bluuebunny/crossref_metadata_2025 huggingface dataset:
Dating ice cores from a high Alpine glacier with a flow model for cold firn
Authors: Lüthi M. , Funk M.
Published: November 2007

A flow model for cold firn proves to be very successful in calculating the age-depth relation of several deep ice cores drilled on Colle Gnifetti, Monte Rosa, Swiss Alps. The compressibility of firn is taken into account by an appropriate constitutive equation, first employed in glaciology by Gagliardini and Meyssonnier (1997), which is implemented in a finite-element code. Flow models of the Colle Gnifetti saddle glaciation in two and three dimensions are based on digital elevation maps of the surface σnd the bedrock, based on radio-echo soundings of the ice thickness. Firn density and the englacial temperature fields are either prescribed or calculated in coupled models. Measured surface velocities, density profiles, the ages of chemically dated layers in ice cores and the closure of a 100 m deep borehole provide benchmarks for the models. The good agreement of modeled and measured quantities confirms that the model includes the relevant physical processes and particularly that the firn flow law is well suited for this type of glacier. The study provides new constraints on the age of the ice near the base as well as the source regions of the ice in the cores.

An exceptional flow behavior of the basal ice layer was detected in measurements of borehole closure and inclination. Measurtxl6ed deformation rates exceed upper bounds derived from the flow models, and are thus attributed to altered rheological properties.
Tidal movement of Nioghalvfjerdsfjorden glacier, northeast Greenland: observations and modelling
Authors: Reeh Niels , Mayer Christoph , Olesen Ole B. , Christensen Erik Lintz , Thomsen Henrik Højmark
Published: November 2007

Nioghalvfjerdsfjorden glacier is a >60 km long and 20 km wide floating outlet glacier located at 79°30’ N, 22° W, draining a large area of the northeast Greenland ice sheet. Climate, mass-balance and dynamics studies were carried out on the glacier in three field seasons in 1996, 1997 and 1998. As part of this work, tidal-movement observations were carried out by simultaneous differential global positioning system (GPS) measurements at several locations distributed on the glacier surface. The GPS observations were performed continuously over several tidal cycles. At the same time, tiltmeter measurements were carried out in the grounding zones along the glacier margins and upstream, where the glacier leaves the main ice sheet A tide gauge installed in the sea immediately in front of the glacier front recorded the tide in the open sea during the field seasons. The observations show that the main part of the glacier tongue responds as a freely floating plate to the phase and amplitude of the local tide in the sea. However, kilometre-wide flexure zones exist along the marginal and upstream grounding lines. Attempts to model the observed tidal deflection and tilt patterns in the flexure zone by elastic-beam theory are unsuccessful, in contrast to previous findings by other investigators. The strongest disagreement between our measurements and results derived from elastic-beam theory is a significant variation of the phase of the tidal records with distance from the grounding line (most clearly displayed by the tilt records). We suggest that the viscous properties of glacier ice must be taken into account, and consequently that a viscoelastic-beam model must be used to adequately describe tidal bending of floating glaciers.
Tidewater glaciers: frontal flow acceleration and basal sliding
Authors: Vieli Andreas , Funk Martin , Blatter Heinz
Published: November 2007

A numerical glacier-flow model (finite-element method) is used to suggest the processes that control the flow behind the calving front of a tidewater glacier. The model is developed for grounded calving glaciers and includes an effective-pressure-dependent sliding law The sliding law is implemented by adding a soft basal layer with a variable viscosity The model is applied on Hansbreen, a tidewater calving glacier in Svalbard. Comparison between modeled surface velocities and observed velocity data shows good agreement. We conclude that the flow of a grounded calving glacier can be modeled with an effective-pressure-dependent sliding law
Raman scattering and neutron-diffraction studies of fresh ice and Antarctic ice
Authors: Fukazawa Hiroshi , Mae Shinji , Ikeda Susumu
Published: November 2007

