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.
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.
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 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.
Despite the extensive use of 10Be as the most significant information source on past solar activity, there has been only one record (Dye‐3, Greenland) providing annual resolution over several ...centuries. Here we report a new annual resolution 10Be record spanning the period 1389–1994 AD, measured in an ice core from the NGRIP site in Greenland. NGRIP and Dye‐3 10Be exhibits similar long‐term variability, although occasional short term differences between the two sites indicate that at least two high resolution 10Be records are needed to assess local variations and to confidently reconstruct past solar activity. A comparison with sunspot and neutron records confirms that ice core 10Be reflects solar Schwabe cycle variations, and continued 10Be variability suggests cyclic solar activity throughout the Maunder and Spörer grand solar activity minima. Recent 10Be values are low; however, they do not indicate unusually high recent solar activity compared to the last 600 years.
Atmospheric circulation leaves few direct traces in the geological record, making reconstructions of this crucial element of the climate system inherently difficult. We produced a regional ...Mediterranean synthesis of paleo-proxy data from the sea surface to alpine altitudes. This provides a detailed observational context for change in the three-dimensional structure of atmospheric circulation between the Last Glacial Maximum (LGM, ~23,000 to 19,000 years ago) and the present. The synthesis reveals evidence for frequent cold polar air incursions, topographically channeled into the northwestern Mediterranean. Anomalously steep vertical temperature gradients in the central Mediterranean imply local convective precipitation. We find the LGM patterns to be analogous, though amplified, to previously reconstructed phases of enhanced meridional winter circulation during the Maunder Minimum (the Little Ice Age).
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 have determined the production yields for radionuclides in Al
2O
3, SiO
2, S, Ar, K
2SO
4, CaCO
3, Fe, Ni and Cu targets, which were irradiated with slow negative muons at the Paul Scherrer ...Institute in Villigen (Switzerland). The fluences of the stopped negative muons were determined by measuring the muonic X-rays. The concentrations of the long-lived and short-lived radionuclides were measured with accelerator mass spectrometry (AMS) and γ-spectroscopy, respectively. Special emphasis was put on the radionuclides
10Be,
14C and
26Al produced in quartz targets,
26Al in Al
2O
3 and S targets,
36Cl in K
2SO
4 and CaCO
3 targets, and
53Mn in Fe
2O
3 targets. These targets were selected because they are also the naturally occurring target minerals for cosmic ray interactions in typical rocks. We also present results of calculations for depth-dependent production rates of radionuclides produced after cosmic ray μ
− capture, as well as cosmic ray-induced production rates of geologically relevant radionuclides produced by the nucleonic component, by μ
− capture, by fast muons and by neutron capture.
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.
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.
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