Environment of Earth

November 12, 2010

LAST ICE AGE

Filed under: Environment,Palaeoenvironment — gargpk @ 8:42 am
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Louis Aggasiz was one of the first scientists to study the clues of the ice age. An erratic is a large boulder, and when Aggasiz told some scientists that the boulders had been left there by a glacier they thought that he was out of his mind. The reason Louis Aggasiz proved that they had been put there by glaciers is because they were made of a kind of rock that you can’t find naturally in that area – granite. Because of that he proved that they can’t be from there, they were from somewhere else. Other proof that the ice age really existed is: polished bedrock, sand and gravel piles, big valleys, and rough mountain tops.

About 1/3 of the earth was ice. The most recent ice age was almost 10,000 years ago. As the earth started warming up the ice started to melt. The last ice age left traces that it was there. It left GLACIERS!!! Sheets of ice covered valleys and rivers. Ice spread to different parts of the world. Scientists called it the ice age. It kept melting, then froze again. This went on for about a million years. About 10,000 years ago the earth started to warm up. Sheets of ice started to melt. As the ice melted it left lakes and broad valleys with a mixture of rocks and soil. The only ice left was up high in the mountains. The glaciers that you see now are what is left over from the ice age.

The Geography of the Last Glacial Period

At the time of the LGM (map of glaciation), approximately 10 million square miles (~ 26 million square kilometers) of the earth was covered by ice. During this time, Iceland was completely covered as was much of the area south of it as far as the British Isles. In addition, northern Europe was covered as far south as Germany and Poland. In North America, all of Canada and portions of the United States were covered by ice sheets as far south as the Missouri and Ohio Rivers.

The Southern Hemisphere experienced the glaciation with the Patagonian Ice Sheet that covered Chile and much of Argentina and Africa and portions of the Middle East and Southeast Asia experienced significant mountain glaciation.

During the ice age countries like the Britain, France, Spain and Germany were very cold. At the northern and southern part of the earth the sheets of ice were much colder than they are today. Nobody knows why the ice age started, or why it stopped after 25,000 years. All we know is that it came and went very slowly.

Glacial Climate and Sea Level

The North American and European ice sheets of the last glaciation began forming after a prolonged cold stage with increased precipitation (mostly snow in this case) took place. Once the ice sheets began forming, the cold landscape altered typical weather patterns by creating their own air masses. The new weather patterns that developed reinforced the initial weather that created them, plunging the various areas into a cold glacial period.

The warmer portions of the globe also experienced a change in climate due to glaciation in that most of them became cooler but drier. For example rainforest cover in West Africa was reduced and replaced by tropical grasslands because of a lack of rain.

At the same time, most of the world’s deserts expanded as they became drier. The American Southwest, Afghanistan, and Iran are exceptions to this rule however as they became wetter once a shift in their air flow patterns took place.

Finally, as the last glacial period progressed leading up to the LGM, sea levels worldwide dropped as water became stored in the ice sheets covering the world’s continents. Sea levels went down about 164 feet (50 meters) in 1,000 years. These levels then stayed relatively constant until the ice sheets began to melt toward the end of the glacial period.

Flora and Fauna

During the last glaciation, shifts in climate altered the world’s vegetation patterns from what they had been prior to the formation of the ice sheets. However, the types of vegetation present during the glaciation are similar to those found today. Many such trees, mosses, flowering plants, insects, birds, shelled mollusks, and mammals are examples.

Because of all the ice the land was shaped much, much differently. The land looked bare because it was too cold for beech and oak trees to grow. There would be an few fir trees here and there. No grass grew, just shrubs, bushes, and moss grass. In the northern parts of North America, Europe, and Asia there is still tundra.

The animals were different from today too. Back then there were woolly mammoth, woolly rhinos, cave bears, bison, wolves, horses, and herds of reindeer like modern day reindeer. Woolly mammoth, cave bear, and woolly rhino are now extinct.

Some mammals also went extinct around the world during this time but it is clear that they did live during the last glacial period. Mammoths, mastodons, long-horned bisons, saber toothed cats, and giant ground sloths are among these.

Forest contraction in north equatorial Southeast Asia during the

by CM Wurster – 2010 – Cited by 1Related articles
31 Aug 2010 Forest contraction in north equatorial Southeast Asia during the Last Glacial Period. Christopher M. Wurstera,1,2,; Michael I. Birdb,
http://www.pnas.org/content/107/35/15508

People During the Ice Age

Human history also began in the Pleistocene and we were heavily impacted by the last glaciation. Most importantly, the drop in sea level aided in our movement from Asia into North America as the landmass connecting the two areas in the Alaska’s Bering Straight (Beringia) surfaced to act as a bridge between the areas.

During the ice age the men would set a trap for their food. When an animal fell for the trap the men would go kill it. Then the men would work on cutting the mammoth into big chunks, and then carried the chunks of meat to their cave. There the women and children would cut the mammoth meat into pieces that they were able to cook. The ice age people lived 35,000 years ago.

The ice age with glaciation came and very slowly in comparison to the span of human life. Therefore, the people that lived at the time didn’t realize that it was getting colder and colder, nor did they know that they were becoming the ice age hunters. Most of the ice age hunters lived in the western, central part of Europe.

The ice age people painted pictures of various animals e.g. woolly mammoth, woolly rhinos, bison etc.  on the sides of their caves, and the skeletons of the animals have been found in caves.There are cuts from the hunters’ knives in the bones and the knives were sitting beside them.

Today’s Remnants of the Last Glaciation

Though the last glaciation ended about 12,500 years ago, remnants of this climatic episode are common around the world today. For example, increased precipitation in North America’s Great Basin area created enormous lakes (map of lakes) in a normally dry area. Lake Bonneville was one and once covered most of what is today Utah. Great Salt Lake is today’s largest remaining portion of Lake Bonneville but the old shorelines of the lake can be seen on the mountains around Salt Lake City.

Various landforms also exist around the world because of the enormous power of moving glaciers and ice sheets. In Canada’s Manitoba for instance, numerous small lakes dot the landscape. These were formed as the moving ice sheet gouged out the land beneath it. Over time, the depressions formed filled with water creating “kettle lakes.”

Finally, the many glaciers still present around the world today are some of the most famous remnants of the last glaciation. Most ice today is located in Antarctica and Greenland but some is also found in Canada, Alaska, California, Asia, and New Zealand. Most impressively though are the glaciers still found in the equatorial regions like South America’s Andes Mountains and Mount Kilimanjaro in Africa.

Most of the world’s glaciers are famous today however for their significant retreats in recent years. Such a retreat represents a new shift in the earth’s climate- something that has happened time and time again over the earth’s 4.6 billion year history and will no doubt continue to do in the future.

Just The Facts

  • There were about 11 different ice ages.
  • The ice ages were during the earth’s 4.6 billion years of history.
  • The last ice age was called “The Great Ice Age” and was 11,000 years ago.
  • During the “Great Ice Age” over a third of the earth was covered in ice. During the ice age the air had less carbon dioxide in it.
  • Right now we are living in a mini ice age.
  • There are two explanations of why the ice ages might have occurred: 1.The temperatures were much colder so it never rained, only snowed. 2. The earth changed its tilt away from the sun

Timeline of glaciation

From Wikipedia, the free encyclopedia

There have been five known ice ages in the Earth’s history, with the Earth experiencing the Quaternary Ice Age during the present time. Within ice ages, there exist periods of more severe glacial conditions and more temperate referred to as glacial periods and interglacial periods, respectively. The Earth is currently in an interglacial period of the Quaternary Ice Age, with the last glacial period of the Quaternary having ended approximately 10,000 years ago with the start of the holocene.

Known ice ages

500 million year record shows current and previous two major glacial periods

Name Period (Ma) Period Era
Quaternary 2.58 – Present Neogene Cenozoic
Karoo 360 – 260 Carboniferous and Permian Paleozoic
Andean-Saharan 450 – 420 Ordovician and Silurian Paleozoic
Cryogenian
(or Sturtian-Varangian)
800 – 635 Cryogenian Neoproterozoic
Huronian 2400 – 2100 Siderian and Rhyacian Paleoproterozoic

Descriptions

The second ice age, and possibly most severe, is estimated to have occurred from 850 to 635 Ma (million years) ago, in the late Proterozoic Age and it has been suggested that it produced a second[1]Snowball Earth” in which the earth iced over completely. It has been suggested also that the end of this second cold period[1] was responsible for the subsequent Cambrian Explosion, a time of rapid diversification of multicelled life during the Cambrian era. However, this hypothesis is still controversial[2][3], though is growing in popularity among researchers as evidence in its favor has mounted.

A minor series of glaciations occurred from 460 Ma to 430 Ma. There were extensive glaciations from 350 to 250 Ma. The current ice age, called the Quaternary glaciation, has seen more or less extensive glaciation on 40,000 and later, 100,000 year cycles.

Quaternary glacial cycles

Glacial and interglacial cycles as represented by atmospheric CO2, measured from ice core samples going back 650,000 years

Originally, the glacial and interglacial periods of the Quaternary Ice Age were named after characteristic geological features, and these names varied from region to region. It is now more common to refer to the periods by their marine isotopic stage number.[4] The marine record preserves all the past glaciations; the land-based evidence is less complete because successive glaciations may wipe out evidence of their predecessors. Ice cores from continental ice accumulations also provide a complete record, but do not go as far back in time as marine data. Pollen data from lakes and bogs as well as loess profiles provided important land-based correlation data.[5] The names system has not been completely filled out since the technical discussion moved to using marine isotopic stage numbers. For example, there are five Pleistocene glacial/interglacial cycles recorded in marine sediments during the last half million years, but only three classic interglacials were originally recognized on land during that period (Mindel, Riss and Würm).[6]

Land-based evidence works acceptably well back as far as MIS 6, but it has been difficult to coordinate stages using just land-based evidence before that. Hence, the “names” system is incomplete and the land-based identifications of ice ages previous to that are somewhat conjectural. Nonetheless, land based data is essentially useful in discussing landforms, and correlating the known marine isotopic stage with them.[5]

The last glacial and interglacial periods of the Quaternary are named, from most recent to most distant, as follows. Dates shown are in thousand years before present.

Land-based chronology of Quaternary glacial cycles

This section’s factual accuracy is disputed. Please see the relevant discussion on the talk page. (May 2008)
Backwards
Glacial
Index
Names Inter/Glacial Period (ka) MIS Epoch
Alpine N. American N. European Great Britain S. American
Flandrian interglacial present – 12 1 Holocene
1st Würm Wisconsin Weichselian
or Vistulian
Devensian Llanquihue glacial period 12 – 110 2-4
& 5a-d
Pleistocene
Riss-Würm Sangamonian Eemian Ipswichian Valdivia interglacial 110 – 130 5e (7, 9?)
2nd Riss Illinoian Saalian Wolstonian or Gipping Santa María glacial period 130 – 200 6
Mindel-Riss Yarmouth Holstein Hoxnian interglacial(s) 200 – 300/380 11[verification needed]
3rd – 5th Mindel Kansan Elsterian Anglian Río Llico glacial period(s) 300/380 – 455 12[verification needed]
Günz-Mindel Aftonian Cromerian* interglacial(s) 455 – 620 13-15
7th Günz Nebraskan Menapian Beestonian Caracol glacial period 620 – 680 16

Older periods of the Quaternary

Name Inter/Glacial Period (ka) MIS Epoch
Pastonian Stage interglacial 600 – 800
Pre-Pastonian Stage glacial period 800 – 1300
Bramertonian Stage interglacial 1300 – 1550

**Table data is based on Gibbard Figure 22.1.[4]

Ice core evidence of recent glaciation

Main article: Ice core

Ice cores are used to obtain a high resolution record of recent glaciation. It confirms the chronology of the marine isotopic stages. Ice core data shows that the last 400,000 years have consisted of short interglacials (10,000 to 30,000 years) about as warm as the present alternated with much longer (70,000 to 90,000 years) glacials substantially colder than present. The new EPICA Antarctic ice core has revealed that between 400,000 and 780,000 years ago, interglacials occupied a considerably larger proportion of each glacial/interglacial cycle, but were not as warm as subsequent interglacials.

