Elemental Geosystems, 5th Edition - Chapter 14

14 Glacial and Periglacial Landscapes A large measure of the freshwater on Earth is frozen, with the bulk of that ice sitting restlessly in just two places—Greenland and Antarctica. The remaining ice covers various mountains and fills alpine valleys. More than 29 million km3 (7 million mi3), or about 77% of all freshwater, is tied up as ice. These deposits of ice, laid down over several million years, provide an extensive frozen record of Earth's climatic history and perhaps some clues to its climatic future. The inference is that rather than distant frozen places of low population, these frozen lands are dynamic and susceptible to change, just as they have been over Earth's past history. The changes in the ice mass worldwide signal vast climatic change and further glacio-eustatic increases in sea level. As you study this chapter, keep this significance in mind. Elemental Geosystems presents the many recent changes occurring at high latitude and polar locations. For example: collapsing and disintegrating ice shelves around Antarctica, the disappearance of almost half of Arctic Ocean ice since 1970, and increasing depth to the active layer in permafrost regions of Canada and Europe leading to failure of structures and roadbeds built on them. As an example, please consult Mark F. Meier (U.S. Geological Survey, Tacoma, Washington), “Contribution of Small Glaciers to Global Sea Level,” Science Vol. 226 (21 December 1984): 1416–1421. He states in his summary that Observed long-term changes in glacier volume and hydrometeorological mass balance models yield data on the transfer of water from glaciers, excluding those in Greenland and Antarctica, to the oceans....These glaciers appear to account for a third to half of observed rise in sea level, approximately that fraction not explained by thermal expansion of the ocean. Outline Headings and Key Terms The first-, second-, and third-order headings that divide Chapter 14 serve as an outline. The key terms and concepts that appear boldface in the text are listed here under their appropriate heading in bold italics. All these highlighted terms appear in the text glossary. Note the check-off box () so you can mark class progress. Your students have this same outline in their Student Study Guide.The icon indicates that there is an accompanying animation or other resource on the CD. The outline headings for Chapter 14: cryosphere Rivers of Ice glacier Alpine Glaciers alpine glacier cirque icebergs Continental Glaciers continental glacier ice sheet ice cap ice field Glacial Processes Budget of a Glacier, Mass Balance Flow of Ice Within a Glacier Formation of Glacial Ice firn glacial ice Glacial Mass Balance firn line ablation equilibrium line Glacial Movement crevasses Glacial Surges glacial surge Glacial Erosion abrasion Glacial Landforms Teton Glacier Notebook Erosional Landforms Created by Alpine Glaciation arête col horn tarn paternoster lake fjord Depositional Landforms Created by Alpine Glaciation glacial drift till stratified drift moraine lateral moraine medial moraine Erosional and Depositional Features of Continental Glaciation till plain outwash plains esker kettle kame roche moutonnée drumlin Periglacial Landscapes periglacial Geography of Permafrost permafrost Continuous and Discontinuous Zones Behavior of Permafrost active layer ice wedge patterned ground Ground Ice and Frozen Ground Phenomena ground ice Frost-Action Processes Hillslope Processes Humans and Periglacial Landscapes The Pleistocene Ice Age Epoch ice age Pluvial Periods and Paleolakes paleolakes lacustrine deposits Deciphering Past Climates: Paleoclimatology Medieval Warm Period and Little Ice Age Mechanisms of Climate Fluctuation Climate and Celestial Relations Climate and Tectonics Climate and Atmospheric Factors Climate and Oceanic Circulation Arctic and Antarctic Regions Geographic Scenes: East Greenland Photo Gallery High Latitude Connection Videos The Antarctic Ice Sheet Summary and Review News Reports News Report 14.1: South Cascade and Alaskan Glaciers Lose Mass News Report 14.2: GRIP and GISP-2: Boring Ice for Exciting History News Report 14.3: An Arctic Ice Sheet? High Latitude Connection 14.1 Climate Change Impacts an Arctic Ice Shelf The URLs related to this chapter of Elemental Geosystems can be found at http://www.prenticehall.com/christopherson Key Learning Concepts After reading the chapter and using this study guide, the student should be able