bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dissolved organic matter in Antarctic sea ice
Authors: Thomas David N. , Kattner Gerhard , Engbrodt Ralph , Giannelli Virginia , Kennedy Hilary , Haas Christian , Dieckmann Gerhard S. 
Published: November 2007

AbstractIt has been hypothesized that there are significant dissolved organic matter (DOM) pools in sea-ice systems, although measurements of DOM in sea ice have only rarely been made. The significance of DOM for ice-based productivity and carbon turnover therefore remains highly speculative. DOM within sea ice from the Amundsen and Bellingshausen Seas, Antarctica, in 1994 and the Weddell Sea, Antarctica, in 1992 and 1997 was investigated. Measurements were made on melted sea-ice sections in 1994 and 1997 and in sea-ice brines in 1992. Dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations in melted ice cores were up to 1.8 and 0.78 mM, respectively, or 30 and 8 times higher than those in surface water concentrations, respectively. However, when concentrations within the brine channel/pore space were calculated from estimated brine volumes, actual concentrations of DOC in brines were up to 23.3 mM and DON up to 2.2 mM, although mean values were 1.8 and 0.15 mM, respectively. There were higher concentrations of DOM in warm, porous summer second-year sea ice compared with colder autumn first-year ice, consistent with the different biological activity supported within the various ice types. However, in general there was poor correlation between DOC and DON with algal biomass and numbers of bacteria within the ice. The mean DOC/DON ratio was 11, although again values were highly variable, ranging from 3 to highly carbon-enriched samples of 95. Measurements made on a limited dataset showed that carbohydrates constitute on average 35% of the DOC pool, with highly variable contributions of 1−99%.
Modeling of the Beaufort ice-ocean climatology change
Authors: Nazarenko Larissa , Tausnev Nickolai 
Published: November 2007

AbstractA coupled ice-ocean model is used to study the sensitivity of the Beaufort Sea climatology to representation of sub-grid-scale eddies; to hypothetically not present and double Mackenzie River discharge; and to approximate climate warming specified through a surface air-temperature increase of 3° C. The eddy effect is considered in two ways: as eddy interaction with sea-floor topography yielding a driving force ("neptune" parameterization) and as eddy diffusion and viscosity. The model with neptune parameterization reproduces surface layer circulation, as well as the bathymetrically steered Beaufort Undercurrent, while the model with usual damping does not simulate the Beaufort Undercurrent. The absence of the strong boundary Beaufort Undercurrent affects the thermohaline structure of the Beaufort Sea which becomes less consistent with observational data. The increase of the Mackenzie River discharge causes more northward transport of sea ice, resulting in sea-ice thinning in Mackenzie Bay, while the absence of the Mackenzie River discharge induces southward sea-ice drift and sea-ice thickening in Mackenzie Bay. The sensitivity study of surface air-temperature warming shows a shrinkage of sea ice by 6% in area and 15% in volume, causing the freshening and warming of the surface ocean layer. The sensitivity studies of river discharge and surface air temperature use the neptune parameterization.
Modelling sea-ice thermodynamics in BALTEX-BASIS
Authors: Cheng Bin , Launiainen Jouko , Vihma Timo , Uotila Juha 
Published: November 2007

AbstractIn this paper, we present the results of a one-dimensional, thermodynamic sea-ice model applied to the Baltic Air-Sea-Ice Study (BASIS) field data. In general, the model results are in good agreement with the measurements, which were made during mild weather conditions with distinct areal and temporal variations in the snow and ice thickness. The total amount of refrozen ice calculated from the surface melting water gives a first-order estimate of snow-ice formation during the BASIS experiment, and this agreed well with the total observed variation in ice thickness. The model slightly overestimated ice growth at the bottom. This may be due to the variation in sea-ice thermal properties, affected by a slush layer between the snow and ice, or to the lack of ice-ocean interaction in the model.
Calculation of wave propagation into land-fast ice
Authors: Chung Hyuck , Fox Colin 
Published: November 2007

