References cited

Gosnell's (2005) popular treatise on Ice (cf. chapter 1) offers a well-crafted and accessible discussion of some of the peculiarities of water, including the delightful quote from James Trefil. Trefil, J. (1986). Meditations at 10,000 Feet A Scientist in the Mountains. Charles Scribner's Sons, New York. Those seeking a more physics-based discussion of the crystal structure of snowflakes will find reward in Fletcher (1971) and Libbrecht (2005). Libbrecht provides some stunning photographs of...

SEA ICE

Land properly speaking no longer exists, nor sea nor air, but a mixture of these things, like a marine lung, in which earth and water and all things are in suspension. Pytheas of Massilia, On The Ocean Quoted from Barry Cunliffe, The Extraordinary Voyage of Pytheas the Greek Pytheas is believed to be the first Western Explorer to document sea ice, encountering it at some undetermined destination (Thule) 7 days' sail north of Britain. Pytheas was an astute observer among other things, he was the...

Changes in Lake River and sea

There is a detailed historical record of freeze-up and breakup of lake, river, and sea ice in many communities, particularly where ship navigation and ice roads are dependent on ice conditions. These observations are local and they often reflect near-shore conditions, so they may not be representative of regional or synoptic conditions. These are nevertheless valuable in documenting changes in ice cover during the past century, particularly for river and lake ice. In many freshwater ice...

Basal Flow

In addition to the internal deformation described above, ice can flow at the base where the bed is at the pressure melting point, through some combination of subglacial sediment deformation and decoupled sliding over the bed. Large-scale basal flow generally requires pressurized subglacial meltwater, which can lubricate the bed, float the ice, or weaken subglacial sediments. Subglacial hydrology plays a pivotal role in fast-flowing glaciers and ice streams. High subglacial water pressures can...

Preface

All Canadians come into a world that is shaped by snow and ice, and I am exceptionally privileged in this regard. I was born in the heart of winter in Matheson, Ontario, a small mining town in the northern part of the province where one can count on snow cover from Halloween to Mother's Day. For half a year the snow is part of your fabric, and for the other half of the year one can bike, run, and paddle the landforms and lakes formed by the great ice sheets that carved the landscape. I took up...

Sea Level Rise

The loss of ice from mountain glaciers, Greenland, and Antarctica is contributing significantly to sea level rise. Global mean sea levels have risen by approximately 20 cm since 1900, with glacier contributions making up roughly half of this total. Thermal expansion as the oceans warm is the other main driver of sea-level rise. In the first decade of the 21st century, losses in glacier ice and the two continental ice sheets account for about two-thirds of the ca. 33 mm of sea level rise. Of the...

Lake

Lake ice forms due to cooling and freezing from above, driven by radiative and sensible heat losses to the atmosphere in the autumn and winter. The surface energy balance described in chapter 3 is applicable here. Snow falling in open water can provide an additional energy sink, due to the latent energy removed from the lake to melt the snow. If temperatures reach 4 C as a lake cools, the density maximum of water at this temperature (see figure 2.2) results in curious behavior. Dense surface...

Seaice thermodynamics

The discussions in chapters 2-4 are salient to many aspects of sea-i ce thermodynamics. Brine content influences the thermal properties of sea ice, relative to freshwater ice, but temperature evolution and ice thickness are still broadly governed by vertical diffusion. Heat advection from percolation of brine and meltwater can also be significant. Similar to lake ice, heavy snow cover on a thin platform of sea ice can submerge the ice, causing flooding that creates snow ice. Freezing of...

Thermodynamic Properties Of Snow And

The thermal characteristics of snow and ice play an important role in determining exchanges of energy Physical Properties of Snow and Ice at 0 C 1000 917 720-940 20-150 250-550 550-830 0.1 0.1-0.6 0.1-0.7 0.8-0.9 0.4-0.6 0.3-0.4 0.56 2.11 1.91 0.03-0.06 0.1-0.7 0.7-1.5 conductivity (W m-1 C-1) Heat capacity (m2 s-1) Latent heat of fusion (J g-1) Latent heat of sublimation (J g-1) Thermal properties for a temperature of -2 C, a salinity of 5 ppt, and a density of 850 kg m-3. 'Thermal...

Birth Of The Polar Ice Sheets

Excepting the massive blips associated with episodes of global or near-global ice cover, the Earth has been icefree for much of its history. During the Paleozoic and Mesozoic eras, from about 550 to 65 Ma, life expanded dramatically on the planet, and there is little evidence of glaciations through this time. The Cretaceous period, from 144 to 65 Ma, was the apex of the Mesozoic, characterized by sea levels 200 m higher than present, deep ocean temperatures of up to 15 C, and tropical flora and...

