Land of Extremes – A Natural History of The Arctic North Slope of Alaska - Softcover

Huryn, Alexander; Hobbie, John

Softcover

ISBN 10: 1602231818 ISBN 13: 9781602231818

Publisher: University of Chicago Press, 2012

Synopsis

This book is a comprehensive guide to the natural history of the North Slope, the only Arctic tundra in the United States. The first section provides detailed information on climate, geology, landforms, and ecology. The second provides a guide to the identification and natural history of the common animals and plants and a primer on the human prehistory of the region from the Pleistocene through the mid-twentieth century. The appendix provides the framework for a tour of the natural history features along the Dalton Highway, a road connecting the crest of the Brooks Range with Prudhoe Bay and the Arctic Ocean, and includes information about mile markers where travelers may safely pull off to view geologic formations, plants, birds, mammals, and fish. Featuring hundreds of illustrations that support the clear, authoritative text, "Land of Extremes" reveals the Arctic tundra as an ecosystem teeming with life.

About this title

About the Author

John Hobbie is a senior scholar at the Ecosystems Center, Marine Biological Laboratory in Woods Hole, Massachusetts. He is a founding researcher of the Toolik Field Station in Alaska and former director of the Arctic Long-Term Ecological Research Project there.

Excerpt. © Reprinted by permission. All rights reserved.

LAND OF EXTREMES

A NATURAL HISTORY OF THE ARCTIC NORTH SLOPE OF ALASKABy Alexander D. Huryn John E. Hobbie

University of Alaska Press

Copyright © 2012 University of Alaska Press
All right reserved.
ISBN: 978-1-60223-181-8

Contents

Acknowledgments...........................................................................................xiiiPreface...................................................................................................xv1. Introduction...........................................................................................12. Bedrock Geology........................................................................................93. Glacial Geology........................................................................................174. Permafrost and Patterned Ground........................................................................235. Habitats and Ecology...................................................................................316. Mushroom Madness.......................................................................................537. Lichens................................................................................................578. Mosses and Liverworts..................................................................................639. Vascular Plants........................................................................................6710. Invertebrates.........................................................................................11311. Fish..................................................................................................15112. Reptiles and Amphibians...............................................................................16513. Birds.................................................................................................16714. Mammals...............................................................................................21115. Human Natural History Through the Mid-Twentieth Century...............................................243Appendix: Guide to Natural History Along the Dalton Highway: Atigun Pass to Deadhorse.....................255Endnotes..................................................................................................281Sources...................................................................................................287Index.....................................................................................................301

Chapter One

Introduction

The North Slope

The North Slope, also known as the Arctic Slope, is that part of northern Alaska where rivers drain into the Arctic Ocean north of Point Hope (Map 1). It is enormous, with an area equal to Nebraska or South Dakota (about 200,000 km²) and extending from about 68°N to 71°N at its greatest width. The North Slope contains three major physiographic regions: the Brooks Range, Arctic Foothills, and Arctic Coastal Plain. These are arranged as east–west trending bands parallel to the arctic coast, with the Arctic Coastal Plain most northerly and the Brooks Range most southerly. Each region has characteristic plant and animal communities due to differences in geology, topography, and climate. Nevertheless, they are all considered tundra. There are two types of tundra. Alpine tundra refers to mountain habitats above the tree line. Arctic tundra refers to habitats beyond the northern tree line. This book is an introduction to the natural history of the North Slope, the only arctic tundra in the United States.

Why the "Arctic"?

The Arctic is precisely defined as that part of the Northern Hemisphere where the sun is visible above the horizon for 24 hours during the summer solstice (around June 21) and is hidden below the horizon for 24 hours during the winter solstice (around December 22). The lowest latitude at which this occurs is about 66°33'N, which marks the position of the Arctic Circle and delimits the southern boundary of the Arctic. As one moves north from the Arctic Circle, the period of continuous daylight ("polar day") or darkness ("polar night") lengthens. At the southern North Slope village of Anaktuvuk Pass (68°8'N) in 2010, for example, the sun rose on May 25 and did not set again until July 18 (a 54-day polar day), while the polar day for the northern North Slope town of Barrow (71°17'N) lasted from May 11 to August 1 (82 days). Conversely, the polar night lasted from December 7, 2010, to January 4, 2011 (28 days), at Anaktuvuk Pass and from November 19, 2010, to January 21, 2011, at Barrow (63 days). Those unfamiliar with the relatively low arctic latitudes of the North Slope may have the impression that polar day and night are relatively constant periods of light and darkness. This is not so. During the polar day there are noticeable declines in light and temperature even on the summer solstice because the sun strikes the ground at a low angle during the early morning hours. During the polar night, even on the winter solstice, there is sufficient midday twilight to perform outdoor chores without a headlamp or lantern.