References

1.        ^ a b Miracle Planet: Snowball Earth, (2005) documentary, Canadian Film Board, rebroadcast 25 April 2009 on the Science Channel (HD)

2.        ^ van Andel, Tjeerd H. (1994) New Views on an Old Planet: A History of Global Change 2nd ed. Cambridge University Press, Cambridge, UK, ISBN 0521447550

3.        ^ Rieu, Ruben et al. (2007) “Climatic cycles during a Neoproterozoic “snowball” glacial epoch” Geology 35(4): pp. 299–302

4.        ^ a b Gibbard, P. and van Kolfschoten, T. (2004) “The Pleistocene and Holocene Epochs” Chapter 22 In Gradstein, F. M., Ogg, James G., and Smith, A. Gilbert (eds.), A Geologic Time Scale 2004 Cambridge University Press, Cambridge, ISBN 0521781426

5.        ^ a b Davis, Owen K. “Non-Marine Records: Correlatiuons withe the Marine Sequence” Introduction to Quaternary Ecology University of Arizona

6.        ^ Kukla, George (2005) “Saalian supercycle, Mindel/Riss interglacial and Milankovitch’s dating” Quaternary Science Reviews 24(14/15): pp. 1573-1583

Origin and definition of last glacial period

The last glacial period is sometimes colloquially referred to as the “last ice age”, though this use is incorrect because an ice age is a longer period of cold temperature in which ice sheets cover large parts of the Earth, such as Antarctica. Glacials, on the other hand, refer to colder phases within an ice age that separate interglacials. Thus, the end of the last glacial period is not the end of the last ice age. The end of the last glacial period was about 12,500 years ago, while the end of the last ice age may not yet have come: little evidence points to a stop of the glacial-interglacial cycle of the last million years.

The last glacial period is the best-known part of the current ice age, and has been intensively studied in North America, northern Eurasia, the Himalaya and other formerly glaciated regions around the world. The glaciations that occurred during this glacial period covered many areas, mainly on the Northern Hemisphere and to a lesser extent on the Southern Hemisphere. They have different names, historically developed and depending on their geographic distributions: Fraser (in the Pacific Cordillera of North America), Pinedale, Wisconsinan or Wisconsin (in central North America), Devensian (in the British Isles), Midlandian (in Ireland), Würm (in the Alps), Mérida (in Venezuela), Weichselian (in Scandinavia and Northern Europe), Vistulian (in northern Central Europe), Valdai in Eastern Europe and Zyryanka in Siberia, Llanquihue in Chile, and Otira in New Zealand.

Vegetation types at time of last glacial maximum.

The last glaciation centered on the huge ice sheets of North America and Eurasia. Considerable areas in the Alps, the Himalaya and the Andes were ice-covered, and Antarctica remained glaciated.

Canada was nearly completely covered by ice, as well as the northern part of the USA, both blanketed by the huge Laurentide ice sheet. Alaska remained mostly ice free due to arid climate conditions. Local glaciations existed in the Rocky Mountains and the Cordilleran ice sheet and as ice fields and ice caps in the Sierra Nevada in northern California.[2] In Britain, mainland Europe, and northwestern Asia, the Scandinavian ice sheet once again reached the northern parts of the British Isles, Germany, Poland, and Russia, extending as far east as the Taimyr Peninsula in western Siberia.[3] Maximum extent of western Siberian glaciation was approximately 18,000 to 17,000 BP and thus later than in Europe (22,000–18,000 BP).[4] Northeastern Siberia was not covered by a continental-scale ice sheet.[5] Instead, large, but restricted, icefield complexes covered mountain ranges within northeast Siberia, including the Kamchatka-Koryak Mountains.[6]

The Arctic Ocean between the huge ice sheets of America and Eurasia was not frozen throughout, but like today probably was only covered by relatively shallow ice, subject to seasonal changes and riddled with icebergs calving from the surrounding ice sheets. According to the sediment composition retrieved from deep-sea cores there must even have been times of seasonally open waters.[7]

Outside the main ice sheets, widespread glaciation occurred on the AlpsHimalaya mountain chain. In contrast to the earlier glacial stages, the Würm glaciation was composed of smaller ice caps and mostly confined to valley glaciers, sending glacial lobes into the Alpine foreland. To the east the Caucasus and the mountains of Turkey and Iran were capped by local ice fields or small ice sheets.[8],[9] In the Himalaya and the Tibetan Plateau, glaciers advanced considerably, particularly between 47,000–27,000 BP[10] and in contrast to the widespread contemporaneous warming elsewhere.[11] The formation of a contiguous ice sheet on the Tibetan Plateau is controversial.[12][13][14]

Other areas of the Northern Hemisphere did not bear extensive ice sheets but local glaciers in high areas. Parts of Taiwan for example were repeatedly glaciated between 44,250 and 10,680 BP[15] as well as the Japanese Alps. In both areas maximum glacier advance occurred between 60,000 and 30,000 BP[16] (starting roughly during the Toba catastrophe). To a still lesser extent glaciers existed in Africa, for example in the High Atlas, the mountains of Morocco, the Mount Atakor massif in southern Algeria, and several mountains in Ethiopia. In the Southern Hemisphere, an ice cap of several hundred square kilometers was present on the east African mountains in the Kilimanjaro Massif, Mount Kenya and the Ruwenzori Mountains, still bearing remnants of glaciers today.[17]

Glaciation of the Southern Hemisphere was less extensive because of current configuration of continents. Ice sheets existed in the Andes (Patagonian Ice Sheet), where six glacier advances between 33,500 and 13,900 BP in the Chilean Andes have been reported.[18] Antarctica was entirely glaciated, much like today, but the ice sheet left no uncovered area. In mainland Australia only a very small area in the vicinity of Mount Kosciuszko was glaciated, whereas in Tasmania glaciation was more widespread.[19] An ice sheet formed in New Zealand, covering all of the Southern Alps, where at least three glacial advances can be distinguished.[20] Local ice caps existed in Irian Jaya, Indonesia, where in three ice areas remnants of the Pleistocene glaciers are still preserved today.[21]

Named local glaciations

A. Pinedale or Fraser glaciation, in the Rocky Mountains, USA

The Pinedale (central Rocky Mountains) or Fraser (Cordilleran ice sheet) glaciation was the last of the major glaciations to appear in the Rocky Mountains in the United States. The Pinedale lasted from approximately 30,000 to 10,000 years ago and was at its greatest extent between 23,500 and 21,000 years ago.[22] This glaciation was somewhat distinct from the main Wisconsin glaciation as it was only loosely related to the giant ice sheets and was instead composed of mountain glaciers, merging into the Cordilleran Ice Sheet.[23] The Cordilleran ice sheet produced features such as glacial Lake Missoula, which would break free from its ice dam causing the massive Missoula floods. Geologists estimate that the cycle of flooding and reformation of the lake lasted on average of 55 years and that the floods occurred approximately 40 times over the 2,000 year period between 15,000 and 13,000 years ago.[24] Glacial lake outburst floods such as these are not uncommon today in Iceland and other places.

B. Wisconsin glaciation, in North America

The Wisconsin Glacial Episode was the last major advance of continental glaciers in the North American Laurentide ice sheet. This glaciation is made of three glacial maxima separated by interglacial warm periods (such as the one we are living in). These glacial maxima are called, from oldest to newest, Tahoe, Tenaya, and Tioga. The Tahoe reached its maximum extent perhaps about 70,000 years ago, perhaps as a byproduct of the Toba super eruption. Little is known about the Tenaya. The Tioga was the least severe and last of the Wisconsin Episode. It began about 30,000 years ago, reached its greatest advance 21,000 years ago, and ended about 10,000 years ago. At the height of glaciation the Bering land bridge permitted migration of mammals such as humans to North America from Siberia.

It radically altered the geography of North America north of the Ohio River. At the height of the Wisconsin Episode glaciation, ice covered most of Canada, the Upper Midwest, and New England, as well as parts of Montana and Washington. On Kelleys Island in Lake Erie or in New York’s Central Park, the grooves left by these glaciers can be easily observed. In southwestern Saskatchewan and southeastern Alberta a suture zone between the Laurentide and Cordilleran ice sheets formed the Cypress Hills, which is the northernmost point in North America that remained south of the continental ice sheets.

The Great Lakes are the result of glacial scour and pooling of meltwater at the rim of the receding ice. When the enormous mass of the continental ice sheet retreated, the Great Lakes began gradually moving south due to isostatic rebound of the north shore. Niagara Falls is also a product of the glaciation, as is the course of the Ohio River, which largely supplanted the prior Teays River.

With the assistance of several very broad glacial lakes, it carved the gorge now known as the Upper Mississippi River, filling into the Driftless Area and probably creating an annual ice-dam-burst.

In its retreat, the Wisconsin Episode glaciation left terminal moraines that form Long Island, Block Island, Cape Cod, Nomans Land, Marthas Vineyard, Nantucket, Sable Island and the Oak Ridges Moraine in south central Ontario, Canada. In Wisconsin itself, it left the Kettle Moraine. The drumlins and eskers formed at its melting edge are landmarks of the Lower Connecticut River Valley.

C.  Greenland glaciation

In Northwest Greenland, ice coverage attained a very early maximum in the last glacial period around 114,000. After this early maximum, the ice coverage was similar to today until the end of the last glacial period. Towards the end glaciers readvanced once more before retreating to their present extent.[25] According to ice core data, the Greenland climate was dry during the last glacial period, precipitation reaching perhaps only 20% of today’s value.[26]

D. Devensian & Midlandian glaciation, in Britain and Ireland

The name Devensian glaciation is used by British geologists and archaeologists and refers to what is often popularly meant by the latest Ice Age. Irish geologists, geographers, and archaeologists refer to the Midlandian glaciation as its effects in Ireland are largely visible in the Irish Midlands.

The effects of this glaciation can be seen in many geological features of England, Wales, Scotland, and Northern Ireland. Its deposits have been found overlying material from the preceding Ipswichian Stage and lying beneath those from the following Flandrian stage of the Holocene.

The latter part of the Devensian includes Pollen zones I-IV, the Allerød and Bølling Oscillations, and the Older and Younger Dryas climatic stages.

E.  Weichselian glaciation, in Scandinavia and northern Europe

Alternative names include: Weichsel or Vistulian glaciation (named after the Polish river Vistula or its German name Weichsel). During the glacial maximum in Scandinavia, only the western parts of Jutland were ice-free, and a large part of what is today the North Sea was dry land connecting Jutland with Britain. It is also in Denmark that the only Scandinavian ice-age animals older than 13,000 BC are found.[citation needed] In the period following the last interglacial before the current one (Eemian Stage), the coast of Norway was also ice-free.[citation needed]

The Baltic Sea, with its unique brackish water, is a result of meltwater from the Weichsel glaciation combining with saltwater from the North Sea when the straits between Sweden and Denmark opened. Initially, when the ice began melting about 10,300 ybp, seawater filled the isostatically depressed area, a temporary marine incursion that geologists dub the Yoldia Sea. Then, as post-glacial isostatic rebound lifted the region about 9500 ybp, the deepest basin of the Baltic became a freshwater lake, in palaeological contexts referred to as Ancylus Lake, which is identifiable in the freshwater fauna found in sediment cores. The lake was filled by glacial runoff, but as worldwide sea level continued rising, saltwater again breached the sill about 8000 ybp, forming a marine Littorina Sea which was followed by another freshwater phase before the present brackish marine system was established. “At its present state of development, the marine life of the Baltic Sea is less than about 4000 years old,” Drs. Thulin and Andrushaitis remarked when reviewing these sequences in 2003.

Overlying ice had exerted pressure on the Earth’s surface. As a result of melting ice, the land has continued to rise yearly in Scandinavia, mostly in northern Sweden and Finland where the land is rising at a rate of as much as 8–9 mm per year, or 1 meter in 100 years. This is important for archaeologists since a site that was coastal in the Nordic Stone Age now is inland and can be dated by its relative distance from the present shore.

