Eemian: Wikis

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Two ice core temperature records; the Eemian is at a depth of about 1500-1800 meters in the lower graph

Eemian, once called the Eemian Interglacial period, is temporally equivalent to the Sangamonian Stage (sensu stricto) in North America, the Ipswichian Stage in the UK, and the Riss-Würm interglacial in the Alps. It is the second-to-latest interglacial period of the Ice Age. It began about 130,000 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. 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 / 71.1725°N 25.79444°E / 71.1725; 25.79444. 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. The Hippopotamus was distributed as far north as rivers Rhine and Thames.[4] 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,[5] and by 114,000 years ago, a glacial era had returned.

Kaspar et al. (GRL, 2005) perform a comparison of a coupled general circulation model (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.[6]

Contents

Definition of the Eemian

Bittium reticulatum Picture from Harting (1886) assigned by him as 'Index fossil' for the Eemian.

The Eemian Stage 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 located. 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 this stage 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

Eemian erosion surface in a fossil coral reef on Great 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.[7]

Sea level at peak was probably 4-6m higher than today (references in Overpeck et al., 2006), with much of this extra water 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 in the Holocene, hence the thermal expansion difference from today is small. Because of the sea level drop since the Eemian, 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 Eemian.

Ipswichian Stage

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

References

  1. ^ Willerslev, Eske; et al. (2007). "Ancient Biomolecules from Deep Ice Cores Reveal a Forested Southern Greenland". Science 317 (5834): 111–114. doi:10.1126/science.1141758. PMID 17615355.  
  2. ^ Cuffey, Kurt M.; Marshall, Shawn J. (2000). "Substantial contribution to sea-level rise during the last interglacial from the Greenland ice sheet". Nature 404: 591–594. doi:10.1038/35007053.  
  3. ^ Otto-Bliesner, Bette L.; et al. (2006). "Simulating Arctic Climate Warmth and Icefield Retreat in the Last Interglaciation". Science 311 (5768): 1751–1753. doi:10.1126/science.1120808. PMID 16556838.  
  4. ^ van Kolfschoten, Th. (2000). "The Eemian mammal fauna of central Europe". Netherlands Journal of Geosciences 79 (2/3): 269–281. http://www.njgonline.nl/publish/articles/000099/article.pdf.  
  5. ^ Sirocko, Frank; et al. (2005). "A late Eemian aridity pulse in central Europe during the last glacial inception". Nature 436 (7052): 833–836. doi:10.1038/nature03905. PMID 16094365.  
  6. ^ Kaspar, Frank; et al. (2005). "A model-data comparison of European temperatures in the Eemian interglacial". Geophysical Research Letters 32 (L11703): L11703. doi:10.1029/2005GL022456.  
  7. ^ Wilson, Mark A.; et al. (1998). "Paleontological evidence of a brief global sea-level event during the last interglacial". Lethaia 31: 241–250. http://www3.wooster.edu/geology/WilsonEtAl98.pdf.  

Further reading

  • Bosch, J. H. A.; Cleveringa, P.; Meijer, T. (2000). "The Eemian stage in the Netherlands: history, character and new research". Geologie en Mijnbouw / Netherlands Journal of Geosciences 79 (2/3): 135–145. http://www.njgonline.nl/publish/articles/000085/article.pdf.  
  • 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.
  • Overpeck, Jonathan T.; et al. (2006). "Paleoclimatic Evidence for Future Ice-Sheet Instability and Rapid Sea-Level Rise". Science 311 (5768): 1747–1750. doi:10.1126/science.1115159. PMID 16556837.  
  • 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. doi:10.1130/G21321.1.  
  • 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.

External links

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