 2007

AbstractAnnual and winter (December–April) sea-ice area and extent are calculated for the Greenland Sea (GS) and Barents Sea (BS) from daily ice concentrations obtained from space-borne microwave radiometry for 1979–2003. The ice extent decreases significantly, particularly during winter, by 65 000 km2(decade)–1in the GS and by 72 000 km2(decade)–1in the BS. Ice-extent fractions (of these total extents) occupied by ice of five different ice-concentration ranges are calculated and analyzed. Changes in these fractions are again significant and most pronounced during winter. In the GS, the fraction of close to very compact ice (65–95%) decreases by 17 000 km2(decade)–1and the fraction of very compact ice (>95%) increases by 29 000 km2(decade)–1, corresponding to a loss of 19% and a gain of 58% relative to the 25 year mean, respectively. In the BS, the fraction of close to compact ice (65–85%) increases by 26 000km2(decade)–1and the fraction with compact to very compact ice (>85%) decreases by 66 000 km2(decade)–1, corresponding to a gain of 30% and a loss of 67% relative to the 25 year mean, respectively. The changing surface wind pattern analyzed from ERA-40 data favours this increasing (decreasing) ice compactness in the GS (BS).
The importance of diurnal processes for the Seasonal cycle of Sea-ice microwave brightness temperatures during early Summer in the Weddell Sea, Antarctica
Authors: Willmes Sascha , Bareiss Jörg , Haas Christian , Marcel Nicolaus  
Published: December 2007

AbstractOver the perennial Sea ice in the western and central Weddell Sea, Antarctica, the onset of Summer is accompanied by a Significant decrease of Sea-ice brightness temperatures (Tb) as observed by passive-microwave radiometers Such as the Special Sensor Microwave/Imager (SSM/I). The Summer-specific Tbdrop is the dominant feature in the seasonal cycle of Tbdata and represents a conspicuous difference to most Arctic Sea-ice regions, where the onset of Summer is mostly marked by a rise in Tb. Data from a 5 week drift Station through the western Weddell Sea in the 2004/05 austral Summer, Ice Station POLarstern (IsPOL), helped with identifying the characteristic processes for Antarctic Sea ice. In Situ glaciological and meteorological data, in combination with SSM/I Swath Satellite data, indicate that the cycle of repeated diurnal thawing and refreezing of Snow (‘freeze–thaw cycles’) is the dominant process in the Summer Season, with the absence of complete Snow wetting. The resulting metamorphous Snow with increased grain Size, as well as the formation of ice layers, leads to decreasing emissivity, enhanced volume Scattering and increased backscatter. This causes the Summer Tbdrop.
Factors affecting fast-ice break-up frequency in Lützow-Holm Bay, Antarctica
Authors: Ushio Shuki 
Published: December 2007

AbstractAntarctic fast-ice variation is investigated using satellite images and ship’s ice navigation logs, focusing on break-up phenomena in Lützow-Holm Bay. Although spatio-temporal scales for breakup events vary somewhat for each event, their commencement is generally in autumn and almost always in the same region. Specifically, the 1997/98 break-up event occurred over a wide area and continued for a long time after the initial break-up. Since then, break-ups have recurred until 2004, and a total of 20 annual events have been detected and monitored since 1980. Moreover, information from icebreaker navigation logs shows that unstable fast-ice conditions occurred in the 1980s and after the late 1990s. From the analysis of surface meteorological data and the offshore pack-ice distribution, anomalously shallow snow-cover depths and a peculiar retreat pattern of the ice edge are found to be factors that favour fast-ice break-up. The pack-ice distribution controls the propagation of ocean swell inside the bay; encroaching swells are likely to mechanically disintegrate fast-ice during autumn prior to the annual formation of the protective pack-ice cover to the north. Less snow cover also leads to fast-ice weakening as the melt season progresses and broken floes are then transported offshore by prevailing southerly winds.
A model for wave scattering in the marginal ice zone based on a two-dimensional floating-elastic-plate solution
Authors: Kohout Alison L. , Meylan Michael H. 
Published: December 2007

AbstractWe present a model for wave propagation in the marginal ice zone (MIZ). The model is based on a two-dimensional linear water wave floating-elastic-plate solution in the frequency domain using a matched eigenfunction expansion. The model is fully coherent so the results are dependent on exact geometry, and we show firstly that this dependence can be effectively removed by averaging over random floe lengths. We present a range of predictions from the model which show various curves of transmitted energy as a function of the floe thickness, number of floes and wave period. These curves show that it is possible with this simple model to make predictions about wave intensity with distance into the MIZ. The results predict that the MIZ acts as a low-pass filter and and that the filtering is strongly dependent on floe thickness and number but that it is independent of floe length.
Growth of first-year landfast Antarctic sea ice determined from winter temperature measurements
Authors: Purdie Craig R. , Langhorne Patricia J. , Leonard Greg H. , Haskell Tim G. 
Published: December 2007

