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PLEISTOCENE GLACIAL INTERGLACIAL CYCLES -Disha Gupta
THE PLEISTOCENE EPOCH
Pleistocene Epoch : 1.8 million to 10,000years ago Holocene Epoch : since 10,000 years ago
Some basic definitions Glacial Period : When discussing climate change over millions of years, periods during which the Northern Hemisphere had ice sheets. Includes the Pleistocene and Holocene, including current.
Glacial Interval/ Ice Age : Time during the Pleistocene when more than just Greenland / Antarctica have ice sheets.
Interglacial Period/ Interval : Time during the Pleistocene when only Greenland/ Antarctica have ice sheets.(the Holocene, includes current )
Background Information ▲ Over its history, the earth has undergone many periods of extensive glaciations. ▲ Often, this resulted when plate movements positioned large continental blocks over the
poles. ▲ Much of the Mesozoic and Cenozoic, however, were characterized by mild climates. ▲ Therefore, the glacial and interglacial cycles of the Pleistocene represented a dramatic
• Pleistocene glaciation is the period in Earth's history also known as the Quaternary glaciation or the current ice age.
• It is important to recognize that the Pleistocene was a series of real ice ages, separated by relatively short periods.
• The shorter and warmer intervals between the recurrent Pleistocene glaciations are termed interglacials.
• The Pleistocene started 2.6 million years ago and lasted until the termination of the Weichsel glaciation about 11,711 years ago.
• Through much of this period, the Earth's northern and southern regions were covered by kilometer thick glaciers.
The Pleistocene ice ages were a natural continuation of the cooling of Earth that had taken place throughout Cenozoic. Time progresses from left to right.
What caused the Pleistocene ice ages?
✓ Scientists once believed that they had resulted from changes in the output of solar radiation from the sun. This does not appear to be the case.
✓ Instead, the Pleistocene ice ages are seen to have resulted from changes in the Earth’s orbit which, in turn, resulted in changes in incident solar radiation.
✓ These changes are known as Milankovitch cycles.
✓ Over long periods of time 30% of Earth's land masses was thus covered by dazzling white ice and snow, and thereby Earth's albedo increased dramatically, and a very high proportion of solar radiation was reflected back to space, which intensified further cooling.
The Pleistocene was a time of fluctuating colder climates that resulted in a number of extensive glaciations or ICE AGES. At present, ice covers about 10% of the land surface, whereas at its maximum extent during the Pleistocene it covered about 30%.
The major effects of this ice age were
▲ Erosion of land and the deposition of material
▲ The modification of river systems
▲ The creation of millions of lakes
▲ Changes in sea level
▲ The development of pluvial lakes far from the ice margins
▲ The isostatic adjustment of the earth's crust
▲ Abnormal winds
World during Pleistocene glaciation
♦ During the ice ages global average annual temperature was 5-10 degrees colder than today.
♦ A large part of the world's water was for long periods locked up in gigantic ice sheets.
♦ The water level in the World's oceans became very low, and the continents suffered from dust storms.
♦ The cycle time between cold periods and warm periods was 41,000 years. The temperature difference between cold and warm periods was about 4 degrees or less.
Oxygen has some story to tell
• There were variations in the frequency of oxygen isotopes between actual glaciations and interglacial during middle and late Pleistocene.
• It is compiled from analysis of oxygen isotopes in sediments on the seabed. These were known MIS means Marine Isotope Stages in Pleistocene.
• Oxygen has two naturally occurring isotopes, namely, O-16 and O-18.
• O-16 constitutes 99.762% and has 8 protons and 8 neutrons, in total 16. O-18 constitutes 0.2% and has 8 protons and 10 neutrons, a total of 18.
• When water evaporates, water molecules, which contain the light isotope, will evaporate faster than water molecules containing the heavy isotope.
• Building up glaciers on the continents requires evaporation of a lot of water from the sea, which then accumulates as ice on land.
• The ice will be enriched with the light isotope, while the remaining water will be enriched with the heavy isotope.
• The ratio O-18/O-16 in sea water must therefore have been higher in glaciations periods than in the interglacial.
• The Isotope ratio in organisms with shells (e.g. mussels) reflects the isotope ratio of the water at the time they lived. When they died, they sank to the bottom and became to sediments in the seabed.
• In cores from the seabed scientists can find the preserved shells, measure the isotopic ratio and thereby obtain an indication of the extent of ice on land, when the organisms lived.
• On geological congresses it has been agreed that the Pleistocene ice age ended about 11,711 years ago, and we have defined that present is a brand new period, called the Holocene.
• But, however, we can define and decide that the present Holocene warm period is an interglacial, of which there have already been many.
• With high probability the glaciers will return to the northern and southern parts of the world's continents, only we do not know when.