Thick Ice Layer Research Articles

Winter phytoplankton communities in different depths of three mesotrophic lakes (Łęczna-Włodawa Lakeland, Eastern Poland)

AbstractPhytoplankton samples were collected from three mesotrophic lakes: Piaseczno, Rogóźno and Krasne during winter seasons (from January to March). The samples were analyzed for species analysis and abundance of planktonic algae in relation to different depths of water column (0–7 m). Selected water physical-chemical parameters were also measured. Abundance of phytoplankton depended strongly on the thickness of snow and ice cover or mixing conditions. The maximal phytoplankton total number reached about 5 × 106 ind. L−1 beneath the clear ice in the Krasne Lake, minimal numbers were recorded under the thick snow and ice layers in the Piaseczno Lake (2 × 103 ind. L−1). The winter phytoplankton communities were dominated by flagellates principally cryptomonads (Cryptomonas spp. Rhodomonas minuta), euglenophytes (Trachelomonas volvocina, T. volvocinopsis), dinoflagellates (Peridinium bipes, Gymnodinium helveticum) and chrysophytes (Mallomonas elongata, M. akrokomos, Dinobryon sociale) or non-motile small species of blue-green algae (e.g. Rhabdoderma lineare, Limnothrix redekei), diatoms (Stephanodiscus spp., Asterionella formosa), and green algae (e.g. Scenedesmus spp., Monoraphidium spp.). Phytoplankton abundance and structure showed differentiation during the winter season and along the water column as well.

Ion enrichment of snowmelt runoff water caused by basal ice formation

AbstractOnce meltwater reaches the base of a snowpack it can infiltrate the underlying stratum, runoff, or refreeze and form a basal ice layer. Basal ice formation is most common early in melt over saturated or very cold frozen soils. Initial meltwater becomes enriched in ion concentrations compared to the parent snow due to ion fractionation during thaw and percolation through the snowpack. If ion exclusion occurs during basal ice formation, further enrichment of initial runoff water ion concentrations might occur. The influence of basal ice formation on runoff water chemistry was examined by comparing ion concentrations in runoff water that had sustained basal ice contact, to meltwater before basal ice contact. A series of experiments, involving melting a snowpack in a large insulated box over a cold impermeable substrate in a temperature‐controlled room, were carried out. A cooling system at the chemically inert base ensured formation of basal ice during snowmelt. Meltwater samples were collected throughout melt from within the snowpack using an extraction tube; runoff water was collected at the base. All samples were analysed for major anions and cations. Results showed that formation of basal ice layers can sometimes enrich the initial runoff water compared to meltwater before basal ice contact. Ion concentrations in basal ice contact runoff water were up to sixteen times greater than those in no‐contact meltwater; however, on average, basal ice contact runoff water showed 1·5 times the ion concentrations of the no‐contact meltwater. Enrichment was greatest with the rapid formation of a thick basal ice layer. The implications are that basal ice formation alters both meltwater ion pathway and concentration. When no basal ice is present, enhanced infiltration of meltwater ion load can cause relatively dilute runoff water. When basal ice is present all meltwater runs off and further ion‐concentration enrichment occurs. Copyright © 2008 John Wiley & Sons, Ltd.

Polarization patterns of thick clouds: overcast skies have distribution of the angle of polarization similar to that of clear skies

The distribution of polarization in the overcast sky has been practically unknown. Earlier the polarization of light from heavily overcast skies (when the Sun's disc was invisible) has been measured only sporadically in some celestial points by point-source polarimetry. What kind of patterns of the degree p and angle alpha of linear polarization of light could develop after transmission through a thick layer of ice or water clouds? To answer this question, we measured the p and alpha patterns of numerous totally overcast skies on the Arctic Ocean and in Hungary by full-sky imaging polarimetry. We present here our finding that depending on the optical thickness of the cloud layer, the pattern of alpha of light transmitted through the ice or water clouds of totally overcast skies is qualitatively the same as the alpha pattern of the clear sky. Under overcast conditions the value of alpha is determined predominantly by scattering on cloud particles themselves. Nevertheless, the degrees of linear polarization of light from overcast skies were rather low (p<or=16%). Our results obtained under overcast conditions complete the earlier findings that the alpha pattern of the clear sky also appears in partly cloudy, foggy, and smoky skies. Our results show that the celestial distribution of the direction of polarization is a very robust pattern being qualitatively always the same under all possible sky conditions. This is of great importance for the orientation of polarization-sensitive animals based on sky polarization under conditions when the Sun is not visible.