In order to investigate the temperature dependence of vibrational spectra of ice, we measured the Raman spectra of artificial ice Ih in the temperature range 198–270 K. The frequency of translational lattice vibrations decreases with increases in the measurement temperature, and the rate of decrease discontinuously changes at 237 K. The discontinuous change of the rate of decrease is consistent with the phase transition from a proton-disordered arrangement to a proton-ordered arrangement at the ice temperature Ti = 237 K in polar ice sheets, as proposed by Fukazawa and others (1998b). We then compared the Raman spectra of translational lattice vibrations in ice Ih and Antarctic ice and examined the possible effects of the phase transition on the geophysical properties of Antarctic ice. We also report preliminary results of the neutron powder diffraction of Dome Fuji (DF) Antarctic ice, and discuss arrangements of protons in DF ice.
Predictions in avalanche forecasting
Authors: McClung D. M.
Published: November 2007

Verification of avalanche forecasts depends on the spatial and temporal scale of the forecast, and the classes of informational entropy of data implicit in the forecast. First I present a classification system for avalanche forecasts based on these parameters. Verification of models in avalanche forecasting may consist of two stages. Often, the first stage is to ensure that the model matches the scales (space and time) and the classification of forecast and that redundant variables and parameters are eliminated. Once that is achieved, verification can proceed to the second stage, testing the model against relevant field data and situations. I provide an example based on the public-danger scale bulletin used for warnings in the back country in North America and Europe. Using data on deaths and accidents from Alpine Europe with Bayesian statistics, I conclude the danger scale has more classes than necessary for back-country applications. This could be a first stage prior to actual verification of this experience-based model.
Quantifying grain-shape changes in snow subjected to large temperature gradients
Authors: Fierz Charles , Baunach Thorsten
Published: November 2007

Snow-cover models are used in many applications in today’s snow and ice research. Although physically based models allow the evolution of the internal structure of the snow cover to be followed very closely a quantitative and objective description of the layer texture’s evolution in snow subjected to large temperature gradients is still required, in order to both improve and verify existing snow-cover models. Based on experiments done in the cold laboratory as well as on field observations on snow subjected to kinetic-growth metamorphism, we present new results on the quantification of texture-related parameters. Problems such as linking objective laboratory work to pragmatic field observations and finding a reproducible method to measure shape-related parameters are discussed. Finally a new shape parameter is proposed, zero curvature, which differentiates well between depth hoar, faceted crystals and snow types with rounded grains. It also shows a pronounced dependence on temperature gradient.
Dynamic observations of dislocation/grain-boundary interactions in ice
Authors: Baker I. , Liu F. , Jia K. , Hu X. , Cullen D. , Dudley M.
Published: November 2007

Dislocation/grain-boundary (GB) interactions have been studied in situ in polycrystalline ice using synchrotron X-ray topography in the temperature range 0° to –15°C GBs were observed to act both as sources of lattice dislocations and as strong obstacles to dislocation motion. Dislocations were observed to form pile-ups at GBs upon loading. Generally the basal slip system with the highest Schmid factor was found to be the most active, and dislocations were emitted from GB facets as semi-hexagonal loops in order to relieve the stress build-up from GB sliding. When the relative orientation of two adjacent grains and the orientation of the GB between them with respect to the loading direction discouraged GB sliding, thus suppressing dislocation nucleation at the GB, dislocations originating in one grain piled up at the GB and led to slip transmission through the GB The latter geometrical arrangement is rarely encountered, suggesting that slip transmission through grain boundaries in ice is a rare event. When basal slip was suppressed, i.e. when the loading direction lay in the basal plane, slip occurred by the glide of a fast edge segment on non-basal planes.
A comparison of balance velocities, measured velocities and thermomechanically modelled velocities for the Greenland ice sheet
Authors: Bamber J. L. , Hardy R. J. , Huybrechts P. , Joughin Ian
Published: November 2007

Balance velocities for the Greenland ice sheet have been calculated from a new digital-elevation model, accumulation-rates compilation and an existing ice-thickness grid, using a two-dimensional finite-difference scheme. The pattern of velocities over the ice sheet is presented and compared with velocities derived from synthetic-aperture-radar interferometry for part of northern Greenland and a limited number of global positioning system data. This comparison indicated that the balance-velocity scheme and boundary conditions used here provide a remarkably good representation of the dynamics of the ice sheet inland from the margins. It is suggested, therefore, that these balance-velocity data could provide a valuable method of constraining a numerical ice-sheet model. The balance velocities were compared with the diagnostic velocity field calculated from several different configurations of a numerical ice-sheet model. The general pattern of flow agrees well. The detail, however, is quite different. For example, the large (>300km) ice stream in the northeast is not generated by the numerical model and much of the detailed flow pattern is completely lost due to the limited model resolution and limitations in the model physics.
Surface topography of Dome Concordia (Antarctica) from kinematic interferential GPS and bedrock topography
Authors: Capra A. , Cefalo R. , Gandolfi S. , Manzoni G. , Tabacco I. E. , Vittuari L.
Published: November 2007

