Cosmogenic and bomb-produced7Be in stratospheric air

Concentration of⁷Be has been measured in 15 air filters flown at 18·3 km in the latitudes 10 to 25°N and longitudes 80 to 96°W. Testing of nuclear weapons in atmosphere increased⁷Be considerably, on two occasions, above the expected cosmic-ray production level in the stratosphere. This provides evidence for the existence of interhemispheric mixing,via stratosphere.     

Radiocarbon age distribution of groundwater in the Konya Closed Basin, central Anatolia, Turkey

Annual abstraction of 2.6?×?10⁹ m³ of groundwater in the 53,000 km² Konya Closed Basin of central Turkey has caused a head decline of 1 m/year over the last few decades. Therefore, understanding the hydrogeology of this large endorheic basin, in a semi-arid climate, is important to sustainable resource management. For this purpose, the groundwater’s radiocarbon age distribution has been investigated along a 150-km transect parallel to regional flow. Results show that the groundwater ranges in age from Recent at the main recharge area of the Taurus Mountains in the south, to about 40,000 years around the terminal Salt Lake located in the north. In this predominantly confined flow system, radiocarbon ages increase linearly by distance from the main recharge area and are in agreement with the hydraulic ages. The mean velocity of regional groundwater flow (3 m/year) is determined by the rate of regional groundwater discharge into the Salt Lake. Calcite dissolution, dedolomitization and geogenic carbon dioxide influx appear to be the dominant geochemical processes that determine the carbon isotope composition along the regional flow path. The groundwater’s oxygen-18 content indicates more humid and cooler paleorecharge. A maximum drop of 5°C is inferred for the past recharge temperature.     

Marine biogeochemistries of Be and Al: A study based on cosmogenic10Be, Be and Al in marine calcite, aragonite, and opal

The geochemical behaviors of Be and Al in ocean waters have been successfully studied in recent years using natural, cosmogenic, radioactive¹⁰Be and²⁶Al as tracers. The present day dissolved concentrations and distribution of the stable and radioactive isotopes of Be and Al in ocean waters have revealed their short residence times and appreciable effects of exchange fluxes at the coastal and ocean-sediment interfaces. It follows that concentrations of these particle-active elements must have varied in the past with temporal changes in climate, biological productivity and aeolian flux of continental detritus to the oceans. We therefore investigated the feasibility of extending the measurements of Be and Al isotope concentrations in marine systems to the 10³–10⁶ y BP time scale. We report here the discovery of significant amounts of intrinsic Be and Al in marine foraminiferal calcite and coral aragonite, and of Al in opal (radiolarians) and aragonite (coral), which makes it possible to determine¹⁰Be/Be and²⁶Al/Al in oceans in the past. We also report measured¹⁰Be/⁹Be in foraminiferal calcite in Pacific Ocean cores, which reveal that the concentrations and ratios of the stable and cosmogenic isotopes of Be and Al have varied significantly in the past 30 ky. The implications of these results are discussed.     

Age,budget and dynamics of an active salt extrusion in Iran

The Hormuz salt of Kuh-e-Namak, Iran began rising through its Phanerozoic cover in Jurassic times and had surfaced by Cretaceous times. In Miocene times, the still-active Zagros folds began to develop and the salt is still extruding to feed a massive topographic dome and two surface flows of salt which have previously been called salt glaciers but are here called namakiers.Two crude but independent estimates for the rate of salt extrusion and loss are shown to balance the salt budget if the current salt dynamics are assumed to be in steady state. First, to replace the extrusive salt likely to be lost in solution in the annual rainfall, the salt must rise at an average velocity of about 11 cm a^?1. Second, the foliation pattern shows that the extruding (and partially dissolved) salt column spreads under its own weight. The maximum height of the salt dome is consistent with a viscous fluid with a viscosity of 2.6 × 10¹⁷ poises extruding from its orifice at a rate of almost 17 cm a^?1. Both estimates are consistent in indicating that salt can extrude onto the surface 42–85 times faster than the average long term rate at which salt diapirs rise to the surface.The structure, fabrics, textures and deformation mechanisms of the impure halite all change along the path of the extrusive salt from the dome down the length of both namakiers. Such changes tend to occur when the flowing salt encounters changes in its boundary conditions, and the recognition of buried namakiers is discussed in the light of such observations. Episodes of salt flow at a rate of 0.5 m per day have been measured along the margin of the N namakier after significant rain showers. Such brief episodes of rapid flow alternate with long periods when the namakier is dry and stationary. The shape of the colour bands cropping out on the N namakier indicate that the flow over the surface of impure salt with a mylonitic texture obeys a power law with n ≈ 3. Although the reported annual rainfall has the potential of dissolving both namakiers in about 2000 years, a superimposed thin marine cover may protect static parts of them for as long as 30,000 to 300,000 years.     

