To install click the Add extension button. That's it.

The source code for the WIKI 2 extension is being checked by specialists of the Mozilla Foundation, Google, and Apple. You could also do it yourself at any point in time.

4,5
Kelly Slayton
Congratulations on this excellent venture… what a great idea!
Alexander Grigorievskiy
I use WIKI 2 every day and almost forgot how the original Wikipedia looks like.
Live Statistics
English Articles
Improved in 24 Hours
Added in 24 Hours
Languages
Recent
Show all languages
What we do. Every page goes through several hundred of perfecting techniques; in live mode. Quite the same Wikipedia. Just better.
.
Leo
Newton
Brights
Milds

Penultimate Glacial Period

From Wikipedia, the free encyclopedia

Diagram showing the feedback loop the cooled Earth during the Penultimate Glacial Period.[1]
Diagram showing the feedback loop the cooled Earth during the Penultimate Glacial Period.[1]

The Penultimate Glacial Period (PGP) is the glacial age that occurred before the Last Glacial Period. The penultimate glacial period is officially unnamed just like the Last Glacial Period. The word penultimate simply means second to last. While the penultimate glacial period is a part of the ongoing Quaternary ice age, which began 2.58 million years ago, the penultimate glacial period lasted from ~194,000 years ago, to ~135,000 years ago.[2] The penultimate glacial period also occurred during the Marine Isotope age 6 (MIS6).[3] At the glacial ages’ height, it is known to be the most extensive expansion of glaciers in the last 400,000 years over Eurasia, and could be the second or third coolest glacial period over the last 1,000,000 years, as shown by ice cores.[4] Due to this, the global sea level drop between 92 m, and 150 m below modern-day global mean sea level.[2] The penultimate glacial period expanded ice sheets and shifted temperature zones worldwide, which had a variety of effects on the world’s environment, and the beings that lived in it.[1]

Cause

Much like the last glacial period, the penultimate glacial period was caused by a great orbital eccentricity of Earth.[5] This eccentricity causes greater seasonal impacts than normal because it limits the amount of sunlight that reaches the earth’s surface, lowering the temperature.[6] Due to this, northern insolation (the amount of sunlight that reaches the surface) is reduced, this means when it’s summer, less heat is exposed to the snows of the winter, which don't completely melt.[2] This buildup of ice and snow over thousands of years eventually leads to residual ice sheets, which would also reflect light away from the earth, further cooling the earth.[7] A decrease in greenhouse gas concentrations such as CO2, are a result of the expanded ice sheets.[5] This is because as the Earth cooled, and ice sheets expanded, the ocean waters became colder, which then could absorb more CO2 from the atmosphere.[8] These factors all feedback into each other, as the ice sheets extended, more CO2 was absorbed, and more light was reflected off the ice sheets, furthermore expanding the ice sheets, this exponential cooling set the world into a glacial period.[8]

Effects in Europe

In northern Europe, the biggest expansion of glaciation of the last 400,000 years had covered the northern region in a thick ice sheet, which caused a drastic reduction of vegetation.[8] In the Mediterranean, polar winds brought from the now extended ice sheets, brought cooler and wetter conditions that had a significant downfall in large vegetation such as trees.[5] Pollen sequences found from MIS 6 indicated that early in the glacial period, tree abundance fluctuated heavily.[9]

Later in the glacial period, extreme conditions were followed by a mainly treeless landscape all across Europe.[9] This rendered Europe a polar desert just south of the now expanded ice sheets, and the rest of Europe was left with a sporadic herb based plant cover.[9] In Europe, north of the Alps, laid a tundra-steppe that was predominantly grasses, sedges, and chenopods.[9] While land south of the Alps laid discontinuous steppe vegetation patterns.[9] There were some refugee areas for trees to survive, in the sheltered areas of the mountainous Alps, and the western Balkans, temperatures tree populations survived.[9] This was due to temperature variations not being extreme in these locations, as well as precipitation still being sufficient.[9] This is unlike the rest of Europe, where in France, pollen samples revealed a precipitation decrease of almost 60% compared to the modern day.[8] The drastic changing of the climate also resulted in increased storms in the north Atlantic, affecting Europe as well as North America.[2]

Effects in Asia

Isotope dating was conducted in Hulu Cave, eastern China, and found that the penultimate glacial period’s presence was felt in central China.[10] The dating showed an increased presence of oxygen-18, an isotope that reflects the meteoric water and cave temperature, as well as precipitation of the penultimate glacial period.[10] This data led to the confirmation of intense monsoons that impacted most of south-east Asia, and up to modern day Xi’an China.[10] The monsoons intensity increase is due to the orbital shifting of the planet, but was amplified by the ice sheets that formed for the same reason.[10] These factors combined, then affected the atmospheric hydrological cycle, creating more intense seasonal winds that led to increased participation over south-east Asia.[10]

Effects in North America

In contrast to Europe, there is no geological evidence to support a similarly sized ice sheet in North America.[2] Ice-rafted debris from the Hudson area indicates that during MIS6, the amount of icebergs in the North Atlantic were much lower compared to the last glacial period.[1] Although, simulations testing the extent of an ice sheet in North America, have shown that a smaller ice sheet is probable, as the simulation produced weather data that is consistent with hypothesized temperatures at the time.[1] This simulation showed the precipitation rates over North America doubled during MIS6, which would have been a result of the icy winds expanding southward further into the continent, as well as the increased storms.[1]

Effects on Homo sapiens in Africa

Early Homo sapiens, then located primarily in Africa, were around to experience the penultimate glacial period, and it was at least the second glacial period that early humans experienced, along with human relatives such as the European dwelling Neanderthals, and the Denisovans in Asia.[3] There are many hypotheses on how Homo sapiens were affected during the penultimate glacial period, some hypotheses suggest the Glacial Period caused a bottleneck, due to habitat changes which led to a decreased population, in an already small sample of about 10,000 Homo sapiens.[3] Oceanic cores, taken from western Africa, show the deserts expanded, pushing the savannah and the tropical rainforests downward, and oak trees occupying the Mediterranean coast, disappeared.[9] This is thought to have occurred due to southward migration of the subtropical, and high pressure zone of the Mediterranean.[9] This dislocation of vegetation was thought to have displaced Homo sapiens.[9] However, studies have shown that the region in which the early humans occupied, was very lightly disturbed, and a bottleneck, due to the penultimate glacial period, is unlikely.[3]

References

  1. ^ a b c d e Manabe, S.; Broccoli, A. J. (1985). "The influence of continental ice sheets on the climate of an ice age". Journal of Geophysical Research. 90 (D1): 2167. Bibcode:1985JGR....90.2167M. CiteSeerX 10.1.1.352.9495. doi:10.1029/JD090iD01p02167.
  2. ^ a b c d e Colleoni, Florence; Wekerle, Claudia; Näslund, Jens-Ove; Brandefelt, Jenny; Masina, Simona (1 April 2016). "Constraint on the penultimate glacial maximum Northern Hemisphere ice topography (≈140 kyrs BP)". Quaternary Science Reviews. 137: 97–112. Bibcode:2016QSRv..137...97C. doi:10.1016/j.quascirev.2016.01.024.
  3. ^ a b c d Sjödin, Per; E. Sjöstrand, Agnès; Jakobsson, Mattias; Blum, Michael G.B. (1 July 2012). "Resequencing Data Provide No Evidence for a Human Bottleneck in Africa during the Penultimate Glacial Period". Molecular Biology and Evolution. 29 (7): 1851–1860. doi:10.1093/molbev/mss061. PMID 22319141.
  4. ^ Jouzel, J.; Barkov, N. I.; Barnola, J. M.; Bender, M.; Chappellaz, J.; Genthon, C.; Kotlyakov, V. M.; Lipenkov, V.; Lorius, C.; Petit, J. R.; Raynaud, D.; Raisbeck, G.; Ritz, C.; Sowers, T.; Stievenard, M.; Yiou, F.; Yiou, P. (July 1993). "Extending the Vostok ice-core record of palaeoclimate to the penultimate glacial period". Nature. 364 (6436): 407–412. Bibcode:1993Natur.364..407J. doi:10.1038/364407a0. S2CID 4329245.
  5. ^ a b c Roucoux, K. H.; Tzedakis, P. C.; Lawson, I. T.; Margari, V. (August 2011). "Vegetation history of the penultimate glacial period (Marine isotope stage 6) at Ioannina, north-west Greece". Journal of Quaternary Science. 26 (6): 616–626. Bibcode:2011JQS....26..616R. doi:10.1002/jqs.1483.
  6. ^ Holbourn, Ann; Kuhnt, Wolfgang; Clemens, Steven; Prell, Warren; Andersen, Nils (December 2013). "Middle to late Miocene stepwise climate cooling: Evidence from a high-resolution deep water isotope curve spanning 8 million years". Paleoceanography. 28 (4): 688–699. Bibcode:2013PalOc..28..688H. doi:10.1002/2013PA002538.
  7. ^ Baumann, Karl-Heinz; Lackschewitz, Klas S.; Mangerud, Jan; Spielhagen, Robert F.; Wolf-Welling, Thomas C.W.; Henrich, Rüdiger; Kassens, Heidemarie (1 March 1995). "Reflection of Scandinavian Ice Sheet Fluctuations in Norwegian Sea Sediments during the Past 150,000 Years" (PDF). Quaternary Research. 43 (2): 185–197. Bibcode:1995QuRes..43..185B. doi:10.1006/qres.1995.1019.
  8. ^ a b c d Wainer, Karine; Genty, Dominique; Blamart, Dominique; Bar-Matthews, Miryam; Quinif, Yves; Plagnes, Valérie (15 April 2013). "Millennial climatic instability during penultimate glacial period recorded in a south-western France speleothem". Palaeogeography, Palaeoclimatology, Palaeoecology. 376: 122–131. Bibcode:2013PPP...376..122W. doi:10.1016/j.palaeo.2013.02.026.
  9. ^ a b c d e f g h i j Van Andel, T.; Tzedakis, P. C. (1 January 1996). "Palaeolithic landscapes of Europe and environs, 150,000-25,000 years ago: An overview". Quaternary Science Reviews. 15 (5–6): 481–500. Bibcode:1996QSRv...15..481V. doi:10.1016/0277-3791(96)00028-5.
  10. ^ a b c d e Cheng, Hai; Edwards, R. Lawrence; Wang, Yongjin; Kong, Xinggong; Ming, Yanfang; Kelly, Megan J.; Wang, Xianfeng; Gallup, Christina D.; Liu, Weiguo (1 March 2006). "A penultimate glacial monsoon record from Hulu Cave and two-phase glacial terminations". Geology. 34 (3): 217–220. Bibcode:2006Geo....34..217C. doi:10.1130/G22289.1.


This page was last edited on 6 July 2021, at 09:12
Basis of this page is in Wikipedia. Text is available under the CC BY-SA 3.0 Unported License. Non-text media are available under their specified licenses. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc. WIKI 2 is an independent company and has no affiliation with Wikimedia Foundation.