F.  Würm glaciation, in the Alps

The term Würm is derived from a river in the Alpine foreland, approximately marking the maximum glacier advance of this particular glacial period. The Alps have been the area where first systematic scientific research on ice ages has been conducted by Louis Agassiz in the beginning of the 19th century. Here the Würm glaciation of the last glacial period was intensively studied. Pollen analysis, the statistical analyses of microfossilized plant pollens found in geological deposits, has chronicled the dramatic changes in the European environment during the Würm glaciation. During the height of Würm glaciation, ca 24,000–10,000 ybp, most of western and central Europe and Eurasia was open steppe-tundra, while the Alps presented solid ice fields and montane glaciers. Scandinavia and much of Britain were under ice.

During the Würm, the Rhône Glacier covered the whole western Swiss plateau, reaching today’s regions of Solothurn and Aarau. In the region of Bern it merged with the Aar glacier. The Rhine Glacier is currently the subject of the most detailed studies. Glaciers of the Reuss and the Limmat advanced sometimes as far as the Jura. Montane and piedmont glaciers formed the land by grinding away virtually all traces of the older Günz and Mindel glaciation, by depositing base moraines and terminal moraines of different retraction phases and loess deposits, and by the pro-glacial rivers’ shifting and redepositing gravels. Beneath the surface, they had profound and lasting influence on geothermal heat and the patterns of deep groundwater flow.

G.  Merida glaciation, in the Venezuelan Andes

The name Mérida Glaciation is proposed to designate the alpine glaciation which affected the central Venezuelan Andes; during the Late Pleistocene. Two main moraine levels have been recognized: one between 2600 and 2700 m, and another between 3000 and 3500 m elevation. The snow line during the last glacial advance was lowered approximately 1200 m below the present snow line (3700 m). The glaciated area in the Cordillera de Mérida was approximately 600 km2; this included the following high areas from southwest to northeast: Páramo de Tamá, Páramo Batallón, Páramo Los Conejos, Páramo Piedras Blancas, and Teta de Niquitao. Approximately 200 km2 of the total glaciated area was in the Sierra Nevada de Mérida, and of that amount, the largest concentration, 50 km2, was in the areas of Pico Bolívar, Pico Humboldt (4,942 m), and Pico Bonpland (4,893 m). Radiocarbon dating indicates that the moraines are older than 10,000 years B.P., and probably older than 13,000 years B.P. The lower moraine level probably corresponds to the main Wisconsin glacial advance. The upper level probably represents the last glacial advance (Late Wisconsin).[27][28][29][30]

H.  Llanquihue glaciation, southern Andes

The Llanquihue glaciation takes its name from Llanquihue Lake in southern Chile which is a fan-shaped piedmont glacial lake. On the lake’s western shores there are large moraine systems of which the innermost belong to the last glacial period. Llanquihue Lake’s varves are a node point in southern Chile’s varve geochronology. During the last glacial maximum the Patagonian Ice Sheet extended over the Andes from about 35°S to Tierra del Fuego at 55°S. The western part appears to have been very active, with wet basal conditions, while the eastern part was cold based. Palsas seems to have developed at least in the unglaciated parts of Isla Grande de Tierra del Fuego. The area west of Llanquihue Lake was ice-free during the LGM, and had sparsely distributed vegetation dominated by Nothofagus. Valdivian temperate rainforest was reduced to scattered remnants in the western side of the Andes.[31]

Lake Pippa was also affected by the Pleistocene, a glacier ripped through the center of it causing a very deep lake in the south atlantic.

I.  Antarctica glaciation

During the last glacial period Antarctica was blanketed by a massive ice sheet, much like it is today. The ice covered all land areas and extended into the ocean onto the middle and outer continental shelf.[32][33] According to ice modelling, ice over central East Antarctica was generally thinner than today.[34]

References

1.        ^ Glaciation of Wisconsin, Lee Clayton, John W. Attig, David M. Mickelson, Mark D. Johnson, and Kent M. Syverson, University of Wisconsin, Dept. of Geology

2.        ^ Clark, D.H.: Extent, timing, and climatic significance of latest Pleistocene and Holocene glaciation in the Sierra Nevada, California. Ph.D. Thesis, Washington Univ., Seattle (pdf, 20 Mb)

3.        ^ Möller, P. et al.: Severnaya Zemlya, Arctic Russia: a nucleation area for Kara Sea ice sheets during the Middle to Late Quaternary. Quaternary Science Reviews Vol. 25, No. 21–22, pp. 2894–2936, 2006. (pdf, 11.5 Mb)

4.        ^ Matti Saarnisto: Climate variability during the last interglacial-glacial cycle in NW Eurasia. Abstracts of PAGES – PEPIII: Past Climate Variability Through Europe and Africa, 2001

5.        ^ Lyn Gualtieri et al.: Pleistocene raised marine deposits on Wrangel Island, northeast Siberia and implications for the presence of an East Siberian ice sheet. Quaternary Research, Vol. 59, No. 3, pp. 399–410, May 2003. Abstract: doi:10.1016/S0033-5894(03)00057-7

6.        ^ Zamoruyev, V., 2004. Quaternary glaciation of north-east Asia. In: Ehlers, J., Gibbard, P.L. (Eds.), Quaternary Glaciations: Extent and Chronology: Part III: South America, Asia, Africa, Australia, Antarctica. Elsevier, Netherlands, pp. 321–323.

7.        ^ Robert F. Spielhagen et al.: Arctic Ocean deep-sea record of northern Eurasian ice sheet history. Quaternary Science Reviews, Vol. 23, No. 11-13, pp. 1455–1483, 2004. Abstract: doi:10.1016/j.quascirev.2003.12.015

8.        ^ Richard S. Williams, Jr., Jane G. Ferrigno: Glaciers of the Middle East and Africa – Glaciers of Turkey. U.S.Geological Survey Professional Paper 1386-G-1, 1991 (pdf, 2.5 Mb)

9.        ^ Jane G. Ferrigno: Glaciers of the Middle East and Africa – Glaciers of Iran. U.S.Geological Survey Professional Paper 1386-G-2, 1991 (pdf, 1.25 Mb)

10.     ^ Lewis A. Owen et al.: A note on the extent of glaciation throughout the Himalaya during the global Last Glacial Maximum, Quaternary Science Reviews, V. 21, No. 1, 2002, pp. 147–157. Abstract: doi:10.1016/S0277-3791(01)00104-4

11.     ^ Quaternary stratigraphy: The last glaciation (stage 4 to stage 2), University of Otago, New Zealand

12.     ^ Matthias Kuhle, 2002: A relief-specific model of the ice age on the basis of uplift-controlled glacier areas in Tibet and the corresponding albedo increase as well as their positiv climatological feedback by means of the global radiation geometry.- Climate Research 20: 1–7.

13.     ^ Matthias Kuhle, 2004: The High Glacial (Last Ice Age and LGM) ice cover in High and Central Asia. Development in Quaternary Science 2 (c, Quaternary Glaciation – Extent and Chronology, Part III: South America, Asia, Africa, Australia, Antarctica, Eds: Ehlers, J.; Gibbard, P.L.), 175–199. (Elsevier B.V., Amsterdam)..

14.     ^ Lehmkuhl, F.: Die eiszeitliche Vergletscherung Hochasiens – lokale Vergletscherungen oder übergeordneter Eisschild? Geographische Rundschau 55 (2):28–33, 2003. English abstract

15.     ^ Zhijiu Cui et al.: The Quaternary glaciation of Shesan Mountain in Taiwan and glacial classification in monsoon areas. Quaternary International, Vol. 97–98, pp. 147–153, 2002. Abstract: doi:10.1016/S1040-6182(02)00060-5

16.     ^ Yugo Ono et al.: Mountain glaciation in Japan and Taiwan at the global Last Glacial Maximum. Quaternary International, Vol. 138–139, pp. 79–92, September–October 2005. Abstract: doi:10.1016/j.quaint.2005.02.007

17.     ^ James A.T. Young, Stefan Hastenrath: Glaciers of the Middle East and Africa – Glaciers of Africa. U.S. Geological Survey Professional Paper 1386-G-3, 1991 (PDF, 1.25 Mb)

18.     ^ Lowell, T.V. et al.: Interhemisperic correlation of late Pleistocene glacial events, Science, v. 269,p. 1541-1549, 1995. Abstract (pdf, 2.3 Mb)

19.     ^ C.D. Ollier: Australian Landforms and their History, National Mapping Fab, Geoscience Australia

20.     ^ A mid Otira Glaciation palaeosol and flora from the Castle Hill Basin, Canterbury, New Zealand, New Zealand Journal of Botany. Vol. 34, pp. 539–545, 1996 (pdf, 340 Kb)

21.     ^ Ian Allison and James A. Peterson: Glaciers of Irian Jaya, Indonesia: Observation and Mapping of the Glaciers Shown on Landsat Images, U.S. Geological Survey professional paper; 1386, 1988. ISBN 0-607-71457-3

22.     ^ Brief geologic history, Rocky Mountain National Park

23.     ^ Ice Age Floods, From: U.S. National Park Service Website

24.     ^ Richard B. Waitt, Jr.: Case for periodic, colossal jökulhlaups from Pleistocene glacial Lake Missoula, Geological Society of America Bulletin, v.96, p.1271-1286, October 1985. Abstract

25.     ^ Svend Funder (ed.) Late Quaternary stratigraphy and glaciology in the Thule area, Northwest Greenland. MoG Geoscience, vol. 22, 63 pp., 1990. Abstract

26.     ^ Sigfus J. Johnsen et al.: A “deep” ice core from East Greenland. MoG Geoscience, vol. 29, 22 pp., 1992. Abstract

27.     ^ * Schubert, Carlos (1998) “Glaciers of Venezuela” United States Geological Survey (USGS P 1386-I)

28.     ^ Late Pleistocene glaciation of Páramo de La Culata, north-central Venezuelan Andes

29.     ^ Mahaney William C., Milner M. W., Kalm Volli, Dirsowzky Randy W., Hancock R. G. V., Beukens Roelf P.: Evidence for a Younger Dryas glacial advance in the Andes of northwestern Venezuela

30.     ^ Maximiliano B., Orlando G., Juan C., Ciro S.: Glacial Quaternary geology of las Gonzales basin, páramo los conejos, Venezuelan andes

31.     ^ http://www.esd.ornl.gov/projects/qen/nercSOUTHAMERICA.html South America during the last 150,000 years.

32.     ^ Anderson, J.B., S.S. Shipp, A.L. Lowe, J.S. Wellner, J.S., and A.B. Mosola, 2002, The Antarctic Ice Sheet during the Last Glacial Maximum and its subsequent retreat history: a review. Quaternary Science Reviews. vol. 21, pp. 49–70.

33.     ^ Ingolfsson, O., 2004, Quaternary glacial and climate history of Antarctica. in: J. Ehlers and P.L. Gibbard, eds., pp. 3–43, Quaternary Glaciations: Extent and Chronology 3: Part III: South America, Asia, Africa, Australia, Antarctica. Elsevier, New York.