Access to glacial and subglacial environments in the Solar System by melting probe technology

A key aspect for understanding the biological and biochemical environment of subglacial waters, on Earth or other planets and moons in the Solar system, is the analysis of material embedded in or underneath icy layers on the surface. In particular the Antarctic lakes (most prominently Lake Vostok) but also the icy crust of Jupiter’s moon Europa or the polar caps of Mars require such investigation. One possible technique to penetrate thick ice layers with small and reliable probes is by melting, which does not require the heavy, complex and expensive equipment of a drilling rig. While melting probes have successfully been used for terrestrial applications e.g. in Antarctic ice, their performance in vacuum is different and theory needs confirmation by tests. Thus, a vacuum chamber has been used to perform a series of melting tests in cold (liquid nitrogen cooled) water ice samples. The feasibility of the method was demonstrated and the energy demand for a space mission could be estimated. Due to the high energy demand in case of extraterrestrial application (e.g. Europa or polar caps of Mars), only heating with radioactive isotopes seems feasible for reaching greater depths. The necessary power is driven by the desired penetration velocity (approximately linearly) and the dimensions of the probe (proportional to the cross section). In comparison to traditional drilling techniques the application of a melting probe for exploration of Antarctic lakes offers the advantage that biological contamination is minimized, since the Probe can be sterilized and the melting channel freezes immediately after the probe’s passage, inhibiting exchange with the surface layers and the atmosphere. In order to understand the physical and chemical nature of the ice layers, as well as for analysing the underlying water body, a melting probe needs to be equipped with a suite of scientific instruments that are capable of e.g. determining the chemical and isotopic composition of the embedded or dissolved materials.

The cold side of life

Barren land covered with huge ice shelves, swept by merciless winds and entrapped by deadly cold seas: that is a common perception of the polar regions. However, this picture could not be more wrong, as both the Arctic and Antarctic are teeming with life that is extraordinarily adapted to the harsh conditions and which often exists at the edge of survival (Fig 1,Fig 2,Fig 3,Fig 4). There has been a growing interest in these psychrophilic organisms, and how they evolved to grow and proliferate at permanently cold temperatures (D'Amico et al , 2006). Yet, it is not only the life sciences that can gain important insights from studying biological communities at the poles. Understanding how polar ecosystems respond to rapid climate change is of global significance; there is evidence that organisms, oceans and the atmosphere in the polar regions interact strongly, influencing each other in complex ways and with potentially major consequences for climate. Figure 1. A jellyfish offshore of McMurdo Station, Ross Island. Photograph by Steve Clabuesch/US National Science Foundation. Figure 2. Chinstrap penguins are about 68 cm (27 inches) tall and weigh about 4 kg (9 pounds). They are social animals and number about 5 million. Photograph by Zee Evans/US National Science Foundation. Figure 3. A crab‐eater seal lounges on an ice floe near the Antarctic Peninsula. Crab‐eaters are the most numerous seals in the world, with a population of more than 15 million. Although they do not eat crabs, they do eat krill and other crustaceans. They will reach a length of over 8 ft (2.44 m) and a weight of up to 500 lb (227 kg). Photograph by Jeffrey Kietzmann/US National Science Foundation. Figure 4. A snailfish, Paraliparis devriesi . Common inhabitants of deeper Antarctic waters, snailfish are characterized by a layer of jelly between the muscle and the …

Superimposed ice formation and surface energy fluxes on sea ice during the spring melt–freeze period in the Baltic Sea

