10Be Data Research Articles

Cosmogenic 10Be‐ and 21Ne‐based model exposure ages of desert pavements in the Thar Desert, India

AbstractThe Thar Desert, India has desert pavements comprising angular‐subangular to well‐rounded gravels at marginally higher elevations than the surrounding terrain. Sedimentological and geomorphic analyses suggest that the pavements are lags of weathered Mesozoic and older bedrock. The presence of Palaeolithic artefacts on the pavement surfaces and occasionally within their matrix was used to infer their antiquity and landscape stability.This study presents the first surface exposure ages based on cosmic‐ray‐produced 10Be and 21Ne for pavements at four sites in the Thar Desert, viz. Bhojka, Hamira, Solanki and Jayal. The computation of model exposure ages assumed that (a) the gravels were derived from cemented conglomerates, uplifted by tectonics and thereafter disintegrated by climate, and (b) cosmogenic nuclide production in the gravels began when the conglomerates approached the surface and, continued during their disintegration, gravity sliding of individual gravels and storage, until the present. Assuming an average burial depth of 50 cm, 21Ne and 10Be data provide ages ranging from 1.30 to 2.92 Ma and 1.11 to 5.4 Ma, respectively, for the two nuclides.Published electron spin resonance ages of Thar calcretes suggest the presence of water and extreme seasonality since 1.54 Ma. Such conditions facilitated the mobilization and precipitation of carbonates. The pavement ages and the minimum age of the conglomerate at 2.51 Ma extend the time of such desertic conditions to > 2.51 Ma and suggest that the initiation of desertic conditions in the Thar was possibly linked to global aridity beginning around 3.6 Ma.Depending on assumptions, cosmic ray surface exposure (10Be) ages at Jayal range between 0.76 and 2.43 Ma. In the context of the Indian Palaeolithic, the presence of tools on the gravel surfaces and within dunes, suggests frequent occupation of this region from at least 0.76 Ma and, parallels Early to Middle Pleistocene Acheulian assemblages from Southern India.

Cosmogenic surface exposure (10Be) dating of raised beaches in Marguerite bay, Antarctic Peninsula: Implications for relative sea-level history

Understanding the dynamics of ice mass loss in polar regions is crucial for deciphering climate change and Glacio Isostatic Adjustment patterns. This study focuses on Marguerite Bay, located in the south-central Antarctic Peninsula. We dated raised beaches to investigate relative sea-level changes using the cosmogenic surface exposure (10Be) method. Previous studies have provided valuable insights into the region's glacial history, but limitations in dating techniques and age estimates necessitate further investigation. By analysing raised shingle beaches in Gaul Cove of Horseshoe Island and the southern coast of Calmette Bay, this research aims to contribute relative sea-level change history for these areas. In Horseshoe Island's Gaul Cove, raised beaches clustered on prominent steps reveal a 15 m relative sea-level change over the last 3.31 ka. Differently, Calmette Bay exhibits a 36 m relative sea-level fall over the last 7.29 ka. These findings indicate significant and differential glacial-isostatic adjustments in both regions during the middle and late Holocene. Additionally, our data reveal accelerated sea-level fall periods corresponding to Holocene deglaciation and glacial advance events, indicating the shorelines' relative sea-level change sensitivity to climate change.

21Ne and 10Be dating of folded fluvial terraces: Constraining active deformation of the Guman fold along the foothill of the western Kunlun mountains (Xinjiang, China)

