Two ice core temperature records; the Last Interglacial is at a depth of about 1500–1800 meters in the lower graphCO2 concentrations over the last 800,000 years as measured from ice cores
TheLast Interglacial, also known as theEemian, was theinterglacial period which began about 130,000 years ago at the end of thePenultimate Glacial Period and ended about 115,000 years ago at the beginning of theLast Glacial Period.[1] It corresponds toMarine Isotope Stage 5e.[2] It was the second-to-latest interglacial period of the current Ice Age, the most recent being theHolocene which extends to the present day (having followed thelast glacial period). During the Last Interglacial, the proportion of CO2 in the atmosphere was about 280 parts per million.[3] The Last Interglacial was one of the warmest periods of the last 800,000 years, with temperatures comparable to and at times warmer (by up to on average 2 degrees Celsius) than the contemporary Holocene interglacial,[4][5] with the maximum sea level being up to 6 to 9 metres higher than at present, with global ice volume likely also being smaller than the Holocene interglacial.[6]
The Last Interglacial is known as the Eemian in northern Europe (sometimes used to describe the global interglacial), Ipswichian in Britain, the Mikulino (also spelled Milukin) interglacial in Russia, the Kaydaky in Ukraine, the Valdivia interglacial inChile, and the Riss-Würm interglacial in theAlps. Depending on how a specific publication defines theSangamonian Stage of North America, the Last Interglacial is equivalent to either all or part of it.
The period falls into theMiddle Paleolithic and is of some interest for the evolution ofanatomically modern humans, who were present inWestern Asia (Skhul and Qafzeh hominins) as well as inSouthern Africa by this time, representing the earliest split of modern human populations that persists to the present time (associated withmitochondrial haplogroup L0).[7] As the most recent point in time with a climate comparable to the Holocene, the Last Interglacial is also of relevance as a point of reference (baseline) for nature conservation.
The Last Interglacial was first recognized fromboreholes in the area of the city ofAmersfoort,Netherlands, byPieter Harting (1875). He named the beds "Système Eémien", after the riverEem on which Amersfoort is located. Harting noticed the marine molluscan assemblages to be very different from the modern fauna of theNorth Sea. Many species from the Last Interglacial layers nowadays show a much more southern distribution, ranging from South of theStrait of Dover toPortugal (Lusitanian faunal province) and even into theMediterranean (Mediterranean faunal province). More information on the molluscan assemblages is given by Lorié (1887), and Spaink (1958). Since their discovery, Last Interglacial beds in the Netherlands have mainly been recognized by their marine molluscan content combined with their stratigraphical position and other palaeontology. The marine beds there are often underlain bytills that are considered to date from theSaalian, and overlain by local fresh water or wind-blown deposits from theWeichselian. In contrast to e.g. the deposits in Denmark, the Last Interglacial deposits in the type area have never been found overlain by tills, nor in ice-pushed positions.
Van Voorthuysen (1958) described theforaminifera from the type site, whereas Zagwijn (1961) published thepalynology, providing a subdivision of this stage into pollen stages. At the end of the 20th century, thetype site was re-investigated using old and new data in a multi-disciplinary approach (Cleveringa et al., 2000). At the same time aparastratotype was selected in theAmsterdam glacial basin in the Amsterdam-Terminal borehole and was the subject of a multidisciplinary investigation (Van Leeuwen, et al., 2000). These authors also published aU/Th age for late Last Interglacial deposits from this borehole of 118,200 ± 6,300 years ago. A historical review of Dutch Last Interglacial research is provided by Bosch, Cleveringa and Meijer, 2000.
