The current performance of all three AMS systems in operation at ETH Zurich, the 6MV HVEC EN-Tandem facility “TANDEM”, the 0.5MV NEC Pelletron “TANDY”, and the 0.2MV system “MICADAS” is summarized. ...Radionuclides routinely measured with these AMS systems include 10Be, 14C, 26Al, 36Cl, 41Ca, 129I and the actinides. The reference materials used for the normalization of the AMS measurements at the ETH Zurich AMS facilities are presented. This paper therefore is a comprehensive status report of all three AMS systems currently operated by the Laboratory of Ion Beam Physics (LIP) at ETH Zurich and documents their performance and operation parameters.
Outlet glaciers grounded on a bed that deepens inland and extends below sea level are potentially vulnerable to 'marine ice sheet instability'. This instability, which may lead to runaway ice loss, ...has been simulated in models, but its consequences have not been directly observed in geological records. Here we provide new surface-exposure ages from an outlet of the East Antarctic Ice Sheet that reveal rapid glacier thinning occurred approximately 7,000 years ago, in the absence of large environmental changes. Glacier thinning persisted for more than two and a half centuries, resulting in hundreds of metres of ice loss. Numerical simulations indicate that ice surface drawdown accelerated when the otherwise steadily retreating glacier encountered a bedrock trough. Together, the geological reconstruction and numerical simulations suggest that centennial-scale glacier thinning arose from unstable grounding line retreat. Capturing these instability processes in ice sheet models is important for predicting Antarctica's future contribution to sea level change.
The tectonic control on landscape morphology and long-term denudation is largely documented for settings with high uplift rates. Relatively little is known about the rates of geomorphic response in ...areas of low tectonic uplift. Here, we evaluate spatial variations in denudation of the Spanish Betic Cordillera based on cosmogenic 10Be-derived denudation rates. Denudation rates are compared to published data on rock uplift and exhumation of the Betic Cordillera to evaluate steady-state topography. The spatial patterns of catchment-wide denudation rates (n=20) are then analysed together with topographic metrics of hillslope and channel morphology. Catchments draining the Betic ranges have relatively low denudation rates (64±54 mmkyr−1), but also show large variation as they range from 14 to 246 mm kyr−1. Catchment-wide denudation is linearly proportional to the mean hillslope gradient and local relief. Despite large spatial variation in denudation, the magnitude and spatial pattern of denudation rates are generally consistent with longer-term local uplift rates derived from elevated marine deposits, fission-track measurements and vertical fault slip rates. This might be indicative of a steady-state topography where rock uplift is balanced by denudation.
•We use 10Be TCN to infer denudation rates in a slow tectonic uplift area.•We examine relations between geomorphic indices, denudation and rock uplift rates.•Spatial pattern of denudation is well related to geomorphic indices and topography.•Magnitude of denudation rates is consistent with longer-term uplift rates.•Betic Cordillera probably approached topographic steady-state.
The quantification of geomorphic process rates on the outcrop- and the orogen-scale is important to describe accurately the interaction between the relative effects of erosion, tectonics and climate ...on landscape evolution. We report single and paired cosmogenic nuclide (
10Be,
26Al and
21Ne) derived erosion rates and exposure ages on hillslope interfluves from the tectonically active western central Andes that show a distinct spatial variation. A positive correlation of erosion rates with elevation and present-day rainfall rates is observed. Erosion rates at lower altitudes–the hyperarid
Coastal Cordillera and the
Western Escarpment with the northern part of the
Atacama Desert–are extremely low and of the order of 10–100 cm/My (nominal exposure ages 1–6 My). In contrast, erosion rates at higher altitudes–the semiarid
Western Cordillera–range up to 4600 cm/My (nominal exposure ages 0.02–0.1 My). This latter average long-term bedrock erosion rate record, suggested to be coupled to an orographically controlled pattern of rainfall, is also reflected in the pattern of denudation rates derived from a short-term decadal record of limited sediment yield data. Specifically, denudation rates calculated from sediment flux data are of a similar order of magnitude as erosion rates deduced from long-lived cosmogenic nuclides from bedrock hillslope interfluves of the
Western Cordillera. Nevertheless, the production and the supply of sediment from the western Andean slope are very limited.