Having provided this pleasingly precise definition of the Arctic, it is important to point out its shortcomings. First, its precision is illusory. The Arctic Circle is not fixed but varies over about 2° during 40,000-year cycles caused by wobbles in the angle of the Earth's axis. Consequently, the location of the famous monument marking where the Dalton Highway crosses the Arctic Circle is only an approximation. Second, it does not adequately delimit the distribution of ecosystems containing communities of organisms adapted to arctic conditions. For example, no biologist would argue that the western shore of the Hudson Bay near Churchill, Manitoba, is not a typical arctic ecosystem, complete with polar bears, arctic foxes, and collared lemmings. Yet Churchill (58°45'N) is clearly south of the Arctic Circle and thus experiences no midnight sun. To accommodate such discrepancies, it has been suggested that the Arctic be defined to include areas of the Northern Hemisphere that have mean July temperatures of 10°C or less. The "10°C July mean-temperature rule" roughly determines the northern limit of tree growth and the southern limit of continuous permafrost. This definition is ecologically sound because it is based on a single key attribute that underlies the structure and function of all arctic communities: a long annual period of deep, dark cold.

Low Arctic versus High Arctic

The Arctic is often subdivided into the "high Arctic" and "low Arctic." The high Arctic includes habitats relatively close to the North Pole (e.g., greater than 75°N). With the exception of limited sedge meadows near streams and below lasting snowbanks, these are best characterized as rocky barrens populated by relatively few plant species (e.g., fewer than 150 vascular plant species). The low Arctic includes habitats closer to the Arctic Circle. These generally have comparatively lush vegetation and high plant diversity (more than 250 vascular plant species). Although all this may seem to be an exercise in hair splitting, it is important to be aware of the large differences between these subdivisions because much of what has been written about arctic ecosystems is based on the high Arctic and may not directly apply to the low Arctic. The North Slope, the focus of this book, provides an excellent example of a low-arctic ecosystem.

Climate

Temperature

The average annual temperature of the North Slope is about -12°C. The warmest month is July (mean near arctic coast = 5 to 8°C, mean in foothills = 12 to 13°C). The coldest is February (mean near arctic coast = -29 to -27°C; mean in foothills = -30°C) because the Arctic Ocean becomes completely covered by ice at this time, dramatically decreasing the transfer of heat from the relatively warm ocean. The major variation in temperatures across the North Slope is related to the distance south of the arctic coast. Coastal regions have warmer winters and colder summers, and interior locations have colder winters and warmer summers. For example, long-term climate records show average July high temperatures of 8°C for Barrow (coastal) to 19°C in Umiat (interior) and average February low temperatures ranging from -30°C at Barrow and -35°C at Umiat. To put all this in perspective, the summer freeze-free period at inland locations can be as much as 30 days; the freeze-free period at Barrow, however, is only 10 days. Needless to say, summers are short everywhere on the North Slope, a place where snowfall can be expected any day of the year!

