Last Interglacial

The Last Interglacial, also known as the Eemian (primarily used in a European context) among other names (including the Sangamonian, Ipswichian, Mikulino, Kaydaky, Valdivia, and 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. 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). During the Last Interglacial, the proportion of in the atmosphere was about 280 parts per million. 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, 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.

The Last Interglacial is known as the Ipswichian in the UK, the Mikulino (also spelled Milukin) 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 Last Interglacial is equivalent to either all or part of it.

The period falls into the Middle Paleolithic and is of some interest for the evolution of anatomically modern humans, who were present in Western Asia (Skhul and Qafzeh hominins) as well as in Southern Africa by this time, representing the earliest split of modern human populations that persists to the present time (associated with mitochondrial haplogroup L0).

Definition
The Last Interglacial was first recognized from boreholes in the area of the city of Amersfoort, Netherlands, by Pieter Harting (1875). He named the beds "Système Eémien", after the river Eem on which Amersfoort is located. Harting noticed the marine molluscan assemblages to be very different from the modern fauna of the North Sea. Many species from the Last Interglacial layers nowadays show a much more southern distribution, ranging from South of the Strait of Dover to Portugal (Lusitanian faunal province) and even into the Mediterranean (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 by tills that are considered to date from the Saalian, and overlain by local fresh water or wind-blown deposits from the Weichselian. 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 the foraminifera from the type site, whereas Zagwijn (1961) published the palynology, providing a subdivision of this stage into pollen stages. At the end of the 20th century, the type site was re-investigated using old and new data in a multi-disciplinary approach (Cleveringa et al., 2000). At the same time a parastratotype was selected in the Amsterdam glacial basin in the Amsterdam-Terminal borehole and was the subject of a multidisciplinary investigation (Van Leeuwen, et al., 2000). These authors also published a U/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.

Global temperatures
The Last Interglacial climate is believed to have been warmer than the current Holocene. The temperature of the Last Interglacial peaked during the early part of the period, around 128,000 to 123,000 years Before Present, before declining during the latter half of the period. Changes in the Earth's orbital parameters from today (greater obliquity and eccentricity, and perihelion), known as Milankovitch cycles, probably led to greater seasonal temperature variations in the Northern Hemisphere. As the Last Interglacial cooled, pCO2 remained stable.

During the northern summer, temperatures in the Arctic region were about 2–4 °C higher than in 2011. The Arctic Last Interglacial climate was highly unstable, with pronounced temperature swings revealed by δ18O fluctuations in Greenlandic ice cores, though some of the instability inferred from Greenland ice core project records may be a result of mixing of Last Interglacial ice with ice from the preceding or succeeding glacial intervals.

The warmest peak of the Last Interglacial was around 125,000 years ago, when forests reached as far north as North Cape, Norway (which is now tundra) well above the Arctic Circle at 71.1725°N, 25.79444°W. Hardwood trees such as hazel and oak grew as far north as Oulu, 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. 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. A 2018 study based on soil samples from Sokli in northern Finland identified abrupt cold spells ca. 120,000 years ago caused by shifts in the North 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. During an insolation maximum from 133,000 to 130,000 BP, meltwater from the Dnieper and Volga caused the Black and Caspian Seas to connect. During the middle of the Last Interglacial, a weakened Atlantic Meridional Overturning Circulation (AMOC) began to cool the eastern Mediterranean region. 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, and by 112,000 BC, ice caps began to form in southern Norway, marking the start of a new glacial period. The Eemian lasted about 1,500 to 3,000 years longer in Southern Europe than in Northern Europe. Kaspar et al. (GRL, 2005) performed a comparison of a coupled general circulation model (GCM) with reconstructed Last Interglacial temperatures for Europe. Central Europe (north of the Alps) was found to be 1 - 2 C-change 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.

Meltwater pulse 2B, approximately 133,000 BP, substantially weakened the Indian Summer Monsoon (ISM).

Trees grew as far north as southern Baffin Island in the Canadian Arctic Archipelago: currently, the northern limit is further south at Kuujjuaq in northern Quebec. Coastal Alaska was warm enough during the summer due to reduced sea ice in the Arctic Ocean to allow Saint 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. The prairie-forest boundary in the Great Plains of the United States lay further west near Lubbock, Texas, whereas the current boundary is near Dallas.

Interglacial conditions ended on Antarctica while the Northern Hemisphere was still experiencing warmth.

Sea level


Sea level at peak was probably 6 to 9 m higher than today, with Greenland contributing 0.6 to 3.5 m, thermal expansion and mountain glaciers contributing up to 1 m, and an uncertain contribution from Antarctica. A 2007 study found evidence that the Greenland ice core site Dye 3 was glaciated during the Last Interglacial, which implies that Greenland could have contributed at most 2 m to sea level rise. 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. Global mean sea 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 the Red Sea coastlines. These reefs often contain internal erosion surfaces showing significant sea level instability during the Last Interglacial.

Along the Central Mediterranean Spanish coast, sea levels were comparable to those of the present. Scandinavia formed an island due to the area between the Gulf of Finland and the White Sea being drowned. Vast areas of northwestern Europe and the West Siberian Plain were inundated.

Fauna
The warmness of the interval allowed temperate-adapted taxa to extend their considerably northward, with range of the hippopotamus (Hippopotamus amphibius) notably extending as far north as North Yorkshire in northern England, thought its range outside of southern Europe did not extend much further east of than the Rhine. The temperate landscapes of Europe were inhabited by large now extinct megafauna including the straight-tusked elephant (Palaeoloxodon antiquus), the narrow-nosed rhinoceros (Stephanorhinus hemitoechus), Merck's rhinoceros (Stephanorhinus hemitoechus), Irish elk (Megaloceros giganteus) and aurochs (Bos primigenius), alongside still-living species like red deer (Cervus elaphus), fallow deer (Dama dama), roe deer (Capreolus capreolus) and wild boar (Sus scrofa), with predators including lions (the extinct Panthera spelaea) and hyenas (Crocuta spelaea), brown bears (Ursus arctos) and wolves (Canis lupus).

In contrast, the range of cold-adapted taxa like the woolly mammoth (Mammuthus primigenius) contracted. The steppe 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 bison Bison 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 the Rancholabrean faunal age in North America. Also during this time period the American 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 preceeding Penultimate Glacial Period.

Paleoanthropology
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. However, unlike previous interglacials they were absent from Britain, likely due to Britain being an island during this time. During the Last Interglacial, Neanderthals engaged in a variety of food-gathering activites, including fishing, as well as big-game hunting, including the largest animals living in Europe at the time, straight-tusked elephants. Modern humans were present outside Africa in Arabia during this interval, as far east as the Persian Gulf.