The Last Interglacial climate is believed to have been warmer than the current Holocene.[8][9] The temperature of the Last Interglacial peaked during the early part of the period, around 128,000 to 123,000 yearsBefore Present, before declining during the latter half of the period.[10] Changes in the Earth's orbital parameters from today (greater obliquity and eccentricity, and perihelion), known asMilankovitch cycles, probably led to greater seasonal temperature variations in the Northern Hemisphere.[citation needed] As the Last Interglacial cooled,pCO2 remained stable.[11]
During the northern summer, temperatures in the Arctic region were about 2–4 °C higher than in 2011.[12] The Arctic Last Interglacial climate was highly unstable, with pronounced temperature swings revealed by δ18O fluctuations in Greenlandic ice cores,[13] though some of the instability inferred fromGreenland ice core project records may be a result of mixing of Last Interglacial ice with ice from the preceding or succeeding glacial intervals.[14]
The warmest peak of the Last Interglacial was around 125,000 years ago, when forests reached as far north asNorth Cape, Norway (which is nowtundra) well above theArctic Circle at71°10′21″N25°47′40″E / 71.17250°N 25.79444°E /71.17250; 25.79444.Hardwood trees such ashazel andoak grew as far north asOulu, Finland. At the peak of the Last Interglacial, the Northern Hemisphere winters were generally warmer and wetter than now, though some areas were actually slightly cooler than today.[citation needed] A cooling event similar to but not exactly mirroring the 8.2-kiloyear event is recorded from Beckentin during the E5 phase of the Eemian, some 6,290 years after the start of interglacial afforestation.[15] A 2018 study based on soil samples fromSokli in northernFinland identified abrupt cold spells ca. 120,000 years ago caused by shifts in theNorth Atlantic Current, lasting hundreds of years and causing temperature drops of a few degrees and vegetation changes in these regions. In Northern Europe, winter temperatures rose over the course of the Last Interglacial while summer temperatures fell.[16] During an insolation maximum from 133,000 to 130,000 BP, meltwater from theDnieper andVolga caused the Black and Caspian Seas to connect.[17] During the middle of the Last Interglacial, a weakenedAtlantic Meridional Overturning Circulation (AMOC) began to cool the eastern Mediterranean region.[18] The period closed as temperatures steadily fell to conditions cooler and drier than the present, with a 468-year-long aridity pulse in central Europe at about 116,000 BC,[19] and by 112,000 BC, ice caps began to form in southern Norway, marking the start of a newglacial period.[20] The Eemian lasted about 1,500 to 3,000 years longer in Southern Europe than in Northern Europe.[21] Kasparet al. (GRL, 2005) performed a comparison of a coupledgeneral circulation model (GCM) with reconstructed Last Interglacial temperatures for Europe. Central Europe (north of the Alps) was found to be 1–2 °C (1.8–3.6 °F) warmer than present; south of the Alps, conditions were 1–2 °C cooler than today. The model (generated using observed greenhouse gas concentrations and Last Interglacial orbital parameters) generally reproduces these observations, leading them to conclude that these factors are enough to explain the Last Interglacial temperatures.[22]
Meltwater pulse 2B, approximately 133,000 BP, substantially weakened the Indian Summer Monsoon (ISM).[23]
Trees grew as far north as southernBaffin Island in theCanadianArctic Archipelago: currently, the northern limit is further south atKuujjuaq in northernQuebec. Coastal Alaska was warm enough during the summer due to reduced sea ice in the Arctic Ocean to allowSaint Lawrence Island (now tundra) to have boreal forest, although inadequate precipitation caused a reduction in the forest cover in interior Alaska and Yukon Territory despite warmer conditions.[24] The prairie-forest boundary in theGreat Plains of theUnited States lay further west nearLubbock, Texas, whereas the current boundary is nearDallas.
Interglacial conditions ended on Antarctica while the Northern Hemisphere was still experiencing warmth.[25]
Last Interglacialerosion surface in a fossil coral reef onGreat Inagua,The Bahamas. Foreground shows corals truncated by erosion; behind the geologist is a post-erosion coral pillar which grew on the surface after sea level rose again.[26]
Sea level at peak was probably 6 to 9 metres (20 to 30 feet) higher than today,[27][28] with Greenland contributing 0.6 to 3.5 m (2.0 to 11.5 ft),[29] thermal expansion and mountain glaciers contributing up to 1 m (3.3 ft),[30] and an uncertain contribution from Antarctica.[31] A 2007 study found evidence that the Greenland ice core siteDye 3 was glaciated during the Last Interglacial,[32] which implies that Greenland could have contributed at most 2 m (6.6 ft) tosea level rise.[33][34] Recent research on marine sediment cores offshore of the West Antarctic Ice Sheet suggest that the sheet melted during the Last Interglacial, and that ocean waters rose as fast as 2.5 meters per century.[35] Global meansea surface temperatures are thought to have been higher than in the Holocene, but not by enough to explain the rise in sea level through thermal expansion alone, and so melting of polar ice caps must also have occurred.