The Preboreal climate reversal and a subsequent solar‐forced climate shift

Accurate chronologies are essential for linking palaeoclimate archives. Carbon‐14 wiggle‐match dating was used to produce an accurate chronology for part of an early Holocene peat sequence from the Borchert (The Netherlands). Following the Younger Dryas–Preboreal transition, two climatic shifts could be inferred. Around 11 400 cal. yr BP the expansion of birch (Betula) forest was interrupted by a dry continental phase with dominantly open grassland vegetation, coeval with the PBO (Preboreal Oscillation), as observed in the GRIP ice core. At 11 250 cal. yr BP a sudden shift to a humid climate occurred. This second change appears to be contemporaneous with: (i) a sharp increase of atmospheric ¹⁴C; (ii) a temporary decline of atmospheric CO₂; and (iii) an increase in the GRIP ¹⁰Be flux. The close correspondence with excursions of cosmogenic nuclides points to a decline in solar activity, which may have forced the changes in climate and vegetation at around 11 250 cal. yr BP. Copyright © 2004 John Wiley & Sons, Ltd.     

Paleoclimate evolution and aridification mechanism of the eastern Tethys during the Callovian–Oxfordian: evidence from geochemical records of the Qiangtang Basin,Tibetan Plateau

Global climate during the Jurassic has been commonly described as a uniform greenhouse climate for a long time. However, the climate scenario of a cool episode during the Callovian–Oxfordian transition following by a warming trend during the Oxfordian (163.53 to 157.4 Ma) is documented in many localities of the western Tethys. It is still unclear if a correlatable climate scenario also occurred in the eastern Tethys during the same time interval. In this study, a detailed geochemical analysis on the 1060 m thick successions (the Xiali and Suowa formations) from the Yanshiping section of the Qiangtang Basin, located in the eastern Tethys margin during the Callovian–Oxfordian periods, was performed. To reveal the climate evolution of the basin, carbonate content and soluble salt concentrations (SO₄²⁻, Cl⁻) were chosen as climatic indices. The results show that the overall climate patterns during the deposition of the Xiali and Suowa formations can be divided into three stages: relatively humid (~ 164.0 to 160.9 Ma), dry (~ 160.9 to 159.6 Ma), semi-dry (~ 159.6 to 156.8 Ma). A similar warming climate scenario also occurred in eastern Tethys during the Callovian–Oxfordian transition (~ 160.9 to 159.6 Ma). Besides, we clarify that the Jurassic True polar wander (TPW), the motion of the lithosphere and mantle with respect to Earth’s spin axis, inducing climatic shifts were responsible for the aridification of the Qiangtang Basin during the Callovian–Oxfordian transition with a review of the paleolatitude of the Xiali formation (19.7 + 2.8/−2.6° N) and the Suowa formation (20.7 + 4.1/−3.7° N). It is because the TPW rotations shifted the East Asia blocks (the North and South China, Qiangtang, and Qaidam blocks) from the humid zone to the tropical/subtropical arid zone and triggered the remarkable aridification during the Middle-Late Jurassic (ca. 165–155 Ma).

