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  • 101
    Publication Date: 2021-11-03
    Description: More than half of the world's large rivers flow towards the ocean crossing passive continental margins. Here using an analytical solution and numerical models, we demonstrate that on passive margins, river basins may be integrated by major margin-parallel channels, which form as a flexural isostatic response of the lithosphere to mechanical/erosional unloading along the margin. We analyzed the downstream courses of large rivers flowing across the passive margins and find that the majority of them (31 of 36) have major margin-parallel channels. Occurrences of these channels are generally consistent with the model predictions, although the exact locations and geometry of these rivers may also be controlled/changed by other factors. Our results suggest that the lithosphere strength has an important control on the geometry of large river systems on passive margins, linking the evolution and routing of the Earth's freshwater systems to its deep interior dynamics.
    Keywords: 551.4 ; passive margins ; axial river formation ; isostatic control ; lithosphere rigidigy ; numerical modeling
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  • 102
    Publication Date: 2021-11-03
    Description: Stable organic carbon and nitrogen isotopes can be used to interpret past vegetation patterns and ecosystem qualities. Here we present these proxies for two loess-palaeosol sequences from the southern Carpathian Basin to reconstruct the palaeoenvironment during the past 350 ka and establish regional commonalities and differences. Until now, isotopic studies on loess sequences from this region were only conducted on deposits from the last glacial cycle. We conducted methodological tests concerning the complete decalcification of the samples prior to stable isotope analyses. Two decalcification methods (fumigation method and wet chemical acidification), different treatment times, and the reproducibility of carbon isotope analyses were tested. Obtained results indicate that the choice of the decalcification method is essential for organic carbon stable isotope analyses of loess-palaeosol sequences because ratios vary by more than 10‰ between the wet chemical and fumigation methods, due to incomplete carbonate removal by the latter. Therefore, we suggest avoiding the fumigation method for studies on loess-palaeosol sequences. In addition, our data show that samples with TOC content 〈0.2% bear increased potential for misinterpretation of their carbon isotope ratios. For our sites, C3-vegetation is predominant and no palaeoenvironmental shifts leading to a change of the dominant photosynthesis pathway can be detected during the Middle to Late Pleistocene. Furthermore, the potential for further stable nitrogen isotope studies is highlighted, since this proxy seems to reflect especially past precipitation patterns and reveals favourable conditions in the southern Carpathian Basin, especially during interstadials.
    Keywords: 551 ; southern Carpathian Basin ; loess-palaeosol sequences ; stable isotope analyses ; Pleistocene ecosystem reconstruction
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  • 103
    Publication Date: 2021-11-03
    Description: In Antarctic and Subantarctic environments, 14C-based age determination is often challenging due to unknown reservoir effects, low organic carbon contents of sediments, and high contributions of petrogenic (14C-free) carbon in ice marginal settings. In this study, we evaluate possible benefits and challenges of compound-specific radiocarbon analysis (CSRA) as a tool for age determination of marine Antarctic and Subantarctic sediment sequences. We present a comprehensive data set of 14C ages obtained on bulk organic carbon, carbonates, and on fatty acids (FA) from three coastal marine sediment cores from Subantarctic South Georgia and East Antarctica. Low molecular weight (LMW) FA represent the least 14C-depleted fraction, indicating that the phytoplankton-derived compounds can be a means of dating sediments. In contrast, vascular plant-derived high molecular weight FA are systematically depleted in 14C relative to the low molecular weight homologues, reflecting processes such as soil formation/erosion in the catchment. Comparative age-depth models show significant differences, depending on the material used for the respective models. While the land plant-derived FA may lead to an overestimation of the actual sediment age, LMW FA reveal complex aquatic reservoir effects. Bulk sedimentary organic carbon 14C ages likely provide appropriate age estimates in settings with low petrogenic carbon input in the Antarctic, whereas CSRA has the potential to produce improved age control in settings with high contributions of petrogenic carbon.
    Keywords: 551 ; Antarctica ; marine sediments ; compound‐specific radiocarbon analysis (CSRA)
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  • 104
    Publication Date: 2021-11-03
    Description: Gelatinous zooplankton can be present in high biomass and taxonomic diversity in planktonic oceanic food webs, yet the trophic structuring and importance of this “jelly web” remain incompletely understood. To address this knowledge gap, we provide a holistic trophic characterization of a jelly web in the eastern tropical Atlantic, based on δ13C and δ15N stable isotope analysis of a unique gelatinous zooplankton sample set. The jelly web covered most of the isotopic niche space of the entire planktonic oceanic food web, spanning 〉 3 trophic levels, ranging from herbivores (e.g., pyrosomes) to higher predators (e.g., ctenophores), highlighting the diverse functional roles and broad possible food web relevance of gelatinous zooplankton. Among gelatinous zooplankton taxa, comparisons of isotopic niches pointed to the presence of differentiation and resource partitioning, but also highlighted the potential for competition, e.g., between hydromedusae and siphonophores. Significant differences in spatial (seamount vs. open ocean) and depth-resolved patterns (0–400 m vs. 400–1000 m) pointed to additional complexity, and raise questions about the extent of connectivity between locations and differential patterns in vertical coupling between gelatinous zooplankton groups. Added complexity also resulted from inconsistent patterns in trophic ontogenetic shifts among groups. We conclude that the broad trophic niche covered by the jelly web, patterns in niche differentiation within this web, and substantial complexity at the spatial, depth, and taxon level call for a more careful consideration of gelatinous zooplankton in oceanic food web models. In light of climate change and fishing pressure, the data presented here also provide a valuable baseline against which to measure future trophic observations of gelatinous zooplankton communities in the eastern tropical Atlantic.
    Keywords: 577.7 ; eastern tropical Atlantic ; gelatinous zooplankton ; isotopic pattern ; food web characterization
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  • 105
    Publication Date: 2021-11-03
    Description: Numerical models are a suitable tool to quantify impacts of predicted climate change on complex ecosystems but are rarely used to study effects on benthic macroalgal communities. Fucus vesiculosus L. is a habitat-forming macroalga in the Baltic Sea and alarming shifts from the perennial Fucus community to annual filamentous algae are reported. We developed a box model able to simulate the seasonal growth of the Baltic Fucus–grazer–epiphyte system. This required the implementation of two state variables for Fucus biomass in units of carbon (C) and nitrogen (N). Model equations describe relevant physiological and ecological processes, such as storage of C and N assimilates by Fucus, shading effects of epiphytes or grazing by herbivores on both Fucus and epiphytes, but with species-specific rates and preferences. Parametrizations of the model equations and required initial conditions were based on measured parameters and process rates in the near-natural Kiel Outdoor Benthocosm (KOB) experiments during the Biological Impacts of Ocean Acidification project. To validate the model, we compared simulation results with observations in the KOB experiment that lasted from April 2013 until March 2014 under ambient and climate-change scenarios, that is, increased atmospheric temperature and partial pressure of carbon dioxide. The model reproduced the magnitude and seasonal cycles of Fucus growth and other processes in the KOBs over 1 yr under different scenarios. Now having established the Fucus model, it will be possible to better highlight the actual threat of climate change to the Fucus community in the shallow nearshore waters of the Baltic Sea.