Analysis of multiple cosmogenic nuclides allows simultaneous determination of erosion rates and exposure ages but also reveals complex exposure histories of non-bedrock samples, such as boulders or amalgamated clast samples. Notably, this study shows that saturation of nuclides, usually assumed in studies where only a single nuclide is analyzed, is rather the exception than the rule, as revealed by erosion island plots. Constant erosion that started much later than the formation age of the rocks or episodic erosion by spalling can partially explain non-steady-state concentrations and more complicated exposure scenarios. Furthermore, the use of multiple nuclides with different half-lives allowed us to infer that no significant variations in long-term erosion rates have occurred and that at the
Western Escarpment erosion rates have been low and constant for most of the late Neogene
. Nevertheless, the time intervals necessary to reach steady-state concentrations for cosmogenic nuclides can be quite different from those needed for landscapes to reach steady state.
We have calculated long-term erosion rates of 20–100 mm/kyr from quartz-contained
10Be in the bedload of middle European rivers for catchments ranging from 10
2 to 10
5 km
2. These rates average over ...10–40 kyr and agree broadly with rock uplift, incision and exhumation rates, historic soil erosion rates, and erosion rates calculated from the measured sediment loads of the same rivers. Moreover, our new erosion rate estimates correlate well with lithology and relief. However, in the Regen, Neckar, Loire, and Meuse catchments, cosmogenic nuclide-derived erosion rates are consistently 1.5–4 times greater than the equivalent rates derived from measured river loads. This may be due to the systematic under-representation of high-magnitude, low-frequency transport events in the gauging records which cover less than a century. Alternatively the discrepancy may derive from spatially non-uniform erosion and preferential tapping of deeper sections of the irradiation profile. A third explanation relates the high cosmogenic nuclide-derived erosion rates to inheritance of an elevated Pleistocene erosion signal. Uncertainties associated with the cosmogenic nuclide-derived erosion rate estimates are not greater than the potential errors in conventional estimates. Therefore, the cosmogenic nuclide approach is an effective tool for rapid, catchment-wide assessment of time-integrated rates of bedrock weathering and erosion, and we anticipate its fruitful application to the Quaternary sedimentary record.
The geomorphic evolution of the Makran Range of SE-Iran and SW-Pakistan has been controlled by the prevailing SW-Asian monsoon and Mediterranean winter rainfall climate and the surface uplift ...processes resulting from the Arabia–Eurasia collision. The impact of climate on Quaternary fluvial and alluvial sequence formation and their regional correlation has been little investigated due to limited age control of these sequences. Using 10Be cosmogenic nuclide exposure ages we established a Middle to Late Pleistocene terrace chronology. Our record tentatively indicates that terrace levels were abandoned towards the transition to or during warmer/pluvial periods (interglacials and/or interstadials) back to Marine Isotope Stage (MIS) 7, but abandoned ages show a large spread. It is hypothesized that pluvial phases correspond with times of enhanced SW-monsoons and a northward shift of the Intertropical Convergence Zone (ITCZ). Furthermore, orbital periodicities can be deduced on frequencies related to obliquity and precession cycles. Overall, caution has to be placed in sampling and interpreting alluvial deposits, which may have complex inheritance patterns and spatially and temporarily variable catchment erosion histories and terrace-channel dynamics.
Beside the dominant climate control on terrace formation, elevated channel steepness indices around major thrusts and numerous knickpoints indicate an additionally tectonic influence on terrace formation. Local incision rates (mean ~0.6–0.8mm·a−1) are variable in space and time but are similar to uplift rates obtained from coastal terraces and thus suggest a regional surface uplift.
•Monsoonal climate controlled the terrace formation of the Makran range.•Terrace age with cosmogenic nuclides constrained back to MIS 7.•Surface uplift rates of the Makran Range are about 0.65mm/yr.
We present a new record from the Última Esperanza region (51°25’-52°25'S), southwestern Patagonia, to unravel the timing and structure of glacial fluctuations during the Last Glacial Termination ...(T1). This sector of southern South America represents the only windward-facing continental landmass in the Southern Hemisphere that intersects the core of the Southern Westerly Wind belt.
Geomorphic, stratigraphic and geochronological evidence indicate the following stages during and since the Last Glacial Maximum (LGM): (i) deposition of prominent moraine complexes during at least two advances dated between ~
39 and >
17.5
ka; (ii) development of an ice-dammed proglacial lake (glacial lake Puerto Consuelo) accompanying ice recession; (iii) active deposition of moraine complexes at intermediate positions followed by recession at ≥
15.2
ka; (iv) lake level drop and subsequent stabilization between 15.2-12.8
ka; (v) a glacial readvance in glacial lake Puerto Consuelo between 14.8-12.8
ka; (vi) ice recession, stabilization, and lake level lowering between 12.8-10.3
ka; and (vii) glacial withdrawal and disappearance of glacial lake Puerto Consuelo prior to 10.3
ka. By comparing our results with the chronologies from neighboring regions we explore whether there was a consistent temporal/geographic pattern of glacial fluctuations during the LGM and T1, and examine their implications at regional, hemispheric, and global scales. The correspondence of these variations with key paleoclimate events recorded in the Southern and the Northern Hemispheres suggest a common forcing that, most likely, propagated through the atmosphere. Regional heterogeneities at millennial timescales probably reflect the influence of processes related to deep ocean circulation, and changes in the position/intensity of the Antarctic Polar Front and Southern Westerly Winds.
