Ice Physics and the Natural Environment

An understanding of the microscopic melting of crystals has eluded researchers for more than a Century. The struggle has stimulated the development of quantum mechanics, concepts of long range order, the role of dimensionality in condensed matter, and more sensitive experimental techniques to test the theories. After years of probing the mechanism within the bulk material, we have discovered that the answer has been lying on the surface.

The freezing of water and the melting of ice, phenomena that are extraordinarily familiar from the world around, are only poorly understood at a molecular level. Like all liquids, water can be undercooled without freezing; like most solids, ice cannot be superheated to a significant extent. The dynamics of these phase transitions, and what they tell about the molecular level structure of interfaces and critical nuclei, is revealed by experiment, computer simulation, and theory. In some regards, water resembles simpler liquids in the kinetics of its changes of state, but in others it is quite different. This chapter explores the microscopic dynamics of freezing and melting, with particular emphasis on the water-ice system.

The most abundant crystal growth problems in the natural environment involve ice, yet in nearly every setting a crucial roadblock to our progress concerns how microscopic processes influence macroscopic behavior. Recent advances in understanding the surface phase transitions that alter the equilibrium and near equilibrium interfacial structure are central to many pattern formation problems during ice crystal growth, the geometric evolution of polycrystals, and the dynamics of frost heave. This chapter focuses on surface, size and impurity effects in the melting, growth and interfacial evolution of ice crystals. The primary focus in melting and growth concerns how the nature of the microscopic interfacial structure at ice/vapor, ice/gaseous-atmosphere and ice/water interfaces influences the growth shapes. The treatment of impurities in solidification dynamics begins at the molecular level and is traced to the long range transport effects that drive interfacial instabilities. Finally, we examine the dynamical implications of taking subfreezing interfaces into a weakly nonequilibrium regime wherein the underlying causes of frost heave are revealed. Experimental, theoretical and computer simulation techniques all play important roles in our evolving understanding of both the basic phenomena under scrutiny and their environmental implications. The fundamental issues are observed in nearly all materials, but their environmental manifestations are most striking in the case of ice, lying as they do at the heart of the evolving shape of a snowflake, the origin of the forces driving cryoturbation in soils and the microscopic basis of charge transfer inside icy clouds.

The three modes of glacier flow (ice deformation, sliding, bed deformation) are described. The pattern of flow-lines is deduced from the principle of mass conservation; the temperature distribution by considering heat sources and heat transfer by conduction and advection. The mechanisms of surging and of the tidewater-glacier instability are outlined. The interpretation of Heinrich Events as evidence of surges of the Laurentide Ice Sheet is critically reviewed.

Glaciers and ice caps exert a strong influence on Earth’s environment and climate. They can grow and decay, change the sea level, control the albedo and shape the mountains and continents on which they reside. During the last glacial period the expanding glaciers surged frequently and brought an enormous number of icebergs into the North Atlantic which caused a whole suite of violent climatic oscillations (Heinrich events, Dansgaard-Oeschger cycles) (Bond et al., 1992; Broecker et al., 1985; Johnsen et al., 1972).

The great global glaciations were a cyclic though rather infrequent phenomenon in the history of the Earth. The Late Palaeozoic (330–270 Ma), the Early Palaeozoic (about 450 Ma), probably also the Late Proterozoic (Vendian: about 600 Ma) glaciations, affected large continents in high latitude south polar position. Asynchronous glaciation affected the southern and the northern continents during the Cenozoic. In Antarctica, it started during Eocene (at about 50 Ma), its ice-cap at sea-level developed in Early Oligocene (at 32–30 Ma), and became a semi-permanent feature of this continent since Early Miocene (22–20 Ma). In the Arctic, the glaciation started much later, during Pliocene (at about 3.4 Ma). Its Pleistocene (2–0.1 Ma) ice-sheets developed around a relatively small Arctic Ocean in northern North America and Eurasia, and in Greenland. Presently, the Arctic glaciation is reduced to a few much reduced ice-caps, the Greenland and the Svalbard ones being the largest. There is a direct correlation between global glaciations and world-ocean level recognizable in Cenozoic marine geological record: low stands of sea level correspond to glacial epochs, while high stands to interglacials. Global-scale glaciations have both terrestrial and extraterrestrial causes.

