Regional beryllium-10 production rate calibration for late-glacial northeastern North America

The major uncertainty in relating cosmogenic-nuclide exposure ages to ages measured by other dating methods comes from extrapolating nuclide production rates measured at globally scattered calibration sites to the sites of unknown age that are to be dated. This uncertainty can be reduced by locating production rate calibration sites that are similar in location and age to the sites to be dated. We use this strategy to reconcile exposure age and radiocarbon deglaciation chronologies for northeastern North America by compiling ¹⁰Be production rate calibration measurements from independently dated late-glacial and early Holocene ice-marginal landforms in this region. ¹⁰Be production rates measured at these sites are 6–12% lower than predicted by the commonly accepted global ¹⁰Be calibration data set used with any published production rate scaling scheme. In addition, the regional calibration data set shows significantly less internal scatter than the global calibration data set. Thus, this calibration data set can be used to improve both the precision and accuracy of exposure dating of regional late-glacial events. For example, if the global calibration data set is used to calculate exposure ages, the exposure-age deglaciation chronology for central New England is inconsistent with the deglaciation chronology inferred from radiocarbon dating and varve stratigraphy. We show that using the regional data set instead makes the exposure age and radiocarbon chronologies consistent. This increases confidence in correlating exposure ages of ice-marginal landforms in northeastern North America with glacial and climate events dated by other means.     

In situ cosmogenic 10Be production-rate calibration from the Southern Alps,New Zealand

We present a ¹⁰Be production-rate calibration derived from an early Holocene debris-flow deposit at about 1000 m above sea level in the central Southern Alps, New Zealand, in the mid-latitude Southern Hemisphere. Ten radiocarbon ages on macrofossils from a soil horizon buried by the deposit date the deposit to 9690 ± 50 calendar years before AD2008. Surface ¹⁰Be concentrations of seven large boulders partially embedded in the stable surface of the deposit are tightly distributed, yielding a standard deviation of ～2%. Conversion of the ¹⁰Be measurements to sea level/high-latitude values using each of five standard scaling methods indicates ¹⁰Be production rates of 3.84 ± 0.08, 3.87 ± 0.08, 3.83 ± 0.08, 4.15 ± 0.09, and 3.74 ± 0.08 atoms g^?1 a^?1, relative to the ‘07KNSTD’ ¹⁰Be AMS standard, and including only the local time-integrated production-rate uncertainties. When including a sea level high-latitude scaling uncertainty the overall error is ～2.5% (1σ) for each rate. To test the regional applicability of this production-rate calibration, we measured ¹⁰Be concentrations in a set of nearby moraines deposited before 18 060 ± 200 years before AD2008. The ¹⁰Be ages are only consistent with minimum-limiting ¹⁴C age data when calculated using the new production rates. This also suggests that terrestrial in situ cosmogenic-nuclide production did not change significantly from Last Glacial Maximum to Holocene time in New Zealand. Our production rates agree well with those of a recent calibration study from northeastern North America, but are 12–14% lower than other commonly adopted values. The production-rate values presented here can be used elsewhere in New Zealand for rock surfaces exposed during or since the last glacial period.     

A reevaluation of in situ cosmogenic 3He production rates

³He is among the most commonly measured terrestrial cosmogenic nuclides, but an incomplete understanding of the ³He production rate has limited robust interpretation of cosmogenic ³He concentrations. We use new measurements of cosmogenic ³He in olivine from a well-dated lava flow at Tabernacle Hill, Utah, USA, to calibrate the local ³He production rate. The new ³He measurements (n = 8) show excellent internal consistency and yield a sea level high latitude (SLHL) production rate of 123 ± 4 at g^?1 yr^?1 following the Lal (1991)/Stone (2000) scaling model [Lal, D., 1991. Cosmic ray labeling of erosion surfaces: in situ nuclide production rates and erosion models. Earth and Planetary Science Letters, 104, 424–439.; Stone, J.O., 2000. Air pressure and cosmogenic isotope production. Journal of Geophysical Research, 105, 23753–23759.]. We incorporate the new measurements from Tabernacle Hill in a compilation of all published production rate determinations, characterizing the mean global SLHL production rates (e.g. 120 ± 9.4 at g^?1 yr^?1 with Lal (1991)/Stone (2000)). The internal consistency of the global ³He production rate dataset is as good as the other commonly used cosmogenic nuclides. Additionally, ³He production rates in olivine and pyroxene agree within experimental error. The ³He production rates are implemented in an age and erosion rate calculator, forming a new module of the CRONUS-Earth web-based calculator, a simple platform for cosmogenic nuclide data interpretation [Balco, G., Stone, J., Lifton, N.A., and Dunai, T.J., 2008. A complete and easily accessible means of calculating surface exposure ages or erosion rates from ¹⁰Be and ²⁶Al measurements. Quaternary Geochronology, 3, 174–195.]. The ³He calculator is available online at http://www.cronuscalculators.nmt.edu/.     

