Past Climate Variability and Change in the Arctic and at High Latitudes

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The U.S. Climate Change Science Program Glossary 198 LGM see Last Glacial Maximum Little Ice Age A period of time during the last millennium (approximately 1500 to 1850 AD) during which summers globally, but particularly in the higher latitudes of the Northern Hemisphere, were colder than during the preceding millennium or the 20th century. The Little Ice Age is widely manifested by the advance of mountain glaciers and ice caps, as well as by periodic crop failures, especially in northwest Europe. Ma Mega-annum; millions of years ago (a point in time). Marine Isotope Stage (MIS) A subdivision of recent geologic time, identified by number (e.g., Marine Isotope Stage 1, or Marine Isotope Stage 8); Marine Isotope Stage 1 includes today, and numbers increase with increasing age. The marine isotope stages were defined from the oxygen-isotope ratios of shells that accumulated on the ocean floor and were collected in sediment cores; shells that grew in cooler water, or at times when more water was stored on land in ice sheets, are isotopically heavier. Intervals of warmer water or smaller ice are labeled with odd numbers (Marine Isotope Stage 1, or 5), and times of colder water or larger ice have even numbers. Marine Isotope Stages average a few tens of thousands of years long, but different stages have different durations. Mass flux Rate at which material passes an observational site. The mass flux added to the surface of a glacier by snowfall may be reported as the ice added to an area during a time interval and thus measured in kilograms per square meter per second (kg/m 2/s) or equivalent units; the mass flux per unit width for flow of a glacier may be reported as kilograms per meter per second (kg/m/s). Medieval Climate Anomaly An interval between AD 1000 and 1300 in which some Northern Hemisphere regions were warmer than during the Little Ice Age that followed. Meristematic The tissue in all plants consisting of undifferentiated cells (meristematic cells) and found in zones of the plant where growth can take place. Methane (CH 4) An atmospheric greenhouse gas with many natural and anthropogenic sources, chief of which are decomposition of organic matter in the absence of oxygen (e.g., in wetlands and landfills), animal digestion and animal waste, and the production and distribution of natural gas, oil, and coal. It is the third most abundant atmospheric greenhouse gas after water vapor and carbon dioxide. The current lower-atmospheric concentration of methane at middle latitudes in the northern hemisphere is approximately 1,847 parts per billion and is stable. This concentration is substantially above the pre-industrial level of about 730 parts per billion. Milankovitch cycles (time scales) The Milankovitch or astronomical theory of climate change is an explanation for cyclical changes in the seasons which result from cyclical changes in the earth’s orbit around the sun. The theory is named for Serbian astronomer Milutin Milankovitch, who calculated the slow changes in the earth’s orbit by careful measurements of the position of the stars and through equations using the gravitational pull of other planets and stars. He determined that the earth “wobbles” in its orbit. The earth’s “tilt” causes seasons, and changes in the tilt of the earth change the strength of the seasons. The seasons can also be accentuated or modified by the eccentricity (degree of roundness) of the orbital path around the sun and by the precession effect, the position of the solstices in the annual orbit. Together, the periods of these orbital motions (40,000 years for tilt, 90,000–100,000 years for eccentricity, and approximately 26,000 years for precession) have become known as Milankovitch cycles and their associated periodicities as Milankovitch time scales. Milankovitch forcing The changes in seasonal and latitudinal distribution of solar energy striking the Earth, which are caused by cyclical features of Earth’s orbit, which cause climate changes, and which were described by the mathematician Milutin Milankovitch. Millennial Occurring or repeating every thousand years. Miocene The geological epoch spanning 23 Ma to 5.3 Ma. MIS see marine isotope stage Model With respect to climate studies, a computer program designed to mimic a natural process or system of processes with the aim of aiding in understanding how the process or system behaves. The representation of the climate system is based on mathematical equations governing the behavior of the various components of the climate system and includes treatment of key physical processes and interactions.