Characterizing the active deformation of the foreland is particularly valuable for understanding the dynamics of regional structural evolution within active contractional orogens. We focus on the Guman fold, one of the most prominent fold-and-thrust belts along the foothill of the Western Kunlun Mountains (Xinjiang, China). The anticline growing above the blind thrust faults progressively deforms river terraces. However, contemporaneous terrace surfaces are buried under young deposits north of the fold. We propose a novel method that extends terrace surfaces above the forelimb of the fold within the extent of deformation determined on the seismic reflection profile, to estimate the sediment thickness after abandonment of the terraces. Furthermore, cosmogenic nuclide (10Be and 21Ne) depth profile dating was used to determine the exposure ages of the two terrace surfaces: 413–673 kyr for T1b and 3.7–5.2 Myr for T3b. Combining the age and deformation amount, the slip rate on the frontal fault ramp within the fold is estimated to be 0.4+0.2/-0.1 mm/yr and 0.17+0.07/-0.03 mm/yr since the abandonment of the T1b and the T3b terrace respectively. These rates represent the recent crustal shortening rate across the Guman fold and likely account for most of the total crustal shortening rate across the Western Kunlun Mountains. However, these rates appear to be notably lower by an order of magnitude compared to the long-term (∼23 Ma) average crustal shortening rate (∼1.1–2.6 mm/yr) in this region. This may indicate a rapid slowing down of the deformation at the scale of the whole Western Kunlun Mountains, possibly related to a regional reorganization.

Responses of geomorphic indices to the northward migration of the Eastern Himalayan syntaxis

The Eastern Himalayan Syntaxis (EHS), featured by an exceptionally intense compression orogeny and an extremely rapid surface erosion rate, stands out as a prime area for investigating surface processes and landscape evolution. Understanding the formation of the EHS holds significant importance in advancing our comprehension of the evolutionary dynamics within the Tibetan Plateau and the complex interplay between endogenic and exogenic geological processes. Currently, two models, namely the tectonic aneurysm and the syntaxis expansion model, have been proposed to explain the formation and evolution of this syntaxis. In this study, we employ a multi-disciplinary approach, integrating geomorphic indices such as slope, relief, hypsometric integral (HI), normalized channel steepness (Ksn), river slope-basin area integration (χ), Gilbert metric, combined with erosion rates on long-medium-short term timescales obtained from thermochronology, cosmogenic nuclides 10Be and landslide disaster probability data. Our findings suggest a relatively high tectonic activity in the confluence of the Yigong and Parlung Rivers in the northern end of the syntaxis. Moreover, our data reveals that spatial variability of tectonic activity is the primary driver of regional geomorphologic features and the spatial-temporal characteristics of erosion observed in the EHS, with lithology and climatic precipitation playing a lesser role. Furthermore, the northward migration of the EHS appears to elucidate the shift of tectonic activity and rapid erosion from the core of the syntaxis near the Namche-Barwa towards the confluence of the Yigong and Parlung Rivers. This northward migration of the EHS underscores the need for increased attention to the high geological hazard risk in the northern part of the EHS.

Variations in the Solar Modulation Parameter Over the Last 9.5 Thousand Years and the Tilt of the Geomagnetic Dipole

Background: Calculations of the solar modulation parameter (Φ) over the past millennia typically use the relationship between the production rate of cosmogenic isotopes, the earth's dipole moment, and the magnitude of Φ. The cosmogenic isotopes 14C and 10Be are typically used in these studies. When studying solar modulation, the cyclic change in dipole tilt is usually not taken into account, which affects estimates of past solar activity. Methods: Tree rings are a reliable basis for obtaining a radiocarbon time scale (IntCal13). However, determining the concentration of 14C in tree rings is a difficult and controversial task. The time scale derived from the 10Be production rate simulation (GICC05) is less reliable. Nevertheless, there is a way to combine the accuracy of the radiocarbon time scale with the reliability of estimates of the 10Be production rate. This method is the synchronization of the radiocarbon and beryllium-10 series. We have selected the most relevant methods for calculating the solar modulation parameter Φ for the Holocene. When calculating Φ, 10Be data synchronized with 14C data were used. The latest data on the earth's dipole moment were considered. Empirical Mode Decomposition (EMD) was used in the analysis of Φ. Results: It has been shown that the first two decomposition modes are oscillating components with periods of 710 and 208 years, the amplitudes of which increase with time, reaching a maximum of 2500 BP. From contemplation, it follows that the 710-year oscillations are apparently caused by fluctuations in the tilt of the earth's dipole. After excluding the EMD component associated with the 710-year cyclicity, a corrected series was obtained for the solar modulation parameter, free from the influence of changes in the tilt of the magnetic dipole. Conclusion: The rate of formation of cosmogenic radionuclides depends on the intensity of penetration of Galactic Cosmic Rays (GCRs) into the earth's atmosphere. Before reaching earth, GCRs must cross the heliosphere, where they are exposed to solar modulation. Adequate consideration of solar modulation parameters is important for the correct interpretation of the rate of production of cosmogenic isotopes and solar activity.

