Research Collection Doctoral Thesis Glacial response to global climate changes Cosmogenic nuclide chronologies from high and low latitudes Author(s): Strasky, Stefan Publication Date: 2008 Permanent Link: https://doi.org/10.3929/ethz-a-005666191 Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library Glacial response to global climate changes: cosmogenic nuclide chronologies from high and low latitudes Stefan Strasky Diss. ETH No. 17569 2008 DISS. ETH NO. 17569 GLACIAL RESPONSE TO GLOBAL CLIMATE CHANGES: COSMOGENIC NUCLIDE CHRONOLOGIES FROM HIGH AND LOW LATITUDES A dissertation submitted to ETH ZURICH for the degree of Doctor of Sciences presented by STEFAN STRASKY dipl. Erdw. BENEFRI, University of Bern born 10.02.1976 citizen of Schwändi GL accepted on the recommendation of Prof. Dr. Rainer Wieler, ETH Zurich, examiner Prof. Dr. Christian Schlüchter, University of Bern, co-examiner Prof. Dr. Carlo Baroni, University of Pisa, co-examiner Dr. Samuel Niedermann, GFZ-Potsdam, co-examiner Prof. Dr. Sean Willett, ETH Zurich, co-examiner 2008 Front cover Campbell glacier tongue flowing into the Ross Sea, Terra Nova Bay, Antarctica. Horizontal width of the picture is ~5 km. Back cover Impressions from fieldwork in Tibet, Antarctica and Europe. From top to down: (1) Landscape in the Shaluli Mountains (view north from Chuanxi Plateau), Tibet. (2) Terminal moraine and tongue basin of the Cuo Ji Gang Wa palaeoglacier, Chuanxi Plateau, Tibet. (3) Large erratic boulder (sample BROW3; ~250 m3). In the back- ground are Boomerang glacier and Mt. Keinath (on the right-hand side of the picture), Deep Freeze Range, Antarctica. (4) Sampling for surface exposure dating. Beacon sandstone sample rhs1, Ricker Hills, Antarctica. (5) Aletsch glacier (Switzerland), the largest and longest glacier in the European Alps. During glacial periods, the Aletsch glacier region was a large ice field that fed into the Rhône valley glacier. (6) Alpine erratic boulder (sample MO-04-01) found on top of the Montoz anticline, Jura Mountains, Switzerland. CONTENTS Abstract 1 Zusammenfassung 3 1 Introduction 5 1.1 Glacial response to climate change 5 1.2 Cosmogenic nuclides: principles and application to glacial systems 5 1.3 Multiple cosmogenic nuclide analyses 6 1.4 Outline of the thesis 7 2 Cosmogenic nuclide production on earth 9 2.1 Introduction 9 2.2 Artificial targets to refine production rate scaling factors for surface exposure dating 11 2.2.1 Introduction 11 2.2.2 Experimental procedures 13 2.2.3 Exposure sites 19 2.2.4 Results 21 2.2.5 Discussion and Conclusions 24 3 Antarctica 29 3.1 Introduction 29 3.2 Surface exposure ages imply multiple low-amplitude Pleistocene variations in East Antarctic Ice Sheet, Ricker Hills, Victoria Land 31 3.2.1 Introduction 32 3.2.2 Study site 33 3.2.3 Sampling 37 3.2.4 Surface exposure dating 38 3.2.5 Results 41 3.2.6 Discussion 43 3.2.7 Conclusions 48 3.3 Multiple cosmogenic nuclides document complex Pleistocene exposure history of glacial drifts in Terra Nova Bay (northern Victoria Land, Antarctica) 53 3.3.1 Introduction 54 3.3.2 Study area 55 3.3.3 Cosmogenic surface exposure dating (SED) 59 3.3.4 Results 64 3.3.5 Discussion 66 3.3.6 Conclusions 69 4 Tibet 75 4.1 Introduction 75 4.2 Glacier extension on the eastern Tibetan Plateau in response to MIS 2 10 21 cooling, with a contribution to Be and Ne methodology 77 4.2.1 Introduction 78 4.2.2 Geology and climate 79 4.2.3 Fieldwork and methods 84 4.2.4 Results 89 4.2.5 Discussion 93 4.2.6 Conclusions 103 4.3 Late Glacial ice advances in southeast Tibet 111 4.3.1 Introduction 111 4.3.2 Study area 114 4.3.3 Cosmogenic nuclide exposure ages 116 4.3.4 Discussion 121 4.3.5 Conclusions 123 5 Europe 129 5.1 Introduction 129 5.2 Oberflächenalter zweier Findlinge aus Niedersachsen – Zeugen einer alten fennoskandischen Vergletscherung in Norddeutschland [Surface exposure dating of two erratic boulders from Niedersachsen – evidence of an old Fennoscandian Ice Sheet advance in Northern Germany] 131 5.2.1 Einführung 132 5.2.2 Probenlokalitäten und Probennahme 134 5.2.3 Die Methode der Oberflächenaltersbestimmung mit kosmogenen Nukliden 135 5.2.4 Resultate 137 5.2.5 Schlussfolgerungen 139 5.3 First results of cosmogenic dated pre-last glaciation erratics from the Montoz area, Jura Mountains, Switzerland 143 5.3.1 Introduction 143 5.3.2 Evidence for glaciation of the Jura Mountains 144 5.3.3 Distribution of the erratic boulders 147 5.3.4 Cosmogenic dating 148 5.3.5 Discussion 154 5.3.6 Conclusions 155 6 Conclusions and outlook 161 I References 163 II Appendix 169 III Dank 181 IV Curriculum Vitae 185 ABSTRACT A direct and visible effect of climate change on the continents is the variable size of ice sheets and glaciers. Considerable ice fluctuations happened in the past, but when and to what