ALBERT

Description: ABSTRACT 36Cl production in the atmosphere is modulated by the magnetic field intensity of both the Sun and the Earth. The record of 36Cl concentration along with that of 10Be in ice cores may therefore provide information as to their variability. To better understand the 36Cl signal in glaciological archives, we measured its concentration in Talos Dome snow samples (mean accumulation rate of 8 g.cm‐2.yr‐1 water equivalent) spanning the 1955 to 1980 C.E. period with a resolution of one sample every 3 years, and in Vostok snow samples (mean accumulation rate of 1.96 g.cm‐2.yr‐1 water equivalent) spanning the 1949 to 2007 C.E. period with a six‐month resolution that had never before been obtained. Marine nuclear bomb tests in the late 1950s produced anthropogenic 36Cl which was injected into the stratosphere and spread around the globe. In the late 1950s this anthropogenic pulse led to an increase of 36Cl concentration at Talos Dome that was more than 100 times higher than the pre‐ and post‐ bomb values. It is noteworthy that the atmosphere of Vostok remains polluted by anthropogenic 36Cl today. This pollution results from gaseous H36Cl mobility at low accumulation sites and implies re‐emission of 36Cl from the snowpack that is not observed at Talos Dome. The 36Cl/Cl‐ ratio may be used to discriminate the stratospheric anthropogenic 36Cl source from the tropospheric natural 36Cl source, which allows us to discuss the immobile vs. mobile 36Cl in the Vostok snowpack.

Description: The Bulnay earthquake of 23 July 1905 ( M w  8.3–8.5), in north-central Mongolia, is one of the world’s largest recorded intracontinental earthquakes and one of four great earthquakes that occurred in the region during the twentieth century. The 375 km long surface rupture of the left-lateral, strike-slip, N095°E-trending Bulnay fault associated with this earthquake is remarkable for its pronounced expression across the landscape and for the size of features produced by previous earthquakes. Our field observations suggest that in many areas the width and geometry of the rupture zone is the result of repeated earthquakes; however, in those areas where it is possible to determine that the geomorphic features are the result of the 1905 surface rupture alone, the size of the features produced by this single earthquake are singular in comparison to most other historical strike-slip surface ruptures worldwide. Along the 80 km stretch, between 97.18° E and 98.33° E, the fault zone is characterized by several meters width and the mean left-lateral 1905 offset is 8.9±0.6 m with two measured cumulative offsets that are twice the 1905 slip. These observations suggest that the displacement produced during the penultimate event was similar to the 1905 slip. Morphotectonic analyses carried out at three sites along the eastern part of the Bulnay fault allow us to estimate a mean horizontal slip rate of 3.1±1.7 mm/yr over the Late Pleistocene–Holocene period. In parallel, paleoseismological investigations show evidence for two earthquakes prior to the 1905 event, with recurrence intervals of ~2700–4000 yrs. Online Material: Table of 10 Be concentrations with sampling information, high-resolution stratigraphic and topographic maps, and 10 Be analyses at various sites.

Description: Only a few chronological constraints on Lateglacial and Early Holocene glacier variability in the westernmost Alps have hitherto been obtained. In this paper, moraines of two palaeoglaciers in the southern Écrins massif were mapped. The chronology of the stabilization of selected moraines was established through the use of 10Be cosmic ray exposure (CRE) dating. The equilibrium line altitude (ELA) during moraine deposition was reconstructed assuming an accumulation area ratio (AAR) of 0.67. Ten pre‐Little Ice Age (LIA) ice‐marginal positions of the Rougnoux palaeoglacier were identified and seven of these have been dated. The 10Be CRE age of a boulder on the lowermost sampled moraine indicates that the landform may have been first formed during a period of stable glaciers at around 16.2±1.7 ka (kiloyears before AD 2017) or that the sampled boulder experienced pre‐exposure to secondary cosmic radiation. The moraine was re‐occupied or, alternatively, shaped somewhat before 12.2±0.6 ka when the ELA was lowered by 230 m relative to the LIA ELA. At least six periods of stable ice margins occurred thereafter when the ELA was 220–160 m lower than during the LIA. The innermost dated moraine stabilized at or before 10.9±0.7 ka. Three 10Be CRE ages from a moraine of the Prelles palaeoglacier indicate a period of stationary ice margins at or before 10.9±0.6 ka when the ELA was lowered by 160 m with respect to the end of the LIA. The presented 10Be CRE ages are in good agreement with those of moraines that have been attributed to the Egesen stadial. Assuming unchanged precipitation, summer temperature in the southern Écrins massif at ~12 ka must have been at least 2 °C lower relative to the LIA.