Precipitation

Precipitation on the North Slope is highly influenced by seasonal patterns of freezing of the Beaufort, Chuchki, and Bering Seas. As continuous sea ice develops, atmospheric moisture is reduced and, as a consequence, precipitation on the North Slope is low from November through April. On the other hand, the lack of near-shore sea ice results in relatively high amounts of precipitation during July and August. Annual precipitation measured on the North Slope ranges from a minimum of 150 mm/yr near Barrow to 550 mm/yr in portions of the Brooks Range (North Slope annual average = 250 mm, or about 10 inches). There are problems with these estimates due to the difficulty of sampling blowing snow, but they nevertheless indicate low precipitation by any measure. To provide perspective, a common definition of a desert is a region receiving less than 250 mm of precipitation annually. By this definition, the North Slope is surely close to a desert—but a very strange one. During summer, the soils of much of the foothills and coastal plain are water saturated and often covered by thick, spongy layers of sphagnum moss. This is because the shallow layer of soil that thaws every summer—the "active layer" (0.3–1.0 m deep, or about 12–39 inches deep)—is sealed by the continuous layer of watertight permafrost below. In low-lying, poorly drained habitats, the water released as the active layer thaws simply has no place to go! The occurrence of water-saturated soils is further facilitated by low rates of evaporation and transpiration (water loss through plant tissues) due to cool summer temperatures. As a consequence of this conspiracy between a shallow active layer, a continuous layer of underlying permafrost, and cool summer temperatures, pools of standing water, extensive wetlands, ponds, lakes, rivers, and streams are all common features of the North Slope landscape. These features defy traditional definitions of a desert, to say the least.

Seasonality

It has been suggested that the traditional concept of the four seasons—winter, spring, summer, autumn—is not useful for the Arctic. There is good reason for this because the calendar dates that define the seasons of temperate regions are of little relevance here. The arctic year can be divided more usefully into a short warm period and a long cold period. The warm period is delimited by the consecutive days centered on mid-July when the mean daily temperature is above freezing (usually 10 to 30 days, although frost may occur on any day). The concepts of spring and autumn are reduced to brief seasons ("spring" from mid- May through mid-June, and "autumn" from mid-August through mid-September). The cold period begins in September when soils and surface water freeze ("freezeup") and lasts until they thaw ("breakup") in May. This concept of a "warm season" and a "cold season" makes sense ecologically and is similar to the concept of tropical seasonality, where the year is divided into monsoon and dry seasons, rather than the traditional four seasons.

Snow

The North Slope is blanketed with snow for almost nine months each year. Consequently, the ecology of plants and nonmigratory animals living here cannot be fully appreciated without some knowledge as to how they are affected by this. Snow performs four major ecological roles. First and foremost it provides insulation that maintains moderate soil temperatures even in the depth of winter. Second, high humidity within the snowpack reduces desiccating effects of dry winter air on buried plants and animals. Third, it provides critical winter habitat for small mammals (e.g., lemmings and voles) while simultaneously hampering foraging by the burial of food sources used by some larger animals (e.g., Dall sheep, caribou) and birds. Finally—although this role occurs only during the spring thaw—the melting snowpack provides a spatially variable water supply that is critical in determining the distribution of tundra plant species.

Insulation

Snow provides excellent insulation. Once a snow layer reaches a depth of 20–80 cm (about 8–31 inches), an uncoupling of air and ground temperatures occurs. The depth at which this occurs is called the "hiemal threshold." The wide range in snow depths at which the hiemal threshold occurs is due to differences in the amount of insulation provided by different types of snow. Low-density "new snow" (about 0.1 g/cm³) provides the highest insulation because it contains many dead-air spaces; high-density "old snow" (about 0.4 g/cm³) provides less insulation due to few dead-air spaces. As new snow becomes old snow a predictable process of structural metamorphism occurs, resulting in the difference in dead-air volume. As snow falls, it forms a layer of the familiar lacy snowflakes (new snow). Within a short time (hours to days depending upon factors such as snow depth, temperature, and wind packing), the snowflakes are compacted into a layer of tightly packed grains (old snow) and the volume of trapped dead air declines while the snow's strength and ability to support weight increase. Regardless of age or state of metamorphism, the insulation value of a snow layer approaching 40–50 cm (about 16–20 inches) is sufficient to maintain relatively constant ground temperatures. When insulated by 50 cm or more of winter snow, ground surface temperatures in the foothills, for example, rarely fall below -4 to -10°C (about 25–14°F) even though air temperatures of -30°C (about -22°F) or less are frequent and long lasting. The insulating effect of snow across the vast distances of the North Slope varies because the winter snowpack is relatively deep inland but relatively shallow near the coast due to wind. Consequently, mean winter ground surface temperatures range from about -6°C in the southern foothills to -20°C on the northern coastal plain.