A new plano-altimetric map of the Dome Concordia (Dome C) area was drawn up from 1995/96 kinematic double-frequency global-positioning-system (GPS) data of two different projects, as well as static GPS data from a geodetic net for deformation analysis and ice-flow velocity measurements covering an area of about 2000 km2.

The GPS surveys were carried out for EPICA during the 10th and 11th Italian Expeditions to choose the optimal location for deep ice-core drilling at Dome C. The accuracy of the kinematic survey was tested by analysing the height-value differences at intersections between different profiles; values ranged from 50–150 mm.

The new map was compared with the 1993 kinematic interferential GPS data and residuals between the 1993 and 1995 data were calculated. The surface topographic values were used to calculate the elevation of the Dome C area bedrock, obtained from the reference ground-based and airborne radio-echo-sounding surveys.
Deformation and recrystallization processes of ice from polar ice sheets
Authors: Duval Paul , Arnaud Laurent , Brissaud Olivier , Montagnat Maureen , de la Chapelle Sophie
Published: November 2007

Information on deformation modes, fabric development and recrystallization processes was obtained by study of deep ice cores from polar ice sheets. It is shown that intracrystalline slip is the main deformation mechanism in polar ice sheets. Grain-boundary sliding does not appear to be a significant deformation mode. Special emphasis was laid on the occurrence of "laboratory" tertiary creep in ice sheets. The creep behavior is directly related to recrystallization processes. Grain-boundary migration associated with grain growth and rotation recrystallization accommodates dislocation slip and counteracts strain hardening. The fabric pattern is similar to that induced only by slip, even if rotation recrystallization slows down fabric development. Fabrics which develop during tertiary creep, and are associated with migration recrystallization, are typical recrystallization fabrics. They are associated with the fast boundary migration regime as observed in temperate glaciers. A decrease of the stress exponent is expected from 3, when migration recrystallization occurs, to a value ≤ 2 when normal grain growth occurs.
Accumulation rates in Dronning Maud Land, Antarctica, as revealed by dielectric-profiling measurements of shallow firn cores
Authors: Oerter H. , Wilhelms F. , Jung-Rothenhäusler F. , Göktas F. , Miller H. , Graf W. , Sommer S.
Published: November 2007

The European Programme for Ice Coring in Antarctica includes a comprehensive pre-site survey on the inland ice plateau of Dronning Maud Land, Antarctica. The German glaciological programme during the 1997/98 field season was carried out along a 1200 km traverse on Amundsenisen and involved sampling the snow cover in pits and by shallow firn cores. This paper focuses on the accumulation studies. The cores were dated by dielectric-profiling and continuous-flow analysis. Distinct volcanogenic peaks and seasonal signals in the profiles served to establish a depth time-scale. The eruptions of Krakatoa, Tambora, an unknown volcano, Kuwae and El Chichon are well-documented in the ice. Variations of the accumulation rates over different times were inferred from the depth time-scales. A composite record of accumulation rates for the last 200 years was produced by stacking 12 annually resolved records. According to this, accumulation rates decreased in the 19th century and increased in the 20th century. The recent values are by no means extraordinary, as they do not exceed the values at the beginning of the 19th century. Variations in accumulation rates are most probably linked to temperature variations indicated in δ18O records from Amundsenisen.
Geostatistical methods for mapping Antarctic ice surfaces at continental and regional scales
Authors: Herzfeld Ute Christina , Stosius Ralf , Schneider Marcus
Published: November 2007

