Climates of Geologic Time Current Weather Finish Ice Core Research Overview and Historical Perspective The Pleistocene and Holocene For Next Class: Read Ch. 11 (pp ) Reminder: Exam 2 on March 4 th

© AMS4 Climates of Geologic Time  Geologic time scale: standard division of Earth history into eons, eras, periods, and epochs based on large-scale geological events

© AMS5

6 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

© AMS7 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 Corresponds to transition between the Precambrian and Phanerozoic Eons Abrupt changes between extreme cold and tropical heat Abrupt changes between extreme cold and tropical heat

© AMS8 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

© AMS9 Climates of the Pleistocene Ice Age  Historical Perspective Glacial theory proposed in the mid-1800s by Swiss naturalist Louis Agassiz 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 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 stagesGeologists subdivided the Pleistocene Epoch into four glacial stages

© AMS10 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 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 negativeIf a glacier loses more ice than it gains, its mass balance is negative glacier thins and shrinks glacier thins and shrinks If a glacier gains more ice mass than it loses, its mass balance is positiveIf a glacier gains more ice mass than it loses, its mass balance is positive glacier thickens and expands glacier thickens and expands

© AMS11 Climates of the Pleistocene Ice Age  Climate and Glaciers Glacial climates favor positive mass balance Glacial climates favor positive mass balance Interglacial climates favor negative mass balance Interglacial climates favor negative mass balance Climate shifted between Climate shifted between glacial and interglacial numerous times during the Pleistocene glacial and interglacial numerous times during the Pleistocene

Definitions  What is the difference between a glacial and interglacial?

© AMS13 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. During major glacial climatic episodes of the Pleistocene Epoch, the Laurentide ice sheet formed over east-central Canada and spread into the U.S.

© AMS14 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 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 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 climatesFollowed by numerous periods of glacial and interglacial climates

© AMS15 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 Last major glacial climatic episode began about 27,000 years ago and reached its peak about 20,000 to 18,000 years ago

© AMS16 Climates of the Pleistocene Ice Age

© AMS17 Climates of the Pleistocene Ice Age Younger Dryas: relatively cool episode from 11,000 to 10,000 years ago Younger Dryas: relatively cool episode from 11,000 to 10,000 years ago Began abruptly when glacial ice lobes disrupted drainage patternsBegan 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 Weakened the meridional overturning circulation, which in turn diminished the warm water flowing into the central and northern North Atlantic Cooled surrounding landsCooled surrounding lands

© AMS18 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 Glacial ice withdrew from North American Great Lakes region about 10,500 years ago Civilization and agriculture developedCivilization and agriculture developed Holocene has had spatially and temporally variable temperature and precipitation Holocene has had spatially and temporally variable temperature and precipitation