bluuebunny/crossref_metadata_2025_split huggingface dataset:
The interaction of ultraviolet light with Arctic sea ice during SHEBA
Authors: Perovich Donald K. 
Published: December 2007

AbstractThe reflection, absorption and transmission of ultraviolet light by a sea-ice cover strongly impacts primary productivity, higher trophic components of the food web, and humans. Measurements of the incident irradiance at 305, 320, 340 and 380 nm and of the photosynthetically active radiation were made from April through September 1998 as part of the SHEBA (Surface Heat Budget of the Arctic Ocean program) field experiment in the Arctic Ocean. In addition, observations of snow depth and ice thickness were made at more than 100 sites encompassing a comprehensive range of conditions. The thickness observations were combined with a radiative transfer model to compute a time series of the ultraviolet light transmitted by the ice cover from April through September. Peak values of incident ultraviolet irradiance occurred in mid-June. Peak transmittance was later in the summer at the end of the melt season when the snow cover had completely melted, the ice had thinned and pond coverage was extensive. The fraction of the incident ultraviolet irradiance transmitted through the ice increased by several orders of magnitude as the melt season progressed. Ultraviolet transmittance was approximately a factor of ten greater for melt ponds than bare ice. Climate change has the potential to alter the amplitude and timing of the annual albedo cycle of sea ice. If the onset of melt occurs at increasingly earlier dates, ultraviolet transmittance will be significantly enhanced, with potentially deleterious biological impacts.
Satellite-based estimates of sea-ice volume flux through Fram Strait
Authors: Spreen Gunnar , Kern Stefan , Stammer Detlef , Forsberg Rene , Haarpaintner Jörg 
Published: December 2007

AbstractSea-ice volume fluxes through Fram Strait, Arctic Ocean, are estimated for the two Icesat measurement periods in February/March and October/November 2003 by combining Sea-ice area fluxes, determined from Space-borne microwave observations, with estimates of the Sea-ice thickness distribution, inferred from measurements of Icesat’s Geoscience Laser Altimeter System (GLAs) instrument. The thickness is derived from Icesat data by converting its Surface elevation measurements into an ice freeboard estimate. Combined with prior information about ice density and Snow depth and density, the freeboard is converted into ice thickness. Uncertainties in freeboard estimates due to geoid model errors are reduced through the use of the recent geoid from the Arctic Gravity Project. Missing information about the ocean circulation and ocean tides is approximated locally by interpolating the Sea Surface height linearly between open leads. Meridional ice volume fluxes estimated for 79˚N using ice drift observed by AMSR-E (QuiksCAT) amount to 168 km3(236km3) and 62 km3(77 km3) for 30 day periods in February/March and October/November 2003, respectively. These values lie in the range of previous results from Similar Studies, but are considerably Smaller than the average ice flux during the 1990s, most likely because of a Smaller ice-drift Speed during 2003.
Covariation of Sea ice and methanesulphonic acid in Wilhelm II Land, East Antarctica
Authors: Foster Annette F.M. , Curran Mark A.J. , Smith Barbara T. , Van Ommen Tas D. , Morgan Vin I. 
Published: December 2007

AbstractSea ice plays an important role in ocean–atmosphere heat exchange, global albedo and the marine ecosystem. Knowledge of variation in Sea-ice extent is essential in order to understand past climates, and to model possible future climate Scenarios. This paper presents results from a Short firn core Spanning 15 years collected from near Mount Brown, Wilhelm II Land, East Antarctica. Variations of methanesulphonic acid (MSA) at Mount Brown were positively correlated with Sea-ice extent from the coastal region Surrounding Mount Brown (60–120˚ E) and from around the entire Antarctic coast (0–360˚ E). Previous results from Law Dome identified this MSA–sea-ice relationship and proposed it as an Antarctic Sea-ice proxy (Curran and others, 2003), with the Strongest results found for the local Law Dome region. Our data provide Supporting evidence for the Law Dome proxy (at another Site in East Antarctica), but a deeper Mount Brown ice core is required to confirm the Sea-ice decline Suggested by Curran and others (2003). Results also indicate that this deeper record may also provide a more circum-Antarctic Sea-ice proxy.
Ice ridging and ice drift in Southern Gulf of St Lawrence, Canada, during winter Storms
Authors: Prinsenberg S.J. , Der Baaren A. Van , Peterson I.K. 
Published: December 2007

