Interglacial

An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene interglacial began at the end of the Pleistocene, about 11,700 years ago.

Ice Age Temperature
Shows the pattern of temperature and ice volume changes associated with recent glacials and interglacials

Interglacials during the Pleistocene

During the 2.5 million year span of the Pleistocene, numerous glacials, or significant advances of continental ice sheets in North America and Europe, have occurred at intervals of approximately 40,000 to 100,000 years. These long glacial periods were separated by more temperate and shorter interglacials.

During interglacials, such as the present one, the climate warms and the tundra recedes polewards following the ice sheets. Forests return to areas that once supported tundra vegetation. Interglacials are identified on land or in shallow epicontinental seas by their paleontology. Floral and faunal remains of species pointing to temperate climate and indicating a specific age are used to identify particular interglacials. Commonly used are mammalian and molluscan species, pollen and plant macro-remains (seeds and fruits). However, many other fossil remains may be helpful: insects, ostracods, foraminifera, diatoms, etc. Recently, ice cores and ocean sediment cores provide more quantitative and accurately dated evidence for temperatures and total ice volumes.

The interglacials and glacials coincide with cyclic changes in the Earth's orbit. Three orbital variations contribute to interglacials. The first is a change in the Earth's orbit around the sun, or eccentricity. The second is a shift in the tilt of the Earth's axis, the obliquity. The third is precession, or wobbling motion of Earth's axis.[1] Warm summers in the Southern hemisphere occur when that hemisphere is tilted toward the sun and the Earth is nearest the sun in its elliptical orbit. Cool summers occur when the Earth is farthest from the sun during that season. These effects are more pronounced when the eccentricity of the orbit is large. When the obliquity is large, seasonal changes are more extreme.[2]

Interglacials are a useful tool for geological mapping and also for anthropologists, as they can be used as a dating method for hominid fossils.[3]

Brief periods of milder climate that occurred during the last glacial are called interstadials. Most (not all) interstadials are shorter than interglacials. Interstadial climate may have been relatively warm but this is not necessarily so. Because the colder periods (stadials) have often been very dry, wetter (so not necessarily warmer) periods have been registered in the sedimentary record as interstadials as well.

The oxygen isotope ratio obtained from seabed sediment core samples, a proxy for average global temperature, is an important source of information about changes in the climate of the earth.

Interglacial optimum

An interglacial optimum, or climatic optimum of an interglacial, is the period within an interglacial that experienced the most 'favourable' climate that occurred during that interglacial, often during the middle part. The climatic optimum of an interglacial follows, and is followed by, phases that are within the same interglacial and that experienced a less favourable climate (but nevertheless a 'better' climate than during the preceding/succeeding glacials). During an interglacial optimum, sea levels rise to their highest values, but not necessarily exactly at the same time as the climatic optimum.

In the present interglacial, the Holocene, the climatic optimum occurred during the Subboreal (5 to 2.5 ka BP, which corresponds to 3000 BC–500 BC) and Atlanticum (9 to 5 ka, which corresponds to roughly 7000 BC–3000 BC). Our current climatic phase following this climatic optimum is still within the same interglacial (the Holocene). This warm period was followed by a gradual decline until about 2,000 years ago, with another warm period until the Little Ice Age (1250–1850).

The preceding interglacial optimum occurred during the Late Pleistocene Eemian Stage, 131–114 ka. During the Eemian the climatic optimum took place during pollen zone E4 in the type area (city of Amersfoort, Netherlands). Here this zone is characterized by the expansion of Quercus (oak), Corylus (hazel), Taxus (yew), Ulmus (elm), Fraxinus (ash), Carpinus (hornbeam), and Picea (spruce). During the Eemian Stage sea level was between 5 and 9.4 meters higher than today [4] and the water temperature of the North Sea was about 2 °C higher than at present.

See also

References

  1. ^ Eldredge, S. "Ice Ages – What are they and what causes them?". Utah Geological Survey. Retrieved 2 March 2013.
  2. ^ Rieke, G. "Long Term Climate".
  3. ^ Kottak, Conard Phillip (2005). Window on Humanity. New York: McGraw-Hill. ISBN 978-0-07-289028-0.
  4. ^ Kopp, R.; et al. (2009). "Probabilistic assessment of sea level during the last interglacial stage". Nature. Retrieved 20 Dec 2018.
Ardleigh Gravel Pit

Ardleigh Gravel Pit is a 1.2 hectare geological Site of Special Scientific Interest south of Ardleigh in Essex. It is a Geological Conservation Review site.The site exposes a succession of Pleistocene levels, with an interglacial between two glacial periods. The interglacial may date back 700,000 years. The site has plant microfossils rare or unique in Britain, and according to Natural England's description in 1992, it may become the type site for a previously unrecognised British early middle Pleistocene interglacial.The site is divided into two areas. The main one is L-shaped, forming the sloping south-east and north-east borders of a water filled pit. A footpath between Slough Lane and Park Farm runs along its north-east boundary. East of the main site is a small linear feature which as been filled in. It is on private land with no public access.