Tenfold lower late quaternary throw rates in central Tibet compared to southern Tibet reflect different extensional deformation mechanisms

Present-day tectonic deformation in central Tibet is characterized by a series of ∼NS-trending grabens which accommodate EW extension. Quantifying the geometry and kinematics of these grabens is essential to understand Cenozoic tectonic deformation and Tibetan Plateau evolution. Here, we focus on the Norma Co graben (NCG), i.e., the southern segment of the Shuanghu-Norma Co graben (SH-NCG) system, which is the most prominent graben system within the Qiangtang terrane in central Tibet. We study its tectonic and geomorphologic characteristics to determine the late Quaternary throw rates of the normal faults bounding the graben, based on high-resolution satellite images interpretation, field investigation, and cosmogenic 10Be dating (n = 23). Using terrestrial LiDAR, UAV, and kinematic GPS, we precisely measure vertical offsets (up to 15 m) of ∼90–120 ka-old alluvial surfaces, yielding a throw rate of 0.10(+0.04/-0.03) mm/yr. This rate is ten times lower than those published along other NS-trending grabens in southern Tibet, reflecting different deformation mechanisms, as previously suggested: grabens in eastern Qiangtang formed by rapid eastward block extrusion, those in western Qiangtang formed by distributed extension on numerous scattered normal faults, and those in southern Tibet result from divergent orthogonal thrusting along the curved Himalayan arc.

Net evolution of subglacial sediment transport in the Quebec–Labrador sector of the Laurentide Ice Sheet

The Laurentide Ice Sheet's (LIS) interior had a dynamic polythermal base, but the spatiotemporal variations of subglacial processes related to ice divide migration and other transient changes remain largely unknown, limiting our understanding of regional glacial dynamics. Previous studies focused on the regional glacial landform record, while ice sheet models lacked detailed parameterization within these regions, leading to an overestimation of cold-based subglacial conditions' extent and duration. In this study, glacial sediment dispersal patterns as identified by heavy minerals, clasts, and multivariate statistics of till matrix geochemistry were used to assess ice sheet dynamics within the Quebec–Labrador sector of the LIS. The earliest ice-flow phase produced and transported till across the study area (>175 km). However, major oxide data from till matrix geochemistry show a correlation with underlying bedrock, and this relationship is relatively common in areas of thin till cover and resistant bedrock lithologies. These results suggest a switch from an early phase of widespread erosion and long, sustained sediment transport to one of more limited erosion, perhaps abrasion dominant and shorter transport. Till compositional data and related dispersal patterns add supporting evidence to earlier ice sheet reconstructions based on ice-flow indicators and 10Be data together suggesting a transition from widespread uniform warm-based conditions during the earliest ice flow, followed by the development of an ice divide, its migration, and more sporadic warm-based conditions. Consequently, a thorough understanding of ice-flow history is essential for ice sheet modelling and future mineral exploration programs in inner ice sheet regions of the LIS.