A GIS-based approach to site vegetated buffer strips for erosion control within an agricultural catchment in southern England

Agricultural soil erosion is largely attributed to arable intensification and increased mechanization. Runoff from arable land and intensively managed grassland transports sediment and contaminants across the landscape and into watercourses, causing crop loss, land degradation, and water quality issues. One low-cost and low-maintenance nature-based mitigation approach is the implementation of vegetated buffer strips (VBS): grassland sited along field margins to trap sediment and contaminants, reducing transportation and diffuse pollution rates. GIS modelling using remotely sensed landscape indices and land parcel data can provide an efficient means of identifying priority areas for intervention at sub-catchment or farm system scales. We develop and test a scalable runoff risk model in the lower Rother catchment, West Sussex. The model uses the Normalized Difference Vegetation Index (NDVI) applied to satellite images as an erodibility proxy and identifies locations along pathways that are conceivably at greatest risk of sediment accumulation and transfer, guided by field observations. We assess current and historical field boundaries near high-risk locations, evaluating the potential capacity of their margins to contribute to runoff risk reduction using an innovative ranking system. Recommendations are made for VBS implementation and the value of historical field boundary and margin restoration is discussed. Our method offers a rapid approach with minimal data requirements to identify high-risk sediment runoff locations and priority sites for intervention. The tool has the potential to guide decision-makers responsible for targeting and implementing soil erosion and runoff control measures such as VBS, while also maximizing agri-environmental and cultural benefits.     

Intertidal boulder transport: A proposed methodology adopting Radio Frequency Identification (RFID) technology to quantify storm induced boulder mobility

Boulder transport is an area of growing interest to coastal scientists as a means of improving our understanding of the complex interactions between extreme wave activity and the evolution of rocky coasts. However, our knowledge of the response of intertidal boulder deposits to contemporary storm events remains limited due to a lack of quantifiable field-based evidence. We address this by presenting a methodology incorporating Radio Frequency Identification (RFID) tagging and Differential Global Positioning Navigation Satellite System (DGNSS) technology to monitor and accurately quantify the displacement of RFID tagged boulders resulting from storm wave activity. Based on preliminary findings we highlight the suitability of the technology and methodology to better understand the spatial and temporal response of intertidal boulders to contemporary storm events. We inserted RFID tags in 104 limestone boulders (intermediate axes from 0.27 to 2.85 m) across a range of morphogenic settings at two sites on the intertidal shore platforms at Bembridge, Isle of Wight (UK). Fifteen topographic surveys were conducted between July 2015 and May 2017 to relocate and record tagged boulder locations (tag recovery rate: 91%). The relocated boulder coordinate data from both sites identified 164 individual transport events in 63% of the tagged boulder array amounting to 184.6 m of transport, including the displacement of a boulder weighing more than 10 tonnes. Incidents of boulder quarrying and overturning during transport were also recorded, demonstrating that despite the relatively sheltered location, intertidal boulders are created and regularly transported under moderate storm conditions. This suggests that contemporary storm events have a greater propensity to mobilise boulders in the intertidal range than has previously been realised. Consequently, by documenting our methodology we provide guidance to others and promote further use of RFID technology to enable new hypotheses on boulder transport to be tested in a range of field settings and wave regimes. © 2018 John Wiley & Sons, Ltd.     

Bioaugmentation in a Well‐Characterized Fractured Rock DNAPL Source Area

A field demonstration was performed at Edwards Air Force Base to assess bioaugmentation for treatment of a well‐characterized tetrachloroethene (PCE) dense nonaqueous phase liquid (DNAPL) source area in fractured rock. Groundwater recirculation was employed to deliver remedial amendments, including bacteria, to facilitate reductive dechlorination and enhance DNAPL dissolution. An active treatment period of 9 months was followed by a 10‐month posttreatment rebound evaluation. Dechlorination daughter products were observed in both the shallow and deep fracture zones following treatment. In the shallow fracture zone, the calculated DNAPL mass removed was approximately equal to the DNAPL mass estimated using partitioning tracer testing, and no rebound in chlorinated ethenes or ethene was observed during the posttreatment period. A maximum DNAPL dissolution enhancement factor of 5 was observed in the shallow fracture zone. In the deep fracture zone, only approximately 45% of the DNAPL mass—as estimated via partitioning tracer testing—was removed and rebound in the total molar chlorinated ethenes + ethene was observed. The difference in behavior between the shallow and deep fracture zones was attributed to DNAPL architecture and the fracture flow field.     