Creeting St Mary Pits

Creeting St Mary Pits is a 5.4 hectare geological Site of Special Scientific Interest south Creeting St Mary in Suffolk. It is a Geological Conservation Review site.These former quarries are the type site for the 'Creeting Sands', which are believed to be intertidal and shallow marine deposits from an early Pleistocene interglacial. It is described by Natural England as a key stratigraphic site.This site is in three areas, and there is public access to the southern one, but not to the northern ones.

Cromerian Stage

The Cromerian Stage or Cromerian Complex, also called the Cromerian (German: Cromerium), is a stage in the Pleistocene glacial history of north-western Europe, mostly occurring more than half a million years ago. It is named after the East Anglian town of Cromer in England where interglacial deposits that accumulated during part of this stage were first discovered. The stratotype for this interglacial is the Cromer Forest Bed situated at the bottom of the coastal cliff near West Runton (East Anglia). The Cromerian stage preceded the Anglian and Elsterian glacials and show an absence of glacial deposits in western Europe, which led to the historical terms Cromerian interglacial and the Cromerian warm period (German: Kromer-Warmzeit). It is now known that the Cromerian consisted of multiple glacial and interglacial periods.

Eemian

The Eemian (also called the last interglacial, Sangamonian Stage, Ipswichian, Mikulin, Kaydaky, penultimate, Valdivia or Riss-Würm) was the interglacial period which began about 130,000 years ago at the end of the Penultimate Glacial Period and ended about 115,000 years ago at the beginning of the Last Glacial Period. It corresponds to Marine Isotope Stage 5e. Although sometimes referred to as the "last interglacial" (in the "most recent previous" sense of "last"), it was the second-to-latest interglacial period of the current Ice Age, the most recent being the Holocene which extends to the present day (having followed the last glacial period). The prevailing Eemian climate was, on average, around 1 to 2 degrees Celsius (1.8 to 3.6 Fahrenheit) warmer than that of the Holocene. However, due to global warming, the past few July global temperatures likely surpassed the (long-term average) July temperatures of the Eemian period. During the Eemian, the proportion of CO2 in the atmosphere was about 280 parts per million.The Eemian is known as the Ipswichian in the UK, the Mikulin interglacial in Russia, the Valdivia interglacial in Chile and the Riss-Würm interglacial in the Alps. Depending on how a specific publication defines the Sangamonian Stage of North America, the Eemian is equivalent to either all or part of it.

Flandrian interglacial

The Flandrian interglacial or stage is the name given by geologists and archaeologists in the British Isles to the first, and so far only, stage of the Holocene epoch (the present geological period), covering the period from around 12,000 years ago, at the end of the last glacial period to the present day. As such, it is in practice identical in span to the Holocene. Present climatological theory (based on analysis of Milankovitch cycles) forecasts that the present Flandrian climate should decline in temperature towards a global climate similar to that of the ice age. Less orbital eccentricity may have the effect of moderating this temperature downturn.The Flandrian began as the relatively short-lived Younger Dryas climate downturn came to an end. This formed the last gasp of the Devensian glaciation, the final stage of the Pleistocene epoch and is traditionally seen as the latest warm interglacial in a series that has been occurring throughout the Quaternary geological period.

The first part of the Flandrian, known as the Younger Atlantic, was a period of fairly rapid sea level rise, known as the Flandrian transgression and associated with the melting of the Fenno-Scandian, Scottish, Laurentide and Cordilleran glaciers.

Fjords were formed during the Flandrian transgression when U-shaped glaciated valleys were inundated with water.

Glacial period

A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate between glacial periods. The last glacial period ended about 15,000 years ago. The Holocene epoch is the current interglacial. A time with no glaciers on Earth is considered a greenhouse climate state.

Global cooling

Global cooling was a conjecture during the 1970s of imminent cooling of the Earth's surface and atmosphere culminating in a period of extensive glaciation.

Press reports at the time did not accurately reflect the scientific literature. The current scientific opinion on climate change is that the Earth underwent global warming throughout the 20th century and continues to warm.

Holstein interglacial

The Holstein interglacial (German: Holstein-Warmzeit or Holstein-Interglazial), also called the Mindel-Riss interglacial (Mindel-Riß-Interglazial) in the Alpine region, is the third to last major interglacial before the Holocene, the present warm period. It followed directly after the Elster glaciation and came before the Saale glaciation, during the Middle Pleistocene. The more precise timing is controversial since Holstein is commonly correlated to two different marine isotope stages, MIS 11 (424-374 thousand years ago) and MIS 9 (337-300 thousand years ago). This ambiguity is much related to the correlation problem described in more detail in the article 'Elster glaciation'.