Deglaciation of the highest mountains in Scandinavia at the Younger Dryas–Holocene transition: evidence from surface exposure‐age dating of ice‐marginal moraines

Surface exposure–age dating was applied to rock surfaces associated with ice‐marginal moraines at elevations of ~1520–1780 m a.s.l. on the slopes of Galdhøpiggen and Glittertinden, the two highest mountains in Scandinavia located in the Jotunheimen mountains of central southern Norway. This is important for understanding the pattern and timing of wastage of the Scandinavian Ice Sheet at the Younger Dryas–Holocene transition. Cosmogenic exposure dating (here 10Be dating) of boulders from the moraine ridges yielded overall mean ages (corrected for glacio‐isostatic uplift, surface erosion and snow shielding) of ~11.6 ka from Galdhøpiggen and ~11.2 ka from Glittertinden. Similar 10Be ages were also obtained from additionally collected proximal and distal erratic boulders and bedrock samples. These enabled age calibration of Schmidt‐hammer R‐values and independent Schmidt‐hammer exposure‐age dating (SHD) of the moraine ridges, which yielded comparable mean SHD ages of ~10.8 and ~10.6 ka from the Galdhøpiggen and Glittertinden sites, respectively. Taking account of the age resolution and other limitations of both dating techniques, the results suggest that the two sets of moraines have approximately the same age but that neither technique can distinguish unambiguously between moraine formation in the late Younger Dryas or Early Holocene. Together with features of moraine‐ridge morphology and estimates of equilibrium‐line altitude depression of ~360–575 m (corrected for land uplift), the results imply moraine formation during short‐lived re‐advances of active glaciers, at least the lower reaches of which were warm‐based. It is concluded that the local glaciers remained active and advanced during deglaciation either very late in the Younger Dryas or very early in the Holocene, possibly in response to the Preboreal Oscillation at ~11.4 ka. The study supports the concept of a thin Younger Dryas ice sheet and places time constraints on the timing of final deglaciation in southern Norway.

Impact of Quaternary Glaciations on Denudation Rates in North Pamir—Tian Shan Inferred From Cosmogenic 10Be and Low‐Temperature Thermochronology

AbstractWe explore the spatial and temporal variations in denudation rates in the northern Pamir—Tian Shan region using 10Be‐derived denudation rates from modern (n = 110) and buried sediment (2.0–2.7 Ma; n = 3), and long‐term exhumation rates from published apatite fission track (AFT; n = 705) and apatite (U‐Th‐Sm)/He (AHe; n = 211) thermochronology. We found moderate correlations between denudation rates and topographic metrics and weak correlations between denudation rates and annual rainfall, highlighting complex linkages among tectonics, climate, and surface processes that vary locally. The 10Be data show a spatial trend of decreasing modern denudation rates from west to east, suggesting that deformation and precipitation control denudation in the northern Pamir and western Tian Shan. Farther east, the denudational response of the landscape to Quaternary glaciations is more pronounced and reflected in our data. Modern 10Be denudation rates are generally higher than the long‐term AFT and AHe exhumation rates across the studied area. In the Kyrgyz Tian Shan, on average, the highest 10Be denudation rates are recorded in the Terskey range, south of Lake Issyk‐Kul. Here, modern denudation rates are higher than 10Be‐derived paleo‐denudation rates, which are comparable in magnitude with the long‐term exhumation rates inferred from AFT and AHe. We propose that denudation in the region, particularly in the Terskey range, remained relatively steady during the Neogene and early Pleistocene. Denudation increased due to glacial‐interglacial cycles in the Quaternary, but this occurred after the onset and intensification of the Northern Hemisphere glaciations at 2.7 Ma.