Ice particles play important roles in modulating radiative and hydrological fluxes and chemical composition in the troposphere, and in creation of the large in-cloud electric fields that give rise to lightning. These roles depend on the numbers, shapes, sizes, surface properties and spatial distributions of the particles. In this paper we discuss current understanding of the important processes involving tropospheric ice particles, with particular focus on the roles of atmospheric impurities (i.e., nonwater substance) of both natural and anthropogenic origins. For additional background material see [1, 2, 3, 4].

Liquid and solid particles in polar stratospheric clouds are of central importance for the depletion of stratospheric ozone. Surface-catalyzed and diffusion-controlled bulk reactions on/in the particles, convert halogens, which derive from compounds of mainly anthropogenic origin, from relatively inert reservoir species into forms that efficiently destroy ozone. The microphysics of these particles under cold stratospheric conditions is still uncertain in many respects, in particular concerning phase transitions like freezing nucleation and deposition nucleation. Furthermore, there are indications that the rates of key heterogeneous reactions have not yet been established with sufficient accuracy to enable a reliable diagnosis of observed ozone losses by means of global models. This paper is a shortened version of an Annual Review of Physical Chemistry ¹ which surveys this rapidly developing field.

A simple model of the Northern Hemisphere climate is presented that emphasizes the role of sea ice. The model is used to investigate the response of the climate to increased concentration of greenhouse gases, the predicted amplification of climatic warming in the arctic, the possibility of multiple equilibria, and the waiting times between transitions from one equilibrium to another.

The presence of ice changes the environmental conditions in fresh and salt water bodies in a number of dramatic fashions. Therefore, forecasting ice is of great importance for the inhabitants of cold climate regions. This is the case in, for example, safe navigation, winter roads, off shore exploration, fishing and weather forecasting. The purpose of the chapter is to outline the modelling of cold water bodies and discuss how the models can be used in the development of forecasting systems. Instead of beginning with the fully three-dimensional coupled atmosphere-ice-ocean/lake equations, we start from simple physically based models and develop more advanced models as the complexity of the problems demands.

At maximum extent the sea ice covers some 8% of the Southern Hemisphere and 5% of the Northern Hemisphere and thus has a significant influence on the productivity of large ocean areas. The structure, extent and distribution of sea ice not only influences biogenic production within the ice system, but also affects pelagic and benthic systems under the ice and near ice edges. The sea ice in Polar Oceans provides a unique environment utilised by a diverse group of organisms ranging in size from single-celled algae within the ice to meter-long algal assemblages, dominated by diatoms, attached to the lower surface of the ice, and from protozoans to marine mammals. Sea ice (sympagic) biota play an important role in high Arctic food webs. Ice algae may serve as an inocculum for marginal ice zone blooms and form the base of food webs culminating in polar cod (Lønne and Gulliksen 1989), seals (Nilssen et al. 1995) and seabirds (Lønne and Gabrielsen 1992). Matter entering this lipid-rich food web may reach higher trophic levels in areas geographically distant from its place of origin, due to passive transport of sea ice biota in Arctic ice drift (Falk-Petersen et al. 1990

Water in small spaces, like water in small droplets, does not freeze at 0°C. Neither does water that is very close to a mineral surface. Rather, depending on how small, and how close, the water freezes at temperatures that may be several degrees below 0°C. Thus as soils freeze, ice forms first in large openings and then gradually spreads into the smaller and smaller pores only as the temperature falls further.

The Arctic region is usually defined as an area to the north of the Polar circle (66,5° N latitude). Climatologists consider July isotherm +10°C as the southern border of Arctic. A majority of experts define the Arctic as the area north of the southern limit of seasonal ocean ice, or in the case of land areas, north of the limit of forest. There are also other suggestions for latitude, geographic and climatic Arctic borders. In Russian legislation and in most of the social-economic investigations the term “Arctic” is used rather rarely. Meanwhile Russian statistics are based on administrative regioning of the country. In accordance with these 9 integrated administrative units (20 administrative regions) are related to the Russian Arctic (Fig. 1). Together with the marine economic zone and continental shelf the Russian Arctic constitutes more than 30% of the territory of the Russian Federation. Geographically in the south the Russian Arctic is bordered by the sparse growths of northern taiga and includes polar deserts, tundra, forest-tundra, and northern taiga. The main features of the Arctic are:

Polycrystalline ice (I_h) near its melting point is observed to contain microscopic veins of water, 10–100 μm in width, which follow the three-grain intersections. The veins form a connected network. Their existence and their detailed geometry are explained by the relative surface energies of the liquid-solid interfaces and the grain boundaries. The veins meet in fours at the four-grain intersection points, forming tetrahedra with open corners and non-spherical faces, whose shapes have been computed.