    Keywords: 577.7 ; Baltic sea ; benthic macroalgal communities ; Fucus growth ; biotic and biotic interactions
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  • 106
    Publication Date: 2021-11-03
    Description: The Gravity Recovery and Climate Experiment (GRACE) mission ended its operation in October 2017, and the GRACE Follow-On mission was launched only in May 2018, leading to approximately 1 year of data gap. Given that GRACE-type observations are exclusively providing direct estimates of total water storage change (TWSC), it would be very important to bridge the gap between these two missions. Furthermore, for many climate-related applications, it is also desirable to reconstruct TWSC prior to the GRACE period. In this study, we aim at comparing different data-driven methods and identifying the more robust alternatives for predicting GRACE-like gridded TWSC during the gap and reconstructing them to 1992 using climate inputs. To this end, we first develop a methodological framework to compare different methods such as the multiple linear regression (MLR), artificial neural network (ANN), and autoregressive exogenous (ARX) approaches. Second, metrics are developed to measure the robustness of the predictions. Finally, gridded TWSC within 26 regions are predicted and reconstructed using the identified methods. Test computations suggest that the correlation of predicted TWSC maps with observed ones is more than 0.3 higher than TWSC simulated by hydrological models, at the grid scale of 1° resolution. Furthermore, the reconstructed TWSC correctly reproduce the El Nino-Southern Oscillation (ENSO) signals. In general, while MLR does not perform best in the training process, it is more robust and could thus be a viable approach both for filling the GRACE gap and for reconstructing long-period TWSC fields globally when combined with statistical decomposition techniques.
    Keywords: 551.48 ; GRACE ; total water storage change ; predidicting method
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  • 107
    Publication Date: 2021-10-28
    Description: Submarine permafrost is perennially cryotic earth material that lies offshore. Most submarine permafrost is relict terrestrial permafrost beneath the Arctic shelf seas, was inundated after the last glaciation, and has been warming and thawing ever since. As a reservoir and confining layer for gas hydrates, it has the potential to release greenhouse gasses and impact coastal infrastructure, but its distribution and rate of thaw are poorly constrained by observational data. Lengthening summers, reduced sea ice extent and increased solar heating will increase water temperatures and thaw rates. Observations of gas release from the East Siberian shelf and high methane concentrations in the water column and air above it have been attributed to flowpaths created in thawing permafrost. In this context, it is important to understand the distribution and state of submarine permafrost and how they are changing. We assemble recent and historical drilling data on regional submarine permafrost degradation rates and review recent studies that use modelling, geophysical mapping and geomorphology to characterize submarine permafrost. Implications for submarine permafrost thawing are discussed within the context of methane cycling in the Arctic Ocean and global climate change.
    Keywords: 551.38 ; Arctic ; offshore ; submarine permafrost ; subsea ; thaw rates
    Language: English
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  • 108
    Publication Date: 2021-10-28
    Description: It is widely assumed that the ventilation of the Southern Ocean played a crucial role in driving glacial-interglacial atmospheric CO2 levels. So far, however, ventilation records from the Indian sector of the Southern Ocean are widely missing. Here we present reconstructions of water residence times (depicted as ΔΔ14C and Δδ13C) for the last 32,000 years on sediment records from the Kerguelen Plateau and the Conrad Rise (~570- to 2,500-m water depth), along with simulated changes in ocean stratification from a transient climate model experiment. Our data indicate that Circumpolar Deep Waters in the Indian Ocean were part of the glacial carbon pool. At our sites, close to or bathed by upwelling deep waters, we find two pulses of decreasing ΔΔ14C and δ13C values (~21–17 ka; ~15–12 ka). Both transient pulses precede a similar pattern in downstream intermediate waters in the tropical Indian Ocean as well as rising atmospheric CO2 values. These findings suggest that 14C-depleted, CO2-rich Circumpolar Deep Water from the Indian Ocean contributed to the rise in atmospheric CO2 during Heinrich Stadial 1 and also the Younger Dryas and that the southern Indian Ocean acted as a gateway for sequestered carbon to the atmosphere and tropical intermediate waters.
    Keywords: 551 ; radiocarbon ; ventilation ; Southern Ocean ; Younger Dryas ; carbon cycle ; Indian Ocean
    Language: English
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  • 109
    Publication Date: 2021-10-28
    Description: There is a converging body of evidence supporting a measurable slowdown of the Atlantic Meridional Overturning Circulation (AMOC) as climate warms and Northern Hemisphere ice sheets inexorably shrink. Within this context, we assess the variability of the AMOC during the Holocene based on a marine sediment core retrieved from the deep northwest Atlantic, which sensitively recorded large-scale deglacial transitions in deep water circulation. While there is a diffuse notion of Holocene variability in Labrador and Nordic Seas overturning, we report a largely invariable deep water circulation for the last ~11,000 years, even during the meltwater pulse associated with the 8.2-ka event. Sensitivity tests along with high-resolution 231Pa/230Th data constrain the duration and the magnitude of possible Holocene AMOC variations. The generally constant baseline during the Holocene suggests attenuated natural variability of the large-scale AMOC on submillennial timescales and calls for compensating effects involving the upstream components of North Atlantic Deep Water.
