Modelling ecohydrological feedbacks in forest and grassland plots under a prolonged drought anomaly in Central Europe 2018–2020

Recent studies have highlighted the importance of understanding ecohydrological drought feedbacks to secure water resources under a changing climate and increasing anthropogenic impacts. In this study, we monitored and modelled feedbacks in the soil–plant-atmosphere continuum to the European drought summer 2018 and the following 2 years. The physically based, isotope-aided model EcH₂O-iso was applied to generic vegetation plots (forest and grassland) in the lowland, groundwater-dominated research catchment Demnitzer Millcreek (NE Germany; 66 km²). We included, inter alia, soil water isotope data in the model calibration and quantified changing “blue” (groundwater recharge) and “green” (evapotranspiration) water fluxes and ages under each land use as the drought progressed. Novel plant xylem isotope data were excluded from calibration but were compared with simulated root uptake signatures in model validation. Results indicated inter-site differences in the dynamics of soil water storage and fluxes with contrasting water age both during the drought and the subsequent 2 years. Forest vegetation consistently showed a greater moisture stress, more rapid recovery and higher variability in root water uptake depths from a generally younger soil water storage. In contrast, the grassland site, which had more water-retentive soils, showed higher and older soil water storage and groundwater recharge fluxes. The damped storage and flux dynamics under grassland led to a slower return to younger water ages at depth. Such evidence-based and quantitative differences in ecohydrological feedbacks to drought stress in contrasting soil-vegetation units provide important insights into Critical Zone water cycling. This can help inform future progress in the monitoring, modelling and development of climate mitigation strategies in drought-sensitive lowlands.     

Comparison of Five Numerical Codes for Automated Tracing of Coronal Loops

The three-dimensional (3D) modeling of coronal loops and filaments requires algorithms that automatically trace curvilinear features in solar EUV or soft X-ray images. We compare five existing algorithms that have been developed and customized to trace curvilinear features in solar images: i) the oriented-connectivity method (OCM), which is an extension of the Strous pixel-labeling algorithm (developed by Lee, Newman, and Gary); ii) the dynamic aperture-based loop-segmentation method (developed by Lee, Newman, and Gary); iii) unbiased detection of curvilinear structures (developed by Steger, Raghupathy, and Smith); iv) the oriented-direction method (developed by Aschwanden); and v) ridge detection by automated scaling (developed by Inhester). We test the five existing numerical codes with a TRACE image that shows a bipolar active region and contains over 100 discernable loops. We evaluate the performance of the five codes by comparing the cumulative distribution of loop lengths, the median and maximum loop length, the completeness or detection efficiency, the accuracy, and flux sensitivity. These algorithms are useful for the reconstruction of the 3D geometry of coronal loops from stereoscopic observations with the STEREO spacecraft, or for quantitative comparisons of observed EUV loop geometries with (nonlinear force-free) magnetic field extrapolation models.     

Permeable Asphalt: A New Tool to Reduce Road Salt Contamination of Groundwater in Urban Areas

Chloride contamination of groundwater in urban areas due to deicing is a well‐documented phenomenon in northern climates. The objective of this study was to evaluate the effects of permeable pavement on degraded urban groundwater. Although low impact development practices have been shown to improve stormwater quality, no infiltration practice has been found to prevent road salt chlorides from entering groundwater. The few studies that have investigated chlorides in permeable asphalt have involved sampling directly beneath the asphalt; no research has looked more broadly at surrounding groundwater conditions. Monitoring wells were installed upgradient and downgradient of an 860 m² permeable asphalt parking lot at the University of Connecticut (Storrs, Connecticut). Water level and specific conductance were measured continuously, and biweekly samples were analyzed for chloride. Samples were also analyzed for sodium (Na), calcium (Ca), and magnesium (Mg). Analysis of variance analysis indicated a significantly (p < 0.001) lower geometric mean Cl concentration downgradient (303.7 mg/L) as compared to upgradient (1280 mg/L). Concentrations of all alkali metals increased upgradient and downgradient during the winter months as compared to nonwinter months, indicating that cation exchange likely occurred. Despite the frequent high peaks of chloride in the winter months as well as the increases in alkali metals observed, monitoring revealed lower Cl concentrations downgradient than upgradient for the majority of the year. These results suggest that the use of permeable asphalt in impacted urban environments with high ambient chloride concentrations can be beneficial to shallow groundwater quality, although these results may not be generalizable to areas with low ambient chloride concentrations.     

Development and Re‐Evaluation of Tourmaline Reference Materials for In Situ Measurement of Boron δ Values by Secondary Ion Mass Spectrometry

Six tourmaline samples were investigated as potential reference materials (RMs) for boron isotope measurement by secondary ion mass spectrometry (SIMS). The tourmaline samples are chemically homogeneous and cover a compositional range of tourmaline supergroup minerals (primarily Fe, Mg and Li end‐members). Additionally, they have homogeneous boron delta values with intermediate precision values during SIMS analyses of less than 0.6‰ (2s). These samples were compared with four established tourmaline RMs, that is, schorl IAEA‐B‐4 and three Harvard tourmalines (schorl HS#112566, dravite HS#108796 and elbaite HS#98144). They were re‐evaluated for their major element and boron delta values using the same measurement procedure as the new tourmaline samples investigated. A discrepancy of about 1.5‰ in δ¹¹B was found between the previously published reference values for established RMs and the values determined in this study. Significant instrumental mass fractionation (IMF) of up to 8‰ in δ¹¹B was observed for schorl–dravite–elbaite solid solutions during SIMS analysis. Using the new reference values determined in this study, the IMF of the ten tourmaline samples can be modelled by a linear combination of the chemical parameters FeO + MnO, SiO₂ and F. The new tourmaline RMs, together with the four established RMs, extend the boron isotope analysis of tourmaline towards the Mg‐ and Al‐rich compositional range. Consequently, the in situ boron isotope ratio of many natural tourmalines can now be determined with an uncertainty of less than 0.8‰ (2s).     

Pure elastic stiffness of sand represented by response envelopes derived from cyclic triaxial tests with local strain measurements

Acta Geotechnica - The elastic stiffness of a fine sand at small to moderate strains ( $$\varepsilon \le 2 \times 10^{-4}$$ ) has been studied based on cyclic triaxial tests on cube-shaped samples...     

Biotite Reference Materials for Secondary Ion Mass Spectrometry 18O/16O Measurements

Five new biotite reference materials were calibrated at the SwissSIMS laboratory (University of Lausanne) for oxygen isotope determination by secondary ion mass spectrometry (SIMS) and are available to the scientific community. The oxygen isotope composition of the biotites, UNIL_B1 to B5, was determined by laser‐heating fluorination to be 11.4 ± 0.11‰, 8.6 ± 0.15‰, 6.1 ± 0.04‰, 7.1 ± 0.05‰ and 7.6 ± 0.04‰, respectively. SIMS analyses on spots smaller than 20 μm gave a measurement repeatability of 0.3‰ (2 standard deviation, 2s). The matrix effect due to solid solution in natural biotite could be expressed as a linear function of X_Mg and X_F for biotite. No effect was found for different crystallographic orientations. SIMS analysis allows the oxygen isotope composition of biotite to be measured with a measurement uncertainty of 0.3–0.4‰ (2s) for biotites with similar major element compositions. A measurement uncertainty of 0.5‰ (2s) is realistic when F poor biotites (lower than 0.2% m/m oxides) within the compositional range of X_Mg of 0.3–0.9 were compared from different sessions. The linear correlation with F content offers a reasonable working curve for F‐rich biotites, but additional reference materials are needed to confirm the model.     

Measuring the benefits and costs of community education and outreach in marine protected areas

Conservation organizations often invest considerable resources in education and outreach activities in and around marine protected areas (MPAs). The expectation is that such efforts will change local knowledge, attitudes and ultimately behavior. This is one of the first studies to assess the efficacy of using education and outreach activities to improve community knowledge and attitudes about an MPA. Random sample surveys in 2005 and 2010 (n=1213) before and after education and outreach activities are compared. Program budgets for the same period give the investment levels. With an investment level averaging US$24 per capita/year, the result was an average increase of 33% in “yes” responses across 15 indicators of knowledge and attitudes towards marine conservation. The increase in knowledge and positive attitudes was associated with a large decrease in “not sure” responses, suggesting that community members with fewer initial preconceptions are the most effective target for education and outreach activities. This study demonstrates that investments in MPA education and outreach can generate increases in local knowledge and positive attitudes, and changing knowledge and attitudes is expected to contribute to the long-term compliance with MPA regulations.     

Protracted storage of CR chondrules in a region of the disk transparent to galactic cosmic rays

Renazzo‐type carbonaceous (CR) chondrites are accretionary breccias that formed last. As such they are ideal samples to study precompaction exposures to cosmic rays. Here, we present noble gas data for 24 chondrules and 3 dark inclusion samples (DIs) from Shi?r 033 (CR2). The meteorite was selected based on the absence of implanted solar wind noble gases and an anomalous oxygen isotopic composition of the DIs; the oxygen isotopes match those in CV3 and CO3 chondrites. Our samples contain variable mixtures of galactic cosmic ray (GCR)‐produced cosmogenic noble gases and trapped noble gases of presolar origin. Remarkably, all chondrules have cosmogenic ³He and ²¹Ne concentrations up to 4.3 and 7.1 times higher than the DIs, respectively. We derived an average ³He‐²¹Ne cosmic ray exposure (CRE) age for Shi?r 033 of 2.03 ± 0.20 Ma (2 SD) and excesses in cosmogenic ³He and ²¹Ne in chondrules (relative to the DIs) in the range (in 10^?8 cm³STP/g) 3.99–7.76 and 0.94–1.71, respectively. Assuming present‐day GCR flux density, the excesses translate into average precompaction ³He‐²¹Ne CRE ages of 3.1–27.3 Ma depending on the exposure geometry. The data can be interpreted assuming a protracted storage of a single chondrule generation prior to the final assembly of the Shi?r 033 parent body in a region of the disk transparent to GCRs.     

Coastal upwelling along the north coast of Papua New Guinea and SST cooling over the pacific warm pool: A case study for the 2002/03 El Niño event

We investigate an overlooked mechanism—coastal upwelling—for sea surface temperature (SST) cooling in the western side of the mean location of the Pacific warm pool (WSWP: 5°S–5°N, 140°E–150°E) prior to El Niño onset. We analyze various observed data such as the TRIangle Trans-Ocean buoy Network (TRITON) moored buoy data, Conductivity-Temperature-Depth (CTD) data, satellite data and a hindcast experiment output by a high-resolution ocean general circulation model (OGCM). We focus on the precondition of the 2002/03 El Niño event, for which many datasets are available. Relatively cool water upwelled along the north coast of Papua New Guinea (PNG) during December 2001, prior to the onset of the 2002/03 El Niño event, and then spread out over a wider area to the northeast. Simultaneously, strong west-northerly surface winds occur along the north coast. Heat budget analysis of TRITON buoy data in the WSWP reveals that negative zonal heat advection due to eastward current is the main factor for cooling the mixed layer in the WSWP in contrast to the warming effect of the surface heat flux during the period. This cooling requires a source of colder water to the west. Similar analysis of OGCM outputs also suggests that the upwelled relatively cool water along the PNG north coast, and its northeastward extension to the equatorial region, contributes to cooling of the surface water over the WSWP mainly via negative zonal heat advection. Similar mechanisms are confirmed also for the 1982/83 and 1997/98 El Niño events by analyses of OGCM outputs and historical SST data. The low SST in the WSWP generated a positive zonal SST gradient together with high SST east of the WSWP. It may contribute to enhancement of the westerly surface wind in this region, leading to the onset of the 2002/03 El Niño event.     

Relation between mean stress,thermodynamic, and lithostatic pressure

Pressure is one of the most important parameters to be quantified in geological problems. However, in metamorphic systems the pressure is usually calculated with two different approaches. One pressure calculation is based on petrological phase equilibria and this pressure is often termed thermodynamic pressure. The other calculation is based on continuum mechanics, which provides a mean stress that is commonly used to estimate the thermodynamic pressure. Both thermodynamic pressure calculations can be justified by the accuracy and applicability of the results. Here, we consider systems with low‐differential stress (<1 kbar) and no irreversible volumetric deformation, and refer to them as conventional systems. We investigate the relationship between mean stress and thermodynamic pressure. We discuss the meaning of thermodynamic pressure and its calculation for irreversible processes such as viscous deformation and heat conduction, which exhibit entropy production. Moreover, it is demonstrated that the mean stress for incompressible viscous deformation is essentially equal to the mean stress for the corresponding viscous deformation with elastic compressibility, if the characteristic time of deformation is five times longer than the Maxwell viscoelastic relaxation time that is equal to the ratio of shear viscosity to bulk modulus. For typical lithospheric rocks, this Maxwell time is smaller than c. 10,000 years. Therefore, numerical simulations of long‐term (>10 kyr) geodynamic processes, employing incompressible deformation, provide mean stress values that are close to the mean‐stress value associated with elastic compressibility. Finally, we show that for conventional systems the mean stress is essentially equal to the thermodynamic pressure. However, mean stress and, hence, thermodynamic pressure can be significantly different from the lithostatic pressure.