The Antarctic ice sheet plays a major role in the global system and the large ice streams discharging into the circumpolar sea represent its gateways to the world’s oceans. Satellite radar-altimeter data provide an opportunity for mapping surface elevation at kilometer resolution with meter accuracy. Geostatistical methods have been developed to accomplish this. We distinguish two goals in mapping the Antarctic ice surface: (a) construction of a continent-wide atlas of maps and digital terrain models, and (b) calculation of maps and models suitable for the study of individual glaciers, ice streams and ice shelves. The atlases consist of accurate maps of ice-surface elevation compiled from Seasat, Geosat and ERS-1 altimeter data, covering all of Antarctica surveyed by Geosat (to 72.1° S) and by ERS-1 (to 81.5° S). With a 3 km grid they are the highest-resolution maps available today with continent-wide coverage. The resolution permits geophysical study and facilitates monitoring of changes in ice-surface elevation and changes in flux across the ice-ocean boundary, which is essential for monitoring sea-level changes.
Change in mass balance of polar ice sheets and sea level from high-resolution GCM simulations of greenhouse warming
Authors: Wild Martin , Ohmura Atsumu
Published: November 2007

For projecting future sea level, the mass-balance changes on Greenland and Antarctica are considered to be crucial. Promising tools for such estimates are general circulation models (GCM). Until recently, a major impediment was their coarse grid resolution (3°-6°) causing substantial uncertainties in the mass-balance calculations of the poorly resolved ice sheets. The present study is based on a new climate-change experiment of the highest resolution currently feasible (1.1 °) performed with the ECHAM4 T106 GCM, thereby increasing confidence in the projected mass-balance and sea-level changes. This new experiment, with doubled CO2 concentration, suggests that the mass gain in Antarctica due to increased accumulation exceeds the melt-induced mass loss in Greenland by a factor of three. The resulting mass-balance change on both ice sheets is equivalent to a net sea-level decrease of 0.6 mm a"1 under doubled CO2 conditions. This may compensate for a significant portion of the melt-induced sea-level rise from the smaller glaciers and ice caps, thus leaving thermal expansion as the dominant factor for sea-level rise over the next decades. This compensating effect, however, no longer applies should atmospheric CO2 concentration reach levels well above "doubled the present value". On the contrary, under these conditions, the greenhouse warming would become large enough to induce substantial melting also on the Antarctic ice sheet, thereby significantly accelerating global sea-level rise.
Geostatistical analysis of glacier-roughness data
Authors: Herzfeld Ute Christina , Mayer Helmut , Feller Wolfgang , Mimler Matthias
Published: November 2007

In most glaciological and hydrological models, surface roughness of snow and ice is an important parameter. However, roughness is generally used only as an estimated parameter for lack of available observations. In this paper, we present a method to collect and analyze ice-surface-roughness data using a specially designed instrument for survey and geostatistical methods for analysis. The glacier-roughness sensor (GRS), built at the University of Trier, records variations in microtopography at 0.2 m × 0.1 m resolution when pulled across an ice surface. Global positioning system data are used for location. After several processing steps, the data are analyzed using geostatistical methods. The mathematical tool used to achieve a morphological characterization of ice-surface types is the variogram. GRS data, variograms and surface roughness analysis are ideal matches for morphological characterization, because none of them requires or provides absolute elevation values. Morphology is described not by absolute elevation values, but by the change of elevation in space which is the derivative of elevation (surface-roughness values). The variogram is calculated from incremental values. Parameters extracted from variograms of GRS data serve to distinguish lake surfaces, wind structures, ridge-and- vaUey systems, melting structures and blue-ice areas. Examples are from Jakobshavn Isbræ drainage basin, West Greenland.
Geostatistical characterization of ice surfaces from ERS-1 and ERS-2 SAR data, Jakobshavn Isbræ, Greenland
Authors: Herzfeld Ute Christina , Stauber Monika , Stahl Natalie
Published: November 2007

Synthetic-aperture-radar (SAR) data are useful for the study of polar regions because of their independence of cloud cover and daylight, but their analysis is complicated by a lack of absolute reference in size and grey value. The geostatistical surface-classification approach provides a solution to this problem. Parameters extracted from variograms constitute a feature vector, which is characteristic of a surface morphological province. The goal is the classification of larger areas using the result of a characterization of prototype areas that are homogeneous with respect to ice-surface morphological types. This requires a feasibility study and comparison with ground-truth data. Both issues are investigated in this paper. Examples of 1995 ERS-1 and 1997 ERS-2 SAR data from Jakobshavn Isbræ serve to demonstrate that different ice-surface types can be distinguished automatically with geostatistical surface characterization. Ice-surface microtopography/roughness data collected during expedition MICROTOP 97 to the Jakobshavn Isbræ drainage basin provide the ground-truth data required to investigate whether areas that appear homogeneous on a SAR image are in fact homogeneous in ice-surface morphological properties An analysis of contemporaneous ERS-2 SAR data using geostatistical surface characterization is presented.
Shallow-ice microstructure at Dome Concordia, Antarctica
Authors: Arnaud Laurent , Weiss Jérôme , Gay Michel , Duval Paul
Published: November 2007