34.     ^ P. Huybrechts: Sea-level changes at the LGM from ice-dynamic reconstructions of the Greenland and Antarctic ice sheets during the glacial cycles, Quaternary Science Reviews, V. 21, no. 1-3, pp. 203–231, 2002. Abstract: doi:10.1016/S0277-3791(01)00082-8

Further reading

  • Bowen, D.Q., 1978, Quaternary geology: a stratigraphic framework for multidisciplinary work. Pergamon Press, Oxford, United Kingdom. 221 pp. ISBN 978-0080204093
  • Ehlers, J., and P.L. Gibbard, 2004a, Quaternary Glaciations: Extent and Chronology 2: Part II North America. Elsevier, Amsterdam. ISBN 0-444-51462-7
  • Ehlers, J., and P L. Gibbard, 2004b, Quaternary Glaciations: Extent and Chronology 3: Part III: South America, Asia, Africa, Australia, Antarctica.ISBN 0-444-51593-3
  • Gillespie, A.R., S.C. Porter, and B.F. Atwater, 2004, The Quaternary Period in the United States. Developments in Quaternary Science no. 1. Elsevier, Amsterdam. ISBN 978-0-444-51471-4
  • Harris, A.G., E. Tuttle, S.D. Tuttle, 1997, Geology of National Parks: Fifth Edition. Kendall/Hunt Publishing, Iowa. ISBN 0-7872-5353-7
  • Matthias Kuhle, 1988: The Pleistocene Glaciation of Tibet and the Onset of Ice Ages- An Autocycle Hypothesis. In: GeoJournal 17 (4), Tibet and High-Asia I. 581–596.
  • Mangerud, J., J. Ehlers, and P. Gibbard, 2004, Quaternary Glaciations : Extent and Chronology 1: Part I Europe. Elsevier, Amsterdam. ISBN 0-444-51462-7
  • Sibrava, V., Bowen, D.Q, and Richmond, G.M., 1986, Quaternary Glaciations in the Northern Hemisphere, Quaternary Science Reviews. vol. 5, pp. 1–514.
  • Pielou, E.C., 1991. After the Ice Age : The Return of Life to Glaciated North America. University Of Chicago Press, Chicago, Illinois. ISBN 0-226-66812-6 (paperback 1992)

Ice Ages

About 1/3 of the earth was ice. The most recent ice age was almost 10,000 years ago. As the earth started warming up the ice started to melt. The last ice age left traces that it was there. It left GLACIERS!!! Sheets of ice covered valleys and rivers. Ice spread to different parts of the world. Scientists called it the ice age. It kept melting, then froze again. This went on for about a million years. About 10,000 years ago the earth started to warm up. Sheets of ice started to melt. As the ice melted it left lakes and broad valleys with a mixture of rocks and soil. The only ice left was up high in the mountains. The glaciers that you see now are what is left over from the ice age.

Louis Aggasiz was one of the first scientists to study the clues of the ice age. An erratic is a large boulder, and when Aggasiz told some scientists that the boulders had been left there by a glacier they thought that he was out of his mind. The reason Louis Aggasiz proved that they had been put there by glaciers is because they were made of a kind of rock that you can’t find naturally in that area – granite. Because of that he proved that they can’t be from there, they were from somewhere else. Other proof that the ice age really existed is: polished bedrock, sand and gravel piles, big valleys, and rough mountain tops.

The Geography of the Last Glacial Period

At the time of the LGM (map of glaciation), approximately 10 million square miles (~ 26 million square kilometers) of the earth was covered by ice. During this time, Iceland was completely covered as was much of the area south of it as far as the British Isles. In addition, northern Europe was covered as far south as Germany and Poland. In North America, all of Canada and portions of the United States were covered by ice sheets as far south as the Missouri and Ohio Rivers.

The Southern Hemisphere experienced the glaciation with the Patagonian Ice Sheet that covered Chile and much of Argentina and Africa and portions of the Middle East and Southeast Asia experienced significant mountain glaciation.

Glacial Climate and Sea Level

The North American and European ice sheets of the last glaciation began forming after a prolonged cold stage with increased precipitation (mostly snow in this case) took place. Once the ice sheets began forming, the cold landscape altered typical weather patterns by creating their own air masses. The new weather patterns that developed reinforced the initial weather that created them, plunging the various areas into a cold glacial period.

The warmer portions of the globe also experienced a change in climate due to glaciation in that most of them became cooler but drier. For example rainforest cover in West Africa was reduced and replaced by tropical grasslands because of a lack of rain.

At the same time, most of the world’s deserts expanded as they became drier. The American Southwest, Afghanistan, and Iran are exceptions to this rule however as they became wetter once a shift in their air flow patterns took place.

Finally, as the last glacial period progressed leading up to the LGM, sea levels worldwide dropped as water became stored in the ice sheets covering the world’s continents. Sea levels went down about 164 feet (50 meters) in 1,000 years. These levels then stayed relatively constant until the ice sheets began to melt toward the end of the glacial period.

Flora and Fauna

During the last glaciation, shifts in climate altered the world’s vegetation patterns from what they had been prior to the formation of the ice sheets. However, the types of vegetation present during the glaciation are similar to those found today. Many such trees, mosses, flowering plants, insects, birds, shelled mollusks, and mammals are examples.

Some mammals also went extinct around the world during this time but it is clear that they did live during the last glacial period. Mammoths, mastodons, long-horned bisons, saber toothed cats, and giant ground sloths are among these.

Human history also began in the Pleistocene and we were heavily impacted by the last glaciation. Most importantly, the drop in sea level aided in our movement from Asia into North America as the landmass connecting the two areas in the Alaska’s Bering Straight (Beringia) surfaced to act as a bridge between the areas.

People During the Ice Age

During the ice age the men would set a trap for their food. When an animal fell for the trap the men would go kill it. Then the men would work on cutting the mammoth into big chunks, and then carried the chunks of meat to their cave. There the women and children would cut the mammoth meat into pieces that they were able to cook. The ice age people lived 35,000 years ago.

During the ice age countries like the Britain, France, Spain and Germany were very cold. At the northern and southern part of the earth the sheets of ice were much colder than they are today. Nobody knows why the ice age started, or why it stopped after 25,000 years. All we know is that it came and went very slowly. So that is the reason why the people that lived at the time didn’t realize that it was getting colder and colder, nor did they know that they were becoming the ice age hunters. Most of the ice age hunters lived in the western, central part of Europe.

Because of all the ice the land was shaped much, much differently. The land looked bare because it was too cold for beech and oak trees to grow. There would be an few fir trees here and there. No grass grew, just shrubs, bushes, and moss grass. In the northern parts of North America, Europe, and Asia there is still tundra.

The animals were different from today too. Back then there were woolly mammoth, woolly rhinos, cave bears, bison, wolves, horses, and herds of reindeer like modern day reindeer. Woolly mammoth, cave bear, and woolly rhino are now extinct. How do we know that they existed? Well the ice age people painted pictures of these animals on the sides of their caves, and the skeletons of the animals have been found in caves.There are cuts from the hunters’ knives in the bones and the knives were sitting beside them.

Today’s Remnants of the Last Glaciation

Though the last glaciation ended about 12,500 years ago, remnants of this climatic episode are common around the world today. For example, increased precipitation in North America’s Great Basin area created enormous lakes (map of lakes) in a normally dry area. Lake Bonneville was one and once covered most of what is today Utah. Great Salt Lake is today’s largest remaining portion of Lake Bonneville but the old shorelines of the lake can be seen on the mountains around Salt Lake City.

Various landforms also exist around the world because of the enormous power of moving glaciers and ice sheets. In Canada’s Manitoba for instance, numerous small lakes dot the landscape. These were formed as the moving ice sheet gouged out the land beneath it. Over time, the depressions formed filled with water creating “kettle lakes.”

Finally, the many glaciers still present around the world today are some of the most famous remnants of the last glaciation. Most ice today is located in Antarctica and Greenland but some is also found in Canada, Alaska, California, Asia, and New Zealand. Most impressively though are the glaciers still found in the equatorial regions like South America’s Andes Mountains and Mount Kilimanjaro in Africa.

Most of the world’s glaciers are famous today however for their significant retreats in recent years. Such a retreat represents a new shift in the earth’s climate- something that has happened time and time again over the earth’s 4.6 billion year history and will no doubt continue to do in the future.

Just The Facts

  • There were about 11 different ice ages.
  • The ice ages were during the earth’s 4.6 billion years of history.
  • The last ice age was called “The Great Ice Age” and was 11,000 years ago.
  • During the “Great Ice Age” over a third of the earth was covered in ice. During the ice age the air had less carbon dioxide in it.
  • Right now we are living in a mini ice age.
  • There are two explanations of why the ice ages might have occurred: 1.The temperatures were much colder so it never rained, only snowed. 2. The earth changed its tilt away from the sun

Timeline of glaciation

From Wikipedia, the free encyclopedia

There have been five known ice ages in the Earth’s history, with the Earth experiencing the Quaternary Ice Age during the present time. Within ice ages, there exist periods of more severe glacial conditions and more temperate referred to as glacial periods and interglacial periods, respectively. The Earth is currently in an interglacial period of the Quaternary Ice Age, with the last glacial period of the Quaternary having ended approximately 10,000 years ago with the start of the holocene.

Known ice ages

500 million year record shows current and previous two major glacial periods

Name Period (Ma) Period Era
Quaternary 2.58 – Present Neogene Cenozoic
Karoo 360 – 260 Carboniferous and Permian Paleozoic
Andean-Saharan 450 – 420 Ordovician and Silurian Paleozoic
Cryogenian
(or Sturtian-Varangian)
800 – 635 Cryogenian Neoproterozoic
Huronian 2400 – 2100 Siderian and Rhyacian Paleoproterozoic

Descriptions

The second ice age, and possibly most severe, is estimated to have occurred from 850 to 635 Ma (million years) ago, in the late Proterozoic Age and it has been suggested that it produced a second[1]Snowball Earth” in which the earth iced over completely. It has been suggested also that the end of this second cold period[1] was responsible for the subsequent Cambrian Explosion, a time of rapid diversification of multicelled life during the Cambrian era. However, this hypothesis is still controversial[2][3], though is growing in popularity among researchers as evidence in its favor has mounted.

A minor series of glaciations occurred from 460 Ma to 430 Ma. There were extensive glaciations from 350 to 250 Ma. The current ice age, called the Quaternary glaciation, has seen more or less extensive glaciation on 40,000 and later, 100,000 year cycles.

Quaternary glacial cycles

Glacial and interglacial cycles as represented by atmospheric CO2, measured from ice core samples going back 650,000 years

Originally, the glacial and interglacial periods of the Quaternary Ice Age were named after characteristic geological features, and these names varied from region to region. It is now more common to refer to the periods by their marine isotopic stage number.[4] The marine record preserves all the past glaciations; the land-based evidence is less complete because successive glaciations may wipe out evidence of their predecessors. Ice cores from continental ice accumulations also provide a complete record, but do not go as far back in time as marine data. Pollen data from lakes and bogs as well as loess profiles provided important land-based correlation data.[5] The names system has not been completely filled out since the technical discussion moved to using marine isotopic stage numbers. For example, there are five Pleistocene glacial/interglacial cycles recorded in marine sediments during the last half million years, but only three classic interglacials were originally recognized on land during that period (Mindel, Riss and Würm).[6]

Land-based evidence works acceptably well back as far as MIS 6, but it has been difficult to coordinate stages using just land-based evidence before that. Hence, the “names” system is incomplete and the land-based identifications of ice ages previous to that are somewhat conjectural. Nonetheless, land based data is essentially useful in discussing landforms, and correlating the known marine isotopic stage with them.[5]

The last glacial and interglacial periods of the Quaternary are named, from most recent to most distant, as follows. Dates shown are in thousand years before present.

Land-based chronology of Quaternary glacial cycles

This section’s factual accuracy is disputed. Please see the relevant discussion on the talk page. (May 2008)
Backwards
Glacial
Index
Names Inter/Glacial Period (ka) MIS Epoch
Alpine N. American N. European Great Britain S. American
Flandrian interglacial present – 12 1 Holocene
1st Würm Wisconsin Weichselian
or Vistulian
Devensian Llanquihue glacial period 12 – 110 2-4
& 5a-d
Pleistocene
Riss-Würm Sangamonian Eemian Ipswichian Valdivia interglacial 110 – 130 5e (7, 9?)
2nd Riss Illinoian Saalian Wolstonian or Gipping Santa María glacial period 130 – 200 6
Mindel-Riss Yarmouth Holstein Hoxnian interglacial(s) 200 – 300/380 11[verification needed]
3rd – 5th Mindel Kansan Elsterian Anglian Río Llico glacial period(s) 300/380 – 455 12[verification needed]
Günz-Mindel Aftonian Cromerian* interglacial(s) 455 – 620 13-15
7th Günz Nebraskan Menapian Beestonian Caracol glacial period 620 – 680 16

Older periods of the Quaternary

Name Inter/Glacial Period (ka) MIS Epoch
Pastonian Stage interglacial 600 – 800
Pre-Pastonian Stage glacial period 800 – 1300
Bramertonian Stage interglacial 1300 – 1550

**Table data is based on Gibbard Figure 22.1.[4]

Ice core evidence of recent glaciation

Main article: Ice core

Ice cores are used to obtain a high resolution record of recent glaciation. It confirms the chronology of the marine isotopic stages. Ice core data shows that the last 400,000 years have consisted of short interglacials (10,000 to 30,000 years) about as warm as the present alternated with much longer (70,000 to 90,000 years) glacials substantially colder than present. The new EPICA Antarctic ice core has revealed that between 400,000 and 780,000 years ago, interglacials occupied a considerably larger proportion of each glacial/interglacial cycle, but were not as warm as subsequent interglacials.

