Applications of in situ cosmogenic nuclides to problems in Quaternary geology require increasingly accurate and precise knowledge of nuclide production rates. Production rates depend on the terrestrial cosmic-ray intensity, which is a function of the elevation and geomagnetic coordinates of a sample site and the geomagnetic field intensity. The main goal of this dissertation is to improve the accuracy of cosmogenic dating by providing better constraints on the spatial variability of production rates.In this dissertation I develop a new scaling model that incorporates the best available cosmic-ray data into a framework that better describes the effects of elevation and geomagnetic shielding on production rates. This model is based on extensive measurements of energetic nucleon fluxes from neutron monitor surveys and on more limited data from low-energy neutron surveys. A major finding of this work is that neutron monitors yield scaling factors different from unshielded proportional counters. To verify that the difference is real I conducted an airborne survey of low-energy neutron fluxes at Hawaii (19.7° N 155.5° W) to compare with a nearby benchmark neutron monitor survey. Our data confirm that the attenuation length is energy dependent and suggest that the scaling factor for energetic nucleons is 10% higher between sea level and 4000 m than for low-energy neutrons at this location. An altitude profile of cosmogenic 36Cl production from lava flows on Mauna Kea, Hawaii, support the use of neutron flux measurements to scale production rates but these data do not have enough precision to confirm or reject the hypothesis of energy-dependent scaling factors.

This research aims to understand the natural and human influences on erosion in three tributary watersheds to the Mekong River, Yunnan Province, China and to assess the utility of a novel application of isotopic indicators of erosion. It explores how erosion varies through time and space as a function of physical characteristics of the landscape, tectonic forces, and human alteration of the landscape for forestry and agriculture. To accomplish these goals, I use four sediment-associated radionuclides: in situ 10Be, meteoric 10Be, 210Pbex, and 137Cs. These isotopes accumulate in or on sediment grains, and each accumulates to a different depth on the landscape and has a different half-life. Thus, the isotopes can be used to track sediment as it moves across Earth's surface, each providing unique insight into processes occurring over a certain time period (from ~50 to 50,000 years) or eroding to a certain depth on the landscape. The studied watersheds range from 22° to 27° N latitude, and from 200 to 2500 km2 in area. I collected 54 samples of river-borne sediment within the three study watersheds, and measured the concentration of each isotope in every sample. In addition to the measured isotopic concentrations, I utilize on over 20 years of daily sediment yield data at the outlet of each watershed, hillslope steepness, normalized channel steepness (ksn), contemporary land-use data, elevation, and 56 years of mean annual precipitation data (MAP). Long-term erosion rates scale with topographic parameters in two of the three study basins, indicating that topography, or the underlying tectonic forces responsible for topography, control erosion rates over the past 6,000 to 50,000 years. Isotopic data also show that contemporary erosion is higher in cultivated areas than un-cultivated areas, a direct result of agricultural practices. Contemporary sediment yield, however, has not increased notably due to land-use change; however, under-representation of large stochastic events and sediment trapped by agriculture have reduced sediment yield relative to the long-term average in two of the studied watersheds. Overall, the data imply changes in contemporary erosion that are consistent with Chinese policies that promoted deforestation from the 1950's to the late 1980's and conservation from the late 1990's to present. This proves to be a significant finding, as the result of the top-down approach China has taken with conservation policy has been widely called into question in previous studies. While each isotope has the potential to provide unique information regarding erosional processes, in situ 10Be and 210Pbex proved to be the most useful, while meteoric 10Be was the most challenging to utilize. Though interpretation is complex, measuring all four isotopes on the same sediment samples helps to fully realize the potential of in situ 10Be to estimate background erosion by simultaneously allowing for assessment of contemporary and human induced erosion.