    Keywords: 551 ; AMOC ; Holocene ; high resolution 231Pa/230Th ; Bermuda Rise ; sensitivity tests
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  • 110
    Publication Date: 2021-10-28
    Description: The role of spawning salmonids in altering river bed morphology and sediment transport is significant, yet poorly understood. This is due, in large part, to limitations in monitoring the redd-building process in a continuous and spatially extended way. A complementary approach may be provided through the use of a small seismic sensor network analysing the ground motion signals generated by the agitation of sediment during the redd-building process. We successfully tested the viability of this approach by detecting and locating artificially generated redd signals in a reach of the Mashel River, Washington State, USA. We then utilize records of 17 seismic stations, in which we automatically detected seismic events that were subsequently manually checked, yielding a catalogue of 45 potential redd-building events. Such redd-building events typically lasted between 1 and 20 min and consisted of a series of clusters of 50–100 short energetic pulses in the 20–60 Hz frequency range. The majority (〉90%) of these redd-building events occurred within 11 days, predominantly during the early morning and late afternoon. The seismically derived locations of the signals were in agreement with independently mapped redds. Improved network geometry and installation conditions are required for more efficient detection, robust location and improved energetic insights into redd-building processes in larger reaches. The passive and continuous nature of the seismic approach in detecting redds and describing fish behaviour provides a novel tool for fish biologists and fisheries managers, but also for fluvial geomorphologists, interested in quantifying the amount of sediment mobilized by this ecosystem engineer. When complemented with classic approaches, it could allow for a more holistic picture of the kinetics and temporal patterns (at scales from seconds to multiple seasons) of a key phase of salmonid life cycles. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd
    Keywords: 550 ; environmental seismology ; ecosystem engineers ; salmonid spawning ; gravel-bed rivers ; biogeomorphology
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  • 111
    Publication Date: 2021-10-28
    Description: The magnetic equator in the Brazilian region has moved over 1,100 km northward since 1957, passing the geomagnetic observatory Tatuoca (TTB), in northern Brazil, around 2013. We recovered and processed TTB hourly mean values of the geomagnetic field horizontal (H) component from 1957 until 2019, allowing the investigation of long-term changes in the daily variation due to the influence of secular variation, solar activity, season, and lunar phase. The H day-to-day variability and the occurrence of the counter electrojet at TTB were also investigated. Until the 1990s, ionospheric solar quiet currents dominated the quiet-time daily variation at TTB. After 2000, the magnitude of the daily variation became appreciably greater due to the equatorial electrojet (EEJ) contribution. The H seasonal and day-to-day variability increased as the magnetic equator approached, but their amplitudes normalized to the average daily variation remained at similar levels. Meanwhile, the amplitude of the lunar variation, normalized in the same way, increased from 5% to 12%. Within the EEJ region, the occurrence rate of the morning counter electrojet (MCEJ) increased with proximity to the magnetic equator, while the afternoon counter electrojet (ACEJ) did not. EEJ currents derived from CHAMP and Swarm satellite data revealed that the MCEJ rate varies with magnetic latitude within the EEJ region while the ACEJ rate is largely constant. Simulations with the Thermosphere-Ionosphere-Electrodynamics General Circulation Model based on different geomagnetic main field configurations suggest that long-term changes in the geomagnetic daily variation at TTB can be attributed to the main field secular variation.
    Keywords: 538.7 ; geomagnetism ; space physics ; geomagnetic daily variation ; solar quiet currents ; equatorial electrojet ; equatorial ionosphere
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  • 112
    Publication Date: 2021-10-28
    Description: The presence of gas hydrates (GHs) increases the stiffness and strength of marine sediments. In elasto-plastic constitutive models, it is common to consider GH saturation (Sh) as key internal variable for defining the contribution of GHs to composite soil mechanical behavior. However, the stress-strain behavior of GH-bearing sediments (GHBS) also depends on the microscale distribution of GH and on GH-sediment fabrics. A thorough analysis of GHBS is difficult, because there is no unique relation between Sh and GH morphology. To improve the understanding of stress-strain behavior of GHBS in terms of established soil models, this study summarizes results from triaxial compression tests with different Sh, pore fluids, effective confining stresses, and strain histories. Our data indicate that the mechanical behavior of GHBS strongly depends on Sh and GH morphology, and also on the strain-induced alteration of GH-sediment fabrics. Hardening-softening characteristics of GHBS are strain rate-dependent, which suggests that GH-sediment fabrics dynamically rearrange during plastic yielding events. We hypothesize that rearrangement of GH-sediment fabrics, through viscous deformation or transient dissociation and reformation of GHs, results in kinematic hardening, suppressed softening, and secondary strength recovery, which could potentially mitigate or counteract large-strain failure events. For constitutive modeling approaches, we suggest that strain rate-dependent micromechanical effects from alterations of the GH-sediment fabrics can be lumped into a nonconstant residual friction parameter. We propose simple empirical evolution functions for the mechanical properties and calibrate the model parameters against the experimental data.
    Keywords: 550.78 ; Gas hydrate-bearing sediments ; High-pressure studies ; THCM modelling ; Geomechanics ; Slope stability ; Gas seeps
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  • 113
    Publication Date: 2021-10-28
    Description: In surface waters, the illumination of photoactive engineered nanomaterials (ENMs) with ultraviolet (UV) light triggers the formation of reactive intermediates, consequently altering the ecotoxicological potential of co-occurring organic micropollutants including pesticides due to catalytic degradation. Simultaneously, omnipresent natural organic matter (NOM) adsorbs onto ENM surfaces, altering the ENM surface properties. Also, NOM absorbs light, reducing the photo(cata)lytic transformation of pesticides. Interactions between these environmental factors impact 1) directly the ecotoxicity of photoactive ENMs, and 2) indirectly the degradation of pesticides. We assessed the impact of field-relevant UV radiation (up to 2.6 W UVA/m²), NOM (4 mg TOC/L), and photoactive ENM (nTiO2, 50 µg/L) on the acute toxicity of 6 pesticides in Daphnia magna. We selected azoxystrobin, dimethoate, malathion, parathion, permethrin, and pirimicarb because of their varying photo- and hydrolytic stabilities. Increasing UVA alone partially reduced pesticide toxicity, seemingly due to enhanced degradation. Even at 50 µg/L, nano-sized titanium dioxide (nTiO2) reduced but also increased pesticide toxicity (depending on the applied pesticide), which is attributable to 1) more efficient degradation and potentially 2) photocatalytically induced formation of toxic by-products. Natural organic matter 1) partially reduced pesticide toxicity, not evidently accompanied by enhanced pesticide degradation, but also 2) inhibited pesticide degradation, effectively increasing the pesticide toxicity. Predicting the ecotoxicological potential of pesticides based on their interaction with UV light or interaction with NOM was hardly possible, which was even more difficult in the presence of nTiO2. Environ Toxicol Chem 2020;39:2237–2246. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.