to: • Differentiate between alpine and continental glaciers and describe their principal features. • Describe the process of glacial ice formation and portray the mechanics of glacial movement. • Describe characteristic erosional and depositional landforms created by alpine glaciation and continental glaciation. • Analyze the spatial distribution of periglacial processes and describe several unique landforms and topographic features related to permafrost and frozen ground phenomena. • Explain the Pleistocene ice-age epoch and related glacials and interglacials and describe some of the methods used to study paleoclimatology. Annotated Chapter Review Questions • Differentiate between alpine and continental glaciers and describe their principal features. 1. Describe the location of most freshwater on Earth today. What is the cryosphere? A large measure of the freshwater on Earth is frozen, with the bulk of that ice sitting restlessly in just two places—Greenland and Antarctica. The remaining ice covers various mountains and fills alpine valleys. More than 29 million km3 (7 million mi3) of water, or about 77% of all freshwater, is tied up as ice. Earth’s cryosphere is the portion of the hydrosphere and ground that is perennially frozen, generally at high latitudes and elevations. 2. What is a glacier? What is implied about existing climate patterns in a glacial region? A glacier is a large mass of perennial ice, resting on land or floating shelf-like in the sea adjacent to land. Glaciers form by the accumulation and recrystallization of snow. They move under the pressure of their own mass and the pull of gravity. Today, about 11% of Earth's land area is dominated by these slowly flowing ice streams. During colder episodes in the past, as much as 30% of continental land was covered by glacial ice because below-freezing temperatures prevailed at lower latitudes, allowing snow to accumulate. Relative to elevation, in equatorial mountains, the snowline is around 5000 m (16,400 ft); on midlatitude mountains, such as the European Alps, snowlines average 2700 m (8850 ft); and in southern Greenland snowlines are down to 600 m (1970 ft). 3. Differentiate between an alpine glacier and a continental glacier. With few exceptions, a glacier in a mountain range is called an alpine glacier, or mountain glacier. It occurs in several subtypes. One prominent type is a valley glacier, an ice mass constricted within the confines of a valley. Such glaciers range in length from only 100 m (325 ft) to over 100 km (62 mi). The snowfield that feeds the glacier with new snow is at a higher elevation. As a valley glacier flows slowly downhill, the mountains, canyons, and river valleys beneath its mass are profoundly altered by its passage. A continuous mass of ice is known as a continental glacier and in its most extensive form is called an ice sheet. Two additional types of continuous ice cover associated with mountain locations are designated as ice caps and ice fields. Most glacial ice exists in the snow-covered ice sheets that blanket 80% of Greenland (1.8 million km3, or 0.43 million mi3) and 90% of Antarctica (13.9 million km3, or 3.3 million mi3). 4. Name the three types of continental glaciers. What is the basis for dividing continental glaciers into types? Which type covers Antarctica? The three types are ice sheet, ice cap, and ice field. Both ice caps and ice sheets completely bury the underlying landscape, although an ice cap is somewhat circular and covers an area of less than 50,000 km2 (19,300 mi2). Antarctica alone has 91% of all the glacial ice on the planet as an enormous ice sheet, or more accurately several ice sheets acting in concert. An ice field is the smallest of the three. • Describe the process of glacial ice formation and portray the mechanics of glacial movement. 