The magnitude of global sediment flux from streams to the oceans over the last 5 Ma is poorly quantified, yet important for predicting future fluxes and deciphering the relative control of tectonic uplift, climate change, vegetation, and related feedback mechanisms on landscape evolution. Despite numerous proxy studies on global sediment delivery to the oceans, it remains uncertain whether bulk sedimentation increased, decreased, or remained approximately constant across one of the most significant global climate changes: the Plio-Pleistocene transition. New developments and strategies in the application of cosmic-ray-produced isotopes, in part developed by this thesis, provide records of pre-historic denudation of confined fluvial catchments in Texas and Yukon. Non-glaciated, tectonically passive regions were targeted in contrast to other studies on modern sedimentation rates in order to isolate the climate influence from glacial and tectonic controls. The results suggest that average catchment temperature, and surficial processes and other factors such as vegetation cover associated with temperature, are the primary controls on the variation in landscape denudation in regions lacking tectonics and direct glacial cover. Specifically, warmer temperatures yield higher denudation rates, both at the scale of glacial-interglacial climate change and over the Plio-Pleistocene transition. The implication is that stream sediment flux to the ocean from tropical and temperate regions was higher during the Pliocene than in the Quaternary. However, this may have been balanced by an increase in sediment flux from regions covered by warm-based glaciers during glacial periods, or by increased temporary continental storage during interglacial periods.

Dissertation (PhD)--University of Arizona, Tucson, Arizona, 2005.

<p>  </p> <p>Reconstructing past glacier and ice-sheet extents is important to better understand how glacial systems have responded to past climate changes in hope of constraining predictions of their responses to ongoing anthropogenic climate warming. As such, the most recent period of climatic variations, from the Last Glacial Maximum (LGM, ca. 21 ka) through today, is of great interest as a prominent example of how ice has reacted to past climatic warming events. Surface exposure dating utilizing cosmogenic nuclides can directly constrain when past ice deglaciated in current and former glacial landscapes. Numerous studies have utilized long-lived cosmogenic radionuclides (i.e., 10Be, 26Al) in polar regions to reconstruct glacial systems. However, due to prevalent non-erosive cold-based ice, prior nuclides from pre-LGM can be preserved. </p> <p>The research described in this dissertation applies <em>in situ </em>cosmogenic 14C (<em>in situ</em> 14C), an emerging geochronometer, to polar glacial landscapes in Sweden and Antarctica to constrain the timing and rate of glacial ice retreat. <em>In situ </em>14C more closely reflects the post-LGM deglacial signal in polar regions because it is less likely to preserve prior nuclides (inheritance) under minimally erosive ice. Our cosmogenic 10Be–26Al–14C concentrations near the Riukojietna ice cap, the last remaining ice cap in Sweden, combined with a sedimentary record from a proximal proglacial lake, indicate the ice cap likely survived during a warm period in the Holocene, but was less extensive than today. The <em>in situ</em> 14C exposure data from nunataks in western Dronning Maud Land (DML), East Antarctica indicate significant coastal thickening (up to 850 m) not predicted by models to date. In addition, this work dates the timing of post-LGM ice surface lowering in two drainage basins in western DML. These results demonstrate the significant contribution of <em>in situ</em> 14C in polar regions.</p> <p>In addition to applications of <em>in situ</em> 14C in polar regions, this work also describes the development of a compositionally dependent <em>in situ</em> 14C production rate calculator. The ability to extract <em>in situ</em> 14C from samples which quartz cannot be separated (either quartz-poor or fine-grained) would allow new avenues of research. The computational framework will be a useful tool in efforts to broaden the utility of <em>in situ</em> 14C to quartz-poor and fine-grained rock types. </p>

Soil erosion undermines agricultural productivity, limiting the lifespan of civilizations. For agriculture to be sustainable, soil erosion rates must be low enough to maintain fertile soil, as was present in many agricultural landscapes prior to the initiation of farming. However, there have been few measurements of long-term pre-agricultural erosion rates in major agricultural landscapes. We quantified geological erosion rates in the Midwestern U.S., one of the world’s most productive agricultural areas. We sampled soil profiles from 14 native prairies and measured concentrations of the cosmogenic nuclide 10Be and chemically immobile elements to calculate physical erosion rates. We used the erosion rates and measurements of topographic curvature to estimate a pre- agricultural topographic diffusion coefficient. We find pre-agricultural erosion rates of 0.0001–0.1 mm yr-1 and a site-averaged diffusion coefficient of 0.005 m2 yr-1. The pre- agricultural erosion rates and diffusion coefficient we measured are both orders of magnitude lower than anthropogenic values previously measured in adjacent agricultural fields. The pre-agricultural erosion rates are one to four orders of magnitude lower than the 1 mm yr-1 soil loss tolerance value assigned to these locations by the U.S. Department of Agriculture. Hence, as currently defined, tolerable soil loss will lead to unsustainable erosion of Midwestern soils. However, quantifying natural erosion rates via cosmogenic nuclides provides a means for more robustly defining rates of tolerable soil loss and developing management guidelines that promote soil sustainability.