Description: Abstract More than 2000 analysis of beryllium‐10 (10Be) and sulfate concentrations were performed at a nominal sub‐annual resolution on an ice core covering the last millennium as well as on records from three sites in Antarctica (Dome C, South Pole and Vostok) to better understand the increase in 10Be deposition during stratospheric volcanic eruptions. A significant increase in 10Be concentration is observed in 14 of the 26 volcanic events studied. The slope and intercept of the linear regression between 10Be and sulfate concentrations provide different and complementary information. Slope is an indicator of the efficiency of the draining of 10Be atoms by volcanic aerosols depending on the amount of SO2 released and the altitude it reaches in the stratosphere. Intercept gives an image of the 10Be production in the stratospheric reservoir, ultimately depending on solar modulation. The Samalas event (1257 A.D.) stands out from the others as the biggest eruption of the last millennium with the lowest positive slope of all the events. We hypothetize that the persistence of volcanic aerosols in the stratosphere after the Samalas eruption have drained the stratospheric 10Be reservoir for a decade, meaning that solar reconstructions based on 10Be should be considered with caution during this period. The slope of the linear regression between 10Be and sulfate concentrations can also be used to correct the 10Be snow/ice signal of the volcanic disturbance.

Description: ABSTRACT The abundant production of in situ cosmogenic 36 Cl from potassium renders 36 Cl measurements in K-rich rocks or minerals, such as K-feldspars, potentially useful for precisely dating rock surfaces, either in single-nuclide or in multi-nuclide studies, for example combined with 10 Be measurements in quartz. However, significant discrepancies in experimentally calibrated 36 Cl production rates from spallation of potassium ( 36 P K-sp ), referenced to sea-level/high-latitude (SLHL), limit the accuracy of 36 Cl dating from K-rich lithologies. We present a new 36 Cl calibration using K-feldspars, in which K-spallation is the most dominant 36 Cl production pathway (〉92% of total 36 Cl), thus minimizing uncertainties from the complex multi-pathway 36 Cl production systematics. The samples are derived from boulders of an ∼13.4 ka-old landslide in the Swiss Alps (∼820 m, 46.43°N, 8.85°E). We obtain a local 36 P K-sp of 306 ± 16 atoms 36 Cl (g K) −1 a −1 and an SLHL 36 P K-sp of 145.5 ± 7.7 atoms 36 Cl (g K) −1 a −1 , when scaled with a standard scaling protocol (‘Lm’). Applying this SLHL 36 P K-sp to determine 36 Cl exposure ages of K-feldspars from 10 Be-dated moraine boulders yields excellent agreement, confirming the validity of the new SLHL 36 P K-sp for surface exposure studies, involving 36 Cl in K-feldspars, in the Alps.

Description: Because of its essential role in coupling climate and tectonics, denudation is a key parameter when constraining the history of Earth’s surface. This is particularly true at the Pliocene-Pleistocene transition, and the potential impact of the onset of Quaternary glaciations remains strongly debated. In the present study, we measured in situ cosmogenic 10 Be within continuous late Cenozoic sedimentary sections that had already been dated using magnetostratigraphy. The new data were obtained from four sedimentary basins in the northern and southern Tianshan range (Central Asia). We first thoroughly discuss how in situ cosmogenic 10 Be concentrations can be corrected for radioactive decay and for the contribution of postdepositional cosmogenic accumulation to derive the paleo–denudation rates. Our analysis shows that, in the four sedimentary records, the potential bias remains low enough to consider the derived denudation rates reliable. The four records, although likely influenced by local particularities due to lithological heterogeneity and local tectonics, display similar trends of continuously increasing denudation between ca. 9 Ma and the present. These rates have remained relatively high but steady since 4 Ma, ~1.5 m.y. before the onset of the Quaternary glacial cycles. Though the rejuvenation of the Tianshan range since 11 Ma may explain most of the progressive increase ( x 5) in denudation, our data suggest that the Quaternary glaciations had only a limited impact on denudation in the Tianshan. Our data, however, indicate an increase in the spatial and high-frequency variability (〈1 m.y.) of the denudation rates between 3 and 1 Ma. This may correspond to a transient readjustment of the landscape in response to the onset of Quaternary glacial cycles.

Description: Paradoxical cold conditions during the medieval climate anomaly in the Western Arctic Scientific Reports, Published online: 9 September 2016; doi:10.1038/srep32984

Description: Abstract In this study, we reconstruct the Miocene to Quaternary shortening history across the Qiultag anticline, a complex fault‐bend fold located in southern Tianshan. We studied the Yaha and Kuche sections, where we combined surface structural measurements and seismic imaging to model the stratigraphic horizons. The history of folding was reconstructed based on magnetostratigraphic analyses and eight cosmogenic burial ages in Kuche. Pleistocene deformation rates were also quantified in Yaha based on a deformed fluvial terrace that we dated to ~67 ka using a cosmogenic depth profile. Our results suggest that the fold grew at a mean slip rate of 0.9‐1.3 mm/a in both sections but accelerated to ~2.5 mm/a during the Pleistocene in Kuche. These results support a migration of the deformation toward the basin during the Pleistocene and suggest that most of the present deformation of the Tianshan is accommodated across the external structures of the range.