The shallow-ice microstructure at Dome Concordia, Antarctica, has been studied between 100 m and 580 m. An original digital-image-processing technique has been specially developed to extract ice microstructure (grain boundaries) from thin sections prepared during the two first scientific EPICA field seasons (1997/98 and 1998/99). Using this, not only the mean crystal size, but also crystal-size distributions and shape anisotropy were determined. The mean crystal-size profile as well as crystal-size distributions reveal normal grain growth up to 430 m. Between 430 m and 500 m, a marked decrease of crystal size is observed and compared with a similar trend obtained in the "old" Dome C ice core formerly associated with the Holocene/Last Glacial transition (Duval and Lorius, 1980). This seems to indicate a slightly lower accumulation rate (by <10%) at Dome C. The shapes of the crystal-size distributions, though very similar, do evolve with depth and seem to be sensitive to climatic changes. An increasing flattening of crystal shape is observed with depth. This allowed estimation of the vertical strain rate in the shallow part of the ice sheet.
Simulation of the Antarctic ice sheet with a three-dimensional polythermal ice-sheet model, in support of the EPICA project. II. Nested high-resolution treatment of Dronning Maud Land, Antarctica
Authors: Savvin A. , Greve R. , Calov R. , Mügge B. , Hutter K.
Published: November 2007

The modern dynamic and thermodynamic state of the entire Antarctic ice sheet is computed for a 242 200 year paleoclimatic simulation with the three-dimensional polythermal ice-sheet model SICOPOLIS. The simulation is driven by a climate history derived from the Vostok ice core and the SPECMAP sea-level record. In a 872 km × 436 km region in western Dronning Maud Land (DML), where a deep ice core is planned for EPICA, new high-resolution ice-thickness data are used to compute an improved bedrock topography and a locally refined numerical grid is applied which extends earlier work (Calov and others, 1998). The computed fields of basal temperature, age and shear deformation, together with the measured accumulation rates, give valuable information for the selection of a drill site suitable for obtaining a high-resolution climate record for the last glacial cycle. Based on these results, a possible drill site at 73°59′ S, 00°00′ E is discussed, for which the computed depth profiles of temperature, age, velocity and shear deformation are presented. The geographic origin of the ice column at this position extends 320 km upstream and therefore does not leave the DML region.
Sea ice and climate in 20th- and 21st-century simulations with a global atmosphere-ocean-ice model
Authors: Weatherly John W. , Arblaster Julie M.
Published: November 2007

A global atmosphere-ocean-sea-ice general circulation model (GCM) is used in simulations of climate with greenhouse gas concentrations and sulfate aerosols prescribed from observational data (1870−1995) and future projections (1995−2100). Simulations that include the variability in solar flux from 1870 through 1995 are also performed. The variation in solar flux of ± 2 W m−2 produces a global temperature change of ± 0.2°C in the model. The more recent simulated warming trend produced by increasing greenhouse gases exceeds this solar-flux warming, although the solar flux contributes to some of the simulated present-day warm temperatures. The future increases in greenhouse gases produce an increase in global temperature of 1.2°C over 70 years, with significant decreases in Arctic ice thickness and area. The model exhibits an atmospheric pressure mode similar to the Arctic Oscillation, with different correlation indices between the North Atlantic and North Pacific pressure anomalies.
Sensible- and latent-heat-flux estimates over the Mertz Glacier polynya, East Antarctica, from in-flight measurements
Authors: Roberts Andrew , Allison Ian , Lytle Victoria I.
Published: November 2007