AbstractWe review the various numerical methods that have been developed for calculating the reflection and transmission of ocean waves at a land-fast ice boundary, including recent developments. While an integral form of the solution, found by the Wiener-Hopf technique, has been known for many years, direct numerical computation of this exact solution has been thought to be prohibitively difficult. Instead, several numerical "matching" procedures have been developed, including some that are only approximate, along with asymptotic solutions based on the integral form. Recently it has been discovered that direct calculation of the integral form is feasible, actually requiring less computation than the matching methods. We outline the actual computations required and contrast each method, and provide examples of computation from the integral form.
Satellite-observed variability and trend in sea-ice extent, surface temperature, albedo and clouds in the Arctic
Authors: Comiso Josefino C. 
Published: November 2007

AbstractRecent observations of a decreasing ice extent and a possible thinning of the ice cover in the Arctic make it imperative that detailed studies of the current Arctic environment are made, especially since the region is known to be highly sensitive to a potential change in climate. A continuous dataset of microwave, thermal infrared and visible satellite data has been analyzed for the first time to concurrently study in spatial detail the variability of the sea-ice cover, surface temperature, albedo and cloud statistics in the region from 1987 to 1998. Large warming anomalies during the last four years (i.e. 1995−98) are indeed apparent and spatially more extensive than previous years. The largest surface temperature anomaly occurred in 1998, but this was confined mainly to the western Arctic and the North American continent, while cooling occurred in other areas. The albedo anomalies show good coherence with the sea-ice concentration anomalies except in the central region, where periodic changes in albedo are observed, indicative of interannual changes in duration and areal extent of melt ponding and snow-free ice cover. The cloud-cover anomalies are more difficult to interpret, but are shown to be well correlated with the expected warming effects of clouds on the sea-ice surface. The results from trend analyses of the data are consistent with a general warming trend and an ice-cover retreat that appear to be even larger during the last dozen years than those previously reported.
Variations of surface air temperature and sea-ice extent in the western Antarctic Peninsula region
Authors: Smith Raymond C. , Stammerjohn Sharon E. 
Published: November 2007

AbstractThe western Antarctic Peninsula (WAP) region has experienced a statistically significant warming trend during the past half-century. In addition, a statistically significant anticorrelation between air temperatures and sea-ice extent, as determined from satellite passive-microwave data during the past two decades, has been observed for this region. Consistent with this strong coupling, sea-ice extent in the WAP area has trended down during this period of satellite observations. Further, much of the variability in both air temperature and sea ice in the WAP region has been shown to be influenced by contrasting maritime (warm, moist) and continental (cold, dry) climate regimes. As part of the Palmer Long Term Ecological Research program, the ecological influence of these trends and variability is being studied, and effects have already been demonstrated at all trophic levels. Here we extend earlier observations to include the past decade and focus on the annual cycles of air temperature and sea-ice extent for the past few years, with the aim of placing these recent observations within the context of changes seen in the longer-term records. The more recent years have seen an increasing maritime influence in the WAP region, with corresponding effects on the marine ecosystem.
CRL/NASDA airborne SAR (Pi-SAR) observations of sea ice in the Sea of Okhotsk
Authors: Matsuoka Takeshi , Uratsuka Seiho , Satake Makoto , Kobayashi Tatsuharu , Nadai Akitsugu , Umehara Toshihiko , Maeno Hideo , Wakabayashi Hiroyuki , Nakamura Kazuki , Nishio Fumihiko 
Published: November 2007

AbstractMulti-frequency, multi-polarization airborne synthetic aperture radar (SAR) observations of sea ice in the southern Sea of Okhotsk were carried out in February 1999 in conjunction with RADARSAT SAR observations. The final goal of this study is to clarify the backscattering characteristics and to understand the scattering mechanisms of sea ice in the Sea of Okhotsk by using microwave multiparametric SAR. The airborne SAR (Pi-SAR) has two frequencies (X- and L-band) and multi-polarization (HH, VV, HV, VH) with 1.5 m (X-band) and 3.0 m (L-band) resolution. It was developed by the Communications Research Laboratory (X-band) and the National Space Development Agency of Japan (L-band). We show the frequency dependence and polarization properties of radar backscattering from sea ice. We find that it is possible to distinguish ice types by comparing backscattering from sea ice in the X- and L-bands. Investigation of the polarization characteristics at X-band was very useful for detecting the thin-ice area (e.g. nilas and gray ice).
Sea-ice kinematics measured with GPS drifters
Authors: Leppäranta Matti , Zhanhai Zhang , Haapala Jari , Stipa Tapani 
Published: November 2007