The century-long debate over the origins of inner gorges that were repeatedly covered by Quaternary glaciers hinges upon whether the gorges are fluvial forms eroded by subaerial rivers, or subglacial ...forms cut beneath ice. Here we apply cosmogenic nuclide exposure dating to seven inner gorges along ~500 km of the former Fennoscandian ice sheet margin in combination with a new deglaciation map. We show that the timing of exposure matches the advent of ice-free conditions, strongly suggesting that gorges were cut by channelized subglacial meltwater while simultaneously being shielded from cosmic rays by overlying ice. Given the exceptional hydraulic efficiency required for meltwater channels to erode bedrock and evacuate debris, we deduce that inner gorges are the product of ice sheets undergoing intense surface melting. The lack of postglacial river erosion in our seven gorges implicates subglacial meltwater as a key driver of valley deepening on the Baltic Shield over multiple glacial cycles.
This paper explores the long-term evolution of a subglacial fjord landscape in the Shackleton Range, Antarctica. We propose that prolonged ice-sheet erosion across a passive continental margin caused ...troughs to deepen and lower the surrounding ice-sheet surface, leaving adjacent mountains exposed. Geomorphological evidence suggests a change in the direction of regional ice flow accompanied emergence. Simple calculations suggest that isostatic compensation caused by the deepening of bounding ice-stream troughs lowered the ice-sheet surface relative to the mountains by ~800m. Use of multiple cosmogenic isotopes on bedrock and erratics (26Al, 10Be, 21Ne) provides evidence that overriding of the massif and the deepening of the adjacent troughs occurred earlier than the Quaternary. Perhaps this occurred in the mid-Miocene, as elsewhere in East Antarctica in the McMurdo Dry Valleys and the Lambert basin. The implication is that glacial erosion instigates feedback that can change ice-sheet thickness, extent, and direction of flow. Indeed, as the subglacial troughs evolve over millions of years, they increase topographic relief; and this changes the dynamics of the ice sheet.
•Testing hypothesis of Antarctic landscape evolution with cosmogenic isotopes.•Erosion of troughs by ice sheets exposes intervening mountain massifs.•Glacial erosion changes the dynamics of the ice sheet.•The mountains emerged from the ice sheet by 600–1000m in >14Ma.•Transition from fluvial to glacial landscape in Transantarctic Mountains.
The outward erosional flux is a key factor in the tectonic evolution of mountain belts and there is much debate about the feedbacks between tectonics, erosion and climate. Here we use cosmogenic ...nuclides (
10Be and
26Al) analysed in quartz from river sediments from the Upper Ganges catchment to make the first direct measurements of large-scale erosion rates in a rapidly uplifting mountain belt. The erosion rates are highest in the High Himalaya at 2.7±0.3 mm/yr (1σ errors), fall to 1.2±0.1 mm/yr on the southern edge of the Tibetan Plateau and are 0.8±0.3 to <0.6 mm/yr in the foothills to the south of the high mountains. These relative estimates are corroborated by the Nd isotopic mass balance of the river sediment. Analysis of sediment from an abandoned terrace suggests that similar erosion rates have been maintained for at least the last few thousand years. The data presented here, along with data recently published for European river catchments, demonstrate that a log–linear relationship between relief and erosion rate holds over three orders of magnitude variation in erosion rate and between very different climatic and tectonic regimes.
The erosion rate estimates from cosmogenic nuclides correlate well with exhumation rates calculated from previously published apatite fission track ages in the Indian Himalaya. This confirms that much of the exhumation in the Himalayan mountain chain is now balanced by erosion. However, exhumation rates calculated from high blocking temperature systems, such as
40Ar/
39Ar in muscovite, imply lower exhumation rates. Rocks presently at the surface must have undergone a three- to six-fold increase in exhumation rate within the last few million years. We show how this could be explained either by climatic forcing of erosion rate changes or by tectonics. Published evidence for equally rapid changes of exhumation rate in the past and the probable diachroneity in the time at which the present exhumation rates accelerated imply that tectonics has moderated at least some of the change in exhumation rates.
PDF