5. Trace the evolution of glacial ice from fresh fallen snow. Snow which survives the summer and lasts into the following winter begins a slow transformation into glacial ice. Air spaces among ice crystals are pressed out as snow packs to a greater density. The ice crystals recrystallize under pressure and go through a process of re-growth and enlargement. In a transition step to glacial ice, snow becomes firn, which has a granular texture. As this process continues, many years pass before denser glacial ice is produced. Formation of glacial ice is analogous to formation of metamorphic rock: sediments (snow and firn) are pressured and recrystallized into a dense metamorphic rock (glacial ice). The formation of glacial ice is analogous to formation of a metamorphic rock with sediments (snow and firn) pressured and recrystallized into a dense metamorphic rock (glacial ice). The time taken for such a process is dependent on climatic conditions as noted in the text. A dry climate such as that found in Antarctica may produce glacial ice in 1000 years, whereas a wetter climate may take only a few years to complete the formation process. The term névé is a French term for a mass of hardened snow at the head or in the accumulation area of the glacier. When you see this term used interchangeably with firn, that stems from an earlier English application. The American Geological Institute Glossary of Geology (3rd edition) recommends that we restrict the usage of névé to refer only to the geographic area covered with perennial snow, or the accumulation area at the head of the glacier. Firn on the other hand is representative of the intermediate stage between snow and glacial ice. 6. What is meant by glacial mass balance? What are the basic inputs and outputs underlying that balance? A glacier is fed by snowfall and is wasted by losses from its upper and lower surfaces and along its margins. A snowline called a firn line is visible across the surface of a glacier, indicating where the winter snows and ice accumulation survived the summer melting season. A glacier's area of excessive accumulation is, logically, at colder, higher elevations. The zone where accumulation gain ends and loss begins is the equilibrium line. This area of a glacier generally coincides with the firn line, except in subpolar glaciers, where frozen surface water occurs below the firn line. Glaciers achieve a positive net balance of mass—grow larger—during colder periods with adequate precipitation. In a glacier's lower elevation, losses of mass occur because of surface melting, internal and basal melting, sublimation, wind removal by deflation, and the calving, or breaking off, of ice blocks. In warmer times, the equilibrium line migrates to a higher elevation and the glacier retreats—grows smaller—due to its negative net balance. In data provided to the author by the Ice and Climate Project, University of Puget Sound, Tacoma, Washington 98416, by Robert M. Krimmel, U.S. Geological Survey, it is interesting to note the net mass balance for the South Cascade Glacier, Washington, for the period 1955 through 1998. To update this analysis a new report is now available: Robert M. Krimmel, Water, Ice, Meteorological, and Speed Measurements at South Cascade Glacier, Washington, 2002 Balance Year, USGS Water Resources Report, Tacoma, WA: USGS, 2002. You may want to have your students plot these positive and negative values on a graph, and determine the algebraic sum of the net balance values. The glacier has gone through a net wastage at lower and middle elevations. (Note that this is presented in the Student Study Guide and in the Applied Physical Geography lab manual.) These statistics are graphically illustrated in News Report 14.1, documenting the net mass balance for the South Cascade Glacier in Washington state between 1955 and 1998. The glacier has gone through a net wastage between 1955 and 1998 at lower and middle elevations. In just one year (9/1991 to 10/1992), the terminus retreated 38 m and resulted in other major changes in the glacier. This represents more than a 2% loss in the glacier's mass in that time frame. Net mass balance is specified as cm of water equivalent spread over the entire glacier. South Cascade Glacier Annual Net Mass Balance Data (cm) Year Net balance 1955 +30.00 1956 +20.00 1957 –20.00 1958 –330.00 1959 +70.00 1960 –50.00 1961 –110.00 1962 +20.00 1963 –130.00 1964 +120.00 1965 –17.00 1966 –103.00 1967 –63.00 1968 +1.00 1969 –73.00 1970 –120.00 1971 +60.00 1972 +143.00 1973 –104.00 1974 +102.00 1975 –5.00 1976 +95.00 1977 –130.00 1978 –38.00 1979 –156.00 1980 –102.00 1981 –84.00 1982 +8.00 1983 –77.00 1984 +12.00 1985 –120.00 1986 –71.00 1987 –206.00 1988 –164.00 1989 –71.00 1990 –73.00 1991 –20.00 1992 –201.00 1993 –123.00 1994 –160.00 1995 –69.00 1996 +10.00 1997 +63.00 1998 –186.00 1999 +102.00 2000 +38.00 2001 -157.00 2002 +55.00 2003 -165.00 2004 -210.00 7. What is meant by a glacial surge? What do scientists think produces surging episodes? Some glaciers will lurch forward with little or no warning in a glacial surge. This is not quite as abrupt as it sounds; in glacial terms, a surge can be tens of meters per day. The Jakobshavn Glacier in Greenland, for example, is known to move between 7 and 12 km (4.3 and 7.5 mi) a year. The exact cause of such a glacial surge is still being studied. Some surge events result from a buildup of water pressure in the basal layers of the glacier. Sometimes that pressure is enough to actually float the glacier slightly during the surge. As a surge begins, icequakes are detectable, and ice faults are visible along the margins that separate the glacier from the surrounding stationary terrain. • Describe characteristic erosional and depositional landforms created by alpine glaciation and continental glaciation. 