References

1.        ^ a b Miracle Planet: Snowball Earth, (2005) documentary, Canadian Film Board, rebroadcast 25 April 2009 on the Science Channel (HD)

2.        ^ van Andel, Tjeerd H. (1994) New Views on an Old Planet: A History of Global Change 2nd ed. Cambridge University Press, Cambridge, UK, ISBN 0521447550

3.        ^ Rieu, Ruben et al. (2007) “Climatic cycles during a Neoproterozoic “snowball” glacial epoch” Geology 35(4): pp. 299–302

4.        ^ a b Gibbard, P. and van Kolfschoten, T. (2004) “The Pleistocene and Holocene Epochs” Chapter 22 In Gradstein, F. M., Ogg, James G., and Smith, A. Gilbert (eds.), A Geologic Time Scale 2004 Cambridge University Press, Cambridge, ISBN 0521781426

5.        ^ a b Davis, Owen K. “Non-Marine Records: Correlatiuons withe the Marine Sequence” Introduction to Quaternary Ecology University of Arizona

6.        ^ Kukla, George (2005) “Saalian supercycle, Mindel/Riss interglacial and Milankovitch’s dating” Quaternary Science Reviews 24(14/15): pp. 1573-1583

Origin and definition

The last glacial period is sometimes colloquially referred to as the “last ice age”, though this use is incorrect because an ice age is a longer period of cold temperature in which ice sheets cover large parts of the Earth, such as Antarctica. Glacials, on the other hand, refer to colder phases within an ice age that separate interglacials. Thus, the end of the last glacial period is not the end of the last ice age. The end of the last glacial period was about 12,500 years ago, while the end of the last ice age may not yet have come: little evidence points to a stop of the glacial-interglacial cycle of the last million years.

The last glacial period is the best-known part of the current ice age, and has been intensively studied in North America, northern Eurasia, the Himalaya and other formerly glaciated regions around the world. The glaciations that occurred during this glacial period covered many areas, mainly on the Northern Hemisphere and to a lesser extent on the Southern Hemisphere. They have different names, historically developed and depending on their geographic distributions: Fraser (in the Pacific Cordillera of North America), Pinedale, Wisconsinan or Wisconsin (in central North America), Devensian (in the British Isles), Midlandian (in Ireland), Würm (in the Alps), Mérida (in Venezuela), Weichselian (in Scandinavia and Northern Europe), Vistulian (in northern Central Europe), Valdai in Eastern Europe and Zyryanka in Siberia, Llanquihue in Chile, and Otira in New Zealand.

Vegetation types at time of last glacial maximum.

The last glaciation centered on the huge ice sheets of North America and Eurasia. Considerable areas in the Alps, the Himalaya and the Andes were ice-covered, and Antarctica remained glaciated.

Canada was nearly completely covered by ice, as well as the northern part of the USA, both blanketed by the huge Laurentide ice sheet. Alaska remained mostly ice free due to arid climate conditions. Local glaciations existed in the Rocky Mountains and the Cordilleran ice sheet and as ice fields and ice caps in the Sierra Nevada in northern California.[2] In Britain, mainland Europe, and northwestern Asia, the Scandinavian ice sheet once again reached the northern parts of the British Isles, Germany, Poland, and Russia, extending as far east as the Taimyr Peninsula in western Siberia.[3] Maximum extent of western Siberian glaciation was approximately 18,000 to 17,000 BP and thus later than in Europe (22,000–18,000 BP).[4] Northeastern Siberia was not covered by a continental-scale ice sheet.[5] Instead, large, but restricted, icefield complexes covered mountain ranges within northeast Siberia, including the Kamchatka-Koryak Mountains.[6]

The Arctic Ocean between the huge ice sheets of America and Eurasia was not frozen throughout, but like today probably was only covered by relatively shallow ice, subject to seasonal changes and riddled with icebergs calving from the surrounding ice sheets. According to the sediment composition retrieved from deep-sea cores there must even have been times of seasonally open waters.[7]

Outside the main ice sheets, widespread glaciation occurred on the AlpsHimalaya mountain chain. In contrast to the earlier glacial stages, the Würm glaciation was composed of smaller ice caps and mostly confined to valley glaciers, sending glacial lobes into the Alpine foreland. To the east the Caucasus and the mountains of Turkey and Iran were capped by local ice fields or small ice sheets.[8],[9] In the Himalaya and the Tibetan Plateau, glaciers advanced considerably, particularly between 47,000–27,000 BP[10] and in contrast to the widespread contemporaneous warming elsewhere.[11] The formation of a contiguous ice sheet on the Tibetan Plateau is controversial.[12][13][14]

Other areas of the Northern Hemisphere did not bear extensive ice sheets but local glaciers in high areas. Parts of Taiwan for example were repeatedly glaciated between 44,250 and 10,680 BP[15] as well as the Japanese Alps. In both areas maximum glacier advance occurred between 60,000 and 30,000 BP[16] (starting roughly during the Toba catastrophe). To a still lesser extent glaciers existed in Africa, for example in the High Atlas, the mountains of Morocco, the Mount Atakor massif in southern Algeria, and several mountains in Ethiopia. In the Southern Hemisphere, an ice cap of several hundred square kilometers was present on the east African mountains in the Kilimanjaro Massif, Mount Kenya and the Ruwenzori Mountains, still bearing remnants of glaciers today.[17]

Glaciation of the Southern Hemisphere was less extensive because of current configuration of continents. Ice sheets existed in the Andes (Patagonian Ice Sheet), where six glacier advances between 33,500 and 13,900 BP in the Chilean Andes have been reported.[18] Antarctica was entirely glaciated, much like today, but the ice sheet left no uncovered area. In mainland Australia only a very small area in the vicinity of Mount Kosciuszko was glaciated, whereas in Tasmania glaciation was more widespread.[19] An ice sheet formed in New Zealand, covering all of the Southern Alps, where at least three glacial advances can be distinguished.[20] Local ice caps existed in Irian Jaya, Indonesia, where in three ice areas remnants of the Pleistocene glaciers are still preserved today.[21]

[edit] Named local glaciations

[edit] Pinedale or Fraser glaciation, in the Rocky Mountains, USA

The Pinedale (central Rocky Mountains) or Fraser (Cordilleran ice sheet) glaciation was the last of the major glaciations to appear in the Rocky Mountains in the United States. The Pinedale lasted from approximately 30,000 to 10,000 years ago and was at its greatest extent between 23,500 and 21,000 years ago.[22] This glaciation was somewhat distinct from the main Wisconsin glaciation as it was only loosely related to the giant ice sheets and was instead composed of mountain glaciers, merging into the Cordilleran Ice Sheet.[23] The Cordilleran ice sheet produced features such as glacial Lake Missoula, which would break free from its ice dam causing the massive Missoula floods. Geologists estimate that the cycle of flooding and reformation of the lake lasted on average of 55 years and that the floods occurred approximately 40 times over the 2,000 year period between 15,000 and 13,000 years ago.[24] Glacial lake outburst floods such as these are not uncommon today in Iceland and other places.

[edit] Wisconsin glaciation, in North America

The Wisconsin Glacial Episode was the last major advance of continental glaciers in the North American Laurentide ice sheet. This glaciation is made of three glacial maxima separated by interglacial warm periods (such as the one we are living in). These glacial maxima are called, from oldest to newest, Tahoe, Tenaya, and Tioga. The Tahoe reached its maximum extent perhaps about 70,000 years ago, perhaps as a byproduct of the Toba super eruption. Little is known about the Tenaya. The Tioga was the least severe and last of the Wisconsin Episode. It began about 30,000 years ago, reached its greatest advance 21,000 years ago, and ended about 10,000 years ago. At the height of glaciation the Bering land bridge permitted migration of mammals such as humans to North America from Siberia.

It radically altered the geography of North America north of the Ohio River. At the height of the Wisconsin Episode glaciation, ice covered most of Canada, the Upper Midwest, and New England, as well as parts of Montana and Washington. On Kelleys Island in Lake Erie or in New York’s Central Park, the grooves left by these glaciers can be easily observed. In southwestern Saskatchewan and southeastern Alberta a suture zone between the Laurentide and Cordilleran ice sheets formed the Cypress Hills, which is the northernmost point in North America that remained south of the continental ice sheets.

The Great Lakes are the result of glacial scour and pooling of meltwater at the rim of the receding ice. When the enormous mass of the continental ice sheet retreated, the Great Lakes began gradually moving south due to isostatic rebound of the north shore. Niagara Falls is also a product of the glaciation, as is the course of the Ohio River, which largely supplanted the prior Teays River.

With the assistance of several very broad glacial lakes, it carved the gorge now known as the Upper Mississippi River, filling into the Driftless Area and probably creating an annual ice-dam-burst.

In its retreat, the Wisconsin Episode glaciation left terminal moraines that form Long Island, Block Island, Cape Cod, Nomans Land, Marthas Vineyard, Nantucket, Sable Island and the Oak Ridges Moraine in south central Ontario, Canada. In Wisconsin itself, it left the Kettle Moraine. The drumlins and eskers formed at its melting edge are landmarks of the Lower Connecticut River Valley.

[edit] Greenland glaciation

In Northwest Greenland, ice coverage attained a very early maximum in the last glacial period around 114,000. After this early maximum, the ice coverage was similar to today until the end of the last glacial period. Towards the end glaciers readvanced once more before retreating to their present extent.[25] According to ice core data, the Greenland climate was dry during the last glacial period, precipitation reaching perhaps only 20% of today’s value.[26]

[edit] Devensian & Midlandian glaciation, in Britain and Ireland

The name Devensian glaciation is used by British geologists and archaeologists and refers to what is often popularly meant by the latest Ice Age. Irish geologists, geographers, and archaeologists refer to the Midlandian glaciation as its effects in Ireland are largely visible in the Irish Midlands.

The effects of this glaciation can be seen in many geological features of England, Wales, Scotland, and Northern Ireland. Its deposits have been found overlying material from the preceding Ipswichian Stage and lying beneath those from the following Flandrian stage of the Holocene.

The latter part of the Devensian includes Pollen zones I-IV, the Allerød and Bølling Oscillations, and the Older and Younger Dryas climatic stages.

[edit] Weichselian glaciation, in Scandinavia and northern Europe

Alternative names include: Weichsel or Vistulian glaciation (named after the Polish river Vistula or its German name Weichsel). During the glacial maximum in Scandinavia, only the western parts of Jutland were ice-free, and a large part of what is today the North Sea was dry land connecting Jutland with Britain. It is also in Denmark that the only Scandinavian ice-age animals older than 13,000 BC are found.[citation needed] In the period following the last interglacial before the current one (Eemian Stage), the coast of Norway was also ice-free.[citation needed]

The Baltic Sea, with its unique brackish water, is a result of meltwater from the Weichsel glaciation combining with saltwater from the North Sea when the straits between Sweden and Denmark opened. Initially, when the ice began melting about 10,300 ybp, seawater filled the isostatically depressed area, a temporary marine incursion that geologists dub the Yoldia Sea. Then, as post-glacial isostatic rebound lifted the region about 9500 ybp, the deepest basin of the Baltic became a freshwater lake, in palaeological contexts referred to as Ancylus Lake, which is identifiable in the freshwater fauna found in sediment cores. The lake was filled by glacial runoff, but as worldwide sea level continued rising, saltwater again breached the sill about 8000 ybp, forming a marine Littorina Sea which was followed by another freshwater phase before the present brackish marine system was established. “At its present state of development, the marine life of the Baltic Sea is less than about 4000 years old,” Drs. Thulin and Andrushaitis remarked when reviewing these sequences in 2003.