AbstractThe development of land-fast sea ice and overlying snow was monitored during a 4 week period, until the snow cover had completely disappeared, at a site in the Gulf of Bothnia, Baltic Sea (63.57ú N, 19.85° E). The meteorological and radiative boundary conditions were continuously recorded. During the observation period, a 15 cm thick snow layer on the ice was transformed into a 7 cm thick granular ice layer (superimposed ice) on the ice surface, contributing significantly (about 11%) to the total ice thickness. Approximately 1 cm w.e. of the snow was sublimated. Neither snow-ice formation nor basal ice growth was significant during the same period. The salinity and isotopic (δ18O) composition of the ice indicated that prior to the experiment a 7 cm layer of superimposed ice had already formed. Hence, superimposed ice layers contributed 22% of the total ice thickness by the time all snow had disappeared. The advancing spring, decrease in surface albedo, diurnal cycle in the incoming solar radiation, and synoptic-scale changes in the cloud cover and the air–ice turbulent heat fluxes caused variations in the heat budget of the snowpack. Superimposed ice formation due to refreezing of meltwater occurred during most nights of the study period, and the most important refreezing periods were under such synoptic conditions that the air and snow surface temperatures also remained below zero during daytime. In contrast to typical summer conditions in polar oceans, low snow surface temperatures acted as the primary heat sink for the refreezing of meltwater.

Subglacial conditions during and after stoppage of an Antarctic Ice Stream: Is reactivation imminent?

Borehole observations from the base of the West‐Antarctic Ice Sheet (WAIS) reveal the presence of a 10 to 15 m thick accretionary basal ice layer in the upstream area of Kamb Ice Stream (KIS). This ice layer has formed over a time of several thousand years by freeze‐on of subglacial water to the ice base and has recorded during this time basal conditions upstream of its current location. Analysis of samples and videos sequences from boreholes drilled to the bottom of KIS confirms that KIS‐stoppage was due to basal freeze‐on and that relubrication of the ice stream is well underway. These results further suggest that ice stream cyclicity may be shorter than expected (1000s of years) and that a restart of KIS may be imminent within decades to centuries.

Molecular depth profiling in ice matrices using C 60 projectiles

The prospects of molecular sputter depth profiling using C 60 + projectiles were investigated on thick ice layers prepared by freezing aqueous solutions of histamine onto a metal substrate. The samples were analyzed in a ToF-SIMS spectrometer equipped with a liquid metal Ga + ion source and a newly developed fullerene ion source. The C 60 + beam was used to erode the surface, while static ToF-SIMS spectra were taken with both ion beams alternatively between sputtering cycles. We find that the signals both related to the ice matrix and to the histamine are about two orders of magnitude higher under 20-keV C 60 than under 15-keV Ga bombardment. Histamine related molecular signals are found to increase drastically if the freshly introduced surface is pre-sputtered with C 60 ions, until at a total ion fluence of about 10 13 cm −2 the spectra are completely dominated by the molecular ion and characteristic fragments of histamine. At larger fluence, the signal is found to decrease with a disappearance cross section of approximately 10 −14 cm 2, until at total fluences of about 10 14 cm −2 a steady state with stable molecular signals is reached. In contrast, no appreciable molecular signal could be observed if Ga + ions were used to erode the surface.

Investigation Of The Motion Of A Fixed RotatingSolid Body Over Ice With A Thin Fluid Interface

This article contains a theoretical investigation of the frictional forces on a solid body, such as a curling stone, rotating about a fixed axis, where the retarding force is due to the viscous drag of a thin water layer overlying a thick ice layer. Most introductory physics texts state that this deceleration is due to frictional surface forces, with a constant coefficient of sliding friction. Here, we proceed under the assumption that a fluid boundary layer is formed between the surface of the solid body and the ice as a result of pressure melting. In addition, the interface between the water and ice phases is considered to be a Stefan problem. The resulting fluid layer is responsible for the viscous drag forces that slow and eventually stop the rotating solid body. As a special case, a similar problem obtained by neglecting curvature is examined where the problem may be expressed in Cartesian coordinates rather than radial coordinates. Thus instead of a rotating curling rock, the physical problem is represented by a finite skate blade moving in a straight line over an ice surface with a fluidized interface. To calculate the drag forces experienced by the skate blade we first determine the temperature distribution of the water/ice interface, which requires the solution of a two-dimensional free boundary problem. A simplified problem is considered where the depth of the boundary layer is assumed to be independent of the horizontal position, and thereby we find expressions for the temperature of the water and ice in addition to an expression for the position of the ice water interface. Upon obtaining these results we can calculate the approximate drag experienced by a finite skate blade. At this point we can perform a similar analysis in radial coordinates providing a first approximation of the viscous drag forces of a rotating curling stone.

