Universität zu Köln

Wenwei, Zhao (2017). Quaternary environmental changes in central Chukotka (NE Siberia, Russia) inferred from Lake El’gygytgyn pollen record and biome reconstruction. PhD thesis, Institut für Geologie und Mineralogie.

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Abstract

The thesis aims to reconstruct the Arctic vegetation during the Quaternary and to provide insights into the orbital and internal forcings of the regional climate changes. The sedimentary record of the Lake El’gygytgyn is vital for understanding the response of the vulnerable ecosystems in the Northeast Siberia to climate variations. With the successful recovery of the deep-drilled ICDP 5011-1 sediment cores, high-resolution palynological analysis and biome reconstruction are applied to the time intervals of ~2150 to 2100 ka (MIS 82-79, including the Réunion Subchron polarity reversal event), ~1091 to 715 ka (MIS 31-18, encompassing the Mid-Pleistocene Transition), and ~240.5 to 181.5 ka (MIS 7.5-6.6; mainly the penultimate interglacial). For the interval of 2150-2100 ka (MIS 82-79) during the early Quaternary, the tundra (TUND) biome generally has higher affinity scores as compared to cold steppe (STEP) or cold deciduous forest (CLDE). An exception is a climatic optimum between ~2139-2131 ka, coinciding with MIS 81 (approximately the Réunion Subchron) when the CLDE biome has the highest scores. The coeval pollen spectra indicate that deciduous forest and shrubs expanded in the regional vegetation and the climate was relatively warm and wet. Over the Mid-Pleistocene Transition (1091-715 ka), the pollen spectra reveal seven vegetation successions that have clearly distinguishable glacial-interglacial cycles. Comparing the interglacials during the course of the Mid-Pleistocene Transition, a tendency of a gradual replacement of trees and shrubs by open herbaceous communities can be observed. Since the first large glaciation (MIS 24-22), the long-term tendency of decreasing CLDE biome scores and landscape openness index indicates a prominent aridification in the Northeast Siberia. During the late Quaternary at 240.5-181.5 ka (MIS 7.5-6.6), mixed herbs and shrubs (mainly alder and birch) dominated the regional vegetation. The high-affinity scores of the TUND biome show that the vegetation landscape was generally open. The warm intervals (MIS 7.5, 7.3, and 7.1) were marked by an increase in the CLDE biome scores and a synchronous decrease in the STEP biome scores. Among them, the MIS 7.1 was a climatic optimum phase marked by the highest CLDE biome scores and lasted ~10 ka. The vegetation of cold intervals (glacials/stadials) were dominated by herb tundra. Some of the cold intervals were relatively wet supporting the survival of some stone pines with a sufficient snow cover. In contrast, interglacials/interstadials can be distinguished by the shrub-dominated regional vegetation (Betula-Alnus-Salix). Correspondingly, increases in CLDE biome affinity scores and simultaneous decreases in STEP biome scores characterized the interglacials and vice versa for the glacials. The cyclic pattern of glacial-interglacial climates was primarily forced by the earth’s orbital parameters. The nearly simultaneous peaks of obliquity and precession-related summer insolation probably triggered the onset of most interglacials. The high CLDE biome scores during interglacial periods were basically in phase with the intervals of obliquity values shifting from maxima to minima, highlighting the key role of obliquity cycle driving Arctic vegetation successions during the Quaternary. The internal forcings of the earth system further modulated the regional vegetation and climate. The global cooling during the first large glaciation may have prevented snow from melting and led to an extended ice volume. It, in turn, has caused strong snow- and ice-albedo feedback effect that aggravated glacial conditions causing the significant decline in the diversity and populations of trees and shrubs. The climatic optimum at the substage MIS 7.1 benefited from the preceding mild short-lived MIS 7.2 stadial, whereas the long and cold MIS 7.4 and 8 resulted in extensive and stabilized permafrost preventing vegetation development during MIS 7.3 and 7.5, respectively. It shows the strong imprints of glacials/stadials on the subsequent warm intervals in the high latitudes. This thesis fills the gap of the Arctic vegetation history for the concerned time intervals. It underlines pollen analysis and biome reconstruction as invaluable methods and highlights the potential of Lake El’gygytgyn as a key archive for establishing the framework of long-term Arctic paleoenvironmental changes. This study offers insights into potential scenarios for future climate pattern in the high latitudes and allows a better understanding of the relationship between vegetation, climate, and possible mechanisms.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Wenwei, Zhao pollenzhaoww@gmail.com UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-78760
Date:	2017
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Geosciences > Institute of Geology and Mineralog
Subjects:	Earth sciences
Uncontrolled Keywords:	Keywords Language Quaternary UNSPECIFIED Biome reconstruction UNSPECIFIED Pollen record UNSPECIFIED
Date of oral exam:	13 November 2017
Referee:	Name Academic Title Martin, Melles Prof. Dr. Bernd, Wagner Prof. Dr. Pavel, Tarasov Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/7876