AbstractTemperature profiles of first-year landfast sea ice have been recorded continuously over the 2003 winter growth season at McMurdo Sound, Antarctica. The temperature gradients in the ice were used to calculate the growth rate due to conductive heat flux, which is shown to account for only part of the total ice growth. Remaining ice growth must be due to a negative oceanic heat flux. Significantly, this oceanic heat flux is shown to occur episodically, sometimes with sustained daily rates in excess of –30Wm–2. There is no direct correlation between oceanic heat flux and water temperature. Times of increased oceanic heat flux do coincide with the appearance of platelet ice in cores, and appear to account for the growth of 35% of the total platelet ice depth measured in ice cores.
Retrieval of thin-ice thickness using the L-band polarization ratio measured by the helicopter-borne scatterometer Heliscat
Authors: Kern Stefan , Gade Martin , Haas Christian , Pfaffling Andreas 
Published: December 2007

AbstractClimate warming makes an increasing thin-ice fraction likely to occur in the Arctic, underpinning the need for its regular observation. synchronous helicopter-borne measurements of the sea-ice thickness and like-polarized L-band radar backscatter carried out along identical flight tracks north of svalbard during winter are combined to develop an algorithm to estimate the thin-ice thickness solely from the L-band backscatter co-polarization ratio (LCPR). Airborne ice-thickness and LCPR data are smoothed along track (to reduce noise), co-located and compared. A linear and a logarithmic fit are applied using thickness values between 0.0 and 0.6m and 0.0 and 1.0 m, respectively. The thin-ice thickness is derived from the LCPR data using these fits, first for dependent data (used to obtain the fits) and subsequently for independent data. The results are compared to airborne ice-thickness measurements for ice-thickness values between 0.0 and 0.6m using linear regression. The logarithmic fit gives the most reliable results, with a correlation of 0.72 and a rms difference of 8 cm. It permits us to derive the thickness of thin ice (below 50–60cm thickness) from airborne LCPR data with an uncertainty of about 10 cm.
The surface energy balance of an active ice-covered volcano: Villarrica Volcano, southern Chile
Authors: Brock Benjamin , Rivera Andrés , Casassa Gino , Bown Francisca , Acuña César 
Published: December 2007

AbstractThe energy balance of bare snow and tephra-covered ice near the glacier equilibrium line elevation on Villarrica Volcano, southern Chile, was investigated during 2004 and 2005, combining meteorological, surface temperature and ablation measurements with energy balance modelling. A tephra thermal conductivity of 0.35 Wm–1K–1, and a critical tephra thickness of <5mm at which ablation is reduced compared to bare snow, were obtained from field data. These low values are attributable to the highly porous lapilli particles which make up most of the surface material. Modelled melt totals in the January to March period were 4.95 m and 3.96 m water equivalent (w.e.) in 2004 and 2005, respectively, compared with ∽0.5mw.e. melt for ice buried by >0.1m tephra. Windblown tephra impurities lowered snow albedo, but increased snowmelt by only an estimated 0.28mw.e. over the same period. The net mass balance impact of supraglacial tephra at Villarrica Volcano is therefore positive, as thick ash and lapilli mantle most of the glacier ablation zones, probably reducing annual ablation by several metres w.e. In the accumulation seasons, frequent melting events were recorded with modelled daily snowmelt rates of up to 50 mmw.e.
Geophysical survey of the intra-caldera icefield of Mt Veniaminof, Alaska
Authors: Welch Brian C. , Dwyer Kieran , Helgen Michael , Waythomas Christopher F. , Jacobel Robert W. 
Published: December 2007

AbstractMt Veniaminof is a large active stratovolcano located on the Alaska Peninsula (56.2° N, 159° W). We present results of the first geophysical survey of the icefield that fills much of the 10 km×8 km caldera that was most recently modified during the last major eruption roughly 3700 BP. The subglacial topography and ice volume are derived from an 8MHz radio-echo sounding survey conducted in July 2005. Prominent internal reflectors are assumed to be isochronal ash/acid deposits related to local eruptions. Accumulation rates and basal melt rates are calculated using a Nye one-dimensional steady-state accumulation model applied at a location that approximates an ice divide and calibrated by matching internal reflectors with published records of recent local volcanic eruptions. The model yields order of magnitude estimates of the accumulation rate of 4ma–1water equivalent and 2 ma–1of basal melt. The subsequent geothermal flux of ∽19Wm–2is similar to active hydrothermal vents in volcanic lakes. We suggest that these values represent an upper limit for the geothermal flux within the ice-covered regions of the main caldera. We also analyze likely subglacial meltwater flow paths to examine the implications of recent eruption activity at an active intra-caldera cinder cone. Two lava-producing eruptions from the cinder cone in 1983–84 and 1993–94 melted roughly 0.17km3of ice. The lack of significant deformation of the internal stratigraphy to the south and east of the melt hole suggests that any subglacial drainage in those directions was entirely within subglacial deposits. We suggest that the more likely drainage route was northwest into a large outlet glacier.
Lahars of Ruapehu Volcano, New Zealand: risk mitigation
Authors: Keys Harry J.R. 
Published: December 2007