Because of the sea level drop since the Last Interglacial, exposed fossil coral reefs are common in the tropics, especially in the Caribbean and along theRed Sea coastlines. These reefs often contain internal erosion surfaces showing significant sea level instability during the Last Interglacial.[36]
Along the Central Mediterranean Spanish coast, sea levels were comparable to those of the present.[37]Scandinavia formed an island due to the area between theGulf of Finland and theWhite Sea being drowned. Vast areas of northwestern Europe and theWest Siberian Plain were inundated.[38]
The warmness of the interval allowed temperate-adapted taxa to extend their range considerably northward, with the range of thehippopotamus (Hippopotamus amphibius) notably extending as far north asNorth Yorkshire in northern England,[39] though their range outside of southern Europe did not extend much further east of than theRhine.[40] The temperate landscapes of Europe were inhabited by large now extinct megafauna including thestraight-tusked elephant (Palaeoloxodon antiquus), thenarrow-nosed rhinoceros (Stephanorhinus hemitoechus),Merck's rhinoceros (Stephanorhinus kirchbergensis),Irish elk (Megaloceros giganteus) andaurochs (Bos primigenius), alongside still-living species likered deer (Cervus elaphus),fallow deer (Dama dama),roe deer (Capreolus capreolus) andwild boar (Sus scrofa), with predators including lions (the extinctPanthera spelaea) andcave hyenas (Crocuta (Crocuta)spelaea),brown bears (Ursus arctos) andwolves (Canis lupus).[40][41][42] The Last Interglacial ecosystems of Europe, which existed prior to theglobal wave of megafauna extinctions that occurred during the following Last Glacial Period, has been suggested as a "baseline" reference point for the analysis and restoration of modern European ecosystems.[41][43]
Following the melting of theLaurentide Ice Sheet, a number of North American megafauna species migrated northwards to inhabit northern Canada and Alaska during the Last Interglacial, including the American camelCamelops hesternus,[44]mastodons (genusMammut)[45] the large ground slothMegalonyx jeffersonii, and the bear sized giant beaverCastoroides, with the lower latitudes of Canada being inhabited (in addition to the aformentioned taxa) by species likeColumbian mammoth (Mammuthus columbi),stag-moose (Cervalces), and the llamaHemiauchenia.[46] Thesteppe bison (Bison priscus) migrated into the heartlands of North America from Alaska at the beginning of the Last Interglacial, giving rise to the giant long-horned bisonBison latifrons (which is first known from the Snowmass site in Colorado, dating to around 120,000 years ago) and ultimately all North American bison species, and marking the beginning of theRancholabrean faunal age in North America.[47] Also during this time period theAmerican lion (Panthera atrox) appeared and become widespread across North America, having descended from populations of the Eurasian cave lion (Panthera spelaea) that had migrated into Alaska during the preceding Penultimate Glacial Period.[48]
The range of cold-adapted taxa like thewoolly mammoth (Mammuthus primigenius) contracted towardsrefugia.[49]
Neanderthals managed to colonise the higher latitudes of Europe during this time interval, after having retreated from the region due to unfavourable conditions during the Penultimate Glacial Period.[50] However, unlike previous interglacials, they were absent from Britain, likely due to Britain being an island during this time.[51] During the Last Interglacial, Neanderthals engaged in a variety of food-gathering activities, including fishing,[52] as well as big-game hunting, including the largest animals living in Europe at the time, straight-tusked elephants.[53] Modern humans were present outside Africa in Arabia during this interval, as far east as thePersian Gulf.[54]
^Wilson, M. A.; Curran, H. A.; White, B. (2007). "Paleontological evidence of a brief global sea-level event during the last interglacial".Lethaia.31 (3):241–250.doi:10.1111/j.1502-3931.1998.tb00513.x.
Harting, P., 1875.Le système Éemien Archives Néerlandaises Sciences Exactes et Naturelles de la Société Hollandaise des Sciences (Harlem), 10: 443–454.
Harting, P., 1886.Het Eemdal en het Eemstelsel Album der Natuur, 1886: 95–100.
Lorié, J., 1887.Contributions a la géologie des Pays Bas III. Le Diluvium plus récent ou sableux et le système Eémien Archives Teyler, Ser. II, Vol. III: 104–160.
Müller, Ulrich C.; et al. (2005). "Cyclic climate fluctuations during the last interglacial in central Europe".Geology.33 (6):449–452.Bibcode:2005Geo....33..449M.doi:10.1130/G21321.1.
Spaink, G., 1958.De Nederlandse Eemlagen, I: Algemeen overzicht. Wetenschappelijke Mededelingen Koninklijke Nederlandse Natuurhistorische Vereniging 29, 44 pp.
Van Voorthuysen, J.H., 1958.Foraminiferen aus dem Eemien (Riss-Würm-Interglazial) in der Bohrung Amersfoort I (Locus Typicus). Mededelingen Geologische Stichting NS 11(1957), 27–39.
Zagwijn, W.H., 1961.Vegetation, climate and radiocarbon datings in the Late Pleistocene of the Netherlands. Part 1: Eemian and Early Weichselian. Mededelingen Geologische Stichting NS 14, 15–45.
.jpg)