     

Post‐Last Glacial Maximum glacier fluctuations in the southern Écrins massif (westernmost Alps): insights from 10Be cosmic ray exposure dating

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.     

Geophysical,geochemical and hydrological analyses of water-resource vulnerability to salinization: case of the Uburu-Okposi salt lakes and environs,southeast Nigeria

Until this study, the location and depth of the saline units in Uburu-Okposi salt lake areas and environs have been unknown. This study aimed at delineating the saline lithofacies and dispersal configurations to water bodies, using electrical geophysical methods such as constant separation traversing (CST) and vertical electrical sounding (VES). Results showed weathered zones that represent aquifers mostly at the fourth geoelectric layer: between upper layered aquitards and underlying aquitards at depths 30–140 m. Lateral distribution of resistivity variance was defined by the CST, whereas the VES tool, targeted at low-resistivity zones, detected isolated saline units with less than 10 ohm-m at depths generally >78 m. The saline lithofacies were suspected to link freshwater zones via shear zones, which steer saline water towards the salt lakes and influence the vulnerability of groundwater to salinization. The level of salinization was verified by water sampling and analysis, and results showed general alkaline water type with a mean pH of 7.66. Water pollution was indicated: mean total dissolved solids (TDS) 550 mg/l, electrical conductivity (EC) 510 μS/cm, salinity 1.1‰, Cl^? 200 mg/l, N0₃ ^?35.5 mg/l, Na⁺ 19.6 mg/l and Ca²⁺ 79.3 mg/l. The salinity is controlled by NaCl salt, as deduced from correlation analysis using the software package Statistical Product for Service Solutions (SPSS). Generally, concentrations of dissolved ions in the water of the area are enhanced via mechanisms such as evaporation, dissociation of salts, precipitation run off and leaching of dissolved rock minerals.     

Reconstruction of the variability of the southwest monsoon during the past 3 ka,from the continental margin of the southeastern Arabian Sea

From temporal variation in δ¹⁸O in Globigerinoides ruber and G. sacculifer and geochemical indices of weathering/erosion (chemical index of alteration, Al and Ti), we infer rapid southwest monsoon (SWM) deterioration with dwindling fluvial and detrital fluxes at ca. 450–650, 1000 and 1800–2200 cal. a BP during the late Holocene. We have evaluated the role of solar influx (reconstructed) and high‐latitude climate variability (archived in GRIP and GISP‐2 cores) on SWM precipitation. Broadly, our δ¹⁸O climate reconstruction is concordant with GRIP and GISP‐2, and supports a teleconnection through atmospheric connection between the SWM and the North Atlantic climate – albeit temporal extents of the Little Ice Age and Medieval Warm Period from high latitude are not entirely coeval. Moreover, there is a humid climate and enhanced precipitation during the terminal stages of the Little Ice Age. The medieval warming (ca. AD 800–1300) is not synchronous either, and is punctuated by an arid event centred at 1000 a BP. Although the delineation of the specific influence of solar influx on SWM precipitation is elusive, we surmise that SWM precipitation is a complex phenomenon and local orography along southwestern India may have a role on the entrapment of moisture from the southwest trade winds, when these hit land. Copyright © 2009 John Wiley & Sons, Ltd.     