Overlying ice had exerted pressure on the Earth’s surface. As a result of melting ice, the land has continued to rise yearly in Scandinavia, mostly in northern Sweden and Finland where the land is rising at a rate of as much as 8–9 mm per year, or 1 meter in 100 years. This is important for archaeologists since a site that was coastal in the Nordic Stone Age now is inland and can be dated by its relative distance from the present shore.

[edit] Würm glaciation, in the Alps

The term Würm is derived from a river in the Alpine foreland, approximately marking the maximum glacier advance of this particular glacial period. The Alps have been the area where first systematic scientific research on ice ages has been conducted by Louis Agassiz in the beginning of the 19th century. Here the Würm glaciation of the last glacial period was intensively studied. Pollen analysis, the statistical analyses of microfossilized plant pollens found in geological deposits, has chronicled the dramatic changes in the European environment during the Würm glaciation. During the height of Würm glaciation, ca 24,000–10,000 ybp, most of western and central Europe and Eurasia was open steppe-tundra, while the Alps presented solid ice fields and montane glaciers. Scandinavia and much of Britain were under ice.

During the Würm, the Rhône Glacier covered the whole western Swiss plateau, reaching today’s regions of Solothurn and Aarau. In the region of Bern it merged with the Aar glacier. The Rhine Glacier is currently the subject of the most detailed studies. Glaciers of the Reuss and the Limmat advanced sometimes as far as the Jura. Montane and piedmont glaciers formed the land by grinding away virtually all traces of the older Günz and Mindel glaciation, by depositing base moraines and terminal moraines of different retraction phases and loess deposits, and by the pro-glacial rivers’ shifting and redepositing gravels. Beneath the surface, they had profound and lasting influence on geothermal heat and the patterns of deep groundwater flow.

[edit] Merida glaciation, in the Venezuelan Andes

The name Mérida Glaciation is proposed to designate the alpine glaciation which affected the central Venezuelan Andes; during the Late Pleistocene. Two main moraine levels have been recognized: one between 2600 and 2700 m, and another between 3000 and 3500 m elevation. The snow line during the last glacial advance was lowered approximately 1200 m below the present snow line (3700 m). The glaciated area in the Cordillera de Mérida was approximately 600 km2; this included the following high areas from southwest to northeast: Páramo de Tamá, Páramo Batallón, Páramo Los Conejos, Páramo Piedras Blancas, and Teta de Niquitao. Approximately 200 km2 of the total glaciated area was in the Sierra Nevada de Mérida, and of that amount, the largest concentration, 50 km2, was in the areas of Pico Bolívar, Pico Humboldt (4,942 m), and Pico Bonpland (4,893 m). Radiocarbon dating indicates that the moraines are older than 10,000 years B.P., and probably older than 13,000 years B.P. The lower moraine level probably corresponds to the main Wisconsin glacial advance. The upper level probably represents the last glacial advance (Late Wisconsin).[27][28][29][30]

[edit] Llanquihue glaciation, southern Andes

The Llanquihue glaciation takes its name from Llanquihue Lake in southern Chile which is a fan-shaped piedmont glacial lake. On the lake’s western shores there are large moraine systems of which the innermost belong to the last glacial period. Llanquihue Lake’s varves are a node point in southern Chile’s varve geochronology. During the last glacial maximum the Patagonian Ice Sheet extended over the Andes from about 35°S to Tierra del Fuego at 55°S. The western part appears to have been very active, with wet basal conditions, while the eastern part was cold based. Palsas seems to have developed at least in the unglaciated parts of Isla Grande de Tierra del Fuego. The area west of Llanquihue Lake was ice-free during the LGM, and had sparsely distributed vegetation dominated by Nothofagus. Valdivian temperate rainforest was reduced to scattered remnants in the western side of the Andes.[31]

Modelled maximum extent of the Antarctic ice sheet 21,000 years before present

Lake Pippa was also affected by the Pleistocene, a glacier ripped through the center of it causing a very deep lake in the south atlantic.

[edit] Antarctica glaciation

During the last glacial period Antarctica was blanketed by a massive ice sheet, much like it is today. The ice covered all land areas and extended into the ocean onto the middle and outer continental shelf.[32][33] According to ice modelling, ice over central East Antarctica was generally thinner than today.[34]

References

1.        ^ Glaciation of Wisconsin, Lee Clayton, John W. Attig, David M. Mickelson, Mark D. Johnson, and Kent M. Syverson, University of Wisconsin, Dept. of Geology

2.        ^ Clark, D.H.: Extent, timing, and climatic significance of latest Pleistocene and Holocene glaciation in the Sierra Nevada, California. Ph.D. Thesis, Washington Univ., Seattle (pdf, 20 Mb)

3.        ^ Möller, P. et al.: Severnaya Zemlya, Arctic Russia: a nucleation area for Kara Sea ice sheets during the Middle to Late Quaternary. Quaternary Science Reviews Vol. 25, No. 21–22, pp. 2894–2936, 2006. (pdf, 11.5 Mb)

4.        ^ Matti Saarnisto: Climate variability during the last interglacial-glacial cycle in NW Eurasia. Abstracts of PAGES – PEPIII: Past Climate Variability Through Europe and Africa, 2001

5.        ^ Lyn Gualtieri et al.: Pleistocene raised marine deposits on Wrangel Island, northeast Siberia and implications for the presence of an East Siberian ice sheet. Quaternary Research, Vol. 59, No. 3, pp. 399–410, May 2003. Abstract: doi:10.1016/S0033-5894(03)00057-7

6.        ^ Zamoruyev, V., 2004. Quaternary glaciation of north-east Asia. In: Ehlers, J., Gibbard, P.L. (Eds.), Quaternary Glaciations: Extent and Chronology: Part III: South America, Asia, Africa, Australia, Antarctica. Elsevier, Netherlands, pp. 321–323.

7.        ^ Robert F. Spielhagen et al.: Arctic Ocean deep-sea record of northern Eurasian ice sheet history. Quaternary Science Reviews, Vol. 23, No. 11-13, pp. 1455–1483, 2004. Abstract: doi:10.1016/j.quascirev.2003.12.015

8.        ^ Richard S. Williams, Jr., Jane G. Ferrigno: Glaciers of the Middle East and Africa – Glaciers of Turkey. U.S.Geological Survey Professional Paper 1386-G-1, 1991 (pdf, 2.5 Mb)

9.        ^ Jane G. Ferrigno: Glaciers of the Middle East and Africa – Glaciers of Iran. U.S.Geological Survey Professional Paper 1386-G-2, 1991 (pdf, 1.25 Mb)

10.     ^ Lewis A. Owen et al.: A note on the extent of glaciation throughout the Himalaya during the global Last Glacial Maximum, Quaternary Science Reviews, V. 21, No. 1, 2002, pp. 147–157. Abstract: doi:10.1016/S0277-3791(01)00104-4

11.     ^ Quaternary stratigraphy: The last glaciation (stage 4 to stage 2), University of Otago, New Zealand

12.     ^ Matthias Kuhle, 2002: A relief-specific model of the ice age on the basis of uplift-controlled glacier areas in Tibet and the corresponding albedo increase as well as their positiv climatological feedback by means of the global radiation geometry.- Climate Research 20: 1–7.

13.     ^ Matthias Kuhle, 2004: The High Glacial (Last Ice Age and LGM) ice cover in High and Central Asia. Development in Quaternary Science 2 (c, Quaternary Glaciation – Extent and Chronology, Part III: South America, Asia, Africa, Australia, Antarctica, Eds: Ehlers, J.; Gibbard, P.L.), 175–199. (Elsevier B.V., Amsterdam)..

14.     ^ Lehmkuhl, F.: Die eiszeitliche Vergletscherung Hochasiens – lokale Vergletscherungen oder übergeordneter Eisschild? Geographische Rundschau 55 (2):28–33, 2003. English abstract

15.     ^ Zhijiu Cui et al.: The Quaternary glaciation of Shesan Mountain in Taiwan and glacial classification in monsoon areas. Quaternary International, Vol. 97–98, pp. 147–153, 2002. Abstract: doi:10.1016/S1040-6182(02)00060-5

16.     ^ Yugo Ono et al.: Mountain glaciation in Japan and Taiwan at the global Last Glacial Maximum. Quaternary International, Vol. 138–139, pp. 79–92, September–October 2005. Abstract: doi:10.1016/j.quaint.2005.02.007

17.     ^ James A.T. Young, Stefan Hastenrath: Glaciers of the Middle East and Africa – Glaciers of Africa. U.S. Geological Survey Professional Paper 1386-G-3, 1991 (PDF, 1.25 Mb)

18.     ^ Lowell, T.V. et al.: Interhemisperic correlation of late Pleistocene glacial events, Science, v. 269,p. 1541-1549, 1995. Abstract (pdf, 2.3 Mb)

19.     ^ C.D. Ollier: Australian Landforms and their History, National Mapping Fab, Geoscience Australia

20.     ^ A mid Otira Glaciation palaeosol and flora from the Castle Hill Basin, Canterbury, New Zealand, New Zealand Journal of Botany. Vol. 34, pp. 539–545, 1996 (pdf, 340 Kb)

21.     ^ Ian Allison and James A. Peterson: Glaciers of Irian Jaya, Indonesia: Observation and Mapping of the Glaciers Shown on Landsat Images, U.S. Geological Survey professional paper; 1386, 1988. ISBN 0-607-71457-3

22.     ^ Brief geologic history, Rocky Mountain National Park

23.     ^ Ice Age Floods, From: U.S. National Park Service Website

24.     ^ Richard B. Waitt, Jr.: Case for periodic, colossal jökulhlaups from Pleistocene glacial Lake Missoula, Geological Society of America Bulletin, v.96, p.1271-1286, October 1985. Abstract

25.     ^ Svend Funder (ed.) Late Quaternary stratigraphy and glaciology in the Thule area, Northwest Greenland. MoG Geoscience, vol. 22, 63 pp., 1990. Abstract

26.     ^ Sigfus J. Johnsen et al.: A “deep” ice core from East Greenland. MoG Geoscience, vol. 29, 22 pp., 1992. Abstract

27.     ^ * Schubert, Carlos (1998) “Glaciers of Venezuela” United States Geological Survey (USGS P 1386-I)

28.     ^ Late Pleistocene glaciation of Páramo de La Culata, north-central Venezuelan Andes

29.     ^ Mahaney William C., Milner M. W., Kalm Volli, Dirsowzky Randy W., Hancock R. G. V., Beukens Roelf P.: Evidence for a Younger Dryas glacial advance in the Andes of northwestern Venezuela

30.     ^ Maximiliano B., Orlando G., Juan C., Ciro S.: Glacial Quaternary geology of las Gonzales basin, páramo los conejos, Venezuelan andes

31.     ^ http://www.esd.ornl.gov/projects/qen/nercSOUTHAMERICA.html South America during the last 150,000 years.

32.     ^ Anderson, J.B., S.S. Shipp, A.L. Lowe, J.S. Wellner, J.S., and A.B. Mosola, 2002, The Antarctic Ice Sheet during the Last Glacial Maximum and its subsequent retreat history: a review. Quaternary Science Reviews. vol. 21, pp. 49–70.

33.     ^ Ingolfsson, O., 2004, Quaternary glacial and climate history of Antarctica. in: J. Ehlers and P.L. Gibbard, eds., pp. 3–43, Quaternary Glaciations: Extent and Chronology 3: Part III: South America, Asia, Africa, Australia, Antarctica. Elsevier, New York.