Three Pleistocene glacial advances and a warm episode during MIS-3: Towards a more complete glacial history of the Pamir mountains

Determining the spatial and temporal variations of Pleistocene glaciations is key to understanding present-day climate-driven glacier changes. Glacial chronologies of high-mountain Asia, which are mostly based on cosmogenic 10Be exposure dating of moraine boulders, remain scarce and often inaccurate due to geologically induced age scatter. We present 53 new 10Be exposure ages from rockslides, glacial sediment deposits and glacial erosion surfaces in the southwestern Pamir. In conjunction with previously published 10Be data, we constrain the timing and extent of three major glacial stages in the Pamir. During the Middle Pleistocene, a continuous ice sheet covered most of the Pamir. This stage is older than 200 ka and may have occurred during Marine Isotope Stages (MIS) 8, 10, or 12. The deep valleys of the western Pamir, which contrast with the eastern Pamir plateau, are partly attributed to Middle Pleistocene glacial erosion. Successively less extensive glacial advances occurred during MIS-4/5 (between 60 and 100 ka ago) and during MIS-2 (at 18–22 ka). The last glacial maximum was synchronous in most of the Pamir, except for prolonged glaciation of the Muztagh Ata ice cap until 14 ka ago. Similar to today, Late Pleistocene glaciers were precipitation-limited, with moisture mainly supplied by westerly winds. An episode of increased mass wasting (e.g. Zuvor rockslide: 34 ± 1 ka) and glacier surging correlates with a peak in δ18O values in the Guliya ice core and is attributed to a warmer climate.

Cosmogenic 10Be dating of the oldest moraine in the Hengduan Mountains

Cosmogenic 10Be dating of the oldest moraine in the Hengduan Mountains

Optimising global landscape evolution models with 10Be

Abstract. By simulating erosion and deposition, landscape evolution models (LEMs) offer powerful insights into Earth surface processes and dynamics. Stream-power-based LEMs are often constructed from parameters describing drainage area (m), slope (n), substrate erodibility (K), hillslope diffusion (D), and a critical drainage area (Ac) that signifies the downslope transition from hillslope diffusion to advective fluvial processes. In spite of the widespread success of such models, the parameter values are highly uncertain mainly because the advection and diffusion equations amalgamate physical processes and material properties that span widely differing spatial and temporal scales. Here, we use a global catalogue of catchment-averaged cosmogenic 10Be-derived denudation rates with the aim to optimise a set of LEMs via a Monte Carlo-based parameter search. We consider three model scenarios: advection-only, diffusion-only, and an advection–diffusion hybrid. In each case, we search for a parameter set that best approximates denudation rates at the global scale, and we directly compare denudation rates from the modelled scenarios with those derived from 10Be data. We find that optimised ranges can be defined for many LEM parameters at the global scale. In the absence of diffusion, n∼1.3, and with increasing diffusivity the optimal n increases linearly to a global maximum of n∼2.3. Meanwhile, we find that the diffusion-only model yields a slightly lower misfit when comparing model outputs with observed erosion rates than the advection-only model and is optimised when the concavity parameter is raised to a power of 2. With these examples, we suggest that our approach provides baseline parameter estimates for large-scale studies spanning long timescales and diverse landscape properties. Moreover, our direct comparison of model-predicted versus observed denudation rates is preferable to methods that rely upon catchment-scale averaging or amalgamation of topographic metrics. We also seek to optimise the K and D parameters in LEMs with respect to precipitation and substrate lithology. Despite the potential bias due to factors such as lithology, these optimised models allow us to effectively control for topography and specifically target the relationship between denudation and precipitation. All models suggest a general increase in exponents with precipitation in line with previous studies. When isolating K under globally optimised models, we observe a positive correlation between K or D and precipitation > 1500 mm yr−1, plus a local maximum at ∼300 mm yr−1, which is compatible with the long-standing hypothesis that semi-arid environments are among the most erodible.

