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CLIMATE CHANGE

CLIMATE CHANGE. THE GREAT DEBATE. Session 3. Advancing Franz Josef Glacier in 1996, New Zealand. QUATERNARY ICE AGE.

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CLIMATE CHANGE

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  1. CLIMATE CHANGE THE GREAT DEBATE Session 3

  2. Advancing Franz Josef Glacier in 1996, New Zealand

  3. QUATERNARY ICE AGE • The name is a misnomer because the beginning of the Quaternary at 2.5 Ma marks the onset of ice sheet accumulation in the Northern Hemisphere because by then Greenland and the continents had drifted far enough north to accumulate glacial ice • In Antarctica an ice sheet first accumulated much earlier at about 36 Ma. We do not know whether ice has been present in Antarctica continuously since that time

  4. TASMANIA AND ANTARCTICA • At 36 Ma Tasmania was still very close to Antarctica because the Australian continent had only just separated due to continental drift • A tillite was discovered in a borehole put down by the HEC near Lemonthyme Creek in the Forth River Valley. It was originally described as a Quaternary deposit in the 1960’s but later work has shown that it had to be very much older. It shows that there was glacial ice in Tasmania (Lemonthyme Glaciation) at a time when it was still close to the Antarctic continent

  5. Palaeographic reconstruction of relative positions of Australia and Antarctica at 36 Ma

  6. NORTHERN HEMISPHERE • In the early 20th Century four glacial advances were recognized north of the Alps by Penck and Bruckner: • They were: • Youngest: Würm Glaciation • Riss Glaciation • Mindel Glaciation • Oldest: Günz Glaciation • For half a century this remained the accepted version of major ice advances in the Quaternary but their exact age was unknown

  7. Polar view of northern continents showing maximum extent of glacial ice (after Bowen)

  8. TASMANIAN STORY From 1970 to 1990 Dr Eric Colhoun and a number of research students mapped the extent and nature of glacial landforms in Western Tasmania: They were: Youngest: Margaret Glaciation Henty Glaciation Moore Glaciation Oldest: Linda Glaciation The Margaret Glaciation was the least extensive and the Linda Glaciation the most extensive. The Linda Glaciation occurred more than 783 ka ago

  9. Map shows extent of various glacier advances during the Quaternary (after Kiernan)

  10. RELATIVE DATING • The ages of glacial deposits can rarely be determined directly by radiometric dating • Relative dating is a group of techniques that enables you to group your tills into a number of distinct age categories • Many Tasmanian tills contain pebbles or boulders of dolerite, a very common rock in the state • These pebbles form distinct weathering rinds as the dolerite weathers from the outside inwards due to groundwater percolating through the deposit

  11. Doleritepebbles with rinds between 25 and 35 mm thick typical of tills deposited during the Moore Glaciation

  12. Dolerite boulder with weathering rind more than 100 mm thick typical of deposits of the Linda Glaciation

  13. CLIMATE CHANGE DURING THEQUATERNARY ICE AGE -MILANKOVICH THEORY It is an astronomical theory that attempts to explain climate changes during the Ice Age in terms of variations in the way the Earth orbits around the Sun. It is also known as the Orbital Theory

  14. THEORY DEVELOPMENT Made possible because planetary movements had been closely studied In 1842 orbital theory was first proposed by French scientist Adhemar Further developed by Scottish mechanic James Croll in late 19th Century Final evolution of the theory by Serbian scientist Milankovich in first half of 20thth century

  15. EARTH ORBITAL VARIATIONS Eccentricity measures the extent to which the orbit departs from a perfect circle and has a cycle of approx. 100,000 years Tilt is the angle between the Earth's axis and its plane of rotation and varies from 21.8 to 24.4 degrees. Cycle is approx. 40,000 years Precession refers to the changing time of year when the Earth is closest to the Sun. Today perihelion is in early January. Its cycle is approx. 20,000 years

  16. Eccentricity - a 100,000 year cycle Eccentricity Precession - a 20,000 year cycle Tilt (Obliquity) - a 40,000 year cycle (Precession) (Obliquity)

  17. MILANKOVICH CALCULATIONS • He made all his calculations by hand, a very laborious task because there were no computers in those days • As can be seen in the last diagram, he tried to correlate his data with the four glacial advances that had been documented in both Europe and North America, but the result is not very convincing • At that time there was no continuous geological record of the Quaternary and there was no way of dating Quaternary sediments

  18. When Milankovich died in 1958 there was no convincing evidence to support the orbital theory of climate change Information about Quaternary climate change has since come from deep sea cores, lake cores, ice cores, stalagmites from caves and other sources and methods have been developed to date them. It has confirmed that Milankovich was essentially correct EVIDENCE IN SUPPORT OFMILANKOVICH THEORY

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