Constraining past episodes of climate change and glacial response is critical for understanding future impacts of climate change, especially in the high latitudes where warming is expected to be rapid and most of Earth's glaciers exist. Many studies of past glacier size utilize rare isotopes called cosmogenic nuclides to perform surface exposure dating. Since most areas of Earth's surface that were previously glaciated were covered by erosive ice, which stripped away pre-existing cosmogenic nuclides, surface exposure dating yields the timing of the most recent deglaciation. However, in some high latitude areas where glacial ice is cold-based and non-erosive (so-called 'ghost glaciers'), the assumptions of surface exposure dating are violated. Alternate approaches are required to constrain the complex histories of such landscapes. My doctoral dissertation focuses on both developing and employing alternative approaches to studying glacial history in the high latitudes, where glacial ice is non-erosive and dating rock surfaces with a single cosmogenic nuclide does not yield exposure ages. Here, I utilize optimized laboratory methods, paired analyses of two cosmogenic isotopes (10Be and 26Al), numerical models to assess possible exposure/burial histories, and Monte Carlo simulations to constrain uncertainties. To study the exposure and burial history of long-preserved landscapes in the Arctic, I investigate landscapes in two high-latitude locations: Thule, northwestern Greenland; and Cumberland Sound, southern Baffin Island, Canada. Bedrock surfaces, sampled on Baffin Island, exhibit evidence of long-lived subaerial weathering and have simple 10Be exposure ages up to 160,000 yr, despite being glaciated until ~10,000 yr. Simple exposure ages tend to increase with elevation, suggesting more effective erosion in the fjords and longer-term preservation of the uplands. Minimum limiting total histories calculated with 26Al/10Be range up to several million years, with periods of exposure representing ~20% of the total history, describing surfaces that have been alternately preserved beneath non-erosive glacial ice and weathered subaerially over many glacial/interglacial cycles. Boulders, sampled at both sites, have simple 10Be exposure ages up to 78,000 yr in Thule and 79,000 yr on Baffin Island, and yield multi-modal age distributions. Simple exposure ages of boulders tend to under-estimate bedrock ages in the cases of paired bedrock/boulder samples. Minimum limiting total histories calculated with 26Al/10Be range up to 700,000 yr in Thule and several million years on Baffin Island, with periods of exposure representing only a small portion of the total history. Forward numerical models suggest that boulders have been repeatedly reworked, likely experiencing partial or complete shielding during interglacial periods because of rotation and/or burial by till. The landscapes I assess here preserve histories of hundreds of thousands to millions of years, and represent a complex interplay of interglacial exposure, subglacial preservation beneath cold-based ice, periglacial processes, and subaerial weathering. Although such landscapes represent methodological challenges, they contain valuable information about long-term variations in glacial extent and climate.