Solar, Atmospheric, and Volcanic Impacts on 10Be Depositions in Greenland and Antarctica During the Last 100 Years

AbstractCosmogenic radionuclides (e.g., 10Be) from ice cores are a powerful tool for solar reconstructions back in time. However, superimposed on the solar signal, other factors like weather/climate and volcanic influences on 10Be can complicate the interpretation of 10Be data. A comprehensive study of 10Be records over the recent period, when atmospheric 10Be production and meteorological conditions are relatively well‐known, can improve our interpretation of 10Be records. Here we conduct a systematic study of the production and climate/volcanic signals in Antarctica and Greenland 10Be records, including a new 10Be record from the East GReenland Ice‐core Project site. Greenland and Antarctica records show significant decreasing trends (5%–6.5%/decade) for 1900–1950, which is comparable with the expected production rate inferred from sunspot observations. By comparing 10Be records with reanalysis data and atmospheric circulation patterns, 10Be records from Southern/Southeastern Greenland are significantly correlated with the Scandinavia pattern. Stacking 10Be records from different locations can enhance the production signal. However, this approach is not always straightforward as uncertainties in some records can lead to a weaker solar signal. A strategy can be employed to select records for the bipolar stack by comparing Greenland records with Antarctica records, assuming the shared signal is a production signal. Finally, we observe significant increases (36%–64%) in 10Be depositions in Greenland related to the Agung eruption. This large increase in Greenland 10Be records after the Agung eruption, could be partly explained by the enhanced air mass transport from mid‐latitudes coinciding with the decreased precipitation en‐route.

First <sup>10</sup>Be dates of Late Holocene moraines of the Kashkatash and Irik glaciers, Northern Caucasus

We present 11 10Be ages of the moraines of the Irik and Kashkatash glaciers that allowed identifying and dating several Late Holocene glacier advances for the first time, including a prominent advance exceeding the Little Ice Age (LIA) maximum that occurred at 1.6–1.7 ka at еру Irik Glacier. The advance is dated by the three very close 10Be ages of a moraine (1.57 ± 0.23 ka, 1.63 ± 0.23, and 1.68 ± 0.24 ka) located in the vicinity of the moraines of the Little Ice Age (LIA) maximum advance. The advance that occurred at 1.6–1.7 ka might be a possible analogue of the “Historical” stage described earlier in the Caucasus in literature basing at geomorphic evidence, speculations, and analogues with other mountain regions, but not dated. Another possibility is a potential correlation of this advance with the Late Antique Little Ice Age cooling in 536 to ~660 CE. The age of Irik Glacier advance is close to the humid period identified in the Garabashi (Baksan, Elbrus valley) lake sediments at 1500–1700 years BP. The magnitude of the identified glacier advances over the past two millennia was similar. Between the advance of 1.6–1.7 ka and the position of the glacier in 2022 CE the elevation of the Irik Glacier front increased by 520 m from 2490 to 3010 m asl. Four 10Be dates (0.7 + 0.11, 0.72+0.11, 0.77 + 0.11 and 0.82 + 0.18 ka) of the lateral moraine of the Kashkatash Glacier constrain the advance of the first stage of the LIA. The advance of the 13th century is also dated by 10Be at the Donguz-Orun and Chalaati glaciers located at the Northern and Southern slopes of the Caucasus, respectively. The corresponding cooling in ca 1250–1400 CE is identified in the sedimentary paleoclimatic proxies of Lake Karakel (Teberda valley). A later advance at the Kashkatash Glacier is constrained by only one 10Be date (0.53± 0.13 ka) and needs further confirmation. Till deposited between the 1490s and 1640s at the Greater Azau Glacier is close to the date of this advance of the Kashkatash Glacier. A cooling at that time is recorded in the proxies of Karakel Lake sediments (1500–1630 CE). Three other 10Be dates of two earlier advances at 0.25 + 0.04 ka and between 0.14 + 0.03 and 0.16 ± 0.02 ka at Kashkatash Glacier are indirectly supported by tree-ring, lake sediment, 14C, and historical data. Further research and new data is necessary to increase the credibility and accuracy of the dates of glacier advances of the Late Holocene in the Northern Caucasus.

