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Climates of Geologic TimeCurrent WeatherFinish Ice Core ResearchOverview and Historical Perspective The Pleistocene and Holocene
For Next Class: Read Ch. 11 (pp. 351-354)Reminder: Exam 2 on March 4th
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Climates of Geologic Time
Geologic time scale: standard division of Earth history into eons, eras, periods, and epochs based on large-scale geological events
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Climates of Geologic Time
Absence of bedrock and plate tectonics complicate the reconstruction of past climates
However, available evidence supports some conclusions regarding the climate over geologic time
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Climates of Geologic Time
Geologic evidence supports interval of extreme climate fluctuations beginning about 570 million years ago Corresponds to transition between the
Precambrian and Phanerozoic Eons Abrupt changes between extreme cold and
tropical heat
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Climates of the Pleistocene Ice Age
Plate tectonics has not been a major factor in climate change over the past two million years
Climate of the last two million years favored the development of huge glacial ice sheets
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Climates of the Pleistocene Ice Age
Historical Perspective Glacial theory proposed in the mid-1800s by
Swiss naturalist Louis Agassiz Geologist Thomas C. Chamberlin proposed
that the Ice Age had involved multiple advances and recessions of glacial ice sheets • Geologists subdivided the Pleistocene Epoch into
four glacial stages
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Climates of the Pleistocene Ice Age
Climate and Glaciers The difference between ice mass gain and ice
mass loss over the course of one year is the glacier’s mass balance• If a glacier loses more ice than it gains, its mass
balance is negative glacier thins and shrinks
• If a glacier gains more ice mass than it loses, its mass balance is positive
glacier thickens and expands
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Climates of the Pleistocene Ice Age
Climate and Glaciers Glacial climates favor positive
mass balance Interglacial climates favor
negative mass balance Climate shifted between
glacial and interglacial numerous times during the Pleistocene
Definitions
What is the difference between a glacial and interglacial?
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Climates of the Pleistocene Ice Age
Glaciers and Landscapes During major glacial
climatic episodes of the Pleistocene Epoch, the Laurentide ice sheet formed over east-central Canada and spread into the U.S.
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Climates of the Pleistocene Ice Age
Chronology and Temperature Trends Oxygen isotope analysis of deep-sea
sediment cores shows numerous fluctuations between major glacial and interglacial climatic episodes over the past 600,000 years
A relatively mild interglacial episode, referred to as the Eemian, began about 127,000 years ago and persisted for nearly 7000 years• Followed by numerous periods of glacial and
interglacial climates
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Climates of the Pleistocene Ice Age
Chronology and Temperature Trends Last major glacial climatic episode began
about 27,000 years ago and reached its peak about 20,000 to 18,000 years ago
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Climates of the Pleistocene Ice Age
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Climates of the Pleistocene Ice Age Younger Dryas: relatively cool episode
from 11,000 to 10,000 years ago• Began abruptly when glacial ice lobes
disrupted drainage patterns Weakened the meridional overturning
circulation, which in turn diminished the warm water flowing into the central and northern North Atlantic
• Cooled surrounding lands
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Climates of the Holocene
The Holocene Epoch is the present interglacial Glacial ice withdrew from North American
Great Lakes region about 10,500 years ago• Civilization and agriculture developed
Holocene has had spatially and temporally variable temperature and precipitation
