Building A Paleoclimatic With Marine Isotope Stages

Marine Isotope Stages (abbreviated MIS), sometimes referred to as Oxygen Isotope Stages (OIS), are the discovered pieces of a chronological listing of alternating cold and warm periods on our planet, going back to at least 2.6 million years. Developed by successive and collaborative work by pioneer paleoclimatologists Harold Urey, Cesare Emiliani, John Imbrie, Nicholas Shackleton, and a host of others, MIS uses the balance of oxygen isotopes in stacked fossil plankton (foraminifera) deposits on the bottom of the oceans to build an environmental history of our planet. The changing oxygen isotope ratios hold information about the presence of ice sheets, and thus planetary climate changes, on our earths surface. How Measuring Marine Isotope Stages Work Scientists take sediment cores from the bottom of the ocean all over the world  and then measure the ratio of Oxygen 16 to Oxygen 18 in the calcite shells of the foraminifera. Oxygen 16 is preferentially evaporated from the oceans, some of which falls as snow on continents. Times when snow and glacial ice buildup occur therefore see a corresponding enrichment of the oceans in Oxygen 18. Thus the O18/O16 ratio  changes over time, mostly as a function of the volume of glacial ice on the planet. Supporting evidence for the use of oxygen isotope ratios as proxies of climate change is reflected in the matching record of what scientists believe the reason for the changing amount of glacier ice on our planet. The primary reasons glacial ice varies on our planet was described by Serbian geophysicist and astronomer Milutin Milankovic (or Milankovitch) as the combination of the eccentricity of Earths orbit around the sun, the tilt of the Earths axis and the wobble of the planet bringing the northern latitudes nearer to or farther from the suns orbit, all of which changes the distribution of incoming solar radiation to the planet. Sorting Out Competing Factors The problem is, however, that although scientists have been able to identify an extensive record of global ice volume changes through time, the exact amount of sea level rise, or temperature decline, or even ice volume, is not generally available through measurements of isotope balance, because these different factors are interrelated. However, sea level changes can  sometimes be identified directly in the geological record: for example, datable cave encrustations which develop at sea levels (see Dorale and colleagues). This type of additional evidence ultimately helps sorts out the competing factors in establishing a more rigorous estimation of past temperature, sea level, or the amount of ice on the planet. Climate Change on Earth The following table lists a paleo-chronology of life on earth, including how the major cultural steps fit in, for the past 1 million years. Scholars have taken the MIS/OIS listing well beyond that. Table of Marine Isotope Stages MIS Stage Start Date Cooler or Warmer Cultural Events MIS 1 11,600 warmer the Holocene MIS 2 24,000 cooler last glacial maximum, Americas populated MIS 3 60,000 warmer upper Paleolithic begins; Australia populated, upper Paleolithic cave walls painted, Neanderthals disappear MIS 4 74,000 cooler Mt. Toba super-eruption MIS 5 130,000 warmer early modern humans (EMH) leave Africa to colonize the world MIS 5a 85,000 warmer Howiesons Poort/Still Bay complexes in southern Africa MIS 5b 93,000 cooler MIS 5c 106,000 warmer EMH at Skuhl and Qazfeh in Israel MIS 5d 115,000 cooler MIS 5e 130,000 warmer MIS 6 190,000 cooler Middle Paleolithic begins, EMH evolves, at Bouri and Omo Kibish in Ethiopia MIS 7 244,000 warmer MIS 8 301,000 cooler MIS 9 334,000 warmer MIS 10 364,000 cooler Homo erectus at Diring Yuriahk in Siberia MIS 11 427,000 warmer Neanderthals evolve in Europe. This stage is thought to be the most similar to MIS 1 MIS 12 474,000 cooler MIS 13 528,000 warmer MIS 14 568,000 cooler MIS 15 621,000 ccooler MIS 16 659,000 cooler MIS 17 712,000 warmer H. erectus at Zhoukoudian in China MIS 18 760,000 cooler MIS 19 787,000 warmer MIS 20 810,000 cooler H. erectus at Gesher Benot Yaaqov in Israel MIS 21 865,000 warmer MIS 22 1,030,000 cooler Sources Jeffrey Dorale of the University of Iowa. Alexanderson H, Johnsen T, and Murray AS. 2010.  Re-dating the Pilgrimstad Interstadial with OSL: a warmer climate and a smaller ice sheet during the Swedish Middle Weichselian (MIS 3)?  Boreas  39(2):367-376. Bintanja , R. North American ice-sheet dynamics and the onset of 100,000-year glacial cycles. Nature volume 454, R. S. W. van de Wal, Nature, August 14, 2008. Bintanja, Richard. Modelled atmospheric temperatures and global sea levels over the past million years. 437, Roderik S.W. van de Wal, Johannes Oerlemans, Nature, September 1, 2005. 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