Landscapes evolve in a complex interplay between climate and tectonics. Thus, the geomorphic characteristics of a landscape can only be understood if both, climatic and tectonic signals of past and ongoing processes can be identified. In order to evaluate the impact of both forcing factors it is crucial to quantify the evolution of geomorphic markers in natural environments. The Cenozoic Andes are an ideal setting to evaluate tectonic and climatic aspects of landscape evolution at different time and length scales in different natural compartments. The Andean Cordillera constitutes the type subduction orogen and is associated with the subduction of the oceanic Nazca Plate beneath the South American continent since at least 200 million years. In Chile and the adjacent regions this convergent margin is characterized by active tectonics, volcanism, and mountain building. Importantly, along the coast of Chile megathrust earthquakes occur frequently and influence landscape evolution. In fact, the largest earthquake ever recorded occurred in south-central Chile in 1960 and comprised a rupture zone of ~ 1000 km length. However, on longer time scales beyond historic documentation of seismicity it is not well known, how such seismotectonic segments have behaved and how they influence the geomorphic evolution of the coastal realms. With several semi-independent morphotectonic segments, recurrent megathrust earthquakes, and a plethora of geomorphic features indicating sustained tectonism, the margin of Chile is thus a key area to study relationships between surface processes and tectonics. In this study, I combined geomorphology, geochronology, sedimentology, and morphometry to quantify the Pliocene-Pleistocene landscape evolution of the tectonically active south-central Chile forearc. Thereby, I provide (1) new results about the influence of seismotectonic forearc segmentation on the geomorphic evolution and (2) new insights in the interaction between climate and tectonics with respect to the morphology of the Chilean forearc region. In particular, I show that the forearc is characterized by three long-term segments that are not correlated with short-lived earthquake-rupture zones that may. These segments are the Nahuelbuta, Toltén, and Bueno segments, each recording a distinct geomorphic and tectonic evolution. The Nahuelbuta and Bueno segments are undergoing active tectonic uplift. The long-term behavior of these two segments is manifested in form of two doubly plunging, growing antiforms that constitute an integral part of the Coastal Cordillera and record the uplift of marine and river terraces. In addition, these uplifting areas have caused major changes in flow directions or rivers. In contrast, the Toltén segment, situated between the two other segments, appears to be quasi-stable. In order to further quantify uplift and incision in the actively deforming Nahuelbuta segment, I dated an erosion surface and fluvial terraces in the Coastal Cordillera with cosmogenic 10Be and 26Al and optically stimulated luminescence, respectively. According to my results, late Pleistocene uplift rates corresponding to 0.88 mm a-1 are faster than surface-uplift rates averaging over the last 5 Ma, which are in the range of 0.21 mm a-1. This discrepancy suggests that surface uplift is highly variable in time and space and might preferably concentrate along reverse faults as indicated by a late Pleistocene flow reversal. In addition, the results of exposure dating with cosmogenic 10Be and 26Al indicate that the morphotectonic segmentation of this region of the forearc has been established in Pliocene time, coeval with the initiation of uplift of the Coastal Cordillera about 5 Ma ago, inferred to be related to a shift in subduction mode from erosion to accretion. Finally, I dated volcanic clasts obtained from alluvial surfaces in the Central Depression, a low-relief sector separating the Coastal from the Main Cordillera, with stable cosmogenic 3He and 21Ne, in order to reveal the controls