AbstractA sea-ice dynamics experiment was performed in the Baltic Sea in March 1997. A new type of drifter was constructed based on the global positioning system and mobile-phone data transmission. The drifters worked well and the accuracy was reasonable (std dev. 40 m). Five drifters were used to map ice kinematics in a 20 km size array in the coastal drift-ice zone. The study included periods of onshore motion with ridge formation, and alongshore motion with narrow shear lines. The motion of ice largely occurred in short pulses between which the field stood nearly still. The level of ice speed was much less than that of free drift, while the deformation field was more uniaxial due to the presence of the solid boundary. Drift-ice strength was estimated as 4 × 104 N m−2. Large deformation rates of up to 2% h−1 were observed.
Comparison of interannual snowmelt-onset dates with atmospheric conditions
Authors: Drobot Sheldon D. , Anderson Mark R. 
Published: November 2007

AbstractThe snowmelt-onset date represents an important transitional point in the Arctic surface energy balance, when albedo decreases and energy absorption increases rapidly in response to the appearance of liquid water. Interannual variations in snowmelt onset are likely related to large-scale variations in atmospheric circulation, such as described by the Arctic Oscillation (AO). This research therefore examines the relationship between monthly-averaged AO values and mean annual snowmelt-onset dates over Arctic sea ice in 13 regions, from 1979 to 1998. The objective is to statistically relate variations in mean annual regional snowmelt-onset dates to variations in the AO. Additionally, monthly-averaged 500 hPa heights and 2 m air temperatures are used to illustrate a physical link between snow-melt onset and a positive AO phase. Regression analyses demonstrate that variations in the AO explain a significant portion of the variations in snowmelt onset in the West Central Arctic, Laptev Sea, East Siberian Sea, Hudson Bay and Baffin Bay. Synoptic analyses suggest earlier (later) than average snowmelt onset occurs where warm (cold) air advection and increased (decreased) cyclonic activity are present.
Satellite observations of upper-ocean currents in Terra Nova Bay, Antarctica
Authors: van Woert Michael L. , Meier Walter N. , Zou Cheng-Zhi , Archer Andy , Pellegrini Andrea , Grigioni Paolo , Bertoia Cheryl 
Published: November 2007

AbstractShip and iceberg drifts, along with data from modern satellite-tracked drifting buoys, portray generally northward flow in the southwest Ross Sea. Less is known, however, about the ocean variability in this region. Here we use Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS) imagery to describe a cyclonically rotating gyre in Terra Nova Bay, Antarctica (75° S, 165° E). The image sequence is taken from an exceptionally clear, calm period during winter 1998. Surface currents, derived from tracking drifting ice with a maximum cross-correlation algorithm, were found to be ∼ 20 to 30 cm s−1 Based on scaling arguments, the observed currents appear to be best explained as an oceanic response to a rapidly changing, offshore, katabatic windjet.
Response of the Northern Hemisphere sea ice to greenhouse forcing in a global climate model
Authors: Nazarenko Larissa , Hansen James , Tausnev Nikolai , Ruedy Reto 
Published: November 2007

AbstractThe Q.-flux Goddard Institute of Space Studies (GISS) global climate model, in which an atmospheric general circulation model is coupled to a mixed-layer ocean with specified horizontal heat transports, is used to simulate the transient and equilibrium climate response to a gradual increase of carbon dioxide (1% per year increase of CO2 to doubled CO2). The results indicate that the current GISS model has a high sensitivity with a global annual warming of about 4°C for doubled CO2 . Enhanced warming is found at higher latitudes near sea-ice margins due to retreat of sea ice in the greenhouse experiment. Surface warming is larger in winter than in summer, in part because of the reductions in ice cover and thickness that insulate the winter atmosphere from the ocean. The annual mean reduction of sea-ice cover due to doubled CO2 is about 30% for the Northern Hemisphere. The CO2 experiment has a 70% reduction of sea-ice area and 55% thinning of ice in August in the Northern Hemisphere. Noticeable reduction of sea-ice cover has been found in both historical records and satellite observations. The largest reduction of simulated sea-ice extent occurs in summer, consistent with observations.
Sea-ice concentration retrieval in the Antarctic based on the SSM/ I 85.5 GHz polarization
Authors: Kern Stefan , Heygster Georg 
Published: November 2007