AbstractDuring February and March 2004, Satellite-tracked ice beacons and helicopter-borne Sensors collected ice-drift and ice-thickness data from the Southern Gulf of St Lawrence, Canada, to Study the region’s ice-thickness evolution and ice-drift behavior in response to winter Storms. Three northeasterly Storms passed through the area during the observation period, pushing the pack ice against the north Shore of Prince Edward Island. The resulting Severe ice deformation caused major changes in the ice-thickness distribution of two pack-ice areas tracked by ice beacons that Survived the Storms. The ice drift ranged from 1.4% to 2.9% of the wind Speed during free ice-drift conditions, decreasing to 0% when the pack ice compacted against the Shoreline. Most of the thinner ice deformed first, increasing the mean ice thickness over 6–8 km line Sections around the beacons from 0.6 and 0.3 m before the Storms to 1.9 and 2.0 m after the Storms. The ice-thickness increases can be accounted for by the reduced pack-ice area due to ice ridging. Over the next 4weeks, deformation continued and the mean ice thickness around the beacons increased to 2.8 m, well in excess of the maximum undeformed possible ice growth of 65 cm. Ice charts captured the ice thickness of undeformed and composite ice floes but did not capture the ice volume in ice-rubble fields.
Summer and early-fall Sea-ice concentration in the Ross Sea: comparison of in Situ ASPeCt observations and satellite passive microwave estimates
Authors: Knuth Margaret A. , Ackley Stephen F. 
Published: December 2007

AbstractSea-ice conditions were observed using the AsPeCt observation protocol on three cruises in the Ross Sea spanning the Antarctic Summer Season (APIs, December 1999–February 2000; Anslope 1, March–April 2003; Anslope 2, February–April 2004). An additional dataset was analyzed from helicopter video Surveys taken during the APIs cruise. The helicopter video was analyzed using two techniques: first, as an AsPeCt dataset where it was Sampled visually for ice concentration, floe Sizes and ice type on a point basis at 11 km intervals; Second, computerized image processing on a Subset of nine helicopter flights to obtain ice concentration on a continuous basis (1 S intervals) for the entire flight. This continuous Sampling was used to validate the point-sampling methods to characterize the ice cover; the ‘AsPeCt Sampling’ on the helicopter video and the use of the AsPeCt protocol on the Ship Surveys. The estimates for average ice concentration agreed within 5% for the continuous digitized data and point Sampling at 11 km intervals in this comparison. The Ship and video in Situ datasets were then compared with ice concentrations from SsM/I passive microwave Satellite data derived using the Bootstrap and NAsA-Team algorithms. Less than 50% of the variance in Summer ice concentration observed in Situ was explainable by Satellite microwave data. The Satellite data were also inconsistent in measurement, both underestimating and overestimating the concentration for Summer conditions, but improved in the fall period when conditions were colder. This improvement was in the explainable variance of >70%, although in Situ concentration was underestimated (albeit consistently) by the Satellite imagery in fall.
Measurement of Arctic sea-ice thickness by submarine 5 years after Scicex
Authors: Hughes Nicholas E. , Wadhams Peter 
Published: December 2007

AbstractIn April 2004 the Royal Navy submarine HMS Tireless became the first UK submarine to conduct environmental monitoring in the Arctic Ocean since 1996. As the last US SCICEX (Scientific Ice Expeditions) cruise was in 2000, this has been the only opportunity for a civilian scientist to carry out measurement of ice draft and oceanography over a wide area of the Arctic. This paper presents preliminary results and compares them with similar investigations in the 1970s–90s. The route of Tireless covered a large area of the European sector of the Arctic from 5˚E to 62˚W. Transects were carried out from the marginal ice zone in Fram Strait up to the North Pole and along the 85˚N parallel north of Greenland. As part of work for the European Commission IRIS project, image intensity from the advanced synthetic aperture radar instrument on the European Space Agency’s Envisat satellite has been compared with ice draft from the submarine. The raw data were found to be highly variable, so a moving average was applied, producing a correlation of 0.79. Tireless carried a full oceanographic sensor suite and expendable probes for investigation into changes in the Arctic Ocean. The results from these show further erosion of the Arctic cold halocline layer by advancing Atlantic Water compared to previous climatologies and fieldwork expeditions. Preliminary ice-draft data from 85˚N show deeper ice keels than those encountered by a submarine on the same route in 1987.
Molecular dynamics simulation of ice growth from supercooled pure water and from salt solution
Authors: Carignano M.A. , Baskaran E. , Shepson P.B. , Szleifer I. 
Published: December 2007

AbstractThe kinetics of ice growth on the prismatic and basal planes is studied by molecular dynamics simulations. The time evolution of two systems has been investigated. In one a slab of ice is initially in contact with supercooled water, while in the second the ice is in contact with a supercooled salt solution. The simulations were done at a temperature below the eutectic temperature, and complete solidification is observed. The total freezing time is longer in the systems with ions than in the systems with pure water. The final state for the salt systems always shows the formation of ion clusters. For the ionic system growing on the prismatic plane, an intermediate metastable state is observed before total solidification. The duration of this metastable state depends on the ability of the system to get all the ions participating in cluster formation. The simulations enable understanding of the mechanisms for ice formation under different solution conditions.
Spectral transmission and implications for the partitioning of shortwave radiation in arctic sea ice
Authors: Grenfell Thomas C. , Light Bonnie , Perovich Donald K. 
Published: December 2007