of sediment accumulation in the forearc. My results document that these gently sloping surfaces have been deposited 150 to 300 ka ago. This deposition may be related to changes in the erosional regime during glacial episodes. Taken together, the data indicates that the overall geomorphic expression of the forearc is of post-Miocene age and may be intimately related to a climatic overprint of the tectonic system. This climatic forcing is also reflected in the topography and local relief of the Central and Southern Andes that vary considerably along the margin, determined by the dominant surface process that in turn is eventually controlled by climate. However, relief also partly reflects surface processes that have taken place under past climatic conditions. This emphasizes that due care has to be exercised when interpreting landscapes as mirrors of modern climates. / Landschaften entwickeln sich im komplexen Zusammenspiel von Klima und Tektonik. Demzufolge können sie nur verstanden werden, wenn sowohl klimatische als auch tektonische Signale vergangener und rezenter Prozesse identifiziert werden. Um den Einfluss beider Faktoren zu bewerten, ist es deshalb wichtig, die Evolution geomorphologischer Marker in der Natur zu quantifizieren. Die känozoischen Anden sind eine ideale Region, um tektonische und klimatische Aspekte der Landschaftsentwicklung auf verschiedenen Zeit- und Längenskalen zu erforschen. Sie sind das Modell-Subduktionsorogen, assoziiert mit der Subduktion der ozeanischen Nazca-Platte unter den südamerikanischen Kontinent seit ca. 200 Mio Jahren. In Chile ist dieser konvergente Plattenrand geprägt von aktiver Tektonik, Vulkanismus und Gebirgsbildung. Bedeutenderweise ereignen sich entlang der Küste häufig Megaerdbeben, die die Landschaftsentwicklung stark beeinflussen. Tatsächlich ereignete sich das größte jemals aufgezeichnete Erdbeben mit einer Bruchzone von ca. 1000 km Länge 1960 im südlichen Zentralchile. Nichtsdestotrotz ist auf längeren Zeitskalen über historische Dokumentationen hinaus nicht bekannt, wie sich solche seismotektonischen Segmente verhalten und wie sie die geomorphologische Entwicklung der Küstengebiete beeinflussen. Mit semi-unabhängigen morphotektonischen Segmenten, wiederkehrenden Megaerdbeben und einer Fülle geomorphologischer Marker, die aktive Tektonik anzeigen, ist somit der Plattenrand von Chile ein Schlüsselgebiet für das Studium von Zusammenhängen zwischen Oberflächenprozessen und Tektonik. In dieser Arbeit kombiniere ich Geomorphologie, Geochronologie, Sedimentologie und Morphometrie, um die plio-pleistozäne Landschaftsentwicklung des tektonisch aktiven süd-zentralchilenischen Forearcs zu quantifizieren. Mit dieser Analyse liefere ich (1) neue Ergebnisse über den Einfluss seismotektonischer Forearc-Segmentierung auf die geomorphologischen Entwicklung und (2) neue Erkenntnisse über die Interaktion zwischen Klima und Tektonik bezüglich der Gestaltung des chilenischen Forearcs. Ich zeige, dass der Forearc in drei langlebige morphotektonische Segmente gegliedert ist, die nicht mit kurzlebigen Erdbebenbruchzonen korrelieren. Die Segmente heißen Nahuelbuta, Toltén und Bueno Segment, wovon jedes eine andere geomorphologische und tektonische Entwicklung durchläuft. Die Nahuelbuta und Bueno Segmente unterliegen aktiver tektonischer Hebung. Das langfristige Verhalten dieser beiden Segmente manifestiert sich in zwei beidseitig abtauchenden, wachsenden Antiklinalen, die integraler Bestandteil des Küstengebirges sind und die Hebung von marinen und fluvialen Terrassen aufzeichnen. Die Hebung verursachte weitreichende Veränderungen in den Fließrichtungen des Gewässernetzes. Im Gegensatz dazu ist das Toltén Segment, das sich zwischen den beiden anderen Segmenten befindet, quasi-stabil. Um die Hebung und Einschneidung in dem tektonisch aktiven Nahuelbuta Segment zu quantifizieren, habe ich eine Erosionsfläche und fluviale Terrassen in dem Küstengebirge mit kosmogenem 10Be und 26Al bzw. optisch stimulierter Lumineszenz datiert. Meinen