8. How does a glacier accomplish erosion? Glacial erosion is similar to a large excavation project, with the glacier hauling debris from one site to another for deposition. As rock fails along joint planes, the passing glacier mechanically plucks the material and carries it away. There is evidence that rock pieces actually freeze to the basal layers of the glacier and, once embedded, allow the glacier to scour and sandpaper the landscape as it moves, a process called abrasion. This abrasion and gouging produces a smooth surface on exposed rock, which shines with glacial polish when the glacier retreats. Larger rocks in the glacier act much like chisels, working the underlying surface to produce glacial striations parallel to the flow direction. 9. Describe the evolution of a V-shaped stream valley to a U-shaped glaciated valley. What features are visible after a glacier retreats? W. M. Davis characterized the stages of a valley glacier in a set of drawings published in 1906 and redrawn here in Figure 14.8. Illustration (a) shows a typical river valley with characteristic V-shape and stream-cut tributary valleys that exist before glaciation. Illustration (b) shows that same landscape during a later period of active glaciation. Glacial erosion and transport are actively removing much of the regolith (weathered bedrock) and the soils that covered the preexisting valley landscape. Illustration (c) shows the same landscape at a later time when climates have warmed and ice has retreated. The glaciated valleys now are U-shaped, greatly changed from their previous stream-cut form. You can see the oversteepened sides, the straightened course of the valley, and the presence of hanging valleys and waterfalls. The physical weathering associated with a freeze-thaw cycle has loosened much rock along the steep cliffs, falling to form talus cones along the valley sides during the postglacial period. See Figure 14.8c for labeled details of the features that are formed as a result of the formation, growth, passage, and retreat of an alpine glacier. 10. How is an iceberg generated? Where a glacier ends in the sea, large pieces break off and drift away as icebergs. These are portions of a glacier at drift in the sea. When large pieces of an ice shelf break off, such as the portions of the Ross ice shelf in the west Antarctic area have done during the past few years, enormous tabular islands are formed as a type of iceberg. 11. Differentiate between two forms of glacial drift—till and outwash. Where the glacier melts, debris accumulates to mark the former margins of the glacier—the end and sides. Glacial drift is the general term for all glacial deposits. Direct deposits appear unstratified and unsorted and are called till. In contrast, sorted and stratified glacial drift, characteristic of stream-deposited material, is called outwash and forms an outwash plain of glacio-fluvial deposits across the landscape. 12. What is a morainal deposit? What specific moraines are created by alpine and continental glaciers? Glacial till moving downstream in a glacier can form a marginal unsorted deposit known as a moraine—Figure 14.5 and 14.11. A lateral moraine forms along each side of a glacier. If two glaciers with lateral moraines join, their point of contact becomes a medial moraine. Eroded debris that is dropped at the glacier's farthest extent is called a terminal moraine. However, there also may be end moraines, formed wherever a glacier pauses after reaching a new equilibrium. If a glacier is in retreat, individual deposits are called recessional moraines. And finally, a deposition of till generally spread across a surface is called a ground moraine. 