Synchronizing ice-core and U ∕ Th timescales in the Last Glacial Maximum using Hulu Cave 14C and new 10Be measurements from Greenland and Antarctica

Abstract. Between 15 and 27 kyr b2k (thousands of years before 2000 CE) during the last glacial, Greenland experienced a prolonged cold stadial phase, interrupted by two short-lived warm interstadials. Greenland ice-core calcium data show two periods, preceding the interstadials, of anomalously high atmospheric dust loading, the origin of which is not well understood. At approximately the same time as the Greenland dust peaks, the Chinese Hulu Cave speleothems exhibit a climatic signal suggested to be a response to Heinrich Event 2, a period of enhanced ice-rafted debris deposition in the North Atlantic. In the climatic signal of Antarctic ice cores, moreover, a relative warming occurs between 23 and 24.5 kyr b2k that is generally interpreted as a counterpart to a cool climate phase in the Northern Hemisphere. Proposed centennial-scale offsets between the polar ice-core timescales and the speleothem timescale hamper the precise reconstruction of the global sequence of these climatic events. Here, we examine two new 10Be datasets from Greenland and Antarctic ice cores to test the agreement between different timescales, by taking advantage of the globally synchronous cosmogenic radionuclide production rates. Evidence of an event similar to the Maunder Solar Minimum is found in the new 10Be datasets, supported by lower-resolution radionuclide data from Greenland and 14C in the Hulu Cave speleothem, representing a good synchronization candidate at around 22 kyr b2k. By matching the respective 10Be data, we determine the offset between the Greenland ice-core chronology, GICC05, and the Antarctic chronology for the West Antarctic Ice Sheet Divide ice core (WDC), WD2014, to be 125 ± 40 years. Furthermore, via radionuclide wiggle-matching, we determine the offset between the Hulu speleothem and ice-core timescales to be 375 years for GICC05 (75–625 years at 68 % confidence) and 225 years for WD2014 (−25–425 years at 68 % confidence). The rather wide uncertainties are intrinsic to the wiggle-matching algorithm and the limitations set by data resolution. The undercounting of annual layers in GICC05 inferred from the offset is hypothesized to have been caused by a combination of underdetected annual layers, especially during periods with low winter precipitation, and misinterpreted unusual patterns in the annual signal during the extremely cold period often referred to as Heinrich Stadial 1.

A quantitative assessment of snow shielding effects on surface exposure dating from a western North American 10Be data compilation

A quantitative assessment of snow shielding effects on surface exposure dating from a western North American 10Be data compilation

Basal debris of the NEEM ice core, Greenland: a window into sub-ice-sheet geology, basal ice processes and ice-sheet oscillations

AbstractWe present new data from the debris-rich basal ice layers of the NEEM ice core (NW Greenland). Using mineralogical observations, SEM imagery, geochemical data from silicates (meteoric10Be, εNd,87Sr/86Sr) and organic material (C/N, δ13C), we characterize the source material, succession of previous glaciations and deglaciations and the paleoecological conditions during ice-free episodes. Meteoric10Be data and grain features indicate that the ice sheet interacted with paleosols and eroded fresh bedrock, leading to mixing in these debris-rich ice layers. Our analysis also identifies four successive stages in NW Greenland: (1) initial preglacial conditions, (2) glacial advance 1, (3) glacial retreat and interglacial conditions and (4) glacial advance 2 (current ice-sheet development). C/N and δ13C data suggest that deglacial environments favored the development of tundra and taiga ecosystems. These two successive glacial fluctuations observed at NEEM are consistent with those identified from the Camp Century core basal sediments over the last 3 Ma. Further inland, GRIP and GISP2 summit sites have remained glaciated more continuously than the western margin, with less intense ice-substratum interactions than those observed at NEEM.