High-Resolution Characterization of a Chlorinated Solvent Impacted Aquifer Using a Passive Profiler

A direct-drive high-resolution passive profiler (HRPP) was developed to quantify and delineate concentrations of chlorinated volatile organic compounds (CVOCs), geochemical indicators and CVOC-degrading microorganisms/genes, as well as to perform compound-specific stable isotope analysis (CSIA) of CVOCs and estimate interstitial velocity at <30-cm resolution. The profilers can be coupled together to provide a continuous sample interval and advanced to depths up to approximately 9 m below-ground surface (bgs) within saturated media where direct-push techniques are feasible. The HRPP was field tested in a previous dense nonaqueous phase liquid (DNAPL) source zone at the former Naval Air Station in Alameda, CA. HRPP data sets were compared to the following traditional groundwater data sets: CVOC and anion concentrations in standard and multilevel monitoring well water samples, CVOC concentrations in soil core samples, qualitative contaminant profiles delineated with a membrane interface probe (MIP), microbial community and CSIA profiles from Bio-Traps® deployed in wells, groundwater velocity from passive flux meters (PFMs), lithologic profiles correlated with MIP electrical conductivity (EC), and velocity estimates based on permeability profiles measured with a Geoprobe hydraulic profiling tool (HPT). In some cases, the HRPP data were equivalent to traditional techniques and, in other cases, the HRPP data were more representative of local variability rather than bulk aquifer conditions. Overall the results support the use of the HRPP to provide high-resolution data on concentrations, velocity, and microbial activity in temporary direct-push deployments without well installation, providing a new tool to better assess source zones and contaminated groundwater plumes, even in low permeability media, and to increase the fidelity of site transport models.     

Sub-annual moraine formation at an active temperate Icelandic glacier

This paper presents detailed geomorphological and sedimentological investigations of small recessional moraines at Fjallsjökull, an active temperate outlet of Öræfajökull, southeast Iceland. The moraines are characterized by striking sawtooth or hairpin planforms, which are locally superimposed, giving rise to a complex spatial pattern. We recognize two distinct populations of moraines, namely a group of relatively prominent moraine ridges (mean height ~1.2 m) and a group of comparatively low-relief moraines (mean height ~0.4 m). These two groups often occur in sets/systems, comprising one pronounced outer ridge and several inset smaller moraines. Using a representative subsample of the moraines, we establish that they form by either (i) submarginal deformation and squeezing of subglacial till or (ii) pushing of extruded tills. Locally, proglacial (glaciofluvial) sediments are also incorporated within the moraines during pushing. For the first time, to our knowledge, we demonstrate categorically that these moraines formed sub-annually using repeat uncrewed aerial vehicle (UAV) imagery. We present a conceptual model for sub-annual moraine formation at Fjallsjökull that proposes the sawtooth moraine sequence comprises (i) sets of small squeeze moraines formed during melt-driven squeeze events and (ii) larger push moraines formed during winter re-advances. We suggest the development of this process-form regime is linked to a combination of elevated temperatures, high surface meltwater fluxes to the bed and emerging basal topography (a depositional overdeepening). These factors result in highly saturated subglacial sediments and high porewater pressures, which induces submarginal deformation and ice-marginal squeezing during the melt season. Strong glacier recession during the summer, driven by elevated temperatures, allows several squeeze moraines to be emplaced. This process-form regime may be characteristic of active temperate glaciers receding into overdeepenings during phases of elevated temperatures, especially where their englacial drainage systems allow efficient transfer of surface meltwater to the glacier bed near the snout margin. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

Selection Assistance for the Evaluation of Geoconstruction Technologies for Transportation Applications

A new comprehensive, web-based information system summarizes forty-six geoconstruction technologies, or ground improvement methods, applicable to transportation infrastructure from the following areas: geosynthetics, geotextiles, ground improvement, grouting, slope stabilization, soil reinforcement, soil stabilization, and alternative/recycled materials. Selection assistance was developed as part of the overall information system to aid the user in identifying potential geoconstruction technologies for a project-specific set of conditions. A knowledge base to assist a user in evaluating the current status of each technology with regard to the U.S. practice and the potential applications for each technology is described in detail. Selection assistance includes qualitative ratings for each technology, a listing of the technologies sorted by classification or desired improvement, and a dynamic, Interactive Selection tool. After assisting the user in identifying a short list of potential technologies, the user can access the technology specific data in the information system to further evaluate the technologies. Engineers, planners, and owners will be able to utilize the entire information system to assess the feasibility of technologies to address project-specific requirements and constraints.