Influences On Atmospheric Circulation

In the winter months, the cooling influence of snow-covered surfaces helps to promote the creation of dense, high-pressure (continental polar) air masses, which penetrate to midlatitudes as cold fronts. Strong winds and snowfall are followed by cold, clear weather and temperature inversions as continental polar air masses set up over a region. These air masses form over sea ice and over high-l atitude (i.e. snow-covered) land masses during the winter months due to longwave radiative cooling,...

Specific and Latent Energy

One of the special properties of water is its resistance to phase changes. It requires 334 J to melt 1 g of ice at 0 C, an enormous amount of energy. Of common substances, only ammonia has a higher specific enthalpy (latent heat) of fusion. Direct conversion of ice from the solid to vapor phase is an even greater energy sink sublimation of ice at 0 C requires 2834 J g-1. Energy that is consumed for evaporation or sublimation is unavailable for melting snow and ice, a process that limits...

Snowmelt models

Models of snow melt are needed for regional-scale hy-drological applications such as hydroelectric power generation, flood hazard, and water resources forecasts. They are also necessary for modeling of cryospheric interactions with the climate system and global cryo-spheric response to climate change. A solution of the full surface energy balance described in chapter 3 is desirable for predicting rates of snow melt, but this requires extensive meteorological data that are generally unavailable...

Snowice surface

The surface energy balance of melting snow and ice has been studied extensively, although there are still some unresolved questions. The first challenge is to decide whether a snow or ice surface is two- or three-dimensional that is, is it a surface or a volume It is both in some ways. There is a two-way exchange of energy between the atmosphere and surface, through several different processes of energy transfer, and this determines the net energy that is supplied to or lost from snow or ice...

Introduction To The Cryosphere

In this place, nostalgia roams, patient as slow hands on skin, transparent as melt-water. Nights are light and long. Shadows settle on the shoulders of air. Time steps out of line here, stops to thaw the frozen hearts of icebergs. Sleep isn't always easy in this place where the sun stays up all night and silence has a voice. Claire Beynon, At Home in Antarctica Earth surface temperatures are close to the triple point of water, 273.16 K, the temperature at which water vapor, liquid water, and...

Shortwave Radiation

Shortwave radiation is the main driver of snow and ice melt in most environments. Incoming solar radiation is absorbed and scattered as it traverses the gauntlet of atmospheric gases and aerosols (suspended particles such as water droplets, ice crystals, and dust). The processes of absorption and scattering depend on the wavelength of the electromagnetic radiation and the size of the obstacle (gas or aerosol). Similarly, backscatter (reflection) from ice crystals is also wavelength dependent,...

Snow albedo

Energy Balance Over Snow

The influence of snow and ice in the climate system stems largely from their high albedo. Shortwave radiation is backscattered from snow and ice, with the reflectivity strongly dependent on wavelength. Neglecting this complexity for now, the broadband surface albedo can be defined from the ratio of reflected to incoming shortwave radiation, a QS QS. A range of albedo values for snow and ice is given in table 2.1. Albedo is highly variable, spatially and temporally, so it is not recommended to...

Glacier and ice sheet volume

Glacier area can be well mapped from satellite imagery and aerial photographs, but global ice volume is more difficult to estimate. Mapping of ice thickness requires surface or airborne radar surveys. Electromagnetic wave frequencies of 5-50 MHz are typically used for glacier depth sounding, as these relatively low frequencies limit signal attenuation and allow penetration of radar pulses through several hundred meters of glacier ice. Resolution at these frequencies is of the same order as the...

Snow And Ice Albedo

Snow and ice are the most reflective natural surfaces on the planet, exceeded only by clouds in their influence on planetary albedo. This reduces the net solar radiation that is available to warm the Earth, lowering the mean annual temperature of the planet. The cryosphere also introduces regional and seasonal variability in the absorbed solar radiation that is available. Surface albedo effects of the cryosphere have the greatest impact on regional and local climate through cooling and through...

Snow in the Atmosphere

Snow Ice Crystal Glacier

The physical properties of snow define and shape its influence on climate and society. Temperatures in the middle and upper troposphere are below 0 C, so ice crystals can be found everywhere in the global atmosphere. As discussed in chapter 2, mixed clouds below this temperature consist of a blend of water vapor, ice crystals, and supercooled water droplets. Once nucleated, ice crystals grow through deposition of water vapor. Saturation vapor pressure on the surface of rounded water droplets is...

Internal Deformation

To solve the momentum balance, ice sheet stresses need to be expressed as velocity fields, via a constitutive relation for ice. The rheology of polycrystalline glacier ice is well studied in laboratory and field environments, which reveal that ice deforms as a nonlinear viscous fluid. The original form of the flow law, proposed by John Glen and John Nye in the 1950s, is broadly supported by field studies of tunnel and borehole deformation, as well as observations and modeling of large-scale ice...