Deglacial palaeoclimate at Puerto del Hambre,subantarctic Patagonia,Chile

The primary objective of this study is to further substantiate multistep climatic forcing of late‐glacial vegetation in southern South America. A secondary objective is to establish the age of deglaciation in Estrecho de Magallanes–Bahía Inútil. Pollen assemblages at 2‐cm intervals in a core of the mire at Puerto del Hambre (53°36′21″S, 70°55′53″W) provide the basis for reconstructing the vegetation and a detailed account of palaeoclimate in subantarctic Patagonia. Chronology over the 262‐cm length of core is regulated by 20 AMS radiocarbon dates between 14 455 and 10 089 ¹⁴C yr BP. Of 13 pollen assemblage zones, the earliest representing the Oldest Dryas chronozone (14 455–13 000 ¹⁴C yr BP) records impoverished steppe with decreasing frequencies and loss of southern beech (Nothofagus). Successive 100‐yr‐long episodes of grass/herbs and of heath (Empetrum/Ericaceae) before 14 000 ¹⁴C yr BP infer deglacial successional communities under a climate of increased continentality prior to the establishment of grass‐dominated steppe. The Bølling–Allerød (13 000–11 000 ¹⁴C yr BP) is characterised by mesic grassland under moderating climate that with abrupt change to heath dominance after 12 000 ¹⁴C yr BP was warmer and not as humid. At the time of the Younger Dryas (11 000–10 000 ¹⁴C yr BP), grass steppe expanded with a return of colder, more humid climate. Later, with gradual warming, communities were invaded by southern beech. The Puerto del Hambre record parallels multistep, deglacial palaeoclimatic sequences reported elsewhere in the Southern Andes and at Taylor Dome in Antarctica. Deglaciation of Estrecho de Magallanes–Bahía Inútil is dated close to 14 455 ¹⁴C yr BP, invalidating earlier dates of between 15 800 and 16 590 ¹⁴C yr BP. Copyright © 2000 John Wiley & Sons, Ltd.     

Beryllium-10 contents of core samples from the St. Severin meteorite

Eleven samples taken from along the 35-cm core AIII of the LL-chondrite St. Severin have ¹⁰Be contents ranging from 20 to 28 dpm/kg and averaging 24.5 ± 0.9 dpm/kg. The ¹⁰Be contents increase with depth in the outermost 8 cm while at depths greater than 8 cm the ¹⁰Be contents change little. Calculations based on cross sections for proton-induced reactions that make ¹⁰Be disagree seriously with the measured values. Relatively large cross sections were constructed for neutron-induced reactions below 1 GeV. They give calculated ¹⁰Be production rates that agree with the measured values to within 10%. Cosmogenic ¹⁰Be in stony meteorites is better described as a medium-energy product than as a high-energy one.     

Particle accelerator measurements of10Be in marine accumulations: Intercomparison with beta counting method

Cosmogenic beryllium-10 activities have been measured in marine accumulations of up to ～6 m.y age by conventional beta counting technique and by accelerator mass spectrometry. The two sets of data at¹⁰Be levels of 10⁹–10¹⁰ atoms/g agree within the absolute errors of the two methods. The detection limit for¹⁰Be by the accelerator mass spectrometry is about five orders of magnitude lower than that with the beta counting method.     

Meltwater discharge during the Holocene from the Wilkes subglacial basin revealed by beryllium isotope analysis of marine sediments

Understanding Antarctic Ice Sheet dynamics related to global climate change is of scientific and societal interest as the future behaviour of the ice sheet under the currently changing climate is unknown. We present beryllium‐10 (¹⁰Be) analysis of a high‐resolution marine sediment core from the Adélie Basin near the eastern Wilkes Land margin, which is susceptible to marine ice sheet instability due to the low‐lying nature and down‐sloping trough of the Wilkes Subglacial Basin. Combined with a newly constructed age model using compound specific radiocarbon dates, the data reveal three events associated with high meteoric ¹⁰Be at ca. ~10 ka, ca. ~6.5 ka and from ca. ~4 ka. We interpret these high meteoric ¹⁰Be events to be derived from the deposition of ¹⁰Be released from the ice sheet during meltwater discharge. In particular, the shift to higher meteoric ¹⁰Be concentration at~4 ka may correspond to changes in climate patterns at this time. Copyright © 2019 John Wiley & Sons, Ltd.     

