Eemian

The Eemian Interglacial ( Eemian interglacial synonym ), often referred to simply as the Eemian, the last interglacial period was prior to today, the Holocene. It began around 126,000 years ago and ended 115,000 years ago and is named after the river Eem in the Netherlands.

Scholarship on the Eemian

The Eemian was recognized in 1874 as an independent stratigraphic unit after Pieter Harting had promoted in drilling in the area of Amersfoort (Netherlands) fossil- rich material to light, the species composition was far removed from that of the present-day North Sea. In contrast, many very similar species of snails and mussels in the Atlantic Ocean south of the Strait of Dover were found; their range now extends from the coast of Portugal ( Lusitanian faunal province ) to the Mediterranean ( Mediterranean faunal province ). This was a sign that had during the period in which the sediments were deposited with the fossils that have much higher temperatures than today prevailed at that latitude for Harting. Harting called the deposits " Système Eémien ", after the river Eem near Amersfoort.

Later, the composition of the Dutch molluscan fauna from the Eemian of Lorie (1887 ) and Spaink (1958 ) has been thoroughly investigated. Index fossils were laid down, with the help of the same age stratigraphic layers were identified. It was shown that the layers of the Eemian often deposited on the ground moraines of the Saale glaciation and above them local river gravel or aeolian deposits from the Weichsel glaciation can be found. This suggests a warm period between these two cold periods.

In the Netherlands, however, the deposits of the Eemian are never overshadowed by moraines of the Vistula glaciation.

Van Voorthuysen published a work on the foraminifera of the type locality and Zagwijn few years later the palynology with the pollen zones ( 1961) in 1958. At the end of the twentieth century, the type locality was again and this time multidisciplinary examined on the basis of old and new data ( Clever Inga et al., 2000). Simultaneously, a Para stratotype has been designated, it is within the Glazialbecken of Amsterdam. In the course of drilling Amsterdam Terminal ( Van Leeuwen et al., 2000), this type has been described in an interdisciplinary way. These authors also published a uranium -thorium dating of deposits spätinterglazialen this hole with an age of 118,200 years (± 6300 years ).

A historical overview of the Dutch Eemian studies allow Bosch, Clever Inga and Meijer in 2000.

Duration and climate change

The Eemian interglacial period had a duration of about 11,000 years. It began around 126,000 years ago, according to the Saale ice age or crack ice age ended about 115,000 years ago with the beginning of the last glacial period. The Eemian interglacial period was characterized by relatively stable climatic conditions. The temperature optimum of the interglacial period in Europe was several degrees above today's average temperature. This had the effect, among other things, that the sea level was higher than at present and many plains and basins were flooded ( transgression ).

The beginning of the Eemian interglacial period coincides with the beginning of Jungpleistozäns. This includes the Eemian and the last glacial period. Then began the Holocene warm period those in which we live today. The characteristic point for the beginning of the Eemian interglacial period, the change in the ratio of oxygen isotopes is given approximately 126,000 years ago in the geological time scale. This change can be found in the shells of microorganisms in marine sediments from this period.

With palynological studies of cores from Eifel maars could be shown that during the transition between the Eemian and the last cold period occurred a drought period of 468 years. Forest fires and dust storms affected the forests in the Eifel and left their traces in the sediments. Maybe by changes in ocean currents, there was an absence of precipitation. Fresh water was bound in the ice of the advancing glacier. The drought came abruptly, within 100 years had to give the prevailing forest steppe. Then the trees in the Eifel apparently returned back again, while further north prevailed colder conditions. In the Eifel, the mixed forests could still hold about 8,000 years, until the next pulse of the cold glacial climate variations only allowed for a tundra vegetation. This mixed forest period but no longer part of the Eemian in the strict sense.

Climate changes during the Eemian - Findings from ice cores

Climate research has gained momentum in recent years, many insights into the climate of the past. Helpful included the Summit ice core (72 ° 34 'N, 37 ° 37 ' W ), which was taken from 1990 to 1992 by the European ice core project ( GRIP ), and from NGRIP (North Greenland Ice Core Project) in the years 1996-2003 drawn ice core:

In both cores, among others, the oxygen isotope ratio 18O/16O was investigated, which is mainly determined by the cloud temperature at the time of snow formation, and may thus give direct information about the temperature.

The determination of the time scales is extremely difficult. It has this for the Summit ice core, after comparison with other climate proxies ( ice cores, sediment cores, etc.) is considered to be sufficiently accurate, at least for the last 130 thousand years ago today, especially the fact that folding and flow of the ice sheet in the area of Summit station was largely excluded.

The variations in the oxygen isotope ratio in this ice core indicated suggests that climate fluctuations ( Dansgaard -Oeschger event, Heinrich events ) were not limited to the last ice age, but also be drawn through the profile before this glacial ( Eemian, Saale glaciation ). This is in contrast to the relatively high climatic stability of the current interglacial period ( Holocene, since about 11,700 cal BP). It has therefore been suggested that the stability of the current warm period is the exception rather than the rule.

The violent oscillations in the Summit ice core during the Eemian interglacial period, however, were not in the Vostok ice core ( Antarctica ) still retrieve sediment cores in the deep sea. Therefore, it was initially assumed that the Greenland ice reflects short-term fluctuations in atmospheric and ocean circulation of the North Atlantic region.

It soon turned out that the lowest 10 percent of the ice core were still exposed to folding and flowing. The chronology of the Eemian was thus violently disturbed, why then the NGRIP ice core was recovered and used for comparisons. It had been previously ascertained precisely, that the lower end of the drill core was undisturbed, so as to obtain a clearer picture of the Eemian.

It was found that the Eemian was consistently very stable. The summer temperatures in the northern hemisphere were one to two degrees above today's temperature levels, in Greenland it was as much as 5 ° C warmer. The sea level was 4 to 6 feet above the present level. By comparing with other ice cores in the northwest (Camp Century, 77.2 ° N, 61.1 ° W) and south ( Renland, 71.3 ° N, 26.7 ° W) Greenland turned out that during the entire warm period abschmolz only part of the South Greenlandic ice sheet, the central and nordgrönländische ice sheet, however, despite increased temperatures remained stable. This finding has major impact on the modeling of future sea level rise. The regional differences are expecting a further, in-depth investigation.

In addition, could be seen in the NGRIP ice core that the Eemian interglacial period following ice age was only ushered very slow ( 7000 years ) and took place in front of the truly glacial character in isotope values ​​of a Dansgaard - Oeschger events (DO 25 ), which is very se weak was very similar proceeded ( with an amplitude of 25 per cent the following DO- events ), but the following events. This is a starting point of present studies.

Archaeology of Eemwarmzeit

The Eemian is the time of Mittelpaläolithikums where Neanderthals large parts of Europe and western Asia populated. Outstanding results are hunted forest elephants (see lance of Lehringen or mining Gröbern ) as evidence of a successful big game hunting.