AbstractUsing data from the 85 GHz channels of the Special Sensor Microwave/ Imager (SSM/I) allows a resolution improvement by at least a factor of four compared to the other channels. Consequently higher-resolution sea-ice concentration data can be obtained which in turn can be used to improve the results of numerical weather-prediction (NWP) and global circulation models. The proposed new sea-ice concentration retrieval algorithm (SEA LION algorithm) uses the polarization at 85 GHz (p). Emission from atmospheric water and scattering at the wind-roughened sea surface (weather effect) decrease p and cause an overestimate of the sea-ice concentration. We quantify the weather effect with a radiative transfer model and atmospheric data obtained from NWP models and the other SSM/I channels, and correct p for this effect. Tie points of open water and sea ice are determined for each month separately from daily gridded 85 GHz SSM/I brightness temperatures. Sea-ice concentrations are calculated with the new algorithm for the entire Southern Ocean for each day of the period 1992−98 with a spatial resolution of 12.5 × 12.5 km2. Comparisons of these ice concentrations with Operational Linescan System visible images reveal convincing results concerning the monitoring of coastal polynyas and the break-up of the pack ice in spring. SEA LION sea-ice extents and areas, and comparisons between SEA LION sea-ice concentrations and ship observations, agree with those obtained by the NASA Team and the Bootstrap algorithms:
Ocean wave speed in the Antarctic marginal ice zone
Authors: Fox Colin , Haskell Tim G. 
Published: November 2007

AbstractThe propagation of ocean waves in the marginal ice zone (MIZ) is investigated with the aim of determining whether the loading and scattering of waves by ice floes is significant. Measurements made using instrumented ice floes in the MIZ north of the Ross Sea, Antarctica, during June 1998 are used to determine the frequency-wavelength relationship for propagating ocean waves in that region. This measured-dispersion equation is related to the effective large-scale properties of the MIZ that occur in models for wave propagation and scattering. We present the measured wave speeds to enable estimation of the parameters in these models.
Time-series observations of the structure and properties of brackish ice in the Gulf of Finland
Authors: Kawamura T. , Shirasawa K. , Ishikawa N. , Lindfors A. , Rasmus K. , Granskog M. A. , Ehn J. , Leppäranta M. , Martha T. , Vaikmäe R. 
Published: November 2007

AbstractThe Baltic Sea is a semi-enclosed brackish water basin where sea ice occurs annually. The sea-ice study discussed here was conducted as a Finnish-Japanese cooperative research programme entitled "Ice Climatology of the Okhotsk and Baltic Seas’’ to investigate the structure and properties of the brackish ice in the Baltic Sea. Ice, snow and water samples were collected at Santala Bay, near the mouth of the Gulf of Finland, once a week from 20 January to 12 April 1999. The salinity and oxygen isotopic composition (δ18O) of the samples were measured. The ice samples were analyzed stratigraphically. The ice was composed of a granular upper layer, occupying approximately one-third of the entire ice thickness, and underlying columnar ice toward the bottom. The crystallography structure and δ18O values reveal that the granular ice consisted of two layers with different origins, i.e. snow ice and superimposed ice. The fraction of snow relative to the total thickness was estimated. The limited data show a significant contribution of the snow cover to the sea-ice development. The salinity of the granular ice was higher than that of the columnar ice, implying that the mechanism of entrapment of brine may be different between the two ice types.
A transition in dry-snow slab avalanche triggering modes
Authors: Louchet François 
Published: November 2007