AbstractA dam-break lahar resulting from the last eruption of Ruapehu is expected when Crater Lake reaches a critical high level, probably within the next 1–5 summers. A high level of public consultation, political decision-making and ongoing scientific input has occurred to address the risks. Decisions about managing lahar risk have taken into account the fact that lahars are common on the active Ruapehu Volcano (2797 m) and in valleys draining the mountain and that most lahars are generated by eruptions, about half of which have no useful precursors. Lahars threaten New Zealand’s largest ski area and nationally important infrastructure. Public safety has been the main consideration but the need for long-term risk mitigation and reducing impacts on Tongariro National Park World Heritage Area have also been important. Lahar mitigation on Ruapehu now includes six lahar warning systems, each with active response plans, and some infrastructure isolated from or hardened against lahars.
Review and reassessment of hazards owing to volcano–glacier interactions in Colombia
Authors: Huggel Christian , Ceballos Jorge Luis , Pulgarĺn Bernardo , Ramírez Jair , Thouret Jean-Claude 
Published: December 2007

AbstractThe Cordillera Central in Colombia hosts four important glacier-clad volcanoes, namely Nevado del Ruiz, Nevado de Santa Isabel, Nevado del Tolima and Nevado del Huila. Public and scientific attention has been focused on volcano–glacier hazards in Colombia and worldwide by the 1985 Nevado del Ruiz/Armero catastrophe, the world’s largest volcano–glacier disaster. Important volcanological and glaciological studies were undertaken after 1985. However, recent decades have brought strong changes in ice mass extent, volume and structure as a result of atmospheric warming. Population has grown and with it the sizes of numerous communities located around the volcanoes. This study reviews and reassesses the current conditions of and changes in the glaciers, the interaction processes between ice and volcanic activity and the resulting hazards. Results show a considerable hazard potential from Nevados del Ruiz, Tolima and Huila. Explosive activity within environments of snow and ice as well as non-eruption-related mass movements induced by unstable slopes, or steep and fractured glaciers, can produce avalanches that are likely to be transformed into highly mobile debris flows. Such events can have severe consequences for the downstream communities. Integrated monitoring strategies are therefore essential for early detection of emerging activity that may result in hazardous volcano–ice interaction. Corresponding efforts are currently being strengthened within the framework of international programmes.
Effects of ash layers of the 2004 Grímsvötn eruption on SAR backscatter in the accumulation area of Vatnajökull
Authors: Scharrer K. , Mayer C. , Nagler T. , Münzer U. , Guðmundsson Á. 
Published: December 2007

AbstractThe applicability of volcanic ash deposits on Vatnajökull ice cap, Iceland, as a time reference marker for measuring accumulation by the analysis of time sequential SAR backscatter data was investigated. A volcanic eruption at Grímsvötn caldera, a subglacial volcanic system beneath Vatnajökull, deposited an ash layer north of the vent in early November 2004. This ash layer covered a V-shaped area of ∽88km2 on the glacier surface. The ash fall, which was subsequently buried by snow, reveals a distinct backscatter signal in SAR images. In total, the σ0 backscatter values of 40 ENVISAT-ASAR images were analyzed, covering two post-eruption accumulation periods (4 November 2004 to 31 March 2005 and 25 October 2006 to 14 March 2006). Significant differences over time were observed in the SAR backscatter signals over the deposited ash, which appear to be related to the snow accumulation history. The backscatter signals were compared to meteorological conditions at the time of SAR acquisition and to accumulation data derived from two snow pits, one located within the ash fall. A linear regression analysis between the accumulation data and the SAR backscattering coefficient results in high R2 confidence values (>0.8), indicating that the SAR data can be used for estimating the areal accumulation distribution in areas with an existing ash layer.
Emplacement of a silicic lava dome through a crater glacier: Mount St Helens, 2004–06
Authors: Walder Joseph S. , LaHusen Richard G. , Vallance James W. , Schilling Steve P. 
Published: December 2007