Late Quaternary glacial history of Khentey Mountains,Central Mongolia

Mongolian glaciers have been the subject of relatively little research, resulting in less geochronological constraint than other parts of Central Asia. The Khentey Mountains (latitude 47–51°N, longitude 105–112°E) are a typical landlocked mountain range exhibiting clear geomorphic evidence of late Quaternary glaciation. Yet, compared to western parts of Mongolia such as the Mongolian Altay, Gobi Altay, Khangay, and Khovsgol, glacial history of the Khentey Mountains is poorly understood. To address this, and permit comparison of the Khentey glacier–climate record with other alpine regions in Mongolia, we performed geomorphological mapping and cosmogenic ¹⁰Be surface‐exposure dating in two glaciated regions of the Khentey Mountains: Yestii and Khagiin Khar. Specifically, we measured ¹⁰Be in 34 samples collected from five moraine sequences, which, together with morphostratigraphy, correspond to four main glacial stages: (i) The M_y1 terminal moraine sequence for Yestii (21.0±4.9 ka) and the M_k1 moraine for Khagiin Khar (19.6±2.6 ka), both of which represent the Last Glacial Maximum; (ii) the Lateglacial M_k2 moraine, dated to 16.0±3.5 ka; (iii) the M_k3 moraine, dated to either 17.6±7.0 ka (Lateglacial) or 12.1±1.1 ka (Younger Dryas); and (iv) the currently undated M_k4 moraine (~2200 m a.s.l.), to which we assign a Holocene age. Our results suggest that the timing of maximum glacier extent in Mongolia was regionally variable. In the Khentey Mountains, maximum glaciation occurred during Marine Isotope Stage (MIS) 2, whereas the maximum occurred during MIS 3 in Khangay and Khovsgol and during MIS 4 in the Altay. The MIS 2 glacial maximum in the Khentey Mountains coincided with the global sea level minimum during the Last Glacial Maximum, and was followed by at least three glacial re‐advances during the Lateglacial to possibly the Holocene.     

Multiple fluid components of salt diapirs and salt dome cap rocks, Gulf Coast, U.S.A.

Salt diapirs contain a few percent of anhydrite that accumulated as residue to form anhydrite cap rocks during salt dissolutions. Reported ⁸⁷Sr/⁸⁶Sr ratios of these salt-hosted and cap rock anhydrites in the Gulf Coast, U.S.A., indicate their derivation from Middle Jurassic seawater. However, a much wider range of ⁸⁷Sr/⁸⁶Sr ratios, incorporating a highly radiogenic component in addition to the Middle Jurassic component, has been found in several Gulf Coast salt domes. This wide range of ⁸⁷Sr/⁸⁶Sr ratios of anhydrite within the salt stocks records Sr contributions from both marine water and formation water that has equilibrated with siliciclastics. During cap rock formation this anhydrite either recrystallized in the presence of, or was cemented by, a low-Sr fluid with a Late Cretaceous seawter-type Sr isotope ratio or simply lost Sr during recrystallization. Later, the cap rock was invaded by warm saline brines with high Sr isotope ratios from which barite and metal sulfides were precipitated. Subsequently, low-salinity water hydrated part of the anhydrite bringing to six the total number of fluids that interacted througout the history of salt dome and cap rock growth. The progenitor of these salt diapirs, the Louann Formation, is generally thought to have formed from marine water evaporated to halite and, rarely, higher evaporite facies. Salt domes in the East Texas, North Louisiana, and Mississippi Salt Basins have ⁸⁷Sr/⁸⁶Sr and δ³⁴S values that corroborate a Mid-Jurassic age for the mother salt. However, salt domes in the Houston and Rio Grande Embayments of the Gulf Coast Basin have ⁸⁷Sr/⁸⁶Sr ration ranging to values higher than both Middle Jurassic seawater and all Rb-free marine Phanerozoic rocks. These anomalous ⁸⁷Sr/⁸⁶Sr ratios are probably derived from radiogenic Sr-bearing fluids that equilibrated with siliciclastic rocks and invaded the salt either prior to, or during, diapirism. Potential sources of the radiogenic ⁸⁷Sr component include clay and/or feldspar (located either in older units beneath the Louann Formation or younger units flanking the salt diapirs) and K-salts within the Louann evaporites. Because partial Sr exchange in anhydrite had to take place in a fluid medium, admittance of radiogenic ⁸⁷Sr-bearing fluids into the salt may have led to diapirism by lowering the shear strength of the crystalline salt. The slight number of anomalous ⁸⁷Sr/⁸⁶Sr values in the interior basins indicates that anomalous values are related to areally discrete structural or stratigraphic controls that affected only the Gulf Coast Basin.     