Ergebnissen zufolge sind die spätpleistozänen Hebungsraten, die ca. 0,88 mm a-1 betragen, höher als die Oberflächenhebungsraten, die über die letzten 5 Mio Jahre mitteln und ca. 0,21 mm a-1 betragen. Diese Diskrepanz deutet an, dass die Hebung der Oberfläche räumlich und zeitlich sehr stark variiert und sich präferiert an Aufschiebungen konzentriert. Zusätzlich zeigen die Ergebnisse der Expositionsdatierung mit kosmogenem 10Be und 26Al, dass die morphotektonische Segmentierung im Pliozän etabliert wurde, zeitgleich mit dem Beginn der Hebung des Küstengebirges vor ca. 5 Mio Jahren infolge eines Wechsels des Subduktionsmodus von Erosion zu Akkretion. Schließlich habe ich vulkanische Klasten, die aus alluvialen Flächen im Längstal stammen, mit den stabilen kosmogenen Nukliden 3He und 21Ne datiert, um Aufschluss über die Faktoren zu erhalten, die die Sedimentablagerung im Forearc bestimmen. Meine Ergebnisse weisen darauf hin, dass diese flach einfallenden Oberflächen, die vor 150.000 bis 300.000 Jahren abgelagert wurden, in Zusammenhang mit Änderungen des Erosionsregimes in glazialen Episoden entstanden sind. Zusammenfassend zeigen die Daten, dass der heutige geomorphologische Ausdruck des Forearcs post-Miozän und eng mit einer klimatischen Überprägung des tektonischen Systems verknüpft ist. Der klimatische Einfluss spiegelt sich ebenfalls in der Topographie und dem lokalen Relief der Zentral- und Südanden wider. Beide Parameter variieren stark entlang des Plattenrandes, bestimmt durch den jeweils dominierenden Oberflächenprozess, der wiederum letztendlich vom vorherrschenden Klima abhängt. Allerdings reflektiert das Relief teilweise Oberflächenprozesse, die unter vergangenen Klimaten aktiv waren. Das betont die äußerst große Vorsicht, die nötig ist, wenn Landschaften als Spiegel des aktuellen Klimas interpretiert werden.

In den Hochgebirgen Asiens bedecken Gletscher eine Fläche von ungefähr 115,000 km² und ergeben damit, neben Grönland und der Antarktis, eine der größten Eisakkumulationen der Erde. Die Sensibilität der Gletscher gegenüber Klimaschwankungen macht sie zu wertvollen paläoklimatischen Archiven in Hochgebirgen, aber gleichzeitig auch anfällig gegenüber rezenter und zukünftiger globaler Erwärmung. Dies kann vor allem in dicht besiedelten Gebieten Süd-, Ost- und Zentralasiens zu großen Problem führen, in denen Gletscher- und Schnee-Schmelzwässer eine wichtige Ressource für Landwirtschaft und Stromerzeugung darstellen. Eine erfolgreiche Prognose des Gletscherverhaltens in Reaktion auf den Klimawandel und die Minderung der sozioökonomischen Auswirkungen erfordert fundierte Kenntnisse der klimatischen Steuerungsfaktoren und der Dynamik asiatischer Gletscher. Aufgrund ihrer Abgeschiedenheit und dem erschwerten Zugang gibt es nur wenige glaziologische Geländestudien, die zudem räumlich und zeitlich sehr begrenzt sind. Daher fehlen bisher grundlegende Informationen über die Mehrzahl asiatischer Gletscher. In dieser Arbeit benutze ich verschiedene Methoden, um die Dynamik asiatischer Gletscher auf mehreren Zeitskalen zu untersuchen. Erstens teste ich eine Methode zur präzisen satelliten-gestützten Messung von Gletscheroberflächen-Geschwindigkeiten. Darauf aufbauend habe ich eine umfassende regionale Erhebung der Fliessgeschwindigkeiten und Frontdynamik asiatischer Gletscher für die Jahre 2000 bis 2008 durchgeführt. Der gewonnene Datensatz erlaubt einmalige Einblicke in die topographischen und klimatischen Steuerungsfaktoren der Gletscherfließgeschwindigkeiten in den Gebirgsregionen Hochasiens. Insbesondere dokumentieren die Daten rezent ungleiches Verhalten der Gletscher im Karakorum und im Himalaja, welches ich auf die konkurrierenden klimatischen Einflüsse der Westwinddrift im Winter und des Indischen Monsuns im Sommer zurückführe. Zweitens untersuche ich, ob klimatisch bedingte Ost-West Unterschiede im Gletscherverhalten auch auf längeren Zeitskalen eine Rolle spielen und gegebenenfalls für dokumentierte regional asynchrone Gletschervorstöße relevant sind. Dazu