Characteristics of sea ice

Sea ice forms from freezing of seawater. Dissolved salts predominately NaCl, but many other ions as well depress the freezing point of seawater by approximately 0.054 C ppt-1. For mean ocean water with a salinity of 34.5 ppt, sea ice forms at -1.86 C. Polar waters are often fresher than average seawater, due in part to limited evaporation. For salinities of 25 ppt and 30 ppt, water freezes at -1.35 c and -1.62 c, respectively. Figure 5.1. A variety of Arctic sea-ice types and seasons. (a)...

Density Of Snow And

The geometric arrangement of this lattice structure is spacious, giving water the most unusual property of having a solid phase that is less dense than its liquid phase. At 0 C, water has a density of 1000 kg m-3, whereas pure ice (Jh) has a density of 917 kg m-3. Ice floats in its own melt, one of few substances to do so. Diamonds, germanium, gallium, and bismuth, all structurally similar to ice, also float in their own liquid. Imagine the sight of sunlight sparkling off of a diamond-berg in a...

Internal Energy Balance In Snow And

The internal temperature evolution in a snowpack or a thickness of ice (e.g., a slab of sea ice or the interior section of permafrost or a glacier) is governed by conservation of energy. This is described by the first law of thermodynamics, balancing the rate of change of internal energy with the fluxes and sources of energy in the snowpack. Conductive heat transfer is the main process that governs the rate of change of internal energy in the near-surface layer. In addition, shortwave radiation...

Permafrost Thermodynamics

Like lake, river, and sea ice, permafrost forms due to subzero surface temperatures that induce freezing from above. Surface tension effects retain some liquid water content to low temperatures (-10 C or less), particularly in fine sediments such as clays and silts. However, the 0 c isotherm in the ground generally represents the freezing front the depth at which the phase change begins and ice can be found in the soil or rock matrix. Seasonal ground frost is widespread in midlatitudes and high...

Longwave Radiation

Longwave radiation is also known as infrared, thermal, or terrestrial radiation. It is electromagnetic energy in the spectral band from roughly 3 to 100 mm. Earth surface temperatures produce emissions in this range, with peak terrestrial radiation occurring at a wavelength of about 10 mm. Spectrally integrated longwave radiation can be estimated from the Stefan-Boltzmann equation, Ql eoT4, where e is the thermal emissivity, o is the Stefan-Boltzmann constant, 5.67 X 10-8 W m-2 K-4, and T is...

Mass Balance processes

Glaciers have relatively simple requirements to be viable snow accumulation must exceed ablation. Snow accumulation occurs primarily as meteoric snowfall (derived from atmospheric precipitation), but snow can also accumulate at a site through wind deposition or avalanch-ing. Ablation refers to the loss of snow and ice through melting, sublimation, wind erosion, and calving, a process whereby slabs of ice at the glacier margin mechanically fracture and detach from the main ice mass. This is an...

Energy BuFFER

Melting snow and ice requires a great deal of energy. These phase changes consume sensible heat and radiative energy that would otherwise go into warming up a region. The opposite effect attends the fall freeze-up latent energy is released to the atmosphere, lakes, rivers, oceans, and soil as ice forms from water and vapor. This delays the seasonal decrease in temperatures. Overall then, latent energy exchanges within the seasonal cryosphere act as a thermal buffer, similar to the way in which...

Governing Equations for Glacier Dynamics

Similar to models of atmosphere, ocean, and sea-ice dynamics, the flow of glaciers and ice sheets is mathematically described from the equations for the conservation of mass, momentum, and energy. For a point on the glacier with ice thickness H, the vertically integrated form of the conservation of mass is Figure 6.3. Schematic of glacier flow mechanisms. The surface velocity us ub + ud (s). Basal velocity is the sum of deformation of underlying sediments and decoupled sliding at the ice-bed...

Pleistocene Glacial Cycles

The world changed again beginning at about 2.5 Ma. Figure 9.1b illustrates the onset of the Pleistocene glacial cycles at this time, a turbulent period in Earth history that continues to this day. The planet has experienced more than 40 glacial-interglacial episodes during this period, with ice sheets intermittently flooding large expanses of the Northern Hemisphere continents. As seen in Figure 9.1b, these cycles increased in magnitude over the past million years, indicating that glaciations...

Geography Of Earths Snow And

Perennial ice covers 10.8 of Earth's land surface table 1.1 and figure 1.1 , with most of this ice stored in the great polar ice sheets in Greenland and Antarctica. Smaller glaciers and icefields are numerous the global population is estimated at more than 200,000 but these ice masses cover a relatively small area of the landscape. An additional 15.4 of Earth's land surface is covered by Area and Volume of the Global Cryosphere Area and Volume of the Global Cryosphere Note Sea ice data is from...