34.     ^ P. Huybrechts: Sea-level changes at the LGM from ice-dynamic reconstructions of the Greenland and Antarctic ice sheets during the glacial cycles, Quaternary Science Reviews, V. 21, no. 1-3, pp. 203–231, 2002. Abstract: doi:10.1016/S0277-3791(01)00082-8

Further reading

  • Bowen, D.Q., 1978, Quaternary geology: a stratigraphic framework for multidisciplinary work. Pergamon Press, Oxford, United Kingdom. 221 pp. ISBN 978-0080204093
  • Ehlers, J., and P.L. Gibbard, 2004a, Quaternary Glaciations: Extent and Chronology 2: Part II North America. Elsevier, Amsterdam. ISBN 0-444-51462-7
  • Ehlers, J., and P L. Gibbard, 2004b, Quaternary Glaciations: Extent and Chronology 3: Part III: South America, Asia, Africa, Australia, Antarctica. ISBN 0-444-51593-3
  • Gillespie, A.R., S.C. Porter, and B.F. Atwater, 2004, The Quaternary Period in the United States. Developments in Quaternary Science no. 1. Elsevier, Amsterdam. ISBN 978-0-444-51471-4
  • Harris, A.G., E. Tuttle, S.D. Tuttle, 1997, Geology of National Parks: Fifth Edition. Kendall/Hunt Publishing, Iowa. ISBN 0-7872-5353-7
  • Matthias Kuhle, 1988: The Pleistocene Glaciation of Tibet and the Onset of Ice Ages- An Autocycle Hypothesis. In: GeoJournal 17 (4), Tibet and High-Asia I. 581–596.
  • Mangerud, J., J. Ehlers, and P. Gibbard, 2004, Quaternary Glaciations : Extent and Chronology 1: Part I Europe. Elsevier, Amsterdam. ISBN 0-444-51462-7
  • Sibrava, V., Bowen, D.Q, and Richmond, G.M., 1986, Quaternary Glaciations in the Northern Hemisphere, Quaternary Science Reviews. vol. 5, pp. 1–514.
  • Pielou, E.C., 1991. After the Ice Age : The Return of Life to Glaciated North America. University Of Chicago Press, Chicago, Illinois. ISBN 0-226-66812-6 (paperback 1992)

March 9, 2008

HISTORY AND CAUSES OF CLIMATE CHANGES THROUGH AGES

Filed under: Palaeoenvironment — gargpk @ 2:53 pm
Tags: ,

The climate of Earth has not remained same throughout the geological history of the planet. A broad history of climate changes has been constructed based on palaeogeomorphic studies for the geological past and on observations through network of meteorological stations for the present time. Palaeobotanical studies of the microfossils like pollens, spores etc. as well as megafossils have contributed significantly in elucidating the palaeoclimates and palaeoenvironments of different geological ages in different areas of the earth. An outline of this history of climate changes has been given below.

Precambrian: Very little data is available to deduce the climatic conditions during Precambrian times.

Palaeozoic era (570 to 235 million years B.C.): Somewhat more information is available for this era. It has been deduced that during major part of Palaeozoic era the climate was very warm in all parts of the globe and moisture conditions on the continents fluctuated within wide boundaries.

Towards the end of Palaeozoic, at the boundary between Carboniferous and Permian periods, a glaciation developed. It extended over a large part of the land area that is presently located at tropical latitudes. It is difficult to estimate the geological location of that glaciation during its development since substantial shifts may have subsequently occurred in the location of Earth’s continents and poles. During Permo-carboniferous glaciation, climatic conditions in other regions of Earth were relatively warm.

During Permian period, a thermal zonality appeared and areas of dry climate were greatly enlarged on continents.

Mesozoic era (235 to 66 million B.C.): The climate of this era was relatively uniform. Climatic conditions similar to today’s tropical climate prevailed over a large part of Earth. At higher latitudes, climate was cooler, though it remained quite warm with negligible seasonal changes in temperature. Moisture conditions on the continents appear to have been homogeneous during this era by comparison with the present, even though zones of insufficient and excess humidity did exist. Towards the end of Cretaceous period, the zone of hot climate became less extensive while the zone of dry climatic conditions spread.

Cenozoic era: In passing from Mesozoic to Cenozoic era, no perceptible changes in climate occurred.

During the second half of Tertiary period (towards the middle of Oligocene epoch) a process of progressive cooling began that was most pronounced at middle and especially at high latitudes. Since then, a new climatic zone developed at high latitudes and gradually widened. Its meteorological regime was similar to that of current climatic conditions at middle latitudes. The winter air temperature in that zone fell below zero and this made possible the seasonal formation of snow covers. At the same time the specific properties of continental climates became more pronounced in continental regions distant from the ocean.

During Miocene epoch the cooling process was not uniform and there were periods of temperature rises as well. But these did not alter the general tendency towards an intensification of thermal zonality attributable to declining temperatures at high latitudes.

During the Pliocene epoch the above process was further intensified when the continental glaciation that started during Oligocene in Antarctic (and which continues to exist today) began to spread. Towards the end of Pliocene the climate became warmer than it is today, it was more similar to contemporary climatic conditions than to those of Mesozoic era and of the first half of the Tertiary period.

During Pleistocene epoch the climate differed sharply from preceding conditions in Mesozoic era and the Tertiary period when the thermal zonality was not very pronounced.

Pleistocene epoch began about 1.5 to 2.0 million years ago following an intensification of the cooling that occurred towards the end of Tertiary period at middle and high latitudes. This contributed to development of large continental glaciations. The number of such glaciations and their time of occurrence are known only approximately. Studies in Alps have identified four principal European ice ages termed Gunz, Mindel, Riss and Wurm. Each of these glacial ages could be further subdivided into several stages and glaciations receded during the intervals that divided them. Periods of spread and receding of glaciations occupied only a smaller part of Pleistocene and relatively warm intervening periods were more prolonged. During these warmer periods, ice cover on continents disappeared and existed only in mountainous regions and at high latitudes.

It has been established that the advance and receding of glaciations in Europe, Asia and North America occurred more or less at the same time and a similar correspondence occurred in ice ages in Northern and Southern hemispheres. The spread of ice covers on continents was greatest in regions of more humid maritime climates. In relatively dry climates of Northern Asia, glaciations occupied a relatively small area. During periods of particularly vas glaciations the continental ice cover in Northern Hemisphere reached on the average, 57o North Latitude and in individual regions 40o N latitude. The thickness of continental ice cover over a major part was several hundred meters and in some regions it reached to several kilometers.

With continental glaciation, the boundary of sea polar ice also moved to lower latitudes. This greatly increased the overall area of our globe’s permanent ice cover. During each glaciation period the snow level in mountainous regions not subjected to glaciation moved down by hundreds of meters and sometimes more than a kilometer. During these ice ages the zones of permafrost also increased greatly; their boundary moving to lower latitudes over distances that sometimes reached several thousand kilometers.

During ice ages, along with extensive glaciations, the level of World Ocean declined by 100 to 150 meters below its present level. During warm periods between ice ages, glaciations receded and level of oceans rose by several tens of meters over the present level. The climate of ice ages was characterized by perceptible decline in air temperature in all the regions of world. This reduction in temperature on the average amounted to several degrees below the current temperature and was more pronounced at higher latitudes. In warm periods between ice ages, air temperature was higher than it is today. The influence of ice ages on precipitation is less clear. Some data suggest that moisture conditions in different parts of the world changed in different ways during periods of glaciation. This points to changes in the system of atmospheric circulation produced by glaciations and to corresponding changes in temperature differences between Equator and poles.

Holocene epoch represented a relatively short time period in the history of climate changes that followed the end of Quaternary glaciations. There were several fluctuations in the climatic conditions during this epoch.

Maximal development of Wurmian glaciation occurred approximately 20,000 B.C. and after few thousand years this glaciation was destroyed. After this an epoch followed in which climate was relatively cold and humid at middle latitudes of Northern Hemisphere.

About 12,000 B.C. temperature increased substantially (the Allered) and soon after this a cold period followed. As a result of these climatic fluctuations, Europe’s summer air temperature changed by several degrees.

Between 5,000 to 7,000 B.C. the temperature increased once again and the last large-scale glaciations in Europe and North America disappeared. Post-glaciation temperature increases reached a maximum at that time. Between 5,000 to 6,000 B.C. air temperature at middle latitudes of Northern Hemisphere was about 1 to 3 degrees C higher than today. During this time, changes in atmospheric circulation also occurred. While polar ice boundaries shifted to the north, the sub-tropical high-pressure belt moved to higher latitudes leading to an expansion of arid zones in a number of regions of Europe, Asia and North America. The volume of precipitation in contemporary desert areas at low latitudes also increased. During this period, Sahara’s climate was relatively humid.

Subsequently a trend towards lower temperatures prevailed that was especially pronounced during the fist half of the first millennium B.C. Together with these changes in thermal regime the precipitation regime also changed and gradually approached its present state.

An appreciable rise in temperature occurred at the end of first and beginning of second millennium A.D. At that time polar ice receded to high latitudes. The process of cooling that began in 13th century and reached a maximum at the beginning of 17th century was accompanied by an extension of mountain glaciers and is sometimes referred to as a small ice age. Subsequently temperature increased again and ice has receded. The climatic conditions of 18th and 19th century differed little from those that exist today.

Towards the end of 19th century there has been a gradual increase in air temperature at all latitudes of Northern Hemisphere and in all seasons, especially at high latitudes during cold seasons. Increase in temperature reached a maximum in 1930s when average temperature in Northern Hemisphere increased by about 0.6o C by comparison with the end of 19th century. In 1940s a cooling started that continued until recently. This cooling, however, was relatively slow in comparison with preceding cycle of increased temperatures.

In Northern Hemisphere, increased air temperature has been accompanied by reduction in polar ice area, receding of the boundary of permafrost to high latitudes and a northward movement of forest and tundra boundaries as well other changes in natural conditions. The amount of precipitation in a number of regions of insufficient moisture was reduced as the air temperature increased, particularly during cold seasons of the year. It is also believed that that during the first half of 20th century, temperature increased in Southern Hemisphere as well.

Causes Of Changes In Climate

Until recently studies of the causes underlying changes in climate were made difficult by the absence of a corresponding physical theory. However, in recent years, numerical models of climate theory including the semi-empirical theory of atmospheric thermal regimes have significantly contributed to the studies of causes underlying climatic changes.

Quantitative data concerning climatic conditions in the distant past are not very reliable. Therefore, study of the causes of climatic changes in Prequaternary period is quite difficult while that of Quaternary period is relatively more reliable.

Prequaternary period

The study of the causes of climatic change during Prequaternary period can only be limited to an examination of the secular trend of air temperature during second half of the Mesozoic era and the Tertiary period. Palaeotemperatures determined through the method of isotopic analysis can be reliably used in such studies. In has been established from the studies of palaeotemperatures that during the last 130 million years there has been a tendency for average air temperatures at the Earth’s surface to decline. This tendency was interrupted several times by perceptible increases in air temperature but these were always followed by periods of cooling and did not alter the overall course of climate evolution. In order to explain the changes in climatic conditions, consideration of the influence of fluctuations in the composition of atmosphere and in the structure of the Earth’s surface on the thermal regime is necessary.

1. Effect of atmospheric carbon dioxide on thermal regime of atmosphere

Since carbon dioxide influences the absorption of long-wave radiation, thus sustaining the atmospheric green-house effect, a reduction in its mass produces a decline in air temperature at Earth’s surface. It has been established that only for relatively low concentrations (<0.1%) the dependence of temperature on the concentration of carbon dioxide becomes perceptible. At higher concentrations, changes in the volume of carbon dioxide in the atmosphere influence air temperature insignificantly. As a result, only during Pliocene and Pleistocene epochs the reductions in the atmospheric carbon dioxide content have produced considerable changes in air temperature. Calculations based on semi-empirical theory of thermal regime have shown that during that period the average air temperature at the Earth’s surface has declined by several degrees.

2. Effect of structure of Earth’s surface on thermal regime of atmosphere

During the second half of Mesozoic epoch of Tertiary period, the average elevation of continents was relatively low. As a result, a large part of continental plateform was covered by shallow seas. During that time a large number of uplifts and sinkings of different continental areas occurred but this did not alter the overall pattern in which straights and seas of various sizes separated various continents.