Constraining Holocene 10Be production rates in Greenland

The absence of a production rate calibration experiment on Greenland has limited the ability to link ¹⁰Be exposure dating chronologies of ice‐margin change to independent records of rapid climate change. We use radiocarbon age control on Holocene glacial features near Jakobshavn Isbræ, western Greenland, to investigate ¹⁰Be production rates. The radiocarbon chronology is inconsistent with the ¹⁰Be age calculations based on the current globally averaged ¹⁰Be production rate calibration data set, but is consistent with the ¹⁰Be production rate calibration data set from north‐eastern North America, which includes a calibration site nearby on north‐eastern Baffin Island. Based on the best‐dated feature available from the Jakobshavn Isbræ forefield, we derive a ¹⁰Be production rate value of 3.98 ± 0.24 atoms g a^?1, using the ‘St’ scaling scheme, which overlaps with recently published reference ¹⁰Be production rates. We suggest that these ¹⁰Be production rate data, or the very similar data from north‐eastern North America, are used on Greenland. Copyright © 2011 John Wiley & Sons, Ltd.     

26Al-10Be systematics in deep-sea sediments

We report the development of a NaOH-leaching technique to extract the authigenic Al and Be in marine sediments, which should allow the sedimentary signals of cosmogenic ²⁶Al and ¹⁰Be to be more effectively studied as geochemical/geophysical tracers. The technique has been applied to the study of ²⁶Al and ¹⁰Be in opal-rich sediments from the North Pacific. The ²⁶Al/²⁷Al and ¹⁰Be/⁹Be ratios of ~3 × 10⁻¹⁴ and 1 × 10⁻⁷ leached from the sediments are higher than those in the total sediments by factors of 3–10 and 2–3, respectively. The authigenic ¹⁰Be/⁹Be ratios are similar to those in deep waters at the study site, pointing to the potential usefulness of the ratios in paleoceanographic studies. The fractions of total Be and Al in the sediment studied that are of authigenic origin average about 40 and 17%, respectively. Estimated ²⁶AL/²⁷A1 ratios in detrital sediments are ≤ 10⁻¹⁵, low enough to indicate that the source of ²⁶Al in the ocean mainly comes from atmospheric production. In the study area, the deposition flux of ²⁶Al is comparable to its atmospheric supply. However, the deposition flux of ¹⁰Be is about threefold higher than the atmospheric input, signifying lateral transport of ¹⁰Be from the open ocean to this area of relatively high particle flux. The ²⁶Al/¹⁰Be ratio, being insensitive to the oceanic influx of lithogenic particles, may serve as a valuable proxy for paleoproductivity. Both the authigenic and total-sediment ²⁶Al/²⁷Al and ¹⁰Be/ ⁹Be ratios decreased significantly at ~6 ka, which could reflect an enhanced input of windblown lithogenic particles to the North Pacific. While the enhanced dust input did not significantly alter the deep-water ⁹Be concentration, it contributed to the observed increase of authigenic ⁹Be flux to the sediment.     