AbstractWe present a new set of values for the spectral extinction coefficients,Kλ, for the interior of first-year (FY) and multi-year (MY) Arctic sea ice during the summer melt season measured during SHEBA (Surface Heat Budget of the Arctic Ocean program) and at Barrow, Alaska, USA. Results for FY ice are consistent with previously reported values, and differences can be understood in terms of variations in the concentration of biological and suspended particulate material. The values for the interior of MY ice are lower than previously reported for both bare and ponded ice. For bare MY ice the newKλvalues predict a substantial increase in the solar radiation transmitted through the ice into the upper mixed layer. Ponded MY ice is only slightly more transparent than previously reported, and FY ice values are generally consistent with previously reported values. Assuming an asymmetry parameter of 0.94, the extinction coefficients are consistent with a volume-scattering coefficient of 77 m–1that is constant from 400 to at least 720 nm.
Anomalies of Sea-ice transports in the Arctic
Authors: Martin Torge , Martin Thomas 
Published: December 2007

AbstractIn the Arctic, Sea-ice motion and ice export are prominent processes and good indicators of Arctic climate System variability. Sea-ice drift is Simulated using a dynamic–thermodynamic Sea-ice model, validated with retrievals from SsM/I Satellite observations. Both datasets agree well in reproducing the main Arctic drift patterns. In order to Study inner Arctic transports and ice volume anomalies, the Arctic Ocean is Split by ten boundaries, Separating the central Arctic Ocean from the Nordic and marginal Seas. It is found that the already dominant Sea-ice export through Fram Strait has increased at the expense of export through the Barents Sea in the most recent years investigated. Furthermore, ice export from the Eurasian marginal Seas increased Slightly, followed by greater ice production during the winter. In contrast to this, the Sea-ice volume moved within the Beaufort Gyre distinctly decreased. In total, the ice volume in the central Arctic decreased during the 40 year period covered by this Study. The changes in the ice volume correspond to two wind-driven circulation regimes of the Arctic Sea-ice motion, which recur approximately every 11 years. For the volume anomalies we derived a correlation of –0.59 to the North Atlantic Oscillation (NAO) index, lagging the NAO by 2 years.
Measurement of Sea-ice draft using upward-looking ADCP on an autonomous underwater vehicle
Authors: Banks Christopher J. , Brandon Mark A. , Garthwaite Paul H. 
Published: December 2007

AbstractDuring March 2003, Autosub, an autonomous underwater vehicle (AUV) operated by the UK National Oceanography Centre, Southampton, was deployed under Sea ice north of Thurston Island, Amundsen Sea, Antarctica (at ∽71˚ S, 100˚ W). The vehicle was fitted with an upward-looking 300 kHz acoustic Doppler current profiler (ADCP) to provide current velocity above the AUV. The ADCP also recorded ranges to the ocean–ice interface. Such data can be used to derive Sea-ice draft by using a number of novel processing Steps Such as correcting for the coordinate Systems of the ADCP unit and the vehicle as well as corrections for changes in Sound Speed. This paper outlines the processing Stages required to obtain a probability density function (PDF) of Sea-ice draft and presents PDFs for the region north of Thurston Island. The distribution of ice draft was found to be unimodal, with modes between 2.2 and 2.4 m. Given the uncertainty in Sound Speed, the limit of accuracy was estimated as ∽6 cm.
Geothermal activity in the subglacial Katla caldera, Iceland, 1999–2005, studied with radar altimetry
Authors: Guðmundsson Magnú s T. , Högnadóttir Þórdís , Kristinsson Arnór Bergur , Guðbjörnsson Snæbjörn 
Published: December 2007

AbstractThe Katla caldera is located under the Mýrdalsjökull ice cap and is one of the most hazardous volcanoes in Iceland due to major jökulhlaups that accompany eruptions. Subglacial geothermal activity is manifested in several 10–50m deep depressions (ice cauldrons) within and at the caldera rim and the total geothermal heat output is of the order of a few hundred megawatts. A short-lived but powerful pulse in geothermal heat output took place in 1999, probably including a minor subglacial eruption, when new ice cauldrons formed in three places and an unexpected jökulhlaup occurred. Following these events, a comprehensive monitoring program was set up for Katla, including ice surface elevation profiling from aircraft, to monitor variations in geothermal heat and detect signs of subglacial water accumulation. A radar altimeter coupled with a kinematic GPS is used, achieving an absolute elevation accuracy of 3m and internal consistency of 1–2 m. Profiles across the caldera are flown twice a year. An annual accumulation-ablation cycle in surface elevation with amplitude of 5–10m is observed. By removing this cycle from the data, changes due to subglacial geothermal activity are obtained. After the events in 1999, a decline in geothermal activity was observed. In 2001–03 some ice cauldrons expanded and deepened by 10–15 m, indicating renewed increase in geothermal activity. This trend is also apparent for 2003–05. The increase in geothermal power amounts to a few tens of megawatts. It is likely that the increased thermal output is related to increased seismicity and caused by magma inflow.
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

AbstractDespite 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

AbstractIce 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

AbstractThe 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

AbstractTo 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

AbstractEliot 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.