AbstractThe process of lava-dome emplacement through a glacier was observed for the first time after Mount St Helens reawakened in September 2004. The glacier that had grown in the crater since the cataclysmic 1980 eruption was split in two by the new lava dome. The two parts of the glacier were successively squeezed against the crater wall. Photography, photogrammetry and geodetic measurements document glacier deformation of an extreme variety, with strain rates of extraordinary magnitude as compared to normal alpine glaciers. Unlike normal temperate glaciers, the crater glacier shows no evidence of either speed-up at the beginning of the ablation season or diurnal speed fluctuations during the ablation season. Thus there is evidently no slip of the glacier over its bed. The most reasonable explanation for this anomaly is that meltwater penetrating the glacier is captured by a thick layer of coarse rubble at the bed and then enters the volcano’s groundwater system rather than flowing through a drainage network along the bed.
Estimating the basal melt rate at NorthGRIP using a Monte Carlo technique
Authors: Buchardt Susanne L. , Dahl-Jensen Dorthe 
Published: December 2007

AbstractFrom radio-echo sounding (RES) surveys and ice core data it can be seen that the ice sheet is melting at the base in a large area in Northern Greenland. The RES images reveal internal layers in the ice. The layers are former deposition surfaces and are thus isochrones. Undulations of the isochrones in regions where the base is smooth suggest that the basal melt rate changes over short distances. This indicates that the geothermal heat flux is very high and has large spatial variability in Northern Greenland. In this study, the basal melt rate at the NorthGRIP drill site in North-Central Greenland is calculated by inverse modelling. We use simple one- and two-dimensional flow models to simulate the ice flow along the NNW-trending ice ridge leading to NorthGRIP. The accumulation is calculated from a dynamical model. Several ice flow parameters are unknown and must be estimated along with the basal melt rate using a Monte Carlo method. The Monte Carlo inversion is constrained by the observed isochrones, dated from the timescale established for the NorthGRIP ice core. The estimates of the basal melt rates around NorthGRIP are obtained from both the one- and two-dimensional models. Combining the estimated basal melt rates with the observed borehole temperatures allows us to convert the basal melt rates to geothermal heat flow values. From the two-dimensional model we find the basal melt rate and geothermal heat flux at NorthGRIP to be 6.1 mma–1 and 129 mWm–2, respectively.
Volcano–ice interactions at Prestahnúkur, Iceland: rhyolite eruption during the last interglacial–glacial transition
Authors: McGarvie D.W. , Stevenson J.A. , Burgess R. , Tuffen H. , Tindle A.G. 
Published: December 2007

AbstractPrestahnúkur is a 570m high rhyolite glaciovolcanic edifice in Iceland’s Western Rift Zone with a volume of 0.6 km3. Uniform whole rock, mineral and glass compositions suggest that Prestahnúkur was constructed during the eruption of one magma batch. Ar-Ar dating gives an age of 89± 24 ka, which implies eruption during the transition (Oxygen Isotope substages 5d to 5a) between the Eemian interglacial and the Weichselian glacial period. Prestahnu´kur is unique among published accounts of rhyolite tuyas because a base of magmatically-fragmented tephra appears to be absent. Instead, basal exposures consist of glassy lava lobes and coarse hyaloclastite, above which are single and multiple lava sheets with matrix-supported basal breccias and hyaloclastite upper carapaces. Steepening ramp structures at sheet termini are interpreted as ice-contact features. Interactions between erupting magma and water/ice have affected all lithologies. A preliminary model for the construction of Prestahnúkur involves an effusive subglacial eruption between 2–19 years duration which never became emergent, into an ice sheet over 700m thick. If 700m of ice had built up during this interglacial–glacial transition, this would corroborate models arguing for the swift accumulation of land-based ice in rapid response to global cooling.
Glacier–volcano interactions in the North Crater of Mt Wrangell, Alaska
Authors: Benson Carl , Motyka Roman , McNutt Stephen , Lüthi Martin , Truffer Martin 
Published: December 2007

AbstractGlaciological and related observations from 1961 to 2005 at the summit of Mt Wrangell (62.00° N, 144.02°W; 4317m a.s.l.), a massive glacier-covered shield volcano in south-central Alaska, show marked changes that appear to have been initiated by the Great Alaska Earthquake (Mw = 9.2) of 27 March 1964. The 4×6 km diameter, ice-filled Summit Caldera with several post-caldera craters on its rim, comprises the summit region where annual snow accumulation is 1–2m of water equivalent and the mean annual temperature, measured 10 m below the snow surface, is –20°C. Precision surveying, aerial photogrammetry and measurements of temperature and snow accumulation were used to measure the loss of glacier ice equivalent to about 0.03 km3 of water from the North Crater in a decade. Glacier calorimetry was used to calculate the associated heat flux, which varied within the range 20–140Wm–2; total heat flow was in the range 20–100MW. Seismicity data from the crater’s rim show two distinct responses to large earthquakes at time scales from minutes to months. Chemistry of water and gas from fumaroles indicates a shallow magma heat source and seismicity data are consistent with this interpretation.