Moraine Landforms (typically ridges) composed of sediment deposited at or near the edge of a glacier; a moraine provides an outline of all or part of a glacier at some time. (Note that the term “ground moraine” is sometimes used for a blanket of sediment deposited beneath a glacier, and the term “medial moraine” can be used for a band of debris on the surface of a glacier marking the junction of confluent flows; however, moraine normally is used as given in the main definition here.) m.y. Millions of years (a time interval). N 2O see nitrous oxide NAO see North Atlantic Oscillation Near field The region sufficiently close to the source of a disturbance that some physical processes must be considered that are unimportant at greater distance from the disturbance in the far field. For example, the initial growth of the ice sheet on Greenland lowered the sea level globally (because water evaporated from the ocean was stored in the ice sheet), but the weight of the ice depressed Greenland more than the globally averaged lowering of the sea surface; thus, sea level rose in the near field just beyond the growing ice sheet where sinking under the ice weight was important, whereas sea level fell in the far field where the influence of the weight of the growing ice sheet was small. Negative feedback In climate studies, a process that acts to decrease the magnitude of the climate’s response to an initial forcing. NGRIP North Greenland Ice Sheet Project location and ice core (see Plate 1 for location). Deep drilling at the nGriP site began in 1999 and was completed to bedrock at 3,094 meters in 2003. Nitrous oxide (N 2O) An atmospheric greenhouse gas. It is the fourth most abundant greenhouse gas after water vapor, carbon dioxide, and methane. Natural sources include many biological sources in soil and water, primarily through bacterial breakdown of nitrogen in soils and in Earth’s oceans. Primary humanrelated sources of N 2O are agricultural soil management, animal manure management, sewage treatment, mobile and stationary combustion of fossil fuel, and the manufacture of adipic and nitric acid. The pre-industrial value of N 2O in the Past Climate Variability and Change in the Arctic and at High Latitudes atmosphere was approximately 265 parts per billion; it has increased monotonically since that time. The current atmospheric concentration is approximately 319 parts per billion. North Atlantic Oscillation (NAO) A large-scale see-saw in barometric pressure between the vicinity of Iceland and the Azores. It corresponds with fluctuations in the strength of the main westerly winds across the North Atlantic Ocean and is the primary wintertime weather-maker for the North Atlantic region of the eastern United States and Canada, Greenland, and Europe. When this pressure difference is large the NAO is said to be in positive phase; when it is small the NAO is said to be in negative phase. Northern Annular Mode (NAM) One of the two hemispheric-scale patterns of climate variability (the other is the Southern Annular Mode). The NAM is characterized by a seesaw in the strength of the west-east atmospheric flow along approximately 55°N and 35°N. It is accompanied by displacements of atmospheric mass between the Arctic basin and the mid-latitudes centered about 45°N. Obliquity The angle between the rotational axis of the Earth and a line perpendicular to the plane containing Earth’s orbit about the sun. Earth’s obliquity varies predictably from 22.1° to 24.5° in a 41,000 year cycle. The fact that Earth’s axis of rotation is not perpendicular to the plane of its orbit around the sun (i.e., Earth’s obliquity is not zero) is the origin of the seasons. Oligocene The geological epoch spanning 33.9 Ma to 23 Ma. Orbitally paced Phenomena that are synchronous with cyclical features of the Earth’s orbit are described as orbitally paced. Oscillation (climate) A cyclical change in value between two different states. The North Atlantic Oscillation is a particularly important cyclic variation in atmospheric pressure over the North Atlantic region that is the primary wintertime weather-maker in the North Atlantic region. Ostracode A microfossil group of bivalved crustaceans that secrete a calcareous shell commonly preserved in sediments in the Arctic region. Because many ostracode species have ecological limits controlled by temperature, salinity, oxygen, food, and other factors, they can provide an important tool for paleoceanographic reconstruction in the Arctic. 199
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Past Climate Variability and Change
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Past Climate Variability and Change
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AUTHOR TEAMS FOR THIS REPORT Execut
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ACKNOWLEDGMENTS Many individuals ma
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TABLE OF CONTENTS Executive Summary
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2 The U.S. Climate Change Science P
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4 The U.S. Climate Change Science P
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6 The U.S. Climate Science Program
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Page 169 and 170: CHAPTER 6 ABSTRACT Past Climate Var
Page 171 and 172: second, and the Transpolar Drift, t
Page 173 and 174: EXTENT, IN MILLION SQUARE KILOMETER
Page 175 and 176: Until recently, and for logistical
Page 177 and 178: 1990; Fyles et al., 1994), the nort
Page 179 and 180: FREQUENCY 50 45 40 35 30 25 20 15 1
Page 181 and 182: Seas around icelAnd provide a rare
Page 183 and 184: at least 14 Ma (Darby, 2008). Sever
Page 185 and 186: T. quinqueloba, IN SPECIMENS PER GR
Page 187 and 188: 7 6 5 4 3 2 1 Past Climate Variabil
Page 189 and 190: SEA-ICE COVERAGE, IN NUMBER OF MONT
Page 191 and 192: QUARTZ WEIGHT, IN PERCENT 6 5 4 3 2
Page 193: 6.5 SUMMARY Geological data indicat
Page 201 and 202: GLOSSARY GLOSSARY 8 ka cold event A
Page 203 and 204: CAPE Project Circum-Arctic PaleoEnv
Page 205 and 206: Eccentricity Out of roundness (elli
Page 207: Innuitian sector The ice sheet that
Page 211 and 212: Positive feedback In climate studie
Page 213: Trough-mouth fans Undersea deposits
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Past Climate Variability and Change in the Arctic and at High Latitudes

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