Hoxnian Stage

The Hoxnian Stage is a middle Pleistocene stage (Pleistocene from 2.588 ± .005 million to 11,700 years BP) of the geological history of the British Isles. It precedes the Wolstonian Stage and follows the Anglian Stage. It is equivalent to Marine Isotope Stage 11. Marine Isotope Stage 11 started 424,000 years ago and ended 374,000 years ago. The Hoxnian divided into sub-stages Ho I to Ho IV.The Hoxnian stage has often been correlated to the Holstein Interglacial of northern Continental Europe and the Mindel-Riss Interglacial of the Alps. However, there is ambiguity regarding the correlation of these two interglacials to either MIS 11 or MIS 9, which is related to the MIS 12 / MIS 10 ambiguity described in more detail in the article 'Elster glaciation'.The Hoxnian stage has also been equated to the Yarmouthian (Yarmouth) Stage in North America. However, the Yarmouthian Stage, along with the Kansan, Nebraskan, and Aftonian stages, have been abandoned by North American Quaternary geologists and merged into the Pre-Illinoian Stage. At this time, the Hoxnian and Holstein stages are correlated with a brief part of the Pre-Illinoian Stage lying between the Pre-Illinoian A and Pre-Illinoian B glaciations of North America.The Hoxnian Stage is named after Hoxne in the English county of Suffolk where some of the deposits it created were first found. Plant and vertebrate fossils indicate that it was a period of relatively warm climate. Clactonian and Acheulean flint tools and early human remains have been found dating to this stage.

Ice age

An ice age is a long period of reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth is currently in the Quaternary glaciation, known in popular terminology as the Ice Age. Individual pulses of cold climate are termed "glacial periods" (or, alternatively, "glacials", "glaciations", "glacial stages", "stadials", "stades", or colloquially, "ice ages"), and intermittent warm periods are called "interglacials" or "interstadials" with both climatic pulses part of the Quaternary or other periods in Earth's history.In the terminology of glaciology, ice age implies the presence of extensive ice sheets in both northern and southern hemispheres. By this definition, we are in an interglacial period—the Holocene. The amount of heat trapping gases emitted into Earth's Oceans and atmosphere will prevent the next ice age, which otherwise would begin in around 50,000 years, and likely more glacial cycles.

Marks Tey Brickpit

Marks Tey Brickpit is a 29.5 hectare geological Site of Special Scientific Interest in Marks Tey in Essex. It is a Geological Conservation Review site.This site has a record of pollen throughout the Hoxnian interglacial around 400,000 years ago, and this is the best vegetational record for any British interglacial site. Seasonal layers in lake sediments have made it possible to estimate the duration of the Hoxnian. Clay deposited in the lake is quarried at a brickworks on the site, and this exposes layers above the Hoxnian ones of a later colder period. There is also a Grade II listed early nineteenth-century bottle kiln and brick tile works on the site.The site is overgrown apart from a small area used for brick making. It is private land with no public access, but a small area, which is now a field, can be seen from Marks Tey railway station car park.

Middle Pleistocene

The Middle Pleistocene is a subdivision of the Pleistocene Epoch, from 781,000 to 126,000 years ago (781–126 ka). It is preceded by the Calabrian stage, beginning with the Brunhes–Matuyama reversal, and succeeded by the Tarantian stage (equivalent to the Late or Upper Pleistocene), taken as beginning with the last interglacial (MIS 5).

The tripartite subdivision of the Pleistocene into Lower (Early), Middle and Upper (Late) has been in use since the 1930s.

It is in use as a provisional or "quasi-formal" designation by the International Union of Geological Sciences (IUGS) as of 2018,

pending the ratification of the 2017 proposal by the International Commission on Stratigraphy (Subcommission on Quaternary Stratigraphy, ICSSQS) of the Chibanian stage.The Middle Pleistocene contains the transition from the Lower to Middle Paleolithic in palaeoanthropology, i.e. the emergence of Homo sapiens at 300,000 years ago. The oldest known human DNA dates to the Middle Pleistocene.

Mindel glaciation

The Mindel glaciation (German: Mindel-Kaltzeit, also Mindel-Glazial, Mindel-Komplex or, colloquially, Mindel-Eiszeit) is the third oldest glacial stage in the Alps. Its name was coined by Albrecht Penck and Eduard Brückner, who named it after the Swabian river, the Mindel. The Mindel glacial occurred in the Middle Pleistocene; it was preceded by the Haslach-Mindel interglacial (often regarded as part of Günz) and succeeded by the Mindel-Riss interglacial (Holstein interglacial).