13. What are some common depositional features encountered in a till plain? With the retreat of the glaciers, many relatively flat plains of unsorted coarse till were formed behind terminal moraines. Low, rolling relief and deranged drainage patterns are characteristic of these till plains. As the glacier melts, this unsorted cargo of ablation till is lowered to the ground surface, sometimes covering the clay-rich lodgement till deposited along the base. The rock material is poorly sorted and is difficult to cultivate for farming, but the clays and finer particles can provide a basis for soil development. 14. Contrast a roche moutonnée and a drumlin regarding appearance, orientation, and the way each forms. Two landforms created by glacial action are streamlined hills, one erosional (called a roche moutonnée) and the other depositional (called a drumlin). A roche moutonnée is an asymmetrical hill of exposed bedrock. Its gently sloping upstream side (stoss side) has been polished smooth by glacial action, whereas its downstream side (lee side) is abrupt and steep where rock was plucked by the glacier (Figure 14.14). A drumlin is deposited till that has been streamlined in the direction of continental ice movement, blunt end upstream and tapered end downstream. Multiple drumlins (called swarms) occur in fields in New York and Wisconsin, among other areas. Sometimes their shape is that of an elongated teaspoon bowl lying face down (see Figure 14.15, photo and topo map). • Analyze the spatial distribution of periglacial processes and describe several unique landforms and topographic features related to permafrost and frozen ground phenomena. 15. In terms of climatic types, describe the areas on Earth where periglacial landscapes occur. Include both higher latitude and higher altitude climate types. Periglacial regions occupy over 20% of Earth's land surface (Figure 14.16). The areas are either near permanent ice or are at high elevation, and have ground that is seasonally snow free. Under these conditions, a unique set of periglacial processes operate, including permafrost, frost action, and ground ice. Climatologically, these regions are in subarctic and polar climates (especially tundra). Such climates occur either at high latitude (tundra and boreal forest environments) or high elevation in lower-latitude mountains (alpine environments). 16. Define two types of permafrost, and differentiate their occurrence on Earth. What are the characteristics of each? When soil or rock temperatures remain below 0°C (32°F) for at least two years, a condition of permafrost develops. An area that has permafrost but is not covered by glaciers is considered periglacial. Note that this criterion is based solely on temperature and not on whether water is present. Other than high latitude and low temperatures, two other factors contribute to permafrost: the presence of fossil permafrost from previous ice-age conditions and the insulating effect of snow cover or vegetation that inhibits heat loss. Permafrost regions are divided into two general categories, continuous and discontinuous, that merge along a general transition zone. Continuous permafrost describes the region of the most severe cold and is perennial, roughly poleward of the –7°C (19°F) mean annual temperature isotherm. Continuous permafrost affects all surfaces except those beneath deep lakes or rivers in the areas shown in Figure 14.15. Continuous permafrost may exceed 1000 m in depth (over 3000 ft) averaging approximately 400 m (1300 ft). 17. Describe the active zone in permafrost regions, and relate the degree of development to specific latitudes. The active layer is the zone of seasonally frozen ground that exists between the subsurface permafrost layer and the ground surface. The active layer is subjected to consistent daily and seasonal freezethaw cycles. This cyclic melting of the active layer affects as little as 10 cm depth in the north (Ellesmere Island, 78° N), up to 2 meters in the southern margins (55° N) of the periglacial region, and 15 m in the alpine permafrost of the Colorado Rockies (40° N). See Figure 14.17. 18. What is a talik? Where might you expect to find taliks and to what depth do they occur? A talik (derived from a Russian word) is an unfrozen portion of the ground that may occur above, below, or within a body of discontinuous permafrost or beneath a body of water in the continuous region. Taliks are found beneath deep lakes and may extend to bedrock and noncryotic soil under large deep lakes (Figure 14.17). Taliks form connections between the active layer and groundwater, whereas in continuous permafrost groundwater is essentially cut off from water at the surface. In this way, permafrost disrupts aquifers and causes water supply problems. 