Coastal polynyas can be regions of intense ocean-atmosphere heat transfer. In these polynyas, relatively warm ocean is exposed to cold, dry continental air, resulting in high sea-ice production rates. We have calculated ocean-atmosphere heat fluxes over an area of the Mertz Glacier polynya, East Antarctica, from atmospheric data collected in August 1999. Air-temperature and humidity data were measured using a probe extending from a helicopter undercarriage. Flights were made over the most vigorously ice-producing part of the polynya, within 20 km of the coast in southeast Buchanan Bay, both in very strong katabatic winds (20 m s–1) and during calmer conditions (5 m s–1). The total turbulent heat loss from the surface was nearly 575 W m–2 for the windy case and 250 W m–2 for the calmer one, with a ratio of sensible to latent heat in both cases of slightly more than four. These fluxes are in general agreement with other estimates of heat loss from Antarctic polynyas. Strong katabatic winds, sometimes exceeding 40 m s–1, were common in Buchanan Bay and the heat losses during the strong-wind cafe are probably typical of the region. We suggest that this inner part of the Mertz Glacier polynya has a very high ice-production rate.
An efficient adjustable-layering thermodynamic sea-ice model formulation for high-frequency forcing
Authors: Ukita Jinro , Martinson Douglas G.
Published: November 2007

Recent observations suggest that high-frequency forcing events have profound influence on the air-sea-ice interactions in the polar region. Studying these events with sea-ice models requires close examination of the model sensitivity that may arise from the high-frequency variability of the forcing. We show that the maximum layer thickness is dictated by the time-scale of the forcing variability and that the computation of the surface temperature develops enhanced sensitivity at high-frequency forcing. We resolve these constraints by developing an "adjustable-layering" thermodynamic formulation for ice and snow that re-computes the number of layers required each time-step to satisfy this maximum thickness, which preserves the total enthalpy and general internal thermal gradients. The conservation equations form a tri-diagonal system ideal for a fast and efficient implicit solution. Furthermore, we resolve the issue of the high sensitivity of the surface flux balance by solving the linearized version of the flux boundary condition simultaneously with the overall conservation system. In this paper we develop the analyses specifying the model requirements, describe the model system and test its algorithmic implementation.
Synoptic-scale ice-motion case-studies using assimilated motion fields
Authors: Meier Walter N. , Maslanik James A.
Published: November 2007

Observed and modeled sea-ice motions, combined via an optimal-interpolation assimilation method, are used to study two synoptic events in the Arctic. The first is a convergence event along the north Alaska coast in the Beaufort Sea during November 1992. Assimilation indicates stronger convergence than the stand-alone model, in agreement with Advanced Very High Resolution Radiometer-derived ice motions and Special Sensor Microwave/Imager-derived ice concentrations. The second event pertains to ice formation and advection in Fram Strait and the Barents and Greenland, Iceland and Norwegian Seas. Assimilation indicates export of thick, less saline ice out of the central Arctic into the East Greenland Sea. However, the model indicates little flow through Fram Strait, instead showing strong flow of thin, more saline first-year ice from the Barents Sea westward into the Greenland Sea. These results indicate that assimilation is a useful tool for investigating synoptic events in the Arctic and may be useful for both climate studies and operational analyses
Interannual variability of the sea-ice-induced salt flux in the Greenland Sea
Authors: Toudal Leif , Coon Max D.
Published: November 2007

The Greenland Sea is one of the few places in the World Ocean where deep convection takes place. The convection process is initiated by a density increase originating from rapid cooling and/or a salt flux to the upper layer of the ocean due to brine rejection from ice formation (Rudels 1990; Visbeck and others, 1995). The predominant ice types in the Greenland Sea are frazil/grease ice and pancake ice. A numerical model has been developed relating ice formation and decay of these ice types as observed by the SMMR and SSM/I microwave radiometers and evaluating their contribution to salt redistribution in the Greenland Sea. The model has been used to calculate spatial distribution of the annual integrated net salt flux to the Greenland Sea from ice production and advection for the period 1979−97.
A microscopic approach to investigate bacteria under in situ conditions in sea-ice samples
Authors: Junge Karen , Krembs Christopher , Deming Jody , Stierle Aaron , Eicken Hajo
Published: November 2007

