T285 Deciphering Climate Change and Climate Variability in the Geologic Record Using Palaeosols, Loess, Palaeoweathering Profiles, Pedosedimentary Sequences, and Polygenetic Soils: Their Applications and Limitations as Terrestrial Proxies in Understanding Impacts of Climatic Changes (Posters)

Tuesday, 24 October 2017
9:00 AM - 6:30 PM
Halls 4EF

AN ORGANIC GEOCHEMISTRY PERSPECTIVE ON DEGLACIAL PALEOCLIMATE VARIABILITY IN CENTRAL ALASKA

Paper number: T285-2
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

This study uses organic geochemical techniques to investigate the paleoenvironmental context of human colonization and occupation of eastern Beringia in the Late Glacial period (~15-10 k cal. B.P.). Eastern Beringia is highly significant in archaeology, as it was one of the last global regions to be colonized by humans, and is currently considered the main route for human settlement of the Americas. Numerous questions remain as to why this settlement took place so late in our evolutionary history. Therefore, many researchers look to deglacial climate change to explain the timing and mechanisms of the earliest human occupations of the subarctic.

The quantitative approach presented here tests the relationship between paleoclimatic change and human paleoecology in the Shaw Creek Flats (SCF) region of central Alaska. Loess-paleosol sequences contain well-preserved organic compounds that can be used as a terrestrial proxy for Late Glacial climatic change. This study analyzed the concentration and isotopic composition (dD) of n-alkanes from buried soils and sediments near six of the earliest archaeological localities in central Alaska, including Swan Point, Mead, and the Rosa-Keystone Dune site. Most Late Glacial soils show high n-alkane concentrations, while Holocene and modern soils show poor n-alkane preservation. Isotopic changes indicate fluctuations in temperature and aridity during the Late Glacial and Early Holocene. This project also analyzed buried soils and sediments for concentration and distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs), which can serve as soil temperature and mean annual air temperature (MAAT) proxies. BrGDGT concentrations were moderate to low in most samples, but were still high enough to yield paleotemperature estimates. Significant differences are observed between Late Glacial and Holocene soils, and temperature reconstructions indicate millennial-scale climatic variability related to deglaciation (e.g., Younger Dryas). Together, these records offer a new direction of interdisciplinary research for understanding past environmental and climatic change in SCF. This framework is essential for investigating the relationship between paleoenvironment and human behavior during a period of rapid and dramatic climatic variability.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-304951

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