extent they occurred is not well known. The main goal of this work was to establish local glacial chronologies in key areas for the global climate system (Antarctica, Tibet, northern Europe) and thus to add information needed to further complete the picture of how glaciers responded to climate change. Therefore, moraines and erratic boulders, the direct proof of ice advance or ice sheet expansion, were mapped and dated with in situ produced cosmogenic 21Ne, 10Be and 26Al. S. Strasky measured all neon data presented in this work while A.A. Graf and L. Di Nicola investigated the radionuclides on aliquots of the same samples more or less contemporaneously within the framework of two related PhD projects at the University of Bern. In Antarctica the main emphasis was put on East Antarctic Ice Sheet (EAIS) variations that predate the last glacial maximum (LGM). Past ice volume fluctuations were studied in two presently ice-free areas of Victoria Land, the Ricker Hills, a nunatak at the boundary of the EAIS, and the Northern Foothills, a coastal piedmont in the Terra Nova Bay area. Results from surface exposure ages of erratic boulders form the Ricker Hills suggest that several EAIS variations occurred during the Pleistocene with a major ice advance between 1.13 and 1.38 Ma. However, all recorded ice fluctuations were of limited extent of less than ~500 m above present ice levels. Restricted ice volume changes are also indicated from the Northern Foothills throughout the Pleistocene. Cosmogenic nuclide analyses of a glacially scoured bed- rock surface revealed that coastal summits were sculpted about 4–6 Ma ago and have re- mained ice-free ever since. Below the rounded summits, surfaces were repeatedly exposed and buried by low-erosive ice, as indicated by complex exposure histories of all studied erratic boulders. This finding clearly demonstrates that pre-exposure is much more important than previously assumed and multiple nuclide analyses are a prerequisite for any meaningful surface exposure dating in polar areas. In Tibet the time structure of glacier variations within the last glacial cycle was investigated in two monsoon-influenced sites on the southeastern margin of the Tibetan Plateau. In the surrounding area of Garzê, northern Shaluli Mountains, 10Be exposure ages of a well-defined terminal moraine succession cluster around 20 ka, suggesting a major ice advance during 1 marine isotope stage (MIS) 2, thus being synchronous to the global LGM. However, a significant difference between 21Ne and 10Be exposure ages was observed for these samples and was attributed to a nucleogenic neon component. Evidence for a Late Glacial signal was found in both study sites, more prominent in the Kangding area, and points to the possibility of a link between North Atlantic and east Asian glacial climate. In Europe the focus of interest was the timing of the most extensive Quaternary glaciation of the Alps and the largest extent of the Fennoscandian Ice Sheet in Northern Germany. Two large erratic boulders on a Saalian surface in Niedersachsen, far beyond the LGM ice sheet margin, were analysed for cosmogenic nuclides. The data hint at a major ice sheet expansion during MIS 6. A similar result was found for erratic boulders of Alpine origin, deposited on top of the Swiss Jura Mountains. Surface exposure ages between 126 and 184 ka point most likely to the penultimate glaciation in MIS 6. As cosmogenic nuclide production on earth is crucial for surface exposure dating and cur- rently no consensus on using a common set of production rate scaling factors has yet been reached, a long-term experiment was continued to measure cosmogenic noble gases (3He and 21Ne) as a function of the geographical position in artificial quartz targets. Tests with newly designed targets have shown the suitability of the set-up for this purpose and first measure- ments of two targets exposed at different altitudes in Antarctica for a period of one year revealed promising results. 2 ZUSAMMENFASSUNG Die variable Grösse von Gletschern und Eisschildern ist ein direkter und unübersehbarer Effekt der Klimaveränderungen auf den Kontinenten. In vergangenen Zeiten resultierten be- trächtliche Eisschwankungen; wann genau sie stattfanden und von welchem Ausmass sie waren, ist für viele Gebiete noch nicht ausreichend geklärt. Das Hauptziel dieser Arbeit war es, lokale Gletschergeschichten zu rekonstruieren – dies in Regionen von globaler Klima- Bedeutung (Antarktis, Tibet, Nordeuropa), weil damit ein Beitrag für ein besseres Verständnis der klimabedingten Gletscherschwankungen geleistet werden soll. Zu diesem Zweck wurden Moränen und Findlinge – Zeugen früherer Eisvorstösse – kartiert und deren Oberflächenalter mittels in situ produzierten kosmogenen Nukliden (21Ne, 10Be, 26Al) bestimmt.