During Neogene epoch of Tertiary period, intensive tectonic movements produced the elevation of continents and caused a gradual vanishing of many intercontinental seas. Particularly, the sea on the present-day tertiary of Western Siberia that linked tropical oceans with the polar basin ceased to exist. This resulted in transformation of Arctic Ocean into its today’s condition of a relatively isolated body of water that is linked only with Atlantic Ocean and poorly connected to Pacific Ocean through the very narrow Bering Strait.

Possibly the slow drift of Antarctic was completed during the Tertiary period. It is presumed that such changes in the structure of Earth’s surface produced substantial decline in meridonial heat exchanges in the oceans. Such reductions in meridonial flows of heat in oceans resulting from increases in the levels of continents have contributed to the reduction in temperatures that have taken place at middle and high latitudes during the last 100-150 million years.

The reasons why the temperatures fluctuate over intervals extending to tens of millions of years is an interesting problem. It may be assumed that cause was local changes in circulation processes in the atmosphere and oceans.

Quaternary period

The Quaternary period was preceded by a prolonged evolution of climate in the direction of a more pronounced thermal zonality resulting from changes in Earth’s surface structure. This was largely expressed in a continual decline in air temperature at middle and high latitude. Peculiar climatic conditions during Quaternary period appear to have emerged due to further decline in concentration of carbon dioxide in the atmosphere and also due to drifts and elevation of continents.

1. Effect of decline in atmospheric Carbon dioxide

During Pliocene epoch, climatic conditions began to be influenced by a reduction in the atmospheric carbon dioxide concentration. Such reduction led to a decline in average global air temperature by 2o to 3o C (3o to 5o C at high latitudes). This resulted in development and extension of polar ice caps that in turn, caused further decline in average global temperature, particularly at higher latitudes.

2. Effect of shifts and elevation of continents

Development of polar ice caps sharply increased the sensitivity of thermal regime to even very small changes in climate-forming factors. This made possible the very large oscillations in the boundaries of snow and ice covers on land and in oceans as a result of changes in the location of land in relation to the Sun; earlier this factor had not influenced the climate substantially.

Continuous reduction in atmospheric CO2 contributed to the advance of glaciations, even though the major influence on their scope was a combination of astronomical factors determining the location of Earth’s surface in relation to the Sun. These factors include the eccentricity of Earth’s orbit, the inclination of Earth’s axis in relation to the plane of its orbit and the time of equinoxes. These astronomical changes occur in periods of tens of thousands of years. In comparison to changes in astronomic factors, all other factors appear to have exerted a lesser influence on climatic fluctuations during Quaternary period.

The above conclusions have been verified by using a numerical model that makes possible the calculation of individual ice covers as influenced by external factors. Budyko, M.I. & Vasishcheva, M.A. (1971, The Influence of Astronomical Factors on Quaternary Glaciations. Meteorologiya I gidrologiya. No. 6) studied the climatic conditions during glaciation periods using a model describing the distribution of average latitudinal temperature in different seasons. The study showed that fluctuation in the radiation regime caused by changes in the position of Earth’s surface in relation to Sun may lead to substantial changes in climate. Though average global temperature does not fluctuate much at such times, such modest fluctuations are accompanied by perceptible shifts in the boundaries of ice covers.

Climatic changes in 20th century

Meteorological observations for first half of present century show a trend towards increased temperatures that reached a maximum in 1930s. It appears from the studies of reasons explaining climatic change during this period that the increase in temperature has been caused by an increase in transparency of stratosphere. This caused increased inflow of solar radiation (i.e. increased meteorological Solar constant) into the troposphere and has led to an increase in average global air temperature at Earth’s surface.

The changes in air temperature at different latitudes and in different seasons have depended on:

the optical thickness of stratospheric aerosol and

shifts in the boundaries of sea polar ice.

The shrinking Arctic sea ice due to rise in air temperature has further contributed to increase in air temperature during cold seasons at high latitudes in Northern Hemisphere.

It seems probable that changes in the transparency of stratosphere during first half of this century have been associated with the regime of volcanic activities, particularly with the changes in inflow of the products of volcanic eruptions (including sulphur dioxide) into stratosphere. It is now increasingly being recognized that during last 3 to 4 decades, changes in climate have also begun to depend, atleast in some measure, on human activities. Increasing pollution with rapid industrialization is adding various substances into the atmosphere. This is changing various climatic and meteorological factors causing changes in the climate that are still not well understood.

February 27, 2008

HISTORY OF CLIMATE CHANGES ON EARTH

Filed under: Palaeoenvironment — gargpk @ 2:07 pm
Tags: ,

The climate of Earth has not remained same throughout the geological history of the planet. A broad history of climate changes has been constructed based on palaeogeomorphic studies for the geological past and on observations through network of meteorological stations for the present time. An outline of this history of climate changes has been given below.

Precambrian: Very little data is available to deduce the climatic conditions during Precambrian times.

Palaeozoic era (570 to 235 million years B.C.): Somewhat more information is available for this era. It has been deduced that during major part of Palaeozoic era the climate was very warm in all parts of the globe and moisture conditions on the continents fluctuated within wide boundaries.

Towards the end of Palaeozoic, at the boundary between Carboniferous and Permian periods, a glaciation developed extending over a large part of the land area which is presently located at tropical latitudes. It is difficult to estimate the geological location of that glaciation during its development since substantial shifts may have subsequently occurred in the location of Earth’s continents and poles. During Permocarboniferous glaciation, climatic conditions in other regions of Earth were relatively warm.

During Permian period, a thermal zonality appeared and areas of dry climate were greatly enlarged on continents.

Mesozoic era (235 to 66 million B.C.): The climate of this era was relatively uniform. Climatic conditions similar to today’s tropical climate prevailed over a large part of Earth. At higher latitudes, climate was cooler, though it remained quite warm with negligible seasonal changes in temperature. Moisture conditions on the continents appear to have been homogeneous during this era by comparison with the present, even though zones of insufficient and excess humidity did exist. Towards the end Cretaceous period, the zone of hot climate became less extensive while the zone of dry climatic conditions spread.

Cenozoic era: In passing from Mesozoic to Cenozoic era, no perceptible changes in climate occurred. During the second half of Tertiary period (towards the middle of Oligocene epoch) a process of progressive cooling began that was most pronounced at middle and especially at high latitudes. Since then a new climatic zone developed at high latitudes and gradually widened whose meteorological regime was similar to that of current climatic conditions at middle latitudes. The winter air temperature in that zone fell below zero and this made possible the seasonal formation of snow covers. At the same time the specific properties of continental climates became more pronounced in continental regions distant from the ocean.

During Miocene epoch the cooling process was not uniform and there were periods of temperature rises as well. But these did not alter the general tendency towards an intensification of thermal zonality attributable to declining temperatures at high latitudes.

During the Pliocene epoch the above process was further intensified when the continental glaciation that started during Oligocene in Antarctic (and which continues to exist today) began to spread. Towards the end of Pliocene the climate became warmer than it is today, it was more similar to contemporary climatic conditions than to those of Mesozoic era and of the first half of the Tertiary period.

During Pleistocene epoch the climate differed sharply from preceding conditions in Mesozoic era and the Tertiary period when the thermal zonality was not very pronounced. Pleistocene epoch began about 1.5 to 2.0 million years ago following an intensification of the cooling that occurred towards the end of Tertiary period at middle and high latitudes. This contributed to development of large continental glaciations. The number of such glaciations and their time of occurrence are known only approximately. Studies in Alps have identified four principal European ice ages termed Gunz, Mindel, Riss and Wurm. Each of these glacial ages could be further subdivided into several stages and glaciations receded during the intervals that divided them. Periods of spread and receding of glaciations occupied only a smaller part of Pleistocene and relatively warm intervening periods were more prolonged. During these warmer periods, ice cover on continents disappeared and existed only in mountainous regions and at high latitudes. It has been established that the advance and receding of glaciations in Europe, Asia and North America occurred more or less at the same time and a similar correspondence occurred in ice ages in Northern and Southern hemispheres. The spread of ice covers on continents was greatest in regions of more humid maritime climates. In relatively dry climates of Northern Asia, glaciations occupied a relatively small area. During periods of particularly vas glaciations the continental ice cover in Northern Hemisphere reached on the average, 57o North Latitude and in individual regions 40o N latitude. The thickness of continental ice cover over a major part was several hundred meters and in some regions it reached to several kilometers. With continental glaciation, the boundary of sea polar ice also moved to lower latitudes. This greatly increased the overall area of our globe’s permanent ice cover. During each glaciation period the snow level in mountainous regions not subjected to glaciation moved down by hundreds of meters and sometimes more than a kilometer. During these ice ages the zones of permafrost also increased greatly; their boundary moving to lower latitudes over distances that sometimes reached several thousand kilometers. During ice ages, along with extensive glaciations, the level of World Ocean declined by 100 to 150 meters below its present level. During warm periods between ice ages, glaciations receded and level of oceans rose by several tens of meters over the present level. The climate of ice ages was characterized by perceptible decline in air temperature in all the regions of world. This reduction in temperature on the average amounted to several degrees below the current temperature and was more pronounced at higher latitudes. In warm periods between ice ages, air temperature was higher than it is today. The influence of ice ages on precipitation is less clear. Some data suggest that moisture conditions in different parts of the world changed in different ways during periods of glaciation. This points to changes in the system of atmospheric circulation produced by glaciations and to corresponding changes in temperature differences between Equator and poles.

Holocene epoch represented a relatively short time period in the history of climate changes that followed the end of Quaternary glaciations. There were several fluctuations in the climatic conditions during this epoch. Maximal development of Wurmian glaciation occurred approximately 20,000 B.C. and after few thousand years this glaciation was destroyed. After this an epoch followed in which climate was relatively cold and humid at middle latitudes of Northern Hemisphere. About 12,000 B.C. temperature increased substantially (the Allered) and soon after this a cold period followed. As a result of these climatic fluctuations, Europe’s summer air temperature changed by several degrees. Subsequently temperature increased once again and the last large-scale glaciations in Europe and North America disappeared between 5,000 to 7,000 B.C. At that time, post-glaciation temperature increases reached a maximum. Between 5,000 to 6,000 B.C. air temperature at middle latitudes of Northern Hemisphere was about 1 to 3 degrees C higher than today. During this time, changes in atmospheric circulation also occurred. While polar ice boundaries shifted to the north, the sub-tropical high-pressure belt moved to higher latitudes leading to an expansion of arid zones in a number of regions of Europe, Asia and North America. The volume of precipitation in contemporary desert areas at low latitudes also increased. During that period, Sahara’s climate was relatively humid. Subsequently a trend towards lower temperatures prevailed that was especially pronounced during the fist half of the first millennium B.C. Together with these changes in thermal regime the precipitation regime also changed and gradually approached its present state.

An appreciable rise in temperature occurred at the end of first and beginning of second millennium A.D. At that time polar ice receded to high latitudes. The process of cooling that began in 13th century and reached a maximum at the beginning of 17th century was accompanied by an extension of mountain glaciers and is sometimes referred to as a small ice age. Subsequently temperature increased again and ice has receded. The climatic conditions of 18th and 19th century differed little from those that exist today.

Towards the end of 19th century there has been a gradual increase in air temperature at all latitudes of Northern Hemisphere and in all seasons, especially at high latitudes during cold seasons. Increase in temperature reached a maximum in 1930s when average temperature in Northern Hemisphere increased by about 0.6o C by comparison with the end of 19th century. In 1940s a cooling started that continued until recently. This cooling, however, was relatively slow in comparison with preceding cycle of increased temperatures. In Northern Hemisphere, increased air temperature has been accompanied by reduction in polar ice area, receding of the boundary of permafrost to high latitudes and a northward movement of forest and tundra boundaries as well other changes in natural conditions. The amount of precipitation in a number of regions of insufficient moisture was reduced as the air temperature increased, particularly during cold seasons of the year. It is also believed that that during the first half of 20th century, temperature increased in Southern Hemisphere as well.