Initial borehole results from the Amery Ice Shelf hot-water drilling project

AbstractThe Amery Ice Shelf Ocean Research (AMISOR) project aims to examine and quantify processes involved in the interaction between the ice shelf, the interior grounded ice and the oceanic water masses that circulate beneath it. Two boreholes were melted through the shelf, within 100 km of the calving front, to access the ocean cavity. One (AM02) was at a site where it was believed that basal melt was occurring, and the other (AM01) was in a region with accreted marine ice. At both sites the summertime ocean structure revealed meltwater-modified boundary layers up to 100 m thick immediately beneath the shelf. Salinity and temperature data in the upper cavity at AM02 showed a strong seasonal cycle as a result of a combination of ice-shelf basal melt, and the intrusion of ocean water masses modified by sea-ice processes in Prydz Bay. At AM01, a 200m thick layer of marine ice underlay the meteoric ice, and showed an increase in salinity and decrease in stable-isotope fractionation with depth. The lowest 100m of marine ice was highly permeable, with a rectangular banded textural facies. Other preliminary results from this study are also reported.

Thermal regime and dynamics of the West Antarctic ice sheet

AbstractThe temperature–depth profiles measured in 22 boreholes drilled on the West Antarctic ice sheet exhibit two distinctly different thermal states of its basal ice. The warm state shows on Siple Dome and on Whillans Ice Stream. A relatively colder state, found at the Unicorn, Kamb Ice Stream (former Ice Stream C) and Bindschadler Ice Stream (former Ice Stream D), has basal temperature gradients greater than 50 K km–1. A large block of cold ice stranded and frozen to the bed at the Unicorn and simultaneously much warmer ice existing only a few kilometers across the Dragon shear margin in fast-moving Alley Ice Stream (former Ice Stream B2) poses a paradox. The relatively cold ice at the Unicorn must have come from a source different from the present Whillans Ice Stream catchment area. It is hypothesized that the Unicorn paradox was created by a super-surge. Also, the stagnant Siple Ice Stream, many relict shear margins, cold patches of ice at the Crary Ice Rise, ice rafts embedded in the Ross Ice Shelf, all point to a major event triggered either by an internal instability or by a subareal volcanic eruption. Most of these features appeared to have been formed about 500 years ago. Subsequent freeze-on of a 10–20m thick basal layer of debris-laden ice and water loss caused a slowdown of ice streams and, in the case of Kamb Ice Stream, an almost complete stoppage.

Formation of turbid ice during autumn freeze-up in the Kara Sea

A one-dimensional (vertical) model is used to estimate the mass of ice-rafted sediment in turbid sea ice on the shallow Kara Sea shelf during autumn freeze-up. Sediment is entrained into the ice through aggregation with frazil ice crystals that are diffused downwards by wind-generated turbulence. Data from local meteorological stations are used to force the model, while water stratification and sediment concentrations from the area are used to initiate the model. Model results indicate a 0.2 m thick layer of slush ice created during 48 h with a mean wind of 6 m/s and an air temperature of ?10°C. This ice contains ca. 20 mg/1 of sediment, or in total ca. 2% of the annual sediment discharge by nearby rivers. In shallow areas ( 20 m depth), the strong salinity stratification implies that winds above 18 m/s are needed for the process to be effective. For the rest of the winter months the same process may lead to additional sediment incorporated in a coastal polynya, but the freeze-up alone has the capacity to incorporate the total summer discharge of sediment into the surface ice. Calculated sediment concentrations in the surface ice cover are in the range 3 mg/1-19 g/1, in good agreement with available field data.

Cold climate BMPs: solving the management puzzle

Snowmelt runoff and rain-on-snow events present some of the highest pollutant loading and most difficult management challenges in the course of a year in regions with cold climate. Frozen conduits, thick ice layers, low biological activity, altered chemistry, and saturated or frozen ground conditions all work against effective treatment of melt runoff. Understanding the source, evolution and transition that occurs within a melt event, and defining the management objectives for specific receiving waters will help focus the search for effective management techniques. Solving the management puzzle means putting together a strategy for both soluble and solids-associated water pollutants.

