A Multi-Proxy Study of Holocene Atmospheric Circulation Dynamics Recorded in Lake Sediments in Fennoscandia by Natalie Ann St.Amour A thesis presented to the University of Waterloo in fulfillment of the thesis requirement for the degree of Doctor of Philosophy in Earth Sciences Waterloo, Ontario, Canada, 2009 ©Natalie Ann St.Amour 2009 Library and Archives Bibliothèque et Canada Archives Canada Published Heritage Direction du Branch Patrimoine de l’édition 395 Wellington Street 395, rue Wellington Ottawa ON K1A 0N4 Ottawa ON K1A 0N4 Canada Canada Your file Votre référence ISBN: 978-0-494-55566-8 Our file Notre référence ISBN: 978-0-494-55566-8 NOTICE: AVIS: The author has granted a non- L’auteur a accordé une licence non exclusive exclusive license allowing Library and permettant à la Bibliothèque et Archives Archives Canada to reproduce, Canada de reproduire, publier, archiver, publish, archive, preserve, conserve, sauvegarder, conserver, transmettre au public communicate to the public by par télécommunication ou par l’Internet, prêter, telecommunication or on the Internet, distribuer et vendre des thèses partout dans le loan, distribute and sell theses monde, à des fins commerciales ou autres, sur worldwide, for commercial or non- support microforme, papier, électronique et/ou commercial purposes, in microform, autres formats. paper, electronic and/or any other formats. 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This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. ii Abstract Cellulose-inferred lake water oxygen-isotope records were obtained from five throughflow lakes situated along a north-south transect across Fennoscandia to help develop a better picture of Holocene changes in atmospheric circulation in the region. This research addresses prior evidence for the existence of non-temperature-dependent shifts in δ18O of precipitation in the early Holocene attributed to changes in atmospheric circulation. The validity of this hypothesis is tested through the development of oxygen-isotope records from lake sediments and their interpretation in the context of independent reconstructions of temperature and precipitation from pollen and chironomid head-capsules collected from the same or nearby sites, and well-documented changes in vegetation composition. Records of carbon and nitrogen elemental content and isotopic composition and magnetic susceptibility are included in this multi-proxy investigation. Extensive modern isotope hydrology datasets spanning several years at four of the five sites also help to inform interpretations of the cellulose δ18O records. Key results from this research are: 1) Elevated δ18O in relation to prevailing temperature occurred during the early Holocene (c. 10,000-6000 cal. BP) for sites in northern Fennoscandia (Lake Tibetanus, Lake Spåime), in harmony with previous interpretations suggesting that strong zonal atmospheric circulation led to deepening of the precipitation and isotope shadows in the lee of the Scandes Mountains. 2) Evidence from a southern site (Arbovatten) reveals a previously unrecognized negative offset in the δ18O-temperature relation during the early Holocene, apparently transferred directly from the North Atlantic without the orographic effects associated with a topographic barrier. 3) The modern δ18O-temperature relation appears to have been established throughout Fennoscandia by c. 6000-4000 cal. BP, probably due to generally weaker circumpolar atmospheric circulation in response to lower summer insolation. iii 4) Comparison of two sites (Lake Spåime, Svartkälstjärn) in a west-east transect across central Fennoscandia reveals higher-frequency variability in atmospheric circulation at submillennial scales throughout the Holocene, which appears to be analogous to contemporary variability in the North Atlantic Oscillation (NAO) at seasonal-to-decadal time-scales. Evidence of such NAO-like variability also exists at two northern sites (Lake Keitjoru, Oikojärvi) during the Holocene, likely reflecting variations in summer and winter atmospheric circulation. 5) Complex lake-specific changes in productivity occurred in response to Holocene climate change, as revealed by carbon and nitrogen elemental and isotopic data in lake sediments. A major shift in atmospheric circulation pattern occurring at c. 4000 cal. BP probably led to a reduction in soil-derived 13C-depleted nutrients in five lakes (Lake Keitjoru, Oikojärvi, Lake Spåime, Svartkälstjärn, Arbovatten) associated with changes in terrestrial vegetation. Changes in sediment nitrogen isotope composition also occurred in these lakes at c. 4000 cal. BP, possibly reflecting changing nutrient supply dynamics because of enhanced nitrogen losses during spring snowmelt. iv Acknowledgements I sincerely thank Tom Edwards for providing tremendous amount of support, patience, and a rewarding graduate research experience that included fieldwork in the Peace Athabasca Delta, NWT, and Sweden, and numerous opportunities to present my research at scientific conferences. I sincerely thank Dan Hammarlund for the considerable support he has provided during my program, through e-mailing and travelling to Canada a number of times. And, I greatly appreciated the hospitality I received by Dan and his family when I visited Sweden. I had an incredible experience doing fieldwork at Naimakka and Arbovatten. I sincerely thank Brent Wolfe for always providing suggestions for improvements and directions in my studies, and engaging me in stimulating teaching opportunities. Special thanks goes to Kjell Erik Siikavuopio, Hans-Göran Nilsson, and Kjell-Evert Olsson for their dedication in collecting water samples at the Naimakka Lakes, Svartkälstjärn and Arbovatten, respectively. Thanks in particular to Ian Snowball for helping with the magnetic susceptibility measurements. Discussions with Matt Falcone on the analytical approach of cellulose analysis were gladly welcomed. Laboratory assistance was gratefully appreciated by Tracy Barkhouse and Tiffany Chiu. Thanks also go to the staff at the Environmental Isotope Laboratory and to Bill Mark and Lois Graham for getting my samples processed. An incredible amount of gratitude goes to Elaine Garner at the Graduate Studies Office for providing financial assistance throughout my program and for unwavering confidence in my ability to complete my degree requirements. Financial support was provided by the Swedish Research Council through a grant to Dan Hammarlund and the Natural Sciences and Engineering Research Council of Canada through grants to Tom Edwards. Additional funding was provided by the Northern Scientific Training Program of Indian and Northern Affairs Canada. Sincere gratitude goes to family, especially my husband Mike for incredible patience. v Table of Contents List of Figures........................................................................................................................... x List of Tables ......................................................................................................................... xiv Chapter 1 Introduction................................................................................................1 1.1 Research Objectives ...................................................................................................... 5 1.2 Research Approach....................................................................................................... 8 1.2.1 Modern isotope hydrology........................................................................................ 8 1.2.1.1 Isotopic labeling in the water cycle................................................................................8 1.2.1.2 Evaporation and water balance......................................................................................9 1.2.1.3 Global distribution of isotopes in precipitation............................................................10 1.2.1.4 Oxygen isotope-temperature relations .........................................................................10 1.2.2 Oxygen isotopes in cellulose .................................................................................. 12 1.2.3 Carbon and nitrogen content of lake-sediment organic matter............................... 14 1.2.4 Carbon isotopes in lake sediments.......................................................................... 15 1.2.5 Nitrogen isotopes in lake sediments ....................................................................... 17 1.3 Thesis Organization