Last Interglacial
The Eemian interglacial era (known as the Sangamon interglacial in North America, the Ipswichian interglacial in the UK, and the Riss-Würm interglacial in the Alps) is the second-to-latest interglacial era of the Ice Age. It began about 131,000 years ago. Changes in orbital parameters from today (greater obliquity and eccentricity, and perihelion), known as the Milankovitch cycle, probably led to greater seasonal temperature variations in the Northern Hemisphere, although global annual means temperatures were probably similar to those of the Holocene. The Eemian climate is believed to have been about as stable as, but probably warmer than that of, the Holocene (see ice core). The warmest peak of the Eemian was around 125,000 years ago, when forests reached as far north as North Cape (which is now tundra) in northern Norway well above the Arctic Circle at 71°10′21″N 25°47′40″E / 71.17250°N 25.79444°E. Hardwood trees like hazel and oak grew as far north as Oulu, Finland. Sea levels at that time were 4-6 meters higher than they are now, indicating greater deglaciation than today (mostly from partial melting of the ice sheets of Greenland and Antarctica). One study published in July 2007 found evidence that Dye 3 was glaciated during the Eemian,[1] which implies that Greenland could have contributed at most 2 m (6.6 ft) to sea level rise.[2][3] Scandinavia was an island due to the inundation of vast areas of northern Europe and the West Siberian Plain.
At the peak of the Eemian, the northern hemisphere winters were generally warmer and wetter than now, though some areas were actually slightly cooler than today. Trees grew as far north as southern Baffin Island in the Canadian Arctic Archipelago instead of only as far north as Kuujjuaq in northern Quebec, and the prairie-forest boundary in the Great Plains of the United States lay further west — near Lubbock, Texas, instead of near Dallas, Texas, where the boundary now exists. The era closed as temperatures steadily fell to conditions cooler and drier than the present, with 468-year long aridity pulse in central Europe,[4] and by 114,000 years ago, a glacial era had returned.
Kaspar et al. (GRL, 2005) perform a comparison of a coupled GCM with reconstructed Eemian temperatures for Europe. Central Europe (north of the Alps) is found to be 1-2°C warmer than present; south of the alps conditions are 1-2°C cooler than today. The model (forced with observed GHG concentrations and Eemian orbital parameters) generally reproduces these observations, and hence they conclude that these factors are enough to explain the Eemian temperatures.[5]
Definition of the Eemian
The Eemian Interglacial was first recognized from boreholes in the area of the city of Amersfoort (The Netherlands) by Harting (1875). He named the beds "Système Eémien", after the river Eem on which Amersfoort is banked. Harting noticed the marine molluscan assemblages to be very different from the modern fauna that occurs in the North Sea. Many species from the Eemian 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 about the molluscan assemblages is given by Lorié (1887), and Spaink (1958). Since its discovery, Eemian beds in the Netherlands have mainly been recognized on their marine molluscan content combined with their stratigraphical position and other palaeontology. In the type-area the marine beds 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. Contrary to for instance the deposits in Denmark, the Eemian deposits in the type area have never been found overlain by tills, nor in ice-pushed position.
Van Voorthuysen (1958) described the foraminifera from the type site, whereas Zagwijn (1961) published the palynology, providing a subdivision of the interglacial into pollenstages. At the end of the twentieth 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 and multidisciplinary investigated in the Amsterdam glacial basin in the Amsterdam-Terminal borehole (Van Leeuwen, et al., 2000). These authors also published a U/Th age for late Eemian deposits from this borehole of 118.2 ±6.3 Ka. A historical review of Dutch Eemian research is provided by Bosch, Cleveringa and Meijer, 2000.
Sea level
Sea level at peak was probably 4-6m higher than today (references in Overpeck et al.), with much of this coming from Greenland but some likely to have come from Antarctica. Global mean sea surface temperatures are not thought to have been significantly higher than holocene, hence the thermal expansion difference from today is small.
Ipswichian interglacial
This name is used by British geologists and archaeologists who named it after the town of Ipswich in the English county of Suffolk, where some of the deposits it created were first found.
See also
Notes
- ^ Willerslev, Eske (2007). "Ancient Biomolecules from Deep Ice Cores Reveal a Forested Southern Greenland". Science. 317 (5834): 111–114. doi:10.1126/science.1141758.
{{cite journal}}: Cite has empty unknown parameter:|month=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Cuffey, Kurt M. (2000). "Substantial contribution to sea-level rise during the last interglacial from the Greenland ice sheet". Nature. 404: 591–594. doi:10.1038/35007053.
{{cite journal}}: Cite has empty unknown parameter:|month=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Otto-Bliesner, Bette L. (2006). "Simulating Arctic Climate Warmth and Icefield Retreat in the Last Interglaciation". Science. 311 (5768): 1751–1753. doi:10.1126/science.1120808.
{{cite journal}}: Cite has empty unknown parameter:|month=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Sirocko, Frank (2005). "A late Eemian aridity pulse in central Europe during the last glacial inception". Nature. 436: 833–836. doi:10.1038/nature03905.
{{cite journal}}: Cite has empty unknown parameter:|month=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Kaspar, Frank (2005). "A model-data comparison of European temperatures in the Eemian interglacial". Geophysical Research Letters. 32 (L11703). doi:10.1029/2005GL022456.
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Further reading
- Bosch, J.H.A., P. Cleveringa & T. Meijer, 2000. The Eemian stage in the Netherlands: history, character and new research. Geologie & Mijnbouw / Netherlands Journal of Geosciences, 79(2/3): 135-145.
- Cleveringa, P., Meijer, T., van Leeuwen, R.J.W., de Wolf, H., Pouwer, R., Lissenberg T. and Burger, A.W., 2000. The Eemian stratotype locality at Amersfoort in the central Netherlands: a re-evaluation of old and new data. Geologie & Mijnbouw / Netherlands Journal of Geosciences, 79(2/3): 197-216.
- Harting, P., 1875. Le système Éemien Archives Néerlandaises Sciences Exactes et Naturelles de la Societé Hollandaise des Sciences (Harlem), 10: 443-454.
- Harting, P., 1886. Het Eemdal en het Eemstelsel Album der Natuur, 1886: 95-100.
- Jonathan T. Overpeck, Bette L. Otto-Bliesner, Gifford H. Miller, Daniel R. Muhs, Richard B. Alley, Jeffrey T. Kiehl, 2006. Paleoclimatic Evidence for Future Ice-Sheet Instability and Rapid Sea-Level Rise, Science 311, 24 March 2006.
- 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.
- Spaink, G., 1958. De Nederlandse Eemlagen, I: Algemeen overzicht. Wetenschappelijke Mededelingen Koninklijke Nederlandse Natuurhistorische Vereniging 29, 44 pp.
- Van Leeuwen, R.J. , Beets, D., Bosch, J.H.A., Burger, A.W., Cleveringa, P., van Harten, D., Herngreen, G.F.W., Langereis, C.G., Meijer, T., Pouwer, R., de Wolf, H., 2000. Stratigraphy and integrated facies analysis of the Saalian and Eemian sediments in the Amsterdam-Terminal borehole, the Netherlands. Geologie en Mijnbouw / Netherlands Journal of Geosciences 79, 161-196.
- 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.