Growth of H 2O layers on an ultra-thin Al 2O 3 film: from monomeric species to ice

Adsorption of water on an ultra-thin alumina film grown epitaxially onto NiAl(1 1 0) has been investigated by temperature-programmed desorption, work function measurements, ultraviolet photoelectron spectroscopy, and high-resolution X-ray photoelectron spectroscopy as a function of surface coverage at 100 K. At low coverages monomeric H 2O species are adsorbed and it is proposed that the oxygen lone pair orbitals interact weakly via polarisation forces with the Al 3+ cations of the second layer. No indication for the dissociation of H 2O and the formation of OH − species has been found. For intermediate coverages clustering of H 2O molecules occurs and the growth of a three-dimensional ice layer is observed. Care has to be exercised in photoemission experiments of ice layers, since UV photon-induced dissociation of H 2O in thicker ice layers is indicated.

Water adsorption and growth of ice on epitaxial Fe3O4(111), FeO(111) and Fe2O3(biphase)

Deuterated water adsorption on epitaxially grown FeO(111), Fe3O4(111) and Fe2O3 (biphase) films was investigated in the range 110–320 K by infrared reflection–absorption spectroscopy (IRAS) and temperature programmed desorption (TPD) spectroscopy. At 110 K, a first water layer forms on Fe3O4(111) and Fe2O3 (biphase) before the second and higher layers develop. The first half layer on Fe3O4 adsorbs dissociatively. The second half layer develops features characteristic for hydrogen bonding and the formation of dimers is concluded. Also on Fe2O3(biphase), initial water adsorption is dissociative. A strongly bound minority species is observed. Heating to 169 K causes formation of ice clusters. On FeO(111) adsorption is molecular and weak. On all studied surfaces, thick ice layers grown at 110 K are amorphous. On Fe3O4(111) they transform at 170 K into hexagonal ice (IceH) while up to 10 L on FeO(111) remain amorphous. The mechanisms for adsorption and ice formation correlate with structure and termination of the different oxide surfaces.

The adsorption of xenon on crystalline ice surfaces grown on Pt(111) studied with helium atom scattering

The adsorption of xenon on a thick crystalline ice layer grown in situ on a Pt(111) substrate has been investigated with high resolution helium atom scattering. The dependence of the specular reflectivity during xenon adsorption and desorption reveals a phase that desorbs at 50.5 K, which is thought to correspond to a single monolayer, and a lower coverage 0.25 monolayer phase with a desorption temperature of 53 K. Both phases exhibit (1×1) helium diffraction peaks. Time-of-flight spectra reveal perpendicular vibrational frequencies of ℏω=2.5 meV for both phases and an additional 2.0 meV mode for the monolayer phase.

Formation of turbid ice during autumn freeze-up in the Kara Sea

A one-dimensional (vertical) model is used to estimate the mass of ice-rafted sediment in turbid sea ice on the shallow Kara Sea shelf during autumn freeze-up. Sediment is entrained into the ice through aggregation with frazil ice crystals that are diffused downwards by wind-generated turbulence. Data from local meteorological stations are used to force the model, while water stratification and sediment concentrations from the area are used to initiate the model. Model results indicate a 0.2 m thick layer of slush ice created during 48 h with a mean wind of 6 m/s and an air temperature of ?10°C. This ice contains ca. 20 mg/1 of sediment, or in total ca. 2% of the annual sediment discharge by nearby rivers. In shallow areas (20 m depth), the strong salinity stratification implies that winds above 18 m/s are needed for the process to be effective. For the rest of the winter months the same process may lead to additional sediment incorporated in a coastal polynya, but the freeze-up alone has the capacity to incorporate the total summer discharge of sediment into the surface ice. Calculated sediment concentrations in the surface ice cover are in the range 3 mg/1-19 g/1, in good agreement with available field data.