    Keywords: 363.73 ; Photolysis ; Photocatalysis ; Titanium dioxide ; Pesticide ; UV radiation ; Natural organic matter
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  • 114
    Publication Date: 2021-10-28
    Description: Gelatinous zooplankton (Cnidaria, Ctenophora, and Urochordata, namely, Thaliacea) are ubiquitous members of plankton communities linking primary production to higher trophic levels and the deep ocean by serving as food and transferring “jelly-carbon” (jelly-C) upon bloom collapse. Global biomass within the upper 200 m reaches 0.038 Pg C, which, with a 2–12 months life span, serves as the lower limit for annual jelly-C production. Using over 90,000 data points from 1934 to 2011 from the Jellyfish Database Initiative as an indication of global biomass (JeDI: http://jedi.nceas.ucsb.edu, http://www.bco-dmo.org/dataset/526852), upper ocean jelly-C biomass and production estimates, organism vertical migration, jelly-C sinking rates, and water column temperature profiles from GLODAPv2, we quantitatively estimate jelly-C transfer efficiency based on Longhurst Provinces. From the upper 200 m production estimate of 0.038 Pg C year−1, 59–72% reaches 500 m, 46–54% reaches 1,000 m, 43–48% reaches 2,000 m, 32–40% reaches 3,000 m, and 25–33% reaches 4,500 m. This translates into ~0.03, 0.02, 0.01, and 0.01 Pg C year−1, transferred down to 500, 1,000, 2,000, and 4,500 m, respectively. Jelly-C fluxes and transfer efficiencies can occasionally exceed phytodetrital-based sediment trap estimates in localized open ocean and continental shelves areas under large gelatinous blooms or jelly-C mass deposition events, but this remains ephemeral and transient in nature. This transfer of fast and permanently exported carbon reaching the ocean interior via jelly-C constitutes an important component of the global biological soft-tissue pump, and should be addressed in ocean biogeochemical models, in particular, at the local and regional scale.
    Keywords: 577.1 ; Jelly-C ; carbon ; gelatinous ; zooplankton ; modeling ; transfer efficiency
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  • 115
    Publication Date: 2021-10-28
    Description: Due to seasonal or interannual variability, the relevance of hydrological processes and of the associated model parameters can vary significantly throughout the simulation period. To achieve accurately identified model parameters, temporal variations in parameter dominance should be taken into account. This is not achieved if performance criteria are applied to the entire model output time series. Even when using complementary performance criteria, it is often only possible to identify some of the model parameters precisely. We present an innovative approach to improve parameter identifiability that exploits the information available regarding temporal variations in parameter dominance. Using daily parameter sensitivity time series, we construct a set of sensitivity-weighted performance criteria, one for each parameter, whereby periods of higher dominance of a model parameter and its corresponding process are assigned higher weights in the calculation of the associated performance criterion. These criteria are used to impose constraints on parameter values. We demonstrate this approach by constraining 12 model parameters for three catchments and examine ensemble hydrological simulations generated using these constrained parameter sets. The sensitivity-weighted approach improves in particular the identifiability for parameters whose corresponding processes are dominant only for short periods of time or have strong seasonal patterns. This results overall in slight improvement of model performance for a set of 10 contrasting performance criteria. We conclude that the sensitivity-weighted approach improves the extraction of hydrologically relevant information from data, thereby resulting in improved parameter identifiability and better representation of model parameters.
    Keywords: 551.48 ; parameter identifiability ; parameter constraints ; temporal diagnostic analysis ; sensitivity analysis ; performance criteria
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  • 116
    Publication Date: 2021-10-29
    Description: Tunnel valleys are major features of glaciated margins and they enable meltwater expulsion from underneath a thick ice cover. Their formation is related to the erosion of subglacial sediments by overpressured meltwater and direct glacial erosion. Yet, the impact of pre-existing structures on their formation and morphology remains poorly known. High-quality 3D seismic data allowed the mapping of a large tunnel valley that eroded underlying preglacial delta deposits in the southern North Sea. The valley follows the N–S strike of crestal faults related to a Zechstein salt wall. A change in downstream tunnel valley orientation towards the SE accompanies a change in the strike direction of salt-induced faults. Fault offsets indicate important activity of crestal faults during the deposition of preglacial deltaic sediments. We propose that crestal faults facilitated tunnel valley erosion by acting as high-permeability pathways and allowing subglacial meltwater to reach low-permeability sediments in the underlying Neogene deltaic sequences, ultimately resulting in meltwater overpressure build-up and tunnel valley excavation. Active faults probably also weakened the near-surface sediment to allow a more efficient erosion of the glacial substrate. This control of substrate structures on tunnel valley morphology is considered as a primary factor in subglacial drainage pattern development in the study area.
    Keywords: 551 ; southern North Sea ; Quarternary ; tunnel valley formation ; salt-induced faults
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  • 117
    Publication Date: 2021-10-29
    Description: Soil and lake sediments are important paleoclimate archives often forming a source-sink setting. To better understand magnetic properties in such settings, we studied red soil on low-magnetic bedrock and subrecent sediments of Caohai Lake (CL) in Heqing Basin, China. Red soil is the only important source material for the CL sediments, it is highly magnetic with susceptibilities (χ) of ~10−5 m3/kg. The red soil is dominated by pedogenic nano-magnetite (~10–15 nm) arranged in aggregates of ~100 nm, with particle interaction that causes a wide effective grain size distribution in the superparamagnetic (SP) range tailing into stable single-domain behavior. Transmission electron microscopy and broadband frequency χ(f) suggest partial disintegration of the aggregates and increased alteration of the nanoparticles to hematite during transfer of red soil material to CL. This shifts the domain state behavior to smaller effective magnetic grain sizes, resulting in lower χfd% and χ values, and a characteristic change of χ(f). The SP-stable single-domain distribution of the aggregates in red soil could be climate dependent, and the ratio of saturation remanence to χ is a potential bedrock-specific paleoclimate proxy reflecting it. Magnetic properties of the CL sediments are controlled by an assemblage of nanoparticle aggregates and larger-sized bedrock-derived magnetite. The results challenge the validity of the previous paleoclimate interpretation from the 168-m-long Core-HQ (900–30 ka) in Heqing Basin. Disintegration of aggregates could lead to SP behavior with low χfd% without extinction of individual magnetite nanoparticles, and the χfd%-based assumption of SP magnetite dissolution may be wrong.
    Keywords: 549 ; Heqing Basin ; lake sediments ; red soils ; magnetite ; magnetic signatures
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  • 118
    Publication Date: 2021-10-29
    Description: The monitoring of water quality, especially of karst springs, requires methods for rapidly estimating and quantifying parameters that indicate contamination. In the last few years, fluorescence-based measurements of tryptophan and humic acid have become a promising tool to assess water quality in near real-time. In this study, we conducted comparative tracer tests in a karst experimental site to investigate the transport properties and behavior of tryptophan and humic acid in a natural karst aquifer. These two tracers were compared with the conservative tracer uranine. Fluorescence measurements were conducted with an online field fluorometer and in the laboratory. The obtained breakthrough curves (BTCs) and the modeling results demonstrate that (1) the online field fluorometer is suitable for real-time fluorescence measurements of all three tracers; (2) the transport parameters obtained for uranine, tryptophan, and humic acid are comparable in the fast flow areas of the karst system; (3) the transport velocities of humic acid are slower and the resulting residence times are accordingly higher, compared to uranine and tryptophan, in the slower and longer flow paths; (4) the obtained BTCs reveal additional information about the investigated karst system. As a conclusion, the experiments show that the transport properties of tryptophan are similar to those of uranine while humic acid is partly transported slower and with retardation. These findings allow a better and quantitative interpretation of the results when these substances are used as natural fecal and contamination indicators.