Sediment incorporation in island-arc magmas: Inferences from 10Be

The radioisotope ¹⁰Be has been used as a tracer to evaluate subduction and recycling of sediments in island arcs. As a cosmogenic isotope strongly enriched in oceanic sediments, it is especially suitable for monitoring sediment subduction.We report here ¹⁰Be results for 106 arc volcanic rocks and 33 basalts from mid-ocean ridges, oceanic islands, continental rifts, and continental flood basalt provinces. The 33 basalts from non-arc environments all contain < 1 × 10⁶ atom/gram (g⁻¹) and form a reference or “control group” against which the arc data may be compared. Lavas from the Sunda, Mariana and Halmahera arcs, each with 12 samples, are indistinguishable from the control group. Nine samples from Japan range from 0.1 × 10⁶ to 13.5 × 10⁶ g⁻¹ of ¹⁰Be. Lavas from the Aleutians and Central America (excluding Costa Rica) consistently have ¹⁰Be contents greater than those of the control group, extending to 15.3 × 10⁶ g⁻¹ for the Aleutians and 24 × 10⁶ g⁻¹ for Central America. Both the Japan and Central American arcs show a geographic variation in ¹⁰Be abundances; the Aleutian arc does not.Conceptually, four models may be used to explain the incorporation of ¹⁰Be in island arcs. Model 1 is the limiting case calculation presented in Brownet al. (1982). Physically, it corresponds to an assumption that all ¹⁰Be in the uppermost sediment layers is carried to depth, the ¹⁰Be is mechanically decoupled from the sediment pile and is added to the arc magma source region. This model results in the highest calculated ¹⁰Be contents in arc lavas. In the more physically reasonable Model 2, the ¹⁰Be-rich upper sediments are assumed to mix with the deeper, ¹⁰Be-poor, sediments and the sediments are subsequently incorporated into the source region. Model 3 assumes ¹⁰Be to be incorporated from sedimentary layers encountered during magma ascent. In Model 4 only sediments contained within grabens in the downgoing slab may be subducted. As yet insufficient data exist to permit conclusive evaluation of these models, but correlations between ¹⁰Be contents in arc volcanic rocks and recent sedimentation rates and sediment thickness, measured outboard of the trench, suggest that Model 2 may be the most important mechanism for ¹⁰Be incorporation in many island arcs.     

Response of chironomids to Late Quaternary environmental change in the Taitao Peninsula,southern Chile

An Erratum has been published for this article in Journal of Quaternary Science 17(7) 2002, 721. There is conflicting evidence concerning the extent and timing of late Quaternary climate variability in southern South America and how this may be linked to climate change in the Northern Hemisphere. Critical unresolved questions include whether or not a cool period occurred in southern South America during the Younger Dryas Chronozone (YDC) (11 000–10 000 ¹⁴C yr BP; 13 000–11 200 yr BP), and the timing of wet and dry phases during the Holocene. To date most evidence is from glacial, pollen and beetle records but, in an attempt to resolve these questions, we have used chironomid midges as an independent proxy in one of the first studies of its kind in Patagonia. We investigated the dynamics of midge assemblages during the Late‐glacial and Holocene at Lago Stibnite on the Taitao Peninsula, southern Chile (46°S). Changes in the midge assemblage suggest that the climate may have become cooler and drier during the YDC. During the Holocene there were cyclical changes in the midge assemblage that may have been in response to trophic change and/or to changes in precipitation when conditions appear to have been drier than today at 9400–6300 ¹⁴C yr BP and 2400–1600 ¹⁴C yr BP. Copyright © 2002 John Wiley & Sons, Ltd.     

Late glacial and holocene 10Be production rates for western Norway

We present a new regional calibration of the ¹⁰Be production rate from two well‐dated surfaces in southern Norway: a rock avalanche with ¹⁴C‐dated wood and a precisely dated Younger Dryas moraine. Calculated ¹⁰Be production rates are 4.26 ± 0.13 and 4.65 ± 0.14 at g^?1 a^?1 for the Lal/Stone and Lifton scaling models, respectively. Our regional production rate for southern Norway is 5% lower than the canonical global ¹⁰Be production rate with lower uncertainties. Our ¹⁰Be production rate agrees with regional ¹⁰Be production rates from north‐eastern North America and New Zealand. The ¹⁰Be production rate estimate presented here can be used to improve the precision and accuracy of exposure‐dated ice‐marginal features, as well as other surfaces, in northern Europe. Copyright © 2011 John Wiley & Sons, Ltd.