Microbial populations and activity within sea ice have been well described based on bulk measurements from melted sea-ice samples. However, melting destroys the micro-environments within the ice matrix and does not allow for examination of microbial populations at a spatial scale relevant to the organism. Here, we describe the development of a new method allowing for microscopic observations of bacteria localized within the three-dimensional network of brine inclusions in sea ice under in situ conditions. Conventional bacterial staining procedures, using the DNA-specific fluorescent stain DAPI, epifluorescence microscopy and image analysis, were adapted to examine bacteria and their associations with various surfaces within microtomed sections of sea ice at temperatures from −2° to −15°C. The utility and sensitivity of the method were demonstrated by analyzing artificial sea-ice preparations of decimal dilutions of a known bacterial culture. When applied to natural, particle-rich sea ice, the method allowed distinction between bacteria and particles at high magnification. At lower magnifications, observations of bacteria could be combined with those of other organisms and with morphology and particle content of the pore space. The method described here may ultimately aid in discerning constraints on microbial life at extremely low temperatures.
Spatial and temporal variability in snowmelt onset over Arctic sea ice
Authors: Anderson Mark R. , Drobot Sheldon D.
Published: November 2007

Climate models suggest surface warming in the Arctic will be rapid and pronounced, implying substantial changes in snowmelt onset are likely. This research therefore examines spatial and temporal variability in passive-microwave derived snow-melt-onset dates over Arctic sea ice. The objectives are to understand better the regional characteristics of snowmelt and to document whether the snowmelt-onset record shows signs of climate change. Snowmelt-onset dates are derived with Scanning Multichannel Microwave Radiometer and Special Sensor Microwave/Imager brightness-temperature data, and they are subsequently stratified into 13 regions to analyze spatial and temporal variability. Results illustrate significant spatial variability in snowmelt onset, with the median annual snowmelt-onset date in one region of the Arctic typically being statistically different from most other regions. The examination of temporal variability also shows large interannual differences in the median snowmelt-onset date in most regions. Additionally, trends towards earlier snowmelt onset are documented in the West Central Arctic, Lincoln Sea, Beaufort Sea and Canadian Arctic Archipelago regions.
Sea ice, as the glacial cycles’ climate switch, and interhemispheric thermohaline teleconnections
Authors: Gildor Hezi , Tziperman Eli
Published: November 2007

A box model combining the different physical components of the coupled ocean, atmosphere, sea-ice and land-ice climate system is used to study the possible role of sea ice in the glacial-interglacial oscillations. In this paper we investigate the teleconnection between the two hemispheres, and suggest a mechanism which can explain the observed Southern Ocean sea-ice variability during glacial-interglacial cycles. The teleconnection mechanism involves changes in the temperature of the water transported from the Northern to the Southern Hemisphere by the thermohaline circulation (THC), rather than the amplitude of the THC as has often been suggested. The sequence of events proposed by this model indicates that it would be especially interesting to obtain accurate information on the relative timing of sea-ice and land-ice variations. Fuller general circulation models and new sea-ice proxy data are needed to quantify the relative role of the proposed teleconnection mechanism.
Brine percolation and the transport properties of sea ice
Authors: Golden K. M.
Published: November 2007

Sea ice is distinguished from many other porous composites, such as sandstones or bone, in that its microstructure and bulk material properties can vary dramatically over a small temperature range. For brine-volume fractions below a critical value of about 5%, which corresponds to a critical temperature of about −5°C for salinity of 5 ppt, columnar sea ice is effectively impermeable to fluid transport. For higher brine volumes, the brine phase becomes connected and the sea ice is permeable, allowing transport of brine, sea water, nutrients, biomass and heat through the ice. Over the past several years it has been found that brine transport is fundamental to such processes as sea-ice production through freezing of flooded ice surfaces, the enhancement of thermal and salt fluxes through sea ice, nutrient replenishment for sea-ice algal communities, and to sea-ice remote sensing. Motivated by these observations, recently we have shown how percolation theory can be used to understand the critical behavior of fluid transport in sea ice. We applied a percolation model developed for compressed powders of large polymer particles with much smaller metal particles, which explains the observed behavior of the fluid permeability in the critical temperature regime, as well as Antarctic data on surface flooding and algal growth rates. Moreover, the connectedness properties of the brine phase play a significant role in the microwave signature of sea ice through its effective complex permittivity and surface flooding. Here we review our recent results on brine percolation and its role in understanding the fluid and electromagnetic transport properties of sea ice. We also briefly report on measurements of percolation we made on first-year sea ice during the winter 1999 Mertz Glacier Polynya Experiment.
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

It 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

A 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

In 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

We 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

Recent 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

The 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

Multi-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

A 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

The 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

Ship 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.