Quaternary glaciation
The Cenozoic Ice Age is the current ice age, the ice age of the Cenozoic. In his first glaciated Antarctica before about 30 and since about 2.7 million years ago the Arctic. Since about the beginning of the glaciation the Arctic (longer ) cold periods change (also called glacial ) with ( shorter ) warm periods ( interglacials ) from.
The term Känozoisches ice age overlaps with the term Quaternary ice ages. The latter includes only the period of the Quaternary, from 2.58 million years before present and refers to the existence of extended continental ice sheets in the Northern Hemisphere during this period.
- 4.2.1 Earth's orbital geometry
- 4.2.2 Activity cycles of the sun
- 5.1 Problems of Classification
- 5.2 International Subdivisions 5.2.1 Marine oxygen isotope stratigraphy
- 5.2.2 Magnetostratigrafie
- 6.1 glaciations
- 6.2 sea
- 6.3 Climate and atmosphere
- 6.4 lifeworld
Use of the terms glacial period, ice age, ice age
The term ice age is often used in colloquial synonym for cold period. It was introduced in this sense in 1837 by Karl Friedrich Schimper and later used synonymously with Ice Age. In the technical language has prevailed both for the entire period of the Cenozoic ice age as well as for the older glaciation phases, the wider definition ice age. It includes both the cold periods and the intervening warm periods.
Glaciation of the Arctic
The phase of the Arctic glaciation began about 2.7 million years ago. This was preceded by a slow global cooling that began already in the Eocene. Approximately 4.6 million years ago began the closure of the Isthmus of Panama, which led to great changes in the oceanic flow conditions. This brought an increase in humidity in the Arctic with him, which ultimately provided the "raw material" for the Northern Hemisphere glaciation.
Structure of the current ice age
Within the present-day ice age, there are relatively warm and extremely cold intermediate phases. The cold phases ( cold periods and glacial periods ) are characterized by massive glacier advances. They are at about 90,000 years significantly longer than the heat phase ( warm periods or interglacials ) that only last about 15,000 years. Warm periods often begin quite suddenly, while the cooling is more insidious. The climate change is rarely uniform but with abrupt changes and intervening opposing developments.
An entire cycle of a warm period to the next currently takes a little more than 100,000 years. These cycles duration is, however, valid only been 600,000 to 800,000 years. 2.7 million years ago until about 700,000 years, the duration of one cycle was only about 40,000 years. This is to bring to the almost equally long period, with the obliquity of the ecliptic varies ( position of the earth ), in conjunction. The currently valid 100,000 -year cycle is mainly due to changes in the eccentricity of Earth's orbit. Why did the change in the duration of the warm-cold -term cycles is not clear.
The current " post-glacial ", referred to in the geological time scale than the Holocene is a warm period within a global ice age, which lasted for about 11,000 years. Even in the heat stages of a global ice age the climate in the geological comparison remains relatively cold, the ice cover in the vicinity of the poles and higher mountains remains mostly. Glacier advances into the midlatitudes but regressed and the activity is to much more moderate climate, especially with milder winters.
Causes of the Ice Age
The causes of the general decline since the Eocene are even discussed, while the short-term climate variability can be explained by periodic changes in the Earth's orbital parameters or with periodic variations in solar activity on the best currently mainly changes on Earth.
The search for the causes of the cyclically occurring cold and warm periods is still one of the challenges for paleoclimatology today. It is closely connected with the name James Croll, Milutin Milankovitch and. Both had ideas of the Frenchman Joseph- Alphonse Adhemar developed, according to which changes in the Earth's orbital geometry are responsible for recurrent cold periods.
Earthly causes
Main drive for general cooling in the Paleogene and Neogene were processes of plate tectonics, ie the displacements of the continental plates.
Opening and closure of straits
By closing or opening of the sea routes to changing critical ocean currents (and thus the heat transport ) on the earth.
Thus the drift of Australia and later South America from Antarctica opened in Oligocene two straits ( Tasmanian Passage and Drake Passage ). Thus, a flow system around Antarctica has established itself. This cold current zirkumantarktische isolated Antarctica entirely of warm surface water. Antarctica cooled and the formation of an ice cap over the continent at the South Pole was started around 35 million years ago. Previously, the ocean currents around Antarctica were strongly oriented towards the equator, so that warmer water masses could reach and heat the continent.
