Sangamon Interglacial: Paleoclimatology
and Future Climate Implications
 

by  

Daniel Call 

This webpage was created to satisfy requirements for the Quaternary Geology 
course (ES767) during the fall of 2011 at
Emporia State University. 

Table of Contents

Introduction Evidence of the Past
Ice Coring Expeditions Paleoclimate Reconstruction
Discussion References
 
 

Introduction 

Recent ‘extreme’ weather events, rising carbon dioxide levels and the growing evidence of retreating glaciers have increasingly become the subjects of much debate in the popular press and numerous fields of scientific research. Driving these discussions are questions aimed at discerning what drives the climate on Earth. Several have been noted in previous research: Milankovitch cycles, solar output, continental configurations and the most recent and controversial, carbon dioxide and other greenhouse gas atmospheric concentrations (Hambrey 2004). In order to understand what we should expect, both from a climate change perspective and from a changing biogeographical perspective during our current interglacial phase, scientists have looked to the last interglacial period in the geologic record, the Sangamon Stage (or the Eemian, as it appears in European literature) approximately 114,000 - 130,000 years ago for answers.  

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Evidence of the Past 

When scientists try to recreate past climatic conditions, they usually look for specific clues when doing so. Alfred Wegener, credited with Continental Drift theory, used such clues as fossilized jungle vegetation in Alaska to make the controversial statement that North America must have been at a different latitude in the past and drifted to its current location or the Earth had to have been much hotter to support a jungle at >60°N. Scientists of today have gone much further in their search for clues on past climates. Fossilized leaves still play their role in identifying climate regimes in locations but added to that field of knowledge has been added seedlings and even pollen from continental plants (Koerner 1989). Some have looked to the casts of benthic foraminifera (a type of plankton) in ocean sediments and cores taken from coral reefs around the world to answer questions on past climate (Mercer 1983).  

Others have sought answers from the rocks themselves, drilling wells off the coasts of continents and analyzing the corresponding well logs and various ratios of elements and their isotopes (notably O18 and O16). It has only been in the past 60 - 70 years that scientists have begun to look at drilling and analyzing ice cores on existing glaciers for answers on past climates.  

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Ice Coring Expeditions 


Map of Ice Coring expeditions to Greenland and Antarctica, courtesy National Ice Core Laboratory, modified by Call.

In the early 1930s, glaciers began to be measured systematically for scientific purposes. In the late 1940s to early 1950s, the British-Norwegian-Swedish Antarctic Expedition began taking cores of glacier ice. Modern ice core drilling and the related scientific studies associated with it were developed in the early 1950s under the direction of the U.S. Army Snow, Ice and Permafrost Research Establishment (SIPRE). In 1961, SIPRE was merged with the U.S. Army Arctic Construction and Frost Effects Laboratory to form the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) (Langway 2008).  

By 1966 and 1968, CRREL had been successful in drilling and recovering the entire vertical column of ice from the inland regions of the Greenland and Antarctic ice sheets. By 1970, with expanding contributions and associations with the Universities of Copenhagen, Bern and the Technical University of Denmark, the project was expanded to the Greenland Ice Sheet Program (GISP). GISP’s initial field project would take 11 years to complete and by 1993, 5 ice cores had been drilled in Greenland to bedrock at depths of approximately 3 kilometers. Attempts to identify the ice core stratigraphy, snow accumulation rates and the development of Carbon Dioxide concentration curves for the duration of the age represented by the ice cores were enormously successful. By 1970, a complete profile of the complete signature of the late Pleistocene and Holocene climate cycle was generated, while in 1982, annual snow accumulation layering for the past 8,200 years was compiled (Langway).  

Similar joint ventures have been undertaken in Antarctica, most notably at the Russian station of Vostok, situated in the middle of the East Antarctic Ice sheet. It is there that Russian and French scientists have analyzed and recorded data associated with the 3 km of ice cores that span 420,000 years and the four glacial and interglacial periods covered in that time. The information gleaned from the Vostok site has become one of the most important and heavily cited data collection in the Climatological Sciences today. (Hambrey)  

The most recent ice coring mission was called the North Greenland Eemian Ice Drilling (known as NEEM) and was completed in August of 2011. NEEM was designed to extract ice cores from the Greenland Ice Sheet going back in time some 150,000 years, through the Eemian/Sangamon interglacial and into the last glacial stage. The mission was successful, as nearly 150 meters of Illinoian age glacial ice was recovered, showing that there was indeed a glacial presence on Greenland throughout the Sangamon.(Neils Bohr Institute)  

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Paleoclimate Reconstruction 

It is by using proxy evidence of past lifeforms and information gleaned from layered deposits (both rock and ice) that a broader understanding of past climates can be accomplished. Using 230Th/234Ur isotope dating, scientists have been able to show that the limestones of the Waimanalo Formation of Oahu, Hawaii, were formed at 112 +/- 6 thousand years ago (kya) and 137 +/- 11 kya. The elevations of these reefs and other overlying sedimentary layers above today’s sea level is 2.5 to 5.5 m, suggesting that sea level had to have risen by at least 3 – 6 m above current sea level for the layers to have been deposited. (USGS)  

Similarly, the limestones deposited in coral reef complexes near Bermuda, the Florida Keys and part of the Miami Limestone had to have been formed in seas that are anywhere from 6 to 19 meters higher than current sea level with most sea level estimates being placed at 6 – 10 meters higher than today. These values represent data gathered during 2 of the lower sea stands during the Sangamon with the 3rd being much higher than the others based on ?O18 minimums obtained from oxygen isotope data of deep sea cores (USGS).  

