This NSF-sponsored dissertation projectusesnovel techniques to provide environmental context for human colonization of ancient eastern Beringia (present-day Alaska and the Yukon Territory) during the deglacial period (c. 16,000 to 11,000 calendar years before present, cal yr B.P.). Eastern Beringia is highly significant to archaeologists, as it is currently considered the primary route for human settlement of the Americas. The timing and mechanisms of human colonization are still hotly debated, although many researchers posit that deglacial climate and environmental changes had an impact on this major migratory event. Eastern Beringia also contains some of North America’s oldest archaeological sites (dated between 14,500 and 13,000 cal yr BP), many of which are concentrated in the middle Tanana Valley (mTV) of central Alaska. This rich archaeological record offers a window into human behavior within challenging high-latitude environments, where hunter-gatherer groups had to cope with seasonal extremes in temperature, daylight, and resource availability. Together, these factors make the mTV an ideal natural laboratory for studying the relationships between climate, environment, and human colonization of the New World. 

            In eastern Beringia, there has been great interest in developing deglacial climate proxies (i.e., records of preserved physical characteristics that reflect past climatic conditions). In our study region, the Shaw Creek Flats (SCF) of the mTV, there are numerous pollen and organic geochemistry records from lake cores. However, there is still a need for climate proxies from terrestrial settings that can be directly compared to archaeological occupations. Researchers have used stratigraphy at early archaeological sites to study changing landscapes and environmental conditions. Many early sites are found within thick sequences of wind-blown sediments, including sand and wind-blown silt (loess), that alternate with buried soils or buried soil complexes (pedocomplexes). There is also great need for more quantitative records of climatic conditions; for example, few quantitative proxies for precipitation and air temperature are available for this time period. Such aspects of climate certainly affected early hunter-gatherers in Eastern Beringia, so it is vital to develop datasets that estimate these climatic conditions.

            Our project contributes to these research pursuits by developing microscale proxies of past climate and landscape conditions at six archaeological sites in SCF. We rely on two main techniques: 1) biomarker reconstruction, or the analysis of molecular fossils left behind by plants (n-alkanes) and soil bacteria (brGDGTs), and 2) micromorphology, or the study of in-situsediments and soils under a petrographic microscope. We place particular emphasis on buried soils because they are commonly associated with archaeological occupations. We developed three main datasets using microscale techniques. First, this study estimates deglacial precipitation using the hydrogen isotopic composition (dD) of n-alkanes, compounds synthesized by plants and then preserved in buried soils and sediments. Secondly, we use branched glycerol dialkyl glycerol tetraethers (brGDGTs), compounds produced by soil bacteria, as a proxy for mean annual air temperature (MAAT) and summer air temperature. Third, this project uses soil micromorphology to assess environmental conditions, soil formation, and landscape disturbance from site to site. 

            Data from the compound-specific isotope analyses are still undergoing synthesis and interpretation. We hope to present these datasets in peer-reviewed publications within the next year. Our micromorphology analysis has yielded several notable results. Micromorphology reveals important aspects of soil formation between our study sites. At some sites, we see numerous pedofeatures and other characteristics related to soil formation processes, while at other sites, there are few signs of soil formation. Additionally, some dark brown layers appear to be soils in the field, but at the microscale, they show little evidence of soil formation. In such cases, our analysis reveals a need to reclassify these layers as “sediments,” rather than “soils.” This is important because soils imply stable landscapes, while sediments imply active geologic processes; therefore, classification of stratigraphic layers as soils versus sediments can drastically change models of past environments and regional geologic histories. Another important finding is that our study sites show variability in microscale features, despite their proximity on the landscape. This variability may reflect the strong control exerted by local environmental and climatic conditions, rather than regional conditions. In this way, our project represents a unique opportunity to compare microscale stratigraphy at multiple sites, rather than rely on a single site as a representation of regional climatic or geologic conditions. We plan to submit these results for publication in spring 2019. 

            While molecular climatology and micromorphology techniques are still underutilized in high-latitude subarctic contexts, they offer a new direction for understanding past environmental and climatic change in SCF. Our datasets also serve as a complement for previously developed paleoenvironmental records. Ultimately, we hope that these novel techniques will improve understanding of deglacial environmental conditions in this region of eastern Beringia. We also hope to add to the paleoenvironmental framework for human colonization of subarctic environments. 

Last Modified: 02/12/2019
Modified by: Jennifer Kielhofer