habe ich mittels kosmogener Nuklide Oberflächenalter von erratischen Blöcken auf Moränen ermittelt und eine glaziale Chronologie für das obere Tons Tal, in den Quellgebieten des Ganges, erstellt. Dieses Gebiet befindet sich in der Übergangszone von monsunaler zu Westwind beeinflusster Feuchtigkeitszufuhr und ist damit ideal gelegen, um die Auswirkungen dieser beiden atmosphärischen Zirkulationssysteme auf Gletschervorstöße zu untersuchen. Die ermittelte glaziale Chronologie dokumentiert mehrere Gletscherschwankungen während des Endstadiums der letzten Pleistozänen Vereisung und während des Holzäns. Diese weisen darauf hin, dass Gletscherschwankungen im westlichen Himalaja weitestgehend synchron waren und auf graduelle glaziale-interglaziale Temperaturveränderungen, überlagert von monsunalen Niederschlagsschwankungen höherer Frequenz, zurück zu führen sind. In einem dritten Schritt kombiniere ich Satelliten-Klimadaten mit Eisfluss-Abschätzungen und topographischen Analysen, um den Einfluss der Gletscher Hochasiens auf die Reliefentwicklung im Hochgebirge zu untersuchen. Die Ergebnisse dokumentieren ausgeprägte meridionale Unterschiede im Grad und im Stil der Vergletscherung und glazialen Erosion in Abhängigkeit von topographischen und klimatischen Faktoren. Gegensätzlich zu bisherigen Annahmen deuten die Daten darauf hin, dass das monsunale Klima im zentralen Himalaja die glaziale Erosion schwächt und durch den Erhalt einer steilen orographischen Barriere das Tibet Plateau vor lateraler Zerschneidung bewahrt. Die Ergebnisse dieser Arbeit dokumentieren, wie klimatische und topographische Gradienten die Gletscherdynamik in den Hochgebirgen Asiens auf Zeitskalen von 10^0 bis 10^6 Jahren beeinflussen. Die Reaktionszeit der Gletscher auf Klimaveränderungen sind eng an Eigenschaften wie Schuttbedeckung und Neigung gekoppelt, welche ihrerseits von den topographischen Verhältnissen bedingt sind. Derartige Einflussfaktoren müssen bei paläoklimatischen Rekonstruktion und Vorhersagen über die Entwicklung asiatischer Gletscher berücksichtigt werden. Desweiteren gehen die regionalen topographischen Unterschiede der vergletscherten Gebiete Asiens teilweise auf klimatische Gradienten und den langfristigen Einfluss der Gletscher auf die topographische Entwicklung des Gebirgssystems zurück. / In the high mountains of Asia, glaciers cover an area of approximately 115,000 km² and constitute one of the largest continental ice accumulations outside Greenland and Antarctica. Their sensitivity to climate change makes them valuable palaeoclimate archives, but also vulnerable to current and predicted Global Warming. This is a pressing problem as snow and glacial melt waters are important sources for agriculture and power supply of densely populated regions in south, east, and central Asia. Successful prediction of the glacial response to climate change in Asia and mitigation of the socioeconomic impacts requires profound knowledge of the climatic controls and the dynamics of Asian glaciers. However, due to their remoteness and difficult accessibility, ground-based studies are rare, as well as temporally and spatially limited. We therefore lack basic information on the vast majority of these glaciers. In this thesis, I employ different methods to assess the dynamics of Asian glaciers on multiple time scales. First, I tested a method for precise satellite-based measurement of glacier-surface velocities and conducted a comprehensive and regional survey of glacial flow and terminus dynamics of Asian glaciers between 2000 and 2008. This novel and unprecedented dataset provides unique insights into the contrasting topographic and climatic controls of glacial flow velocities across the Asian highlands. The data document disparate recent glacial behavior between the Karakoram and the Himalaya, which I attribute to the competing influence of the mid-latitude westerlies during winter and the Indian monsoon during summer. Second, I tested whether such climate-related longitudinal differences in glacial