The blocking of the connections between the Atlantic and the Mediterranean ( the remaining between Africa and Eurasia rest of the Tethys Sea ) before about 6 million years ago led to his temporary dehydration with significant influence on the global climate.
The formation of a land bridge between North and South America prior to 4.2 to 2.4 million years ago caused the diversion of warm sea currents to the north, and thus also for the emergence of the Gulf Stream. Although the transport of warm water into the north caused first a warming of the northern hemisphere, but also provided the necessary moisture willing to give rise in Greenland, North America and Northern Europe with further cooling glacier.
Formation of high mountains
Due to the collision of plates it came from the younger Tertiary ( Neogene ) to increased orogeny. The uplift of the mainland in significant heights changed primarily large - and small-scale air currents. The formation of fold mountains such as the Alps, the Rocky Mountains or the Himalayas, which has led to the change in circulation patterns in the atmosphere, also brought the necessary moisture to the continents, which further contributed parts of the northern hemisphere to glaciation. At the same time the high mountains also preferred areas of glacier origin.
One theory sees the highlands of Tibet while in a central role, because it assumes a nearly complete glaciation of the highlands. About the significant increase in the albedo introduced the world to a significant cooling. The closed glaciation of Tibet but partially rejected. Changes in albedo caused by changes in the duration of snow cover in the highlands, however, are undisputed.
More earthly causes
In the Cretaceous and Paleogene there were significantly stronger than in the Neogene and Quaternary volcanism. Since an extensive release of carbon dioxide associated with each volcanic eruption, the CO2 content of the atmosphere at that time was higher. Accordingly stronger worked in the Cretaceous and Paleogene and the natural greenhouse effect of the earth.
Astronomical causes
Earth's orbital geometry
The change in the Earth's orbit geometry caused the Sun, Earth, Moon in the system by mutual gravitational forces. To change the shape of the elliptical Earth orbit (eccentricity ) around the Sun with a period of about 100,000 years, the inclination of the Earth to orbit with a period of about 40,000 years ( obliquity of the ecliptic ), while the day and night are equally long on the elliptical orbit about 25,780 years after return to the same position on the ellipse takes ( precession ). By this so-called Milanković cycles, the distribution of solar energy on the earth is periodically changed.
Inspired by the German meteorologist Wladimir Peter Köppen formulated Milutin Milankovitch in 1941 in his work " The Canon of Erdbestrahlung and its application to the ice age problem," the hypothesis that a cold period always occurs when the summer insolation at high northern latitudes is minimal. Cool summer are according to the Köppen ice build decisive as a cold winter. So Milankovitch studied there for the causes of ice ages, where they are most evident in the high northern latitudes.
The variations in the Earth's orbital parameters ( Milankovitch cycles) were the trigger and appropriate boundary conditions, whose effect but were exacerbated by other factors. To be accepted as a cause for the onset of both the Antarctic as the Northern Hemisphere glaciation tectonic processes and their influence on the oceanic circulation. In addition, the CO2 content of the atmosphere has played a major role, which has a tight coupling with the temperature fluctuations, as various studies of ice cores of Antarctica and Greenland over the last 800,000 years show. Thereafter, the decrease in concentration of the greenhouse gas carbon dioxide is (along with methane and nitrous oxide ) are available for about a third of the change in temperature between hot and cold period, according to a recent publication even for half. Other positive feedback processes such as the ice - albedo feedback, the vegetation cover and the variability of the water vapor content in the atmosphere played an additional role. For the variability of the cold periods between so-called stadials and interstadials feedback effects are assumed in connection with the thermohaline circulation.
Activity cycles of the sun
During the last glacial period, there were two dozen significant climate swings, in which increased within just one decade, the air temperature over the North Atlantic by up to twelve degrees Celsius. This Dansgaard - Oeschger events usually occurred every 1470 years. This periodicity is trying to explain of 87 and 210 years, with an overlay of two known activity cycles of the sun. After 1470 years, the 210cc - cycle seven times, and the 86.5 he cycle is seventeen expired. In today's warm period these Dansgaard - Oeschger events did not recur because the weak sun fluctuations could no longer disturb the stable Atlantic currents of the last 10,000 years.