AbstractWe show that two different types of dry-snow slab avalanches may result from a tensile failure of the slab crown triggered by either a quasi-static or an unstable shear propagation of a basal crack at the slab/substrate interface The triggering conditions for both modes are derived analytically. The latter only takes place if the depth of the top layer is above a critical value, and in a “window” centred around a critical slope of 35.3°, if residual friction on the basal crack surfaces is neglected. The width of this window increases with snow thickness. The introduction of a residual friction on the basal crack surfaces increases the critical slope.
Zoning of snowiness and avalanching in the mountains of western Transcaucasia
Authors: Troshkina E. , Glazovskaya T. , Kondakova N. , Sokolov V. 
Published: November 2007

AbstractIn the mountains of the moist-subtropical zone of Western Transcaucasia seven zones of snowiness are distinguished, depending on the heights from sea level to the tops of mountain ranges. Data are taken from 17 years of snow-avalanche observations. In a legend of a map the quantitative characteristic of the avalanching conditions for each zone is given. Interannual variability of snow depth is up to 100 cm in low mountains and about 600 cm in the middle belt of mountains The inversion of snow accumulation is registered. The frequency cycles of heavy-snow (3–4 years) and of especially heavy-snow (10–12 years) winters are determined. The avalanche danger is provoked not by the total depth of the snow, but by the stormy snowfalls. The particular conditions of creation and development of nival processes are distinguished here: dry avalanches on the crests of mountains, wet avalanches in the middle mountains and slushflows in the low mountains. Despite low avalanche activity, avalanche risk is high due to the factor of unexpectedness.
Avalanche extremes and atmospheric circulation patterns
Authors: Birkeland K.W. , Mock C. J. , Shinker J. J. 
Published: November 2007

AbstractAvalanche forecasters can better anticipate avalanche extremes if they understand the relationships between those extremes and atmospheric circulation patterns. We investigated the relationship between extreme avalanche days and atmospheric circulation patterns at four sites in the western United States: Bridger Bowl, Montana; Jackson Hole, Wyoming; Alta, Utah; and Taos, New Mexico. For each site, we calculated a daily avalanche hazard index based on the number and size of avalanches, and we defined abnormal avalanche events as the top 10% of days with recorded avalanche activity. We assessed the influence of different variables on avalanche extremes, and found that high snow water equivalent and high snowfall correspond most closely to days of high avalanche hazard. Composite-anomaly maps of 500 hPa heights during those avalanche extremes clearly illustrate that spatial patterns of anomalous troughing prevail, though the exact position of the troughing varies between sites. These patterns can be explained by the topography of the western United States, and the low-elevation pathways for moisture that exist to the west of each of the sites. The methods developed for this research can be applied to other sites with long-term climate and avalanche databases to further our understanding of the spatial distribution of atmospheric patterns associated with extreme avalanche days.
Measurements of mass balance in dense snow avalanche events
Authors: Sovilla Betty , Sommavilla Francesco , Tomaselli Alvise 
Published: November 2007

AbstractSince 1993 the Avalanche Centre of Arabba has managed a test site to determine avalanche-dynamics parameters (Sommavilla and others, 1997; Sommavilla and Sovilla, 1998). The system is located on an avalanche track which is representative for the Dolomites, northern Italy It monitors avalanche pressures, speed, flow height and variations of the avalanche shape and extent. In winter 1997/98, together with the standard measurements, a series of new field measurements and observations of the snow cover on the avalanche path were conducted for the first time in order to accurately determine the avalanche mass balance. The information collected is typical for dense flow avalanches which have small dimension and develop mainly along a channelled path. In winter 1997/98, four events were studied. For each event, in several sections from the starting zone to the deposition zone, manual measurements were carried out in order to investigate mass entrainment and deposition processes. The mass evolution of the avalanche has been determined. It is shown that the avalanche mass increases by up to 720% with respect to the initial release mass. This entrainment process is related to the speed reached by the avalanche front. In addition, it has been determined that during the acceleration phase of the avalanche front the underlying snow cover is mostly eroded and there is no deposition of snow. In the deceleration phase, by contrast, erosion decreases progressively, reaching the value zero, while deposition becomes progressively larger. These results underscore the importance of the mass balance as a fundamental component in avalanche-dynamics research.