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Title:Holocene Climatic Changes in the Alaskan Arctic as Inferred from Oxygen-Isotopic Analysis
Author(s):Vachula, Richard S.
Advisor(s):Hu, Feng Sheng
Contributor(s):Hu, Feng Sheng
Department / Program:Geology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:B.S. (bachelor's)
Solar Irradiance
Abstract:Reconstructions of Holocene climate in the Alaskan Arctic allow for better understanding of how the region may respond to future climate changes. However, long-term records from the region are scarce. We conducted lithological and isotopic analyses at Wahoo Lake (69º 4.612, -146º 55.676) to infer Holocene climate variability in northern Alaska. Isotopic composition of modern water from this large, open-basin lake in the northern foothills of the Brooks Range suggests that winter precipitation dominates inputs to the lake. Isotopic composition of Pisidium exhibits large variations throughout the past 11,800 years, with δ18O values ranging between 11.6 and 14.2‰ (VSMOW) and δ13C between -2.3 and -7.1‰ (VPDB). Loss-on-ignition (LOI) shows high carbonate content (8.1-50.9%) in the subbasin sediments between 11.8-6.3 kcal BP, transitioning to lower carbonate (1.3-25.3%) and increased organic content (11.7-65.2%) between 6.3-1.4 kcal BP. High carbonate and elevated δ18O values (13.0-14.0‰) from 11.5-8.5 kcal BP likely reflect lower lake level and possibly evaporative enrichment of lake water, suggesting warm, dry summers during the early Holocene. The disappearance of Pisidium, paired with a decrease in calcite deposition at ~6.5 kcal BP, suggests increasing lake-level in the mid-Holocene, which is supported by a basal date of 5.3 kcal BP from a core of the shallow shelf of the lake. This increase coincided with lake-level increases in interior Alaska and likely resulted from enhanced regional effective moisture. The shelf sediments exhibit a marked increase in carbonate content at ~3.5 kcal BP and δ18O values generally rose from 12.4‰ at 3.5 kcal BP to 13.2‰ at 2.0 kcal BP (range = 11.6-14.2‰), suggesting increasing annual temperatures during this period. After 2.0 kcal BP, δ18O values fluctuate between 11.9-13.3‰, but generally decline until 1.0 kcal BP, suggesting dramatic temperature fluctuations in the late Holocene. These Holocene variations in δ18O values at Wahoo Lake generally correspond to fluctuations in total solar irradiance, suggesting that solar variability may have played an important role in Holocene climate change of the Alaskan Arctic. Understanding the role of solar irradiance on natural variability of climate in this region provides a framework for evaluating climatic response and sensitivity to anthropogenic forcing.
Issue Date:2015-07
Genre:Dissertation / Thesis
Rights Information:Copyright 2015 Richard S.Vachula.
Date Available in IDEALS:2015-07-13

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