Classification and Nomenclature
Problems of structure
Originally, the outline of the current ice age was made on the basis of terrestrial ( of continental ) deposits. A distinction was the individual, one above the other occurring deposits of various cold and warm periods. Problems occurred, however, and occur with the comparison and correlation of the glacial deposits over long distances. So one is, for example, still not sure whether the deposits of the Saale glaciation in northern Germany and the Rißeiszeit in the foothills emerged simultaneously. For this reason, each region has received on Earth own quartärstratigraphische outline.
The numerous local subdivisions with their own names, which can hardly be overlooked by professionals themselves, act on non-specialists often confusing. Thus, the recent cold temporal Eisvorstoß is, Vistula, Würm, Valdai, Devensian - designated its peak a little over 20,000 years ago in northern central Europe than in the northern Alpine region than in northern Russia than in the British Isles than in North America as Wisconsineiszeit. Also for older cold and warm periods, there is a plethora of local names.
Another difficulty of the glacial deposits on the mainland is that they were not deposited continuously ( continuous) and. Instead, follow on phases of fast sedimentation ( such as in glacial advances ) phases without sedimentation or even erosion events. In northern Germany, for example, is not a place known to all the tills of the three major phases of glaciation occur over each other together with the deposits of the intervening warm periods. The correlation must also here be effected over large distances, and may include errors.
International subdivisions
The internationally recognized structure of the ice age is therefore based on the characteristics of marine ( marine) deposits. They have the advantage that they settle continuously favorable locations and contain both the hot-and the cold time deposits.
Marine oxygen isotope stratigraphy
The most important aids in the breakdown of the ice age, the ratios of the stable isotopes of oxygen 16O and 18O in calcareous microorganisms ( foraminifera ). As the lighter isotope 16O enriched compared to the heavier 18O during evaporation, there is a isotopic fractionation of oxygen. Due to the storage of the light isotope 16O in the continental ice sheets during the glacial periods of the ocean at this time is isotopically heavier ( ice effect ). From this, a stratigraphy of marine sediments has been developed, the marine oxygen isotope stratigraphy.
The complete Ice Age was divided into 103 isotope stages. Odd numbers were assigned to warm periods ( interstadials or interglacials ), on the other hand just to cold periods ( glacials ). The current warm period corresponds accordingly to the marine oxygen isotope stage 1 (abbreviated to MIS 1 for the internationally common Marine Isotope Stage 1), the peak of the last ice age corresponds to the MIS 2 Since after the first statement of the structure further isotopic variations could be detected, were additional levels set by appending a letter, for example 5e for the Eemian.
Magnetostratigrafie
Another common structure is based on the fluctuations and reversals of the magnetic field of the earth. Approximately 780,000 and 2,580,000 years ago, there were significant reversals of the magnetic field ("cell reversal " is not to be taken literally, but as a slow removal of the magnetic field and its structure in other polarity ). Furthermore, there were short Umpolungsphasen within the major periods, such as before 1.77 million years ago. One can find traces of it, such as the orientation of magnetic minerals in glacial deposits, so you can date the deposits. This method is suitable for both continental and marine deposits. Therefore, an organization recognized by many scientists limit the Ice Age to the Pliocene the great reversal of the geomagnetic field before 2.58 million years, which agrees well with the first occurrence of glaciations in the northern hemisphere.
Structure in Central Europe
In Central Europe the cold periods are named after rivers, generally indicating the furthest extent of the respective ice sheets. In southern Germany, the icing came from the Alpine glaciers in northern Germany came the ice from the Scandinavian region. It is not backed up except for the recent cold period if the glaciations expired truly running in the Alps and in North Germany. Therefore, the above values with further research may well be changed.
Effects on the soil
Glaciations
During the cold periods of the current ice age, the inland ice and mountain glaciers spread out strong and eventually covered about 32 % of the solid surface. Today, only about 10 % of the land surface of glaciers are covered. Especially in the northern hemisphere large parts of Europe, Asia and North America were glaciated. The traces of glaciation (eg, U-shaped valleys, moraines, glacial striations, the glacial deposits ) are there everywhere today.
The change of the inland ice of Antarctica was not as dramatically during the ice age compared to the Arctic. On the one hand it is believed that this is due to the fact that the build up of ice on land and shallow Schelfen the northern hemisphere is more effective than in zirkumantarktischen ocean areas. On the other hand, Antarctica is almost completely glaciated today. An enlargement of the ice sheet was so there limited. An extension of the ice sheet is mainly attributed to the lowering of the sea level.
During the current post-glacial ( Holocene ) the extent of the glaciers fluctuated widely. After many glaciers had advanced during a cold phase towards the end of the Younger Dryas, occurred in the early Holocene to a reduction, some glaciers disappeared. This applies to the period about 7000 years ago at the height of the post-glacial ( Holocene ) for many glaciers in Iceland and probably some of the Scandinavian Peninsula. In the Alps, most of the glaciers at the time were probably less than the late 20th century. The fact that the present-day glaciers in the Alps or Scandinavia are remnants of the last glaciation, it is frequently assumed, but shall accordingly not for many, they are more than 6,000 years old. Many glaciers reached their maximum extent of several hundred years ago.
Sea level
The formation of continental ice sheets the seas has been massively deprived of water. During the height of the last Ice Age, the sea level was about 120 to 130 m lower than today. This resulted in numerous land bridges. Besides seas and shallow seas like the North Sea were partially or completely dry. Great importance was the land bridge across the Bering Strait today that connected Asia with North America. The exchange of numerous animal and plant species as well as older theories after human colonization of the American continent took place on this land bridge.
Air and atmosphere
During the cold periods fell, globally, due to lower temperatures significantly less rainfall than during warm periods. The changes in precipitation during the cold periods were regional and zonal however very different. While it was rather dry in the high and mid-latitudes, there were significant in the subtropics humid phases. The rand tropical deserts were extremely dry even at this time, while the area of the humid tropics was significantly lower at that time. The available water supply in the high and mid-latitudes, however, was during the ice ages partly higher than today, because the evaporation was significantly lower due to lower temperatures and therefore missing the forest.
The Last Glacial Maximum ( LGM ) was about 21,000 years ago. The average global temperature was about 5-6 K lower than today. Because of the gas inclusions in polar ice, we know that the atmospheric concentration of the greenhouse gases carbon dioxide (CO2), only 70% and methane ( CH4), only 50% of the pre-industrial value was (CO2 LGM: 200 ppmv pre-industrial 288 ppmv today (2005 ): 381 ppmv, CH4 in the LGM: 350 ppbv preindustrial: 750 ppbv, today: 1750 ppbv ).
During the final phases of the individual cold periods increased due to the natural increase of the sunlight out the global temperature, and this was followed, in response to this initial increase, the content of the greenhouse gases CO2 and methane. The time delay is a few hundred years. The same is true for cooling phases, where each cooling attracts a decrease in gas concentration by itself. The temperature development controls the concentrations in a clearly proportional dependence: the curves of CO2 and methane follow the temperature curve with the said time offset almost congruent. This congruence of curves over time is unique and has no discontinuities or tipping situations, so that in the period the related: Sun - Earth's temperature appears to be dominant.
However, it is also discussed that deviates from this context theory: The release of greenhouse gases caused by feedback processes to an acceleration of warming and a further release of greenhouse gases, until finally einstellten equilibrium states and both the climate and the greenhouse gas concentrations in the warm periods relatively stable remained. This mechanism of a natural warming could play a role in the current global warming, since an increase in the content of greenhouse gases due to human activity may be enhanced by this effect and the global temperature continues to rise. The radiation from the sun plays many scientists believe in the current warming of only a subordinate role.
Lifeworld
Climate variability of the Cenozoic ice age had a significant impact on the flora and fauna of their time. With the cool downs and re- warming the air to the corresponding adapted creatures were forced to shift their habitats. Numerous plant and animal species could therefore large rooms not re- colonize or died completely. This effect was in Africa and Europe, where the Mediterranean Sea and extends from east to west mountain ranges barriers to the migration of the species represented, significantly greater than in North America and East Asia.
Characteristic of the Ice Age were animals like mammoths, mastodons, saiga, saber-toothed cats, cave lions, cave bears, and other forms. Also lived Homo heidelbergensis, which grew out of it and the Neanderthals around 40,000 years ago immigrated from Africa modern humans (Homo sapiens ) during cold periods in Europe.