The implications of such a high sea level suggests that massive changes in a number of the elements that factor into establishing a particular global climate regime had to have occurred. Looking at Milankovitch cycles, the Northern Hemisphere, during the Sangamon, would have received higher insolation rates (solar radiation received on a surface during a unit of time) than today and a large portion of Greenland’s Ice Sheet and significant portions of the West Antarctic Ice sheet would have had to melt to produce the sea level rise necessary for coral reef derived limestone formations to have been generated at the elevations that they are present at today (Koerner). 


Vostok Ice Core Data, modified from Hambrey.

Carbon dioxide concentrations weren’t as high in the Sangamon as they are today, but they were still much higher than any of the previous or following glacial periods. This combination of high CO2 and increased insolation due to Milankovitch cycle parameters would have altered the climate regimes around the globe. Global temperatures were thought to be 5-7 °C (9-13 °F) higher than the current interglacial period according to North Atlantic oceanic sediment cores with South Pacific oceanic cores showing a rise of only 3-5 °C (5.4-9 °F). It comes as no surprise with these elevated temperatures that further evidence from soil Carbon-13 fractionation analysis performed on soils across the Midwestern United States suggests that a substantial portion of the Midwest would have been covered by forest and prairie and the transitional boundary line for prairie and forest would have been shifted further west than today due to the increase in precipitation and a more robust influx of warm, moist air from the Gulf of Mexico (USGS).  

Across the majority of Europe, general scientific consensus was that the Eemian climate was much warmer and wetter than today’s environment. This resulted in the development of vast temperate forests and the rapid expansion of species, most notably Carpinus across the area (Turner 2000). Although the Eemian was consistently much warmer, evidence has been building that a large scale late Eemian arid ‘pulse’ dominated central Europe resulting in the widespread takeover of ecological niches by various grasses and shrubby bushes before returning to a warm, somewhat more moist climate dominated by temperate forests just before the most recent glacial stadial (Sirocko, et al. 2005).

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Discussion 

Upon examination of the various types of proxy data that have been gathered to reconstruct the Sangamon/Eemian global climate, it seems safe to say that additional research will be required to unravel the particulars of the Sangamon period. It is known that the climates of both North America and Europe experienced warm and moist conditions with periods of climatic instability, but specifics are generally hard to nail down. As techniques become more refined, the discrepancies that have appeared in scientific publications (notably the ice core C13 and marine sediment records of the North Atlantic) need to be resolved to provide a more clear account of climatic specifics.  

Coupled with the climatic discrepancies are the discrepancies with analyzing how life will respond to the changing environment. As Smith and Buddemeier explained, looking at oceanic chemistry and a number of other factors, a rise in sea level could actually benefit most coral reef complexes if sea level and atmospheric carbon dioxide concentrations rise at anticipated rates within the next 100 years. The net effect would cause a drawdown of atmospheric carbon dioxide as more of this greenhouse gas gets incorporated as CaCO3 as various reef complexes grow. Overall, Smith and Buddemeier make a valid point when they explain that the number of factors affecting coral reef health and viability, coupled with the modest changes expected from various climate change simulations indicate that on a global scale, coral reefs are unlikely to be adversely affected by projected climate change. It is only on the local scale that coral reef communities could be at risk.

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References 

Hambrey, M., and Alean, J., 2004, Glaciers Second Edition: New York, NY., Cambridge University Press, 376 p.  

Koerner, R.M., 1989, Ice core evidence for extensive melting of the Greenland ice sheet in the last interglacial. Science 244.4907: 964+. Academic OneFile. Web accessed 26 Nov. 2011.  

Langway, C.C., Jr., US Army Corps of Engineers, 2008. The History of Early Polar Ice Cores. Cold Regions Research and Engineering Laboratory publication ERDC/CRREL TR-08-1  

Mercer, J.H., 1983. Cenozoic Glaciation in the Southern Hemisphere Annual Review Earth Planetary Sciences Vol. 11: p 99-132  

Neils Bohr Institute, 2011. NEEM ice core drilling in Greenland provides comprehensive new results Oct. 6, 2011. News Posting at http://www.nbi.ku.dk/english/news/news11/drilling_in_greenland. 

Sirocko, F., Seelos, K., Schaber, K., Rein, B., Dreher, F., Diehl, M., Lehne, R., Jäger, K., Krbetschek, M., and Degring, D., 2005. A late Eemian aridity pulse in central Europe during the last glacial inception Nature Vol. 436., p.833-36  

Turner, C., 2000. The Eemian interglacial in the North European plain and adjacent areas Netherlands Journal of Geosciences 79 2/3 p. 217-231 

U.S. Geological Survey. (USGS) Last Interglacial: Timing and Environment (LITE) (2006) Accessed Nov. 22, 2011 at http://esp.cr.usgs.gov/info/lite/index.html. 
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