Distribution of basal melting and freezing beneath tributaries of Ice Stream C: implication for the Holocene decay of the West Antarctic ice sheet

AbstractIce-stream tributaries connect the relatively slow-moving interior of the West Antarctic ice sheet (WAIS) with the fast-flowing Siple Coast ice streams. Basal water underneath these ice streams reduces basal resistance and enables the fast motion of the ice. Basal melting being the only source for this water, it is important to include the distribution of basal melting and freezing into numerical models assessing the stability of the WAIS. However, it is very difficult to constrain its distribution from existing field observations. Past borehole observations confirmed the presence of a wet bed at Byrd Station in the WAIS interior and at different locations within Siple Coast ice streams. However, the recent discovery of a 12–25m thick sediment-laden bubble-free basal ice layer at the UpC boreholes indicates that basal freezing is either currently occurring or had occurred upstream during the last glacial–interglacialcycle.We use a flowline model of ice thermodynamics to assess and quantify the spatial and temporal distribution of basal melting and freezing beneath Ice Stream C tributaries, taking into account the geothermal flux, shear heating and heat conduction away from the bed. Under the assumption that the ice was moving over a weak bed (τb =1–10 kPa) our model is able to reproduce a layer of frozen-on ice similar in thickness to the UpC “sticky spot” basal ice layer. Increased basal melting in the early Holocene possibly could have initiated the Holocene decay of the WAIS, whereas increased freezing rates over the past few thousand years could have decreased the amount of basal water in the system, resulting in a strengthening of the bed. This is consistent with current force-budget calculations for ice-stream tributaries and with observed stoppages and slow-downs of ice streams.

Glacial mass balance of Austre Brøggerbreen (Spitsbergen), 1971–1999, modelled with a precipitation-run-off model

An energy balance based HBV model was calibrated to the run-off from Bayelva catchment in western Spitsbergen, Svalbard. The model simulated the glacier mass balance, and the results were compared to observations at Austre Brøggerbreen for the period 1971-1997. Even though the model was optimized to observed run-off from a catchment in which the glaciers constitute 50% of the area, and not to the observation of glacier mass balance, the model was able to reconstruct the trends and values of the mass balance found through observations. On average the simulation gave a negative net balance of 696 mm. The observed average is 442 mm. The simulated winter accumulation was in average for the same period 9% lower and the summer ablation 17% higher than the observed. The years 1994-96 show deviations between simulated and observed winter accumulation up to 160%. This can probably be accounted for by extreme rainfall during the winter, leading to thick ice layers which make accurate observations difficult. The higher simulated summer ablation might indicate that the glaciers in the catchment as a whole have a larger negative mass balance than Austre Brøggerbreen. The simulations showed that the glacier mass-balance would be in equilibrium with a summer temperature 1.2°C lower than the average over the last decades or with a 100% increase in the winter (snow) precipitation. These are higher values than former estimates. A combined change of temperature and precipitation showed a synergic effect and thereby less extreme values.

Mechanisms of fast flow in Jakobshavn Isbræ, West Greenland: Part III. Measurements of ice deformation, temperature and cross-borehole conductivity in boreholes to the bedrock

AbstractAt a site on the ice sheet adjacent to the Jakobshavn ice stream in West Greenland, ice deformation rates and temperatures have been measured in boreholes to the bedrock at 830 m depth. Enhanced deformation rates were recorded just below the Holocene–Wisconsin transition at 680 m depth. A 31 m layer of temperate ice and the temperature minimum of −22°C at 520 m depth were detected. The good agreement of these data with results of a two-dimensional thermomechanically coupled flow model implies that the model input is adequate. Discrepancies between modelled and measured temperature profiles on a flowline at the ice-stream centre have been attributed to effects not accounted for by the model. We have suggested that the convergent three-dimensional flow leads to a vertical extension of the basal ice entering the stream. A thick basal layer of temperate and Wisconsin ice would explain the fast flow of this ice stream. As a test of this hypothesis, the new core-borehole conductivity (CBC) method has been used to compare conductivity sequences from the ice stream to those of the adjacent ice sheet. The correlation thus inferred suggests that the lowest 270 m of the ice sheet correspond to the lowermost 1700 m of the stream, and, consequently, that the lower part of the ice stream has experienced a very large vertical extension.