Description: Assessment of vertical movements of tectonically bounded blocks is crucial for determination of geohazards in densely inhabited zones, such as the border zone of western Slovakia and eastern Austria. The morphostructure of the Malé Karpaty Mts. divides the Vienna and Danube basins in the Western Carpathian – Eastern Alpine junction, and its neotectonic activity is of high importance. This study was focused on 26Al/10Be burial dating of fluvial sediment in the Stará Garda Cave, located in the central part of the mountains. The structural research revealed predisposition of forming of horizontal passages in low angle to subhorizontal bedrock stratification together with low-grade metamorphic foliation. Fluvial origin of the passages was inferred from mezoscale erosional features on the bedrock as well as from facies character of the well preserved sedimentary profile. Cave sediment was according to petrographic analysis derived from a watershed comparable to recent one of the Stupavský Potok Stream. Three analysed dating samples provided low values of isotopic concentrations, allowing us only to calculate the minimum burial age of the deposit of 1.72 Ma. Assuming the low position of the cave above recent surface streams, resulting maximum incision rate of 26 m/Ma indicates very low uplift of the mountains horst during the Quaternary. The slow incision of the river network  is in good agreement with a widespread preservation of the planation surface called "Mid-mountain level". In contrast are relatively high values of palaeodenudation rates inferred from isotopic concentrations. Generally, our results indicate that the Malé Karpaty Mts. horst underwent relatively intense but short uplift in the Early Pleistocene, followed by very moderate uplift up to the recent. Key words: Western Carpathians, Malé Karpaty Mts., fluvial cave sediment, burial dating, Early Pleistocene, neotectonics. Zgodnja pleistocenska starost fluvialnih sedimentov v jami Stará Garda, ki jo je dala 26Al/10Be datacija: uporabnost za geomorfni razvoj Nizkih Karpatov (Zahodni Karpati) Ocena vertikalnih premikov tektonsko omejenih blokov je ključna za določitev geohazardov v gosto naseljenih območjih. Morfostruktura Malih Karpatov deli Dunajski in Donavski bazen na stičišču Zahodnih Karpatov – Vzhodnih Alp in njegova neotektonska aktivnost je zelo pomembna. Študija se je posvetila 26Al/10Be dataciji fluvialnih sedimentov v jami Stará Garda v osrednjem delu gorovja. Strukturna raziskava je razkrila predispozicijo oblikovanja vodoravnih jamskih rovov pod nizkim kotom v odvisnosti od subhorozontalne stratifikacije kamnine ter tudi z nizko stopnjo metamorfne foliacije. Na fluvialno poreklo rovov smo sklepali iz srednje velikih erozijskih oblik na njihovih stenah kot tudi iz lastnosti faciesov dobro ohranjenega sedimentnega profila. Glede na petrografske analize jamski sediment izhaja iz povodja, ki je primerljiv z recentnim povodjem potoka Stupavský. Trije analizirani vzorci so nam dali nizke vrednosti koncentracij izotopov, ki so nam omogočile le izračun najnižje pokopne starosti sedimenta, ki je znašala 1,72 Ma. Če upoštevamo, da leži jama nizko nad recentnimi vodnimi tokovi, dobimo maksimalno hitrost vrezovanja dolin samo 26 m/Ma, kar kaže na zelo majhen tektonski dvig v času kvartarja. Počasno vrezovanje rečne mreže se dobro ujema s široko ohranjenim uravnanim površjem, imenovanim »Srednjegorska uravnava«. V nasprotju pa so sorazmerno visoke  vrednosti hitrosti paleodenudacije, ki izhajajo iz koncentracij izotopov. Na splošno naši rezultati kažejo, da je bil horst Nizkih Karpatov podvržen relativno močnemu, toda kratkemu dvigovanju v spodnjem pleistocenu, ki mu je sledil zmeren dvig do sedanjosti. Ključne besede: Zahodni Karpati, Nizki Karpati, fluvialni jamski sedimenti, pokopna datacija, starejši pleistocen, neotektonika.  

Description: Heinrich events are characterized by worldwide climate modifications. Over the Altiplano endorheic basin (high tropical Andes), the second half of Heinrich Stadial 1 (HS1a) was coeval with the highstand of the giant paleolake Tauca. However, the atmospheric mechanisms underlying this wet event are still unknown at the regional to global scale. We use cosmic-ray exposure ages of glacial landforms to reconstruct the spatial variability in the equilibrium line altitude of the HS1a Altiplano glaciers. By combining glacier and lake modeling, we reconstruct a precipitation map for the HS1a period. Our results show that paleoprecipitation mainly increased along the Eastern Cordillera, whereas the southwestern region of the basin remained relatively dry. This pattern indicates a southward expansion of the easterlies, which is interpreted as being a consequence of a southward shift of the Bolivian High. The results provide a new understanding of atmospheric teleconnections during HS1 and of rainfall redistribution in a changing climate.