19. What is the difference between permafrost and ground ice? In regions of permafrost, subsurface water that is frozen is termed ground ice. The moisture content of areas with ground ice may very from nearly absent in regions of drier permafrost to almost 100% in saturated soils. From the area of maximum energy loss, freezing progresses through the ground along a freezing front, or boundary between frozen and unfrozen soil. The presence of frozen water in the soil initiates geomorphic processes associated with frost action and the expansion of water volume as it freezes (Chapters 5 and 10). 20. Describe the role of frost action in the formation of various landforms in the periglacial region. The 9% expansion of water as it freezes produces strong mechanical forces that fracture rock and disrupt soil at and below the surface. Frost-action shatters rock, producing angular pieces that form a block field, or felsenmeer, accumulating as part of the arctic and alpine periglacial landscape, particularly on mountain summits and slopes. If sufficient water undergoes the phase change to ice, the soil and rocks embedded in the water are subjected to frost-heaving (vertical movement) and frost-thrusting (horizontal motions). Boulders and slabs of rock generally are thrust to the surface. Soil horizons may appear disrupted as if stirred or churned by frost action, a process termed cryoturbation. Frost action also produces a contraction in soil and rock, opening up cracks for ice wedges to form. Also, there is a tremendous increase in pressure in the soil as ice expands, particularly if there are multiple freezing fronts trapping unfrozen soil and water between them. 21. Relate some of the specific problems humans encounter in developing periglacial landscapes. Human populations in areas that experience frozen ground phenomena encounter various difficulties. Because thawed ground in the active layer above the permafrost zone frequently shifts in periglacial environments, the maintenance of roadbeds and railroad tracks is a particular problem. In addition, any building placed directly on frozen ground will begin to melt itself into the defrosting soil. Thus, the melting of permafrost can create subsidence in structures and complete failure of building integrity (Figure 14.21). • Explain the Pleistocene ice age epoch, and related glacials and interglacials; and describe some of the methods used to study paleoclimatology. 22. What is paleoclimatology? Describe Earth's past climatic patterns. Are we experiencing a normal climate pattern in this era or have scientists noticed any significant trends? Paleoclimatology is the science of past climates. The most recent episode of cold climatic conditions began about 1.65 million years ago, launching the Pleistocene epoch. At the height of the Pleistocene, ice sheets and glaciers covered 30% of Earth's land area, amounting to more than 45 million km2 (17.4 million mi2). The Pleistocene is thought to have been one of the more prolonged cold periods in Earth's history. At least 18 expansions of ice occurred over Europe and North America, each obliterating and confusing the evidence from the one before. The term ice age is applied to any such extended period of cold, even though an ice age is not a single cold spell. Instead, it is a period of generally cold climate, called a glacial, interrupted by brief warm spells, known as interglacials. There is a worldwide retreat of alpine glaciers, higher snowlines in Greenland, and at least three accelerating ice streams on the West Antarctic ice sheet. The reduction in alpine glacial mass balances is particularly true of low and middle elevation glaciers. This trend in ice mass reduction may be attributed to the present century-long increase in mean global air temperatures. Additionally, over the past ten years, we have experienced the warmest years in instrumental history. 23. Define an ice age. When was the most recent? Explain “glacial” and “interglacial” in your answer. The term ice age is applied to any extended period of cold, even though an ice age is not a single cold spell. Instead, it is a period of generally cold climate, called a glacial, interrupted by brief warm spells, known as interglacials. Traditionally, four major glacials and three interglacials were acknowledged for the Pleistocene epoch. (The glacials were named the Nebraskan, Kansan, Illinoian, and Wisconsinan.) In Europe, similar episodes coincided with those in North America, but were given different names. Modern techniques have opened the way for a new chronology and understanding. Currently, glaciologists acknowledge the Illinoian glacial and Wisconsinan glacial, and the Sangamon interglacial between them. These span the past 300,000 years (Figure 14.23). The Illinoian is believed to have had two glacials (designated stages 6 and 8 in the figure), as did part of the Wisconsinan (stages 2 and 4), which is dated at 10,000 to 35,000 years ago. The stages on the chart are numbered back to stage 23, at approximately 900,000 years ago. The Holocene (past 10,000 years) is regarded as either an interglacial or a post-glacial epoch. 24. Summarize what science has learned about the causes of ice ages by listing and explaining at least four possible factors in climate change. The mechanisms that bring on an ice age are the subject of much research and debate. Because past occurrences of low temperatures appear to have followed a pattern, researchers have looked for causes that also are cyclic in nature. They have identified a complicated mix of interacting variables that appear to influence long-term climatic trends, including galactic and Earth-Sun relationships, solar variability, geophysical factors, and geographical-geological factors. 25. Describe the role of ice cores in deciphering past climates. What record do they preserve? Where were they drilled? Ice core analysis has opened the way for a new chronology and understanding of glaciation. Chemical and physical properties of the atmosphere and snow that accumulated each year are frozen into place. Locked into the ice cores are the air bubbles from past atmospheres, which indicate ancient gas concentrations, such as greenhouse gases, carbon dioxide and methane. For example, during cold periods, high concentrations of dust are present, brought by winds from distant dry lands, acting as condensation nuclei. Past volcanic eruptions are recorded in this manner. The presence of ammonia indicates ancient forest fires at lower latitudes and the ratio between stable forms of oxygen is measured with each snowfall. Greenland has been the location of two ice cores, the Greenland Ice Core Project (GRIP) which began in 1989, and more recently, the Greenland Ice Sheet Project (GISP-2) began in 1990. The GRIP catalogued 250,000 years of history, drilling a 3030m deep core, and the GISP-2 core reached bedrock at a 2700 m and records 115,000 years of past climatic history (see Figure 14.1.1, Focus Study 14.1). On the East Antarctic Plateau, 75.1° S, 123.3° E, elevation 3233 m (10,607 ft), approximately 900 km (560 mi) from the coast and 1750 km (1087 mi) from the South Pole, sits Dome C. This is the point on the Antarctic continent where the ice sheet is the thickest (see Figure 14.29c for location; and Figure 14.1.2). Here the ice is 3309 m 22 m deep (10,856 ft). The mean annual surface temperature is –54.5°C (–66.1°F); however, the science crews experience temperatures that range from –50 C° (–58 F°) when they arrive to –25 C° (–13 F°) by midsummer. Dome C is 560 km (348 mi) from the Vostok base, where the previous coring record of 400,000 years was set. The Dome-C 8-year project is part of a 10-country European Project for Ice Coring in Antarctica (EPICA). The ice core provides a high-resolution record of ancient atmospheric gases, ash from volcanic eruptions, and materials from other atmospheric events. Through 2003, coring to a 3190-m (2-mi) depth has brought up 740,000 years of Earth’s past climate history (actually, 807,000 years has been retrieved but not yet analyzed) (Figure 14.1.3). Scientists analyzing the results, report that the Dome-C record affirms the Vostok findings and correlates perfectly with the deep-sea core of oxygen isotope fluctuations in foraminifera shells (microfossils) from the Atlantic Ocean. Confirmed is the finding that the present concentration of carbon dioxide in the atmosphere is the highest it has been in the past 440,000 years and that these changing levels have marched in step with higher and lower temperatures throughout this time span. 26. Explain the relationship between the criteria defining the Arctic and Antarctic regions. Is there any coincidence in these criteria and the distribution of Northern Hemisphere forests on the continents? Climatologists use environmental criteria to define the Arctic and the Antarctic regions (Figure 14.26). For the Arctic area, the 10°C (50°F) isotherm for July is used; it coincides with the visible treeline, which is the boundary between the northern forests and tundra climates, (i.e., a temperature below which boreal forests cannot survive). The Antarctic region is defined by the antarctic convergence, a narrow zone that extends around the continent as a boundary between colder antarctic water and warmer water at lower latitudes. This boundary follows roughly the 10°C (50°F) isotherm for February (Southern Hemisphere summer) and is located near 60° S latitude. The Antarctic region that is covered with sea ice represents an area greater than North America, Greenland, and Western Europe combined! 27. What is the latest news fro the analysis of the Dome C ice core as described in the text?. The term ice age is applied to any extended period of cold, even though an ice age is not a single cold spell. Instead, it is a period of generally cold climate, called a glacial, int 28. What is the significance of having the Dome C ice core include Marine Isotope Stage 11 (MIS 11) shown on Figure 14.23, relative to understanding present climates? This warm spell at MIS 11, from 425,000 to 395,000 years ago, is perfectly recorded in the Dome C core and is of interest because CO2 in the atmosphere during MIS 11 was similar to our pre-industrial level of 280 ppm. Earth’s orbital alignment was similar to that of today as well. The MIS 11 analogy means that a return to the next glacial interval is perhaps 16,000 years in the future. 29. Briefly characterize changes in the cryosphere, specifically in the Arctic and Antarctica regions, that scientists are tracking. Review the “Global Climate Change” section in Chapter 7, where a portrait of high-latitude temperatures and ongoing physical changes to pack ice, ice shelves, and glaciers is presented. News Report 14.3 looks at meltpond occurrence as indicators of changing surface energy budgets. Throughout this text, several High Latitude Connection features described additional dynamics in these polar regions. High Latitude Connection 14.1 covers the Ward Hunt Ice Shelf breakup. See also HLCs 1.1, 3.1, 8.1, and 17.1. 30. What happened to the Ward Hunt Ice Shelf in northern Canada? By late fall 2003 the Ward Hunt Ice Shelf—largest in the Arctic, on the north coast of Ellesmere Island in Nunavut—was breaking up. This shelf had been stable for at least 4500 years. After three decades of mass losses, the ice shelf reached a systems threshold and rapidly broke up between 2000 and 2003 (Figure 14.1.1). Overhead Transparencies 254. 14.1 Alpine glaciers, Ellesmere Island satellite detail 255. 14.2 Ruth and Eldridge glaciers in south-central Alaska 256. 14.3 Image of Eugenie Glacier icebergs break off in Dobbins Bay 257. 14.5 a, b, d Retreating alpine glacier (a) and mass balance (b), (d) satellite image of rivers of ice detail (bottom) 258. 14.6 a, b, c Glacier cross section showing movement dynamics; surface crevasses (middle); Pine Island Glacier at bottom. 259. 14.8 a, b, c Geomorphic handiwork of alpine glaciers (before, during, and after a valley glacier occupies a formerly stream-cut valley) 260. 14.11 a, b, c Continental glacier depositional features 261. 14.12a, b Roche moutonnée, Lembert Dome; development of a roche moutonnée 262. 14.14 Distribution of permafrost in Northern Hemisphere 263. 14.15 Cross section of typical periglacial region in Northern Canada 264. 14.18 Building failure/melting permafrost 265. 14.21a, b Pleistocene glaciation (polar projection with blow-out map of North America 18,000 years ago and smaller map form 9500 years ago) 266. 14.22,a, b, c, d Paleolakes of the western U.S. 267. 14.23 a, b, and c Recent climates from ice cores (top); GISP 2 record 500 years to the present (bottom) 268. 14.24a, b, c Astronomical factors that affect climate cycles 269. 14.26a, b The Arctic and Antarctic regions 270. 14.35 Amundsen-Scott Base, South Pole 271. N.R. 14.1.1 South Cascade Mass Balance graph 272. N.R. 14.1.2a, b Alaskan glaciers mass balances Glacial and Periglacial Processes and Landforms • Glacial and Periglacial Landscapes • • Glacial and Periglacial Landscapes Glacial and Periglacial Landscapes • • Glacial and Periglacial Landscapes Glacial and Periglacial Landscapes • • Glacial and Periglacial Landscapes Glacial and Periglacial Landscapes • • Glacial and Periglacial Landscapes Glacial and Periglacial Landscapes •