    Keywords: 363.61 ; karst aquifer ; water quality ; monitoring ; tracer tests
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  • 119
    Publication Date: 2021-10-29
    Description: This article proposes a novel method for the 3D reconstruction of LoD2 buildings from LiDAR data. We propose an active sampling strategy which applies a cascade of filters focusing on promising samples at an early stage, thus avoiding the pitfalls of RANSAC-based approaches. Filters are based on prior knowledge represented by (nonparametric) density distributions. In our approach samples are pairs of surflets—3D points together with normal vectors derived from a plane approximation of their neighborhood. Surflet pairs provide parameters for model candidates such as azimuth, inclination and ridge height, as well as parameters estimating internal precision and consistency. This provides a ranking of roof model candidates and leads to a small number of promising hypotheses. Building footprints are derived in a preprocessing step using machine learning methods, in particular support vector machines.
    Keywords: 526 ; roof structures ; building models ; automatic derivation ; LiDAR Data
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  • 120
    Publication Date: 2021-10-29
    Description: Intense farming is often associated with the excessive use of manure or fertilizers and the subsequent deterioration of the groundwater quality in many aquifers worldwide. Stable isotopes of dissolved nitrate (δ15N and δ18O) are widely used to determine sources of nitrate contamination and denitrification processes in groundwater but are often difficult to interpret. Thus, Monte Carlo simulations were carried out for a site in lower Bavaria, Germany, in order to explain δ15N observations in a porous groundwater system with two aquifers, the main aquifer (MA) and several smaller perched aquifers (PA). For evaluating potential contributions, frequency distributions of δ15N were simulated deriving from (I) the mixing of different nitrate sources, related to land use, as input to groundwater, combined with (II) transport of nitrate in groundwater and (III) microbial denitrification. Simulation results indicate a source-driven isotopic shift to heavier δ15N values of nitrate in groundwater, which may be explained by land use changes toward a more intensified agriculture releasing high amounts of manure. Microbial denitrification may play a role in the PA, with simulated δ15N distributions close to the observations. Denitrification processes are however unlikely for the MA, as reasonable simulation curve fits for such a scenario were obtained predominantly for unrealistic portions of nitrate sources and related land use. The applied approach can be used to qualitatively and quantitatively evaluate the influence of different potential contributions, which might mask each other due to overlapping δ15N ranges, and it can support the estimation of nitrate input related to land use.
    Keywords: 553.79 ; groundwater ; nitrate contamination ; denitrification ; interpretation
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  • 121
    Publication Date: 2021-10-29
    Description: The timing and mechanisms of the Cretaceous sea incursions into Central Asia are still poorly constrained. We provide a new chronostratigraphic framework based on biostratigraphy and magnetostratigraphy together with detailed paleoenvironmental analyses of Cretaceous records of the proto-Paratethys Sea fluctuations in the Tajik and Tarim basins. The Early Cretaceous marine incursion in the western Tajik Basin was followed by major marine incursions during the Cenomanian (ca. 100 Ma) and Santonian (ca. 86 Ma) that reached far into the eastern Tajik and Tarim basins. These marine incursions were separated by a Turonian-Coniacian (ca. 92–86 Ma) regression. Basin-wide tectonic subsidence analyses imply that the Early Cretaceous sea incursion into the Tajik Basin was related to increased Pamir tectonism. We find that thrusting along the northern edge of the Pamir at ca. 130–90 Ma resulted in increased subsidence in a retro-arc basin setting. This tectonic event and coeval eustatic highstand resulted in the maximum observed geographic extent of the sea during the Cenomanian (ca. 100 Ma). The following Turonian-Coniacian (ca. 92–86 Ma) major regression, driven by eustasy, coincides with a sharp slowdown in tectonic subsidence during the late orogenic unloading period with limited thrusting. The Santonian (ca. 86 Ma) major sea incursion was likely controlled by eustasy as evidenced by the coeval fluctuations in the west Siberian Basin. An early Maastrichtian cooling (ca. 71–70 Ma), potentially connected to global Late Cretaceous trends, is inferred from the replacement of mollusk-rich limestones by bryozoan- and echinoderm-rich limestones.
    Keywords: 551 ; Tajik Basin ; Tarim Basin ; Cretaceous sea incursions ; tectonic subsidence ; proto‐Paratethys Sea
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  • 122
    Publication Date: 2021-10-29
    Description: Chytrid fungal parasites are ubiquitous in aquatic ecosystems and infect a wide array of aquatic organisms, including all phytoplankton groups. In addition to their role as parasites, chytrids serve as food to zooplankton, thereby establishing an alternative trophic link between primary and secondary production in pelagic food webs, the so-called mycoloop. We hypothesized that, in addition to the mycoloop, chytrid infection facilitates grazing of filamentous phytoplankton by rendering it more edible to zooplankton consumers through infection-induced fragmentation. We undertook grazing assays to compare the ability of the key zooplankter Daphnia to graze on a filamentous cyanobacterium in the presence or absence of chytrid infection. A near doubling in mean clearance rates was consistently recorded when Daphnia were fed with infected cultures of the cyanobacterium as compared to uninfected ones. Infected filaments were shorter than noninfected ones, indicating that infection-induced fragmentation undermines resistance of filamentous phytoplankton to grazing. We propose an extended conceptualization of the mycoloop that includes both direct effects (i.e., transfer via grazing of chytrid zoospores) and indirect effects (i.e., trophic upgrading and facilitated grazing on phytoplankton via fragmentation) of chytrid infection on trophic transfer at the base of pelagic food webs.
    Keywords: 579 ; 550.78 ; pelagic food web ; fungal parasites ; increasing ecosystem stability ; experiments
    Language: English
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  • 123
    Publication Date: 2021-10-29
    Description: Columnar jointed lava is an important facies in many geothermal reservoir systems. The permeability of jointed lavas is dominated by the contribution from fracture networks. We use a scaling for the permeability of a set of fractures in a solid or porous mass and extend this to arrays of hexagonal intercolumn fractures. To validate our analytical results, we create numerical domains with relevant geometries and extract system-scale permeability using the LBflow lattice-Boltzmann fluid flow simulation tool. Finally, we model the cooling contraction of columns to extend our results so that they predict the permeability with time after lava emplacement. Importantly, we use these results to estimate the range of permeabilities typical of columnar joints that form during cooling from high temperature and are preserved in the crust at moderate to low temperatures.
