Eemian

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

The Eemian (also Sangamonian, Ipswichian, Mikulin, Kaydaky, Valdivia, Riss-Würm) was the interglacial period which began about 130,000 years ago and ended about 115,000 years ago.[1] It corresponds to Marine Isotope Stage 5e,[2] 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. The prevailing Eemian climate is believed to have been warmer than that of the Holocene.

The Eemian is known as the Ipswichian in the UK, the Mikulin 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 Eemian is equivalent to either all or part of it.

Climate

View of the Eemian-aged coastal terraces of Niebla near Valdivia, Chile.

Global temperatures

The Eemian climate is believed to have been about as stable as that of the Holocene. 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, although global annual mean temperatures were probably similar to those of the Holocene. The warmest peak of the Eemian 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°10′21″N 25°47′40″E / 71.17250°N 25.79444°E / 71.17250; 25.79444. Hardwood trees such as hazel and oak grew as far north as Oulu, Finland.

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 the rivers Rhine and Thames.[3] 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.[4] 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, Texas. The period 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 period had returned.

Kaspar et al. (GRL, 2005) performed a comparison of a coupled general circulation model (GCM) with reconstructed Eemian temperatures for Europe. Central Europe (north of the Alps) was found to be 1–2 °C warmer than present; south of the Alps, conditions were 1–2 °C cooler than today. The model (generated using observed GHG concentrations and Eemian orbital parameters) generally reproduces these observations, leading them to conclude that these factors are enough to explain the Eemian temperatures.[6]

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 6 to 9 m (20 to 30 feet) higher than today,[8][9] with Greenland contributing 0.6 to 3.5 m,[10] thermal expansion and mountain glaciers contributing up to 1 m,[11] and an uncertain contribution from Antarctica.[12] 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 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.

A 2007 study found evidence that the Greenland ice core site Dye 3 was glaciated during the Eemian,[13] which implies that Greenland could have contributed at most 2 m (6.6 ft) to sea level rise.[14][15] Scandinavia was an island due to the inundation of vast areas of northern Europe and the West Siberian Plain.

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, 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 of 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 on the molluscan assemblages is given by Lorié (1887), and Spaink (1958). Since their discovery, Eemian 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 Eemian 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 Eemian deposits from this borehole of 118,200 ± 6,300 years ago. A historical review of Dutch Eemian research is provided by Bosch, Cleveringa and Meijer, 2000.