An Evolving Lithospheric‐Scale Wrench Fault System Along the Eastern End of the Altyn Tagh Fault: Kinematics and Quaternary Activity of the Heishan Fault System, Western China

AbstractThe Altyn Tagh fault (ATF) is a major intracontinental strike‐slip fault system that defines the northern margin of the Tibetan Plateau. The fault system loses its obvious surface expression north of the Qilian Shan fold‐and‐thrust belt, but may link eastward with multiple faults in the northern Hexi Corridor and southern Alxa block. To better understand the potential connectivity and displacement transfer between the ATF and the northern Hexi Corridor fault array, we carried out a multidisciplinary field and remote sensing‐based investigation of the actively deforming Heishan and Jinta'Nanshan region north of Jiayuguan City. We document Quaternary sinistral strike‐slip motion on the Heishan fault (HF) system and active sinistral transpression within a 70‐km‐long, E‐W deforming belt east of the Heishan, which is characterized by multiple left‐stepping, en‐échelon Quaternary folds and linking faults. Cosmogenic10Be dating of displaced terrace surfaces yields a vertical slip rate of ∼0.2 mm/a for the northern Heishan thrust and a sinistral strike‐slip rate of 0.6 ± 0.2 mm/a for the HF. Within the uplifted core of the Heishan massif, the HF contains ductilely deformed Paleozoic basement lithologies with dextral‐sense shear fabrics that indicate that the modern HF has reactivated and inverted an older shear zone. A previously published magnetotelluric profile across the HF system suggests that it roots into a steep, deeply penetrating fault that is unlinked to the Qilian Shan thrust wedge. Instead, we suggest that the active sinistral deformation belt of the Heishan‐Jinta'Nanshan represents the eastward‐evolving, upper crustal expression of the modern ATF system.

Re-evaluation of Cosmogenic 10Be Dating of the Ferromanganese Crust VA13/2 Archiving Interstellar Radionuclides on Earth

Interstellar radionuclides, such as 60Fe, are produced in massive stars, ejected by supernovae and can be recovered in geological archives on Earth. Ferromanganese encrustations on the bottom of Earth’s major oceans represent one important geological archive with a time-record of interstellar radionuclides. The paper of Segl et al. provided the first cosmogenic 10Be dating of the ferromanganese crust VA13/2 in which interstellar 60Fe was discovered. After re-evaluation and comparison with other published and recently acquired data of the same crust, we conclude that the calculated 10Be/9Be data set is wrong by a factor of 9 due to a mathematical lapse. In addition, the ordinate of the corresponding 10Be/9Be graph is in discrepancy with the given data. The updated data set is now in agreement with recently published and acquired data.

Fluctuations of the Universidad Glacier in the Andes of central Chile (34° S) during the latest Holocene derived from a 10Be moraine chronology

The reconstruction of glacier fluctuations during the latest Holocene (<1000 years) is necessary for understanding the climate context preceding the warmer conditions of the 20th and 21st centuries. The glacier records in the Andes of central Chile are suitably located to track former latitudinal changes of the Southern Westerly Winds (SSW), which are mostly unknown at this middle latitude region. Here, we present a reconstruction of the glacial fluctuations using Terrestrial Cosmogenic Nuclides (10Be) dating of boulders resting on moraines and other glacial landforms that make up the moraine complex in the forefield of the Universidad Glacier (34° S). This massive and chaotic-looking moraine was built during the latest Holocene ice advances and subsequent decay of the Universidad Glacier to its present position. Geomorphological mapping and 10Be surface exposure ages (n = 20) show that the Universidad Glacier advanced at least twice to nearly the same maximum extent, first by the 13th to 16th centuries and then by the early to the mid-19th century. Since then, eight moraine ridges denote a rather active and gradual ice demise. We interpret the glacier advances as a response to an equatorward shift of the SWW linked to a long-term negative phase of the Southern Annular Mode (SAM), which embraced net humid and cold atmospheric conditions in central Chile between the 13th century and the mid-19th century. Our glacier chronology is comparable to others from Patagonia and New Zealand, altogether exposing the culmination of the latest Holocene glacial maximum by the mid-19th century, before overall ice decay in a global warming world, with accelerated ice loss since the mid-20th century.