behavior also prevail on longer time scales, and potentially account for observed regionally asynchronous glacial advances. I used cosmogenic nuclide surface exposure dating of erratic boulders on moraines to obtain a glacial chronology for the upper Tons Valley, situated in the headwaters of the Ganges River. This area is located in the transition zone from monsoonal to westerly moisture supply and therefore ideal to examine the influence of these two atmospheric circulation regimes on glacial advances. The new glacial chronology documents multiple glacial oscillations during the last glacial termination and during the Holocene, suggesting largely synchronous glacial changes in the western Himalayan region that are related to gradual glacial-interglacial temperature oscillations with superimposed monsoonal precipitation changes of higher frequency. In a third step, I combine results from short-term satellite-based climate records and surface velocity-derived ice-flux estimates, with topographic analyses to deduce the erosional impact of glaciations on long-term landscape evolution in the Himalayan-Tibetan realm. The results provide evidence for the long-term effects of pronounced east-west differences in glaciation and glacial erosion, depending on climatic and topographic factors. Contrary to common belief the data suggest that monsoonal climate in the central Himalaya weakens glacial erosion at high elevations, helping to maintain a steep southern orographic barrier that protects the Tibetan Plateau from lateral destruction. The results of this thesis highlight how climatic and topographic gradients across the high mountains of Asia affect glacier dynamics on time scales ranging from 10^0 to 10^6 years. Glacial response times to climate changes are tightly linked to properties such as debris cover and surface slope, which are controlled by the topographic setting, and which need to be taken into account when reconstructing mountainous palaeoclimate from glacial histories or assessing the future evolution of Asian glaciers. Conversely, the regional topographic differences of glacial landscapes in Asia are partly controlled by climatic gradients and the long-term influence of glaciers on the topographic evolution of the orogenic system.

Terrestrial cosmogenic nuclides such as beryllium-10 have recently been used as a way to determine basin-average erosion rates around the world. These erosion rates are useful to geomorphologists investigating landscape evolution. The Hangay Mountains in Mongolia are a prime location to use beryllium-10 because of the granitic rocks that provide the quartz needed for cosmogenic analysis as well as the lack of observed evidence of recent or old mass wasting events that mobilize sediment and bedrock with much lower cosmogenic concentrations that cause underestimations of erosion rates. Basin-average erosion rates observed in seven basins across the eastern Hangay Mountains range from 12 m/My to about 20 m/My. These are of similar magnitude to those found in tectonically inactive regions such as the southern Appalachians. Comparing basin-average erosion rates to basin parameters, whole basin relief had the highest calculated R2 value and elevation had the lowest P-value. No strong relationships were seen between erosion rate and mean slope angle, hypsometric integral, area, or mean local relief. The basin-average erosion rates observed in the Hangay were compared to previous studies by Ahnert (1970), Portenga and Biernman (2011), and Matmon et al. (2009). We found erosion rates from the Hangay to be much lower than expected in our analyses. The differences in erosion rates from the Hangay Mountains compared to other places around the world are likely due to the fact that the streams in the Hangay are eroding into alluvium as opposed to bedrock, and are located in a landscape dominanted by diffusive hillslope sediment transport mechanisms. The erosion rate is limited to the amount of sediment that can be transported by the streams.