See also

References

  1. ↑ Dahl-Jensen, D.; Albert, M. R.; Aldahan, A.; Azuma, N.; Balslev-Clausen, D.; Baumgartner, M.; Berggren, A. -M.; Bigler, M.; Binder, T.; Blunier, T.; Bourgeois, J. C.; Brook, E. J.; Buchardt, S. L.; Buizert, C.; Capron, E.; Chappellaz, J.; Chung, J.; Clausen, H. B.; Cvijanovic, I.; Davies, S. M.; Ditlevsen, P.; Eicher, O.; Fischer, H.; Fisher, D. A.; Fleet, L. G.; Gfeller, G.; Gkinis, V.; Gogineni, S.; Goto-Azuma, K.; et al. (2013). "Eemian interglacial reconstructed from a Greenland folded ice core". Nature 493 (7433): 489. Bibcode:2013Natur.493..489N. doi:10.1038/nature11789. PMID 23344358.
  2. ↑ Nicholas J. Shackleton, Maria Fernanda Sanchez-Goni, Delphine Pailler, Yves Lancelot (2002). "Marine Isotope Substage 5e and the Eemian Interglacial" (PDF). Elsevier.
  3. ↑ van Kolfschoten, Th. (2000). "The Eemian mammal fauna of central Europe" (PDF). Netherlands Journal of Geosciences 79 (2/3): 269–281. Retrieved 2 February 2011.
  4. ↑ Vegetation and paleoclimate of the last interglacial period, central Alaska. USGS
  5. ↑ Sirocko, F.; Seelos, K.; Schaber, K.; Rein, B.; Dreher, F.; Diehl, M.; Lehne, R.; Jäger, K.; Krbetschek, M.; Degering, D. (2005). "A late Eemian aridity pulse in central Europe during the last glacial inception". Nature 436 (7052): 833. Bibcode:2005Natur.436..833S. doi:10.1038/nature03905. PMID 16094365.
  6. ↑ Kaspar, F.; Kühl, Norbert; Cubasch, Ulrich; Litt, Thomas (2005). "A model-data comparison of European temperatures in the Eemian interglacial". Geophysical Research Letters 32 (11): L11703. Bibcode:2005GeoRL..3211703K. doi:10.1029/2005GL022456.
  7. ↑ 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. doi:10.1111/j.1502-3931.1998.tb00513.x.
  8. ↑ Dutton, A; Lambeck, K (13 July 2012). "Ice volume and sea level during the last interglacial.". Science (New York, N.Y.) 337 (6091): 216–9. PMID 22798610.
  9. ↑ Kopp, RE; Simons, FJ; Mitrovica, JX; Maloof, AC; Oppenheimer, M (17 December 2009). "Probabilistic assessment of sea level during the last interglacial stage.". Nature 462 (7275): 863–7. PMID 20016591.
  10. ↑ Stone, E.J; Lundt, D.J; Annan, J.D.; Hargreaves, J.C. (2013). "Quantification of Greenland ice-sheet contribution to Last Interglacial sea-level rise". Clim. Past 9: 621–639.
  11. ↑ McKay, Nicholas P.; Overpeck, Jonathan T.; Otto-Bliesner, Bette L. (July 2011). "The role of ocean thermal expansion in Last Interglacial sea level rise". Geophysical Research Letters 38 (14): n/a–n/a. doi:10.1029/2011GL048280.
  12. ↑ Scherer, RP; Aldahan, A; Tulaczyk, S; Possnert, G; Engelhardt, H; Kamb, B (3 July 1998). "Pleistocene collapse of the west antarctic ice sheet". Science (New York, N.Y.) 281 (5373): 82–5. PMID 9651249.
  13. ↑ Willerslev, E.; Cappellini, E.; Boomsma, W.; Nielsen, R.; Hebsgaard, M. B.; Brand, T. B.; Hofreiter, M.; Bunce, M.; Poinar, H. N.; Dahl-Jensen, D.; Johnsen, S.; Steffensen, J. P.; Bennike, O.; Schwenninger, J. -L.; Nathan, R.; Armitage, S.; De Hoog, C. -J.; Alfimov, V.; Christl, M.; Beer, J.; Muscheler, R.; Barker, J.; Sharp, M.; Penkman, K. E. H.; Haile, J.; Taberlet, P.; Gilbert, M. T. P.; Casoli, A.; Campani, E.; Collins, M. J. (2007). "Ancient Biomolecules from Deep Ice Cores Reveal a Forested Southern Greenland". Science 317 (5834): 111. Bibcode:2007Sci...317..111W. doi:10.1126/science.1141758. PMC 2694912. PMID 17615355.
  14. ↑ Cuffey, K. M.; Marshall, S. J. (2000). "Substantial contribution to sea-level rise during the last interglacial from the Greenland ice sheet". Nature 404 (6778): 591–4. doi:10.1038/35007053. PMID 10766239.
  15. ↑ Otto-Bliesner, B. L.; Marshall, Shawn J.; Overpeck, Jonathan T.; Miller, Gifford H.; Hu, Aixue (2006). "Simulating Arctic Climate Warmth and Icefield Retreat in the Last Interglaciation". Science 311 (5768): 1751. Bibcode:2006Sci...311.1751O. doi:10.1126/science.1120808. PMID 16556838.

Further reading

External links

This article is issued from Wikipedia - version of the Wednesday, January 06, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.