An 11,600-year reconstruction of vegetation communities, moisture availability, and land use changes at Lake Khargal, northern Mongolia

Barna, Joshua A.

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Author

Barna, Joshua A.

Chair

Fowell, Sarah J.

Committee

Bigelow, Nancy H.
Mann, Daniel H.

Abstract

The regional response of vegetation to global atmospheric circulation patterns and human influence throughout the Holocene is recorded by environmental proxies in sediment cores from Lake Khargal in northern Mongolia. Pollen, spores, total organic carbon, and grain size analysis indicate that conditions in the watershed were moderately humid at ~11500 cal yr B.P. The vegetation community surrounding Lake Khargal consists of mainly of Artemisia (sage), Poaceae (grass), and Betula (birch) with a modest amount of extra-local Pinus (pine) from nearby boreal forests. Fluctuations in the ratios of these and other taxa show that aridity increased after ~10000 cal yr B.P., reaching its maximum at ~7900 cal yr B.P., which coincides with a global cooling event. Regional moisture availability gradually increases after ~7900 cal yr B.P., reaching its peak at ~2100 cal yr B.P., then decreases toward the present. Evidence of regional human activity appears in the taxonomic record around 5500 cal yr B.P. and persists into today.

Description

Thesis (M.S.) University of Alaska Fairbanks, 2023

Chapter 1: Introduction -- 1.1 The power of palynology -- 1.2 Holocene climate -- 1.3 Mongolian climate patterns -- 1.4 Climate signals from the Westerlies -- 1.5 Climate signals from the Indian Monsoon -- 1.6 Climate signals from the East Asian monsoon -- 1.7 Conclusions -- 1.8 References. Chapter 2: An 11,600-year reconstruction of vegetation communities, moisture availability, and land use changes at Lake Khargal, northern Mongolia -- 2.1 Abstract -- 2.2 Introduction -- 2.2.1 Climate -- 2.3 Materials and methods -- 2.3.1 Limnology and watershed -- 2.3.2 Coring -- 2.3.3 Radiocarbon dates and age models -- 2.3.4 Lacustrine sediment and total organic content -- 2.3.5 Palynology -- 2.3.6 Semi-quantitative Climate Indices -- 2.3.7 Grain size analysis -- 2.4 Results -- 2.4.1 Sediment cores -- 2.4.2 AMS dating -- 2.4.3 Total organic carbon -- 2.4.4 Palynology -- 2.4.5 Grain size analysis -- 2.5 Discussion -- 2.5.1 Vegetation and climate reconstruction -- 2.5.2 Total organic carbon and grain size -- 2.5.3 Climate trends from KHAR5 -- 2.5.4 Climate trends from KHAR11 -- 2.5.5 Summary of environmental changes at Lake Khargal -- 2.6 Conclusions -- 2.6.1 Summary of land use changes -- 2.6.2 Summary of climate variability -- 2.7 References. Chapter 3: Conclusions -- 3.1 Additional analyses -- 3.2 Future work -- 3.3 References. Appendix -- Future work -- Biogenic silica analysis -- Detailed core descriptions -- Stable isotopes.

Date

2023-08

Type

Thesis

Collections

Geosciences