Studies of deformations of an ice cover, its failure, natural ridging and rafting are of vital importance to ice forecasting, navigation and the safety of offshore structures. Waves as a mechanism of transfer of deformation energy play a part on the local scale and mesoscale. In this paper, we discuss the spectral structure of cyclic deformations of the ice floe. We mainly relied on the Sea Ice Mechanics Initiative (SIMI) field experiment, the Beaufort Sea, 1993–94. Of special interest were the data from the West Fall/Winter camp (75°N, 142°W) set up on a 2.1 m thick multi-year ice floe. Tilt-meters, BP-Delta strainmeters and three-axis inertial accelerometers were applied in keeping the record (Fig 1).

The topography of the underside of sea ice is dominated by ice keels (often tens of metres deep) separated by expanses of relatively flat ice extending hundreds of metres horizontally (Davis & Wadhams 1995). However, there is evidence of some local variability in the thickness of sea ice in the flat regions (Wettlaufer 1991) of several centimetres over distances of about a metre. Such variations contribute to the drag exerted by sea ice on the ocean and enhance gravity drainage of brine from its interstices. We describe here a mechanism that can generate corrugations on the underside of sea ice in the presence of ocean shear, caused predominantly by wind-driven drift of the ice.

Atmospheric changes in Central Asia during the 20th century^{i, ii} are influenced by the amount of dust stormsⁱⁱⁱ and other climatic parameters. The arid zones generate enormous quantities of dust particles which undergo transformation, transport and sedimentation, significantly affecting the climate and other aspects of the natural environment.

Ice crystallization dynamics are observed with crossed polarizers in a Hele Shaw cell. Major features include the evolution of two thin ice sheets with parallel crystallite structures. Typical grain boundary grooves are seen at the junctions of most crystallites and water, but occasional giant faceted grooves are observed. The faces of the giant grooves are formed by basal planes, which are nucleated at the lower temperatures at the clefts. The grooves are asymmetric, yet track with the direction of the advancing interface.

Mountainous areas, particularly in the western United States, provide a large fraction of the fresh water supply. This reserve, which supplies most of California’s growing water needs, is vulnerable to changes in climate. Regional precipitation patterns, especially snow, which is a sensitive indicator of temperature and precipitation changes, are predicted to vary according to future climate models.

Neutron scattering data for low-density amorphous ice, produced by low-temperature and low-rate vapour deposition, shows that the dynamical properties of the vapour deposited amorphous ice are different from other low-density ices.

Cometary nuclei are composed mostly of water ice and mineral grains. When a comet passes near the Sun, several processes modify the subsurface layer of the nucleus which, according to theory, produce more cohesion and stratification. Presently a Rosetta mission is being prepared to comet 46P/Wirtanen. Plans are to land on the nucleus and penetrate its subsurface layer with a mechanical tool (experiment Mupus). Thus, understanding of the processes responsible for the evolution of a cometary nucleus is of key importance for the success of the mission and for interpretation of the results. This work is intended to estimate how quickly the process of grain sintering could modify the outer part of nucleus. The numerical model is adopted from previous work by Kossacki [1]; however, at present the evolution of the cometary orbit is included.

Water ice consists about a half of mass and therefore about 0.75 of volume of most of the icy satellites. Differentiated, with water ice forming outer shells, and undifferentiated models of internal structure of the icy satellites of the giant planets are mentioned. It is stressed that the modelling of the evolution of satellitesy’ structure should be supported by laboratory experiments: (i) concerning rheology of compaction of icy/mineral granular porous media, and (ii) concerning kinetics of phase transitions of water ice in these media.