    Keywords: 551 ; fractured lavas ; permeability ; prediction
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  • 124
    Publication Date: 2021-09-27
    Description: At regional to local scales internal variability is expected to be a dominant source of uncertainty in analyzing precipitation extremes and mean precipitation even far into the 21st century. A debated topic is whether a faster increase in subdaily precipitation extremes can be expected. Here we analyzed seasonal maximum precipitation in various time steps (3 hr, days, and 5 days) from a high-resolution 50-member large-ensemble (CRCM5-LE) and compared them to changes in mean precipitation over Europe. Our results show that the magnitude of change in extreme precipitation varies for season and duration. Subdaily extremes increase at higher rates than daily extremes and show higher scaling with temperature. Northern Europe shows widespread scaling above Clausius-Clapeyron of subdaily extremes in all seasons and for daily extremes in winter/spring. Scaling above Clausius-Clapeyron is also visible over Eastern Europe in winter/spring. For most regions and seasons the forced response emerges from the internal variability by midcentury.
    Keywords: 551.6 ; large ensembles ; SMILEs ; Regional Climate Model ; precipitation extremes ; subdaily ; Europe
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  • 125
    Publication Date: 2021-09-27
    Description: In the Antarctic ozone hole, ozone mixing ratios have been decreasing to extremely low values of 0.01–0.1 ppm in nearly all spring seasons since the late 1980s, corresponding to 95–99% local chemical loss. In contrast, Arctic ozone loss has been much more limited and mixing ratios have never before fallen below 0.5 ppm. In Arctic spring 2020, however, ozonesonde measurements in the most depleted parts of the polar vortex show a highly depleted layer, with ozone loss averaged over sondes peaking at 93% at 18 km. Typical minimum mixing ratios of 0.2 ppm were observed, with individual profiles showing values as low as 0.13 ppm (96% loss). The reason for the unprecedented chemical loss was an unusually strong, long-lasting, and cold polar vortex, showing that for individual winters the effect of the slow decline of ozone-depleting substances on ozone depletion may be counteracted by low temperatures.
    Keywords: 551.9 ; ozone ; stratosphere ; ozone loss ; Arctic ; ozone hole ; temperature
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  • 126
    Publication Date: 2021-09-27
    Description: To account for model error on multiple scales in convective-scale data assimilation, we incorporate the small-scale additive noise based on random samples of model truncation error and combine it with the large-scale additive noise based on random samples from global climatological atmospheric background error covariance. A series of experiments have been executed in the framework of the operational Kilometre-scale ENsemble Data Assimilation system of the Deutscher Wetterdienst for a 2-week period with different types of synoptic forcing of convection (i.e., strong or weak forcing). It is shown that the combination of large- and small-scale additive noise is better than the application of large-scale noise only. The specific increase in the background ensemble spread during data assimilation enhances the quality of short-term 6-hr precipitation forecasts. The improvement is especially significant during the weak forcing period, since the small-scale additive noise increases the small-scale variability which may favor occurrence of convection. It is also shown that additional perturbation of vertical velocity can further advance the performance of combination.
    Keywords: 551.5 ; additive noise ; model truncation error ; multiscale ; radar data assimilation ; probabilistic forecasts
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  • 127
    Publication Date: 2021-09-27
    Description: Micron-sized HNO3-containing particles in polar stratospheric clouds are known to denitrify the polar winter stratosphere and support chemical ozone loss. We show that populations of nitric acid trihydrate (NAT) particles with volume-equivalent median radii of 3–7 μm can be detected vortex-wide by means of infrared limb sounding. Key for detection are the applied optical characteristics of highly aspherical particles consisting of the β-NAT phase. Spectroscopic signatures and ambient conditions of detected populations show that these particles play a key role in denitrification of the Arctic winter stratosphere. Complementary gas-phase HNO3 observations indicate collocated highly efficient HNO3 sequestration within days and are consistent with measured spectral signals of populations of large NAT particles. High amounts of condensed gas-phase equivalent HNO3 exceeding 10 ppbv and long persistence of detected populations, despite expected gravitational settling, imply that our understanding of the particles is incomplete.
    Keywords: 551.9 ; polar winter ; stratosphere ; denitrification ; nitric acid trihydrate ; infrared limb sounding
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  • 128
    Publication Date: 2021-09-27
    Description: Fatty acid (FA) compositions provide insights about storage and feeding modes of marine organisms, characterizing trophic relationships in the marine food web. Such compositional data, which are normalized to sum to 1, have values—and thus derived statistics as well—that depend on the particular mix of components that constitute the composition. In FA studies, if the set of FAs under investigation is different in two separate studies, all the summary statistics and relationships between the FAs that are common to the two studies are artificially changed due to the normalization, and thus incomparable. Ratios of FAs, however, are invariant to the particular choice of FAs under consideration—they are said to be subcompositionally coherent. Here, we document the collaboration between a biochemist (M.G.) and a statistician (M.J.G.) to determine a suitable small set of FA ratios that effectively replaces the original data set for the purposes of univariate and multivariate analysis. This strategy is applied to two FA data sets, on copepods and amphipods, respectively, and is widely applicable in other contexts. The selection of ratios is performed in such a way as to satisfy substantive requirements in the context of the respective data set, namely to explain phenomena of interest relevant to the particular species, as well as the statistical requirement to explain as much variance in the FA data set as possible. Benefits of this new approach are (1) univariate statistics that can be validly compared between different studies, and (2) a simplified multivariate analysis of the reduced set of ratios, giving practically the same results as the analysis of the full FA data set.
    Keywords: 578.77
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  • 129
    Publication Date: 2021-09-27
    Description: The Global Carbon Budget 2018 (GCB2018) estimated by the atmospheric CO 2 growth rate, fossil fuel emissions, and modeled (bottom-up) land and ocean fluxes cannot be fully closed, leading to a “budget imbalance,” highlighting uncertainties in GCB components. However, no systematic analysis has been performed on which regions or processes contribute to this term. To obtain deeper insight on the sources of uncertainty in global and regional carbon budgets, we analyzed differences in Net Biome Productivity (NBP) for all possible combinations of bottom-up and top-down data sets in GCB2018: (i) 16 dynamic global vegetation models (DGVMs), and (ii) 5 atmospheric inversions that match the atmospheric CO 2 growth rate. We find that the global mismatch between the two ensembles matches well the GCB2018 budget imbalance, with Brazil, Southeast Asia, and Oceania as the largest contributors. Differences between DGVMs dominate global mismatches, while at regional scale differences between inversions contribute the most to uncertainty. At both global and regional scales, disagreement on NBP interannual variability between the two approaches explains a large fraction of differences. We attribute this mismatch to distinct responses to El Niño–Southern Oscillation variability between DGVMs and inversions and to uncertainties in land use change emissions, especially in South America and Southeast Asia. We identify key needs to reduce uncertainty in carbon budgets: reducing uncertainty in atmospheric inversions (e.g., through more observations in the tropics) and in land use change fluxes, including more land use processes and evaluating land use transitions (e.g., using high-resolution remote-sensing), and, finally, improving tropical hydroecological processes and fire representation within DGVMs.