The Mindel glaciation is commonly correlated to the Elster glaciation of northern Europe. The more precise timing is controversial since Mindel is commonly correlated to two different marine isotope stages, MIS 12 (478-424 thousand years ago) and MIS 10 (374-337 thousand years ago). This ambiguity is much related to the correlation problem described in more detail in the article 'Elster glaciation'.

Pre-Illinoian

The Pre-Illinoian Stage is used by Quaternary geologists for the early and middle Pleistocene glacial and interglacial periods of geologic time in North America from ~2.5–0.2 Ma (million years ago).

Quaternary glaciation

The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial and interglacial periods during the Quaternary period that began 2.58 Ma (million years ago), and is ongoing. Although geologists describe the entire time period as an "ice age", in popular culture the term "ice age" is usually associated with just the most recent glacial period. Since earth still has ice sheets, geologists consider the Quaternary glaciation to be ongoing, with earth now experiencing an interglacial period.

During the Quaternary glaciation, ice sheets appeared. During glacial periods they expanded, and during interglacial periods they contracted. Since the end of the last glacial period the only surviving ice sheets are the Antarctic and Greenland ice sheets. Other ice sheets, such as the Laurentide ice sheet, formed during glacial periods and completely disappeared during interglacials. The major effects of the Quaternary glaciation, have been the erosion of land and the deposition of material, both over large parts of the continents; the modification of river systems; the creation of millions of lakes, including the development of pluvial lakes far from the ice margins; changes in sea level; the isostatic adjustment of the Earth's crust; flooding; and abnormal winds. The ice sheets themselves, by raising the albedo (the extent to which the radiant energy of the Sun is reflected from Earth) created significant feedback to further cool the climate. These effects have shaped entire environments on land and in the oceans, and their associated biological communities.

Before the quaternary glaciation, land-based ice appeared, and then disappeared, during at least four other ice ages.

Sangamonian

The Sangamonian Stage (or Sangamon interglacial) is the term used in North America to designate the last interglacial period. In its most common usage, it is used for the period of time between 75,000 and 125,000 BP. This period of time is equivalent to all of Marine Isotope Stage 5 and the combined Eemian period and early part of the Weichselian glaciation in Europe. Less commonly, the Sangamonian Stage is restricted to the period between 122,000 and 132,000 BP, which is equivalent to Marine Oxygen Isotope Substage 5e and the Eemian period of Europe. It preceded the Wisconsinan (Wisconsin) Stage and followed the Illinoian Stage in North America.

Stadial

Stadials and interstadials are phases dividing the Quaternary period, or the last 2.6 million years. Stadials are periods of colder climate while interstadials are periods of warmer climate.

Each Quaternary climate phase is associated with a Marine Isotope Stage (MIS) number, which describe alternation between warmer and cooler temperatures as measured by oxygen isotope data. Stadials have even MIS numbers and interstadials odd MIS numbers. The current Holocene interstadial is MIS 1 and the Last glacial maximum stadial is MIS 2.

Marine Isotope Stages are sometimes further subdivided into stadials and interstadials by minor climate fluctuations within the overall stadial or interstadial regime, which are indicated by letters. The odd-numbered interstadial MIS 5, also known as the Sangamonian interglacial, contains two periods of relative cooling, and so is subdivided into three interstadials (5a, 5c, 5e) and two stadials (5b, 5d). A stadial isotope stage like MIS 6 would be subdivided by periods of relative warming, and so in that case the first and last subdivisions would be stadials; MIS 6a, 6c and 6e are stadials while 6b and 6d are interstadials.

Timeline of glaciation

There have been five or six major ice ages in the history of Earth over the past 3 billion years.

The Late Cenozoic Ice Age began 34 million years ago, its latest phase being the Quaternary glaciation, in progress since 2.58 million years ago.

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 such an interglacial period of the Quaternary glaciation, with the last glacial period of the Quaternary having ended approximately 11,700 years ago, the current interglacial being known as the Holocene epoch.

Based on climate proxies, paleoclimatologists study the different climate states originating from glaciation.

Wivenhoe Gravel Pit

Wivenhoe Gravel Pit is a 2.1 hectare geological Site of Special Scientific Interest north of Wivenhoe in Essex. It is a Geological Conservation Review site.The site is the type locality for the Wivenhoe Gravel, which was laid down by the River Thames before it was diverted south to its present course by the Anglian glaciation around 450,000 years ago. The gravel was laid down during two cold stages with an intervening interglacial, but the fossils in from this warmer period are not distinctive enough to identify which interglacial they come from. The site is important for establishing the previous course of the Thames. Two worked flints may be evidence of occupation by Homo heidelbergensis around half a million years ago.The pit, which is now water filled, is in a field off Brightlingsea Road opposite Broad Lanes.

Continental glaciations
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Landforms
North America
Eurasia and
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