In a typical thunderstorm the cloud is mainly electrically dipolar, with the principal positive charge in the upper reaches, and the main negative charge near the base. There is active ice formation due to the strong updraft and adiabatic cooling of humid air; temperatures in the negative zone range from about −5°C to −25°C. In this zone there are two main types of ice; small particles which are being carried upward in the updraft, and larger agglomerates, ‘soft hail’, which are falling. The principal charging occurs at collision sites between the two types: the small particles come away positively charged, and the hail negatively charged. Then the small particles continue upward, leaving a net negatively charged zone [1]. Lightning discharges occur between the two charge centers in the cloud and between the negative zone and the ground, so that the ground becomes negatively charged. Thunderstorms are most active during afternoons on seacoasts world wide, and hundreds of storms are active at all times; lightning discharges are so continuous that the Earth is more or less constantly negative with respect to the upper atmosphere. Without the storms, the Earth’s charge would decay in a couple of hours. So much is known and accepted [2].

In the classical drainage theory proposed by Röthlisberger [1] and later extended by Nye [2], ice deformation closure of a subglacial channel is counteracted by melt-back of the channel walls, due to the heat dissipated by water flowing in the channel. The mathematical description of this is by means of an evolution equation for the channel cross-section which has been formulated under the assumption that the cross-sectional shape is circular. For steady flow, the equation reduces to the equilibrium relation derived by Röthlisberger [1], linking water flux, water pressure and hydraulic gradient. For unsteady flow, it has been applied with success to models of glacier outburst floods, or jökulhlaups, in Iceland [e.g., 2] and elsewhere. However, it has recently been suggested that this theory can be generalized to the consideration of non-circular cross-sections. For instance, Hooke et al. [3] suggested broad and low channels as the cause of why measured subglacial water pressures are frequently underestimated by theory. Fowler & Ng [4] proposed a theory of Icelandic jökulhlaups and an improved model for simulating flood hydrographs, by considering a wide channel that has independently evolving depth and width. This configuration resembles the canals in Walder & Fowler’s extension of the classical theory for deformable sediment beds [5]. In this paper, the first steps of analyzing the mathematics of wide subglacial channels of this type are presented. In particular, we outline the formulation of the evolution equations, for the case of ‘hard bed’ drainage where sediment processes can be excluded. We then derive the corresponding equilibrium results and discuss their implications.

The uptake of gases onto ice particles of upper tropospheric cirrus (UT) and lower polar stratosphere (LS) clouds depends on the efficiency and time of the reactive gas interaction that also determines the ice particle impact on heterogeneous chemistry. The HC1 vapor uptake by polycrystalline ice produced by water freezing is investigated under laboratory conditions relevant to UT/LS. The uptake efficiency and ice conductivity were measured simultaneously in a Knudsen cell reactor. Regions with HC1 water solutions in ice are likely to be formed during the HCl—ice interaction. This potentially defines a mechanism of effective and long HC1 uptake by ice particles of cirrus clouds, polar stratospheric clouds (PSCs), and contrails due to fast freezing of submicron water drops.

Atmospheric concentrations of methane have nearly doubled in the last 200 years, and although concentrations are only a few ppm, a molecule of CH₄ has a 20 times greater greenhouse effect than a molecule of C0₂. Methane gas is included within bubbles in the seasonal ice cover on shallow high latitude lakes, and as a result, the ice and underlying water become a significant repository for methane. During the brief period of ice melt in the spring, a large pulse of the methane trapped in the ice and water is released to the atmosphere. During the break-up of 1997, for example, this pulse amounted to 2 g CH₄ m⁻² during the 10 day period following ice-melt [Phelps et al., In press].

The variability of sea ice in the polar regions is an important factor in the climate system particularly because of its strong influence on heat and freshwater transports as well as momentum exchange between ocean and atmosphere. To describe these effects accurately ice conditions need to be known over long time periods and wide regions. Models are able to produce such data but need to be verified by observations (Lemke et al., 1998). One classical model variable which can be validated quite well with remote sensing methods (SMMR, SSM/I) is the ice coverage. Modelled ice drift can be verified by comparing observed and simulated drift trajectories (Kreyscher et al., 1998). Ice thickness observations, however, are only rarely available from drillings, sonar measurements and laser altimeter recordings.

The phonon density of states for ice II has been calculated using a lattice dynamics simulation. The calculated results show that the hydrogen bonds linked to the different six-molecule rings in the structure are significantly weaker in comparison with the interactions within the rings, which may result from the distortion of the hydrogen bonding in the structure.