    Keywords: 551.9 ; atmospheric inversions ; global carbon budget ; dynamic global vegetation models ; carbon cycle
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  • 130
    Publication Date: 2021-09-27
    Description: The magnitudes of river floods in Europe have been observed to change, but their alignment with changes in the spatial coverage or extent of individual floods has not been clear. We analyze flood magnitudes and extents for 3,872 hydrometric stations across Europe over the past five decades and classify each flood based on antecedent weather conditions. We find positive correlations between flood magnitudes and extents for 95% of the stations. In central Europe and the British Isles, the association of increasing trends in magnitudes and extents is due to a magnitude-extent correlation of precipitation and soil moisture along with a shift in the flood generating processes. The alignment of trends in flood magnitudes and extents highlights the increasing importance of transnational flood risk management.
    Keywords: 551.48 ; flood ; synchrony ; magnitude ; climate change ; classification ; spatial statistics
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  • 131
    Publication Date: 2021-09-27
    Description: This investigation attempts to understand the eco-hydrology of, and accordingly suggest an option to manage floodwater for agriculture in, the understudied and data-sparse ephemeral Baraka River Basin within the hyper-arid region of Sudan. Reference is made to the major feature of the basin, that is, the Toker Delta spate irrigation scheme. A point-to-pixel comparison of gridded and ground-based data sets is performed to enhance the estimates of rainfall. Analysis of remotely sensed land use/cover data is performed. The results show a significant reduction of the grassland and barren areas explained by a significant expansion of the cropland and open shrubland (invasive mesquite trees) areas in the delta. The cotton sown area is highly dependent on the flooded area and the discharge volume in the delta. However, the area of this major crop has declined since the early 1990s in favour of cultivation of more profitable food crops. Expansion of mesquite in the delta is problematic, taking hold under increased floodwater, and can only be manged by clearance to provide crop cultivation area. There is a great potential for floodwater harvesting during the rainfall season (June to September). A total seasonal runoff volume of around 4.6 and 10.8 billion cubic metres is estimated at 90 and 50% probabilities of exceedance (reliabilities), respectively. Rather than leaving the runoff generated from rainfall events to pass to the Red Sea or be consumed by mesquite trees, a location for runoff harvesting structure in a highly suitable area is proposed. Such a structure will support any policy shifts towards planning and managing the basin water resources for use in irrigating the agricultural scheme.
    Keywords: 551.48 ; Baraka River Basin ; eco-hydrology ; floodwater harvesting ; land-cover classification ; Mesquite ; Toker Delta
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  • 132
    Publication Date: 2021-09-27
    Description: Rockwall slope erosion is defined for the upper Bhagirathi catchment using cosmogenic Beryllium-10 (10Be) concentrations in sediment from medial moraines on Gangotri glacier. Beryllium-10 concentrations range from 1.1 ± 0.2 to 2.7 ± 0.3 × 104 at/g SiO2, yielding rockwall slope erosion rates from 2.4 ± 0.4 to 6.9 ± 1.9 mm/a. Slope erosion rates are likely to have varied over space and time and responded to shifts in climate, geomorphic and/or tectonic regime throughout the late Quaternary. Geomorphic and sedimentological analyses confirm that the moraines are predominately composed of rockfall and avalanche debris mobilized from steep relief rockwall slopes via periglacial weathering processes. The glacial rockwall slope erosion affects sediment flux and storage of snow and ice at the catchment head on diurnal to millennial timescales, and more broadly influences catchment configuration and relief, glacier dynamics and microclimates. The slope erosion rates exceed the averaged catchment-wide and exhumation rates of Bhagirathi and the Garhwal region on geomorphic timescales (103−105 years), supporting the view that erosion at the headwaters can outpace the wider catchment. The 10Be concentrations of medial moraine sediment for the upper Bhagirathi catchment and the catchments of Chhota Shigri in Lahul, northern India and Baltoro glacier in Central Karakoram, Pakistan show a tentative relationship between 10Be concentration and precipitation. As such there is more rapid glacial rockwall slope erosion in the monsoon-influenced Lesser and Greater Himalaya compared to the semi-arid interior of the orogen. Rockwall slope erosion in the three study areas, and more broadly across the northwest Himalaya is likely governed by individual catchment dynamics that vary across space and time. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons, Ltd.
    Keywords: 551.3 ; supraglacial processes ; sediment flux ; glacier ; climate ; cosmogenic isotopes
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  • 133
    Publication Date: 2021-09-27
    Description: It is shown that it is possible to perform combined X-ray and neutron single-crystal studies in the same diamond anvil cell (DAC). A modified Merrill–Bassett DAC equipped with an inflatable membrane filled with He gas has been developed. It can be used on laboratory X-ray and synchrotron diffractometers as well as on neutron instruments. The data processing procedures and a joint structural refinement of the high-pressure synchrotron and neutron single-crystal data are presented and discussed for the first time.
    Keywords: 548 ; single-crystal X-ray diffraction ; single-crystal neutron diffraction ; high pressure ; diamond anvil cells
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  • 134
    Publication Date: 2021-09-27
    Description: Clouds interact with atmospheric radiation and substantially modify the Earth's energy budget. Cloud formation processes occur over a vast range of spatial and temporal scales, which make their thorough numerical representation challenging. Therefore, the impact of parameter choices for simulations of cloud-radiative effects is assessed in the current study. Numerical experiments are carried out using the ICOsahedral Nonhydrostatic (ICON) model with varying grid spacings between 2.5 and 80 km and with different subgrid-scale parameterization approaches. Simulations are performed over the North Atlantic with either one-moment or two-moment microphysics and with convection being parameterized or explicitly resolved by grid-scale dynamics. Simulated cloud-radiative effects are compared to products derived from Meteosat measurements. Furthermore, a sophisticated cloud classification algorithm is applied to understand the differences and dependencies of simulated and observed cloud-radiative effects. The cloud classification algorithm developed for the satellite observations is also applied to the simulation output based on synthetic infrared brightness temperatures, a novel approach that is not impacted by changing insolation and guarantees a consistent and fair comparison. It is found that flux biases originate equally from clear-sky and cloudy parts of the radiation field. Simulated cloud amounts and cloud-radiative effects are dominated by marine, shallow clouds, and their behavior is highly resolution dependent. Bias compensation between shortwave and longwave flux biases, seen in the coarser simulations, is significantly diminished for higher resolutions. Based on the analysis results, it is argued that cloud-microphysical and cloud-radiative properties have to be adjusted to further improve agreement with observed cloud-radiative effects.
    Keywords: 551.5 ; Cloud-Radiative Effects ; TOA Energy Budget ; High-Resolution Simulations ; Meteosat Observations ; Cloud Classification ; Bias Decomposition
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  • 135
    Publication Date: 2021-09-27
    Description: An abundance of evidence indicates that the tropics are expanding. Despite many attempts to decipher the cause, the underlying dynamical mechanism driving tropical expansion is still not entirely clear. Here, based on observations, multimodel simulations from the Coupled Model Intercomparison Project phase 5 (CMIP5) and purposefully designed numerical experiments, the variations and trends of the tropical width are explored from a regional perspective. We find that the width of the tropics closely follows the displacement of oceanic midlatitude meridional temperature gradients (MMTG). Under global warming, as a first-order response, the subtropical ocean experiences more surface warming because of the mean Ekman convergence of anomalously warm water. The enhanced subtropical warming, which is partially independent of natural climate oscillations, such as the Pacific Decadal Oscillation, leads to poleward advance of the MMTG and drives the tropical expansion. Our results, supported by both observations and model simulations, imply that global warming may have already significantly contributed to the ongoing tropical expansion, especially over the ocean-dominant Southern Hemisphere.
    Keywords: 551.6 ; Tropical Expansion ; Ocean Circulation ; Jet Stream ; Storm Track ; Mid-latitude Temperature Gradients ; Global Warming
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  • 136
    Publication Date: 2021-09-27
    Description: How the solar electromagnetic energy entering the Earth's atmosphere varied since preindustrial times is an important consideration in the climate change debate. Detrimental to this debate, estimates of the change in total solar irradiance (TSI) since the Maunder minimum, an extended period of weak solar activity preceding the industrial revolution, differ markedly, ranging from a drop of 0.75 W m−2 to a rise of 6.3 W m−2. Consequently, the exact contribution by solar forcing to the rise in global temperatures over the past centuries remains inconclusive. Adopting a novel approach based on state-of-the-art solar imagery and numerical simulations, we establish the TSI level of the Sun when it is in its least-active state to be 2.0 ± 0.7 W m−2 below the 2019 level. This means TSI could not have risen since the Maunder minimum by more than this amount, thus restricting the possible role of solar forcing in global warming.
    Keywords: 551.5 ; total solar irradiance
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  • 137
    Publication Date: 2021-09-27
    Description: White-beam X-ray topography has been performed to provide direct evidence of micro-voids in dislocation-free high-purity germanium single crystals. The voids are visible because of a dynamical diffraction contrast. It is shown that voids occur only in dislocation-free parts of the crystal and do not show up in regions with homogeneous and moderate dislocation density. It is further suggested that the voids originate from clustering of vacancies during the growth process. A general method is proposed to verify the presence of voids for any crystalline material of high structural perfection.
    Keywords: 548 ; X-ray topography ; dynamical theory ; high-purity germanium ; vacancies ; voids ; dislocation density ; diffraction contrast
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  • 138
    Publication Date: 2021-09-27
    Description: Vb cyclones are major drivers of extreme precipitation and floods in the study area of hydrological Bavaria (Germany). When assessing climate change impacts on Vb cyclones, internal variability of the climate system is an important underlying uncertainty. Here, we employ a 50-member single-model initial-condition large ensemble of a regional climate model to study climate variability and forced change on Vb cyclones. An artificial neural network detects cutoff lows over central Europe, which are associated with extreme precipitation Vb cyclones. Thus, machine learning filters the large ensemble prior to cyclone tracking. Our results show a striking change in Vb seasonality with a strong decrease of Vb cyclones in summer (−52%) and a large increase in spring (+73%) under the Representative Concentration Pathway 8.5. This change exceeds the noise of internal variability and leads to a peak shift from summer to spring. Additionally, we show significant increases in the daily precipitation intensity during Vb cyclones in all seasons.
    Keywords: 551.6 ; Vb-cyclones ; Machine Learning ; Artificial Neural Networks (ANN) ; Single-Model Large Ensembles ; Internal Variability ; Floods
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  • 139
    Publication Date: 2021-09-27
    Description: Integrated flood management strategies consider property-level precautionary measures as a vital part. Whereas this is a well-researched topic for residents, little is known about the adaptive behaviour of flood-prone companies although they often settle on the ground floor of buildings and are thus among the first affected by flooding. This pilot study analyses flood responses of 64 businesses in a district of the city of Dresden, Germany that experienced major flooding in 2002 and 2013. Using standardised survey data and accompanying qualitative interviews, the analyses revealed that the largest driver of adaptive behaviour is experiencing flood events. Intangible factors such as tradition and a sense of community play a role for the decision to stay in the area, while lacking ownership might hamper property-level adaptation. Further research is also needed to understand the role of insurance and governmental aid for recovery and adaptation of businesses.
    Keywords: 551.489 ; adaptation ; disaster risk reduction ; integrated flood risk management ; risk perception
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  • 140
    Publication Date: 2021-09-27
    Description: The importance of splay-thrust faults in subduction seismogenesis is increasingly acknowledged; however, their elastic interaction with the plate interface remains unclear. Here, we use GPS velocities, constrained by millennial fault slip rates, to study elastic fault-interactions between the plate interface and its upper-plate splay-thrust faults from the southern Hellenic Subduction System (HSS). We find that, despite its largely aseismic character, the HSS plate interface zone is kinematically segmented, with slip rate deficits locally reaching ~85% and ~45% of the plate convergence rate on the western and eastern segments, respectively, and on structures different from those that ruptured historically. Although western Crete has been more active seismically during late Holocene, we find that the eastern HSS has higher seismic potential for large-magnitude (M 〉 6) earthquakes and its interface zone is closer to failure. Elastic fault interactions are responsible for both significant intersegment variability in strain accumulation and uniformity in earthquake rupture segmentation along the HSS over millennial timescales.
    Keywords: 551.22 ; subduction seismogenesis ; GPS ; locking degree ; fault interactions ; earthquake rupture segmentation
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  • 141
    Publication Date: 2021-09-27
    Description: Droughts lead to falling river water levels and consequently expose river sediments. It is well known that from these exposed aquatic sediments, CO2 emits to the atmosphere, but upscaling of CO2 measurements from discrete point measurements to an entire river system remains challenging. Naturally occurring heterogeneous processes must be accounted for to obtain an overall CO2 flux and to assess its significance. We contribute to this challenge by incorporating a two stage scaling approach using in situ CO2 fluxes and remote sensing data. First, by combining optical airborne data with closed chamber measurements at a representative model site during a first scaling stage, we derive land cover type specific CO2 fluxes and identify distance to the water as the