Humidity

A thick snow layer maintains relatively high levels of internal humidity. Following the relatively rapid conversion of new snow to old snow, further structural changes occur that are related to the temperature gradient that forms within the snow layer. The top of the snow layer, which is in contact with the atmosphere, is usually colder than the bottom, which is in contact with the ground. The relatively warm temperature of the ground causes a high rate of sublimation of the ice grains in the bottom of the snow layer. The water vapor produced contributes to high levels of relative humidity (e.g., 100 percent) within the air spaces of the snowpack. Such high levels of humidity greatly enhance the ability of buried plants to avoid desiccation during winter.

Habitat

A thick snow layer provides space near the ground that allows construction of runways and nests by voles, lemmings, shrews, and weasels. This space results from the redistribution of water from the bottom of the snow layer to the top. This process is driven by the diffusion of vapor produced by sublimation at the bottom of the snow layer to the colder top of the snow layer. Here it refreezes and becomes incorporated into a "snow-ice matrix." The snow grains near the top of the snowpack thus increase in size and density at the expense of snow grains near the bottom. As a consequence the bottom of the snow layer is converted to a relatively open matrix of large, brittle, nonadhesive crystals known as "depth hoar" (Fig. 1.1). It is the open space provided by depth hoar that is used as habitat by lemmings, voles, shrews, and weasels, all of which remain active beneath the snow during winter.

Chapter Two

Bedrock Geology

Suspect Terrane?

Most large landmasses are formed by the fusion of distinct blocks of continental crust ("terranes") with different geographical origins. Consequently, each terrane has a unique combination of rocks and fossils. Alaska consists of at least 13 terranes, with one of the largest being the North Slope. The North Slope is considered a "suspect terrane" because it was joined to the northern Alaskan landmass after migrating from an uncertain ("suspect") location. Information based on the fossil record, however, indicates that the North Slope terrane was always part of North America—it just changed location. The most credible explanation of how the present-day North Slope came to be involves the rifting (splitting) of a large chunk of land from northernmost Canada, followed by a jackknife rotation centered near the Mackenzie River delta, and then a final collision with the north coast of ancestral Alaska. The rifting and subsequent rotation was caused by seafloor spreading during the Early Cretaceous (145–112 million years ago, or mya). Consequently, much of the very old geologic features of the North Slope, including the deposition of the oil-producing strata of the Prudhoe Bay oil fields, occurred while it was a part of present-day northern Canada. Following the joining of the North Slope terrane with ancestral Alaska, a long period of north–south contraction resulted in the uplift of the modern Brooks Range and the shedding of enormous volumes of eroded materials toward the north that eventually covered much of the foothills and coastal plain.

Bedrock of the North Slope

The bedrock of the North Slope terrane is primarily sedimentary in origin. In many places it has been distorted by overthrusting and uplifting. This began with the earliest stirrings of the Brooks Range during the Middle Jurassic (202–146 mya, i.e., prior to the migration of the North Slope terrane away from northern Canada) and continued through the Early Cretaceous (146–100 mya) and the Quaternary (less than 1.8 mya). The bedrock of the present-day Brooks Range is often exposed and readily observed. In the foothills and coastal plain, however, it is usually concealed by sediment layers, or more technically "strata," thousands of meters thick. Although the local bedrock geology of the North Slope can be exceedingly complex due to extreme displacement and distortion, the regional pattern is simple. As one ventures from the Continental Divide toward the Arctic Ocean, the successive exposures of bedrock become younger due to northward dipping of bedrock. To simplify this overview of the geology of the North Slope, we will restrict ourselves to bedrock types observed along the convenient cross section provided by the Dalton Highway. These major bedrock types are presented in order of age, from oldest to youngest, beginning at Atigun Pass.

(Continues...)

Excerpted from LAND OF EXTREMESby Alexander D. Huryn John E. Hobbie Copyright © 2012 by University of Alaska Press. Excerpted by permission of University of Alaska Press. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Edition details

• Publisher: University of Chicago Press
• Publication date: 2012
• Language: English
• ISBN 10: 1602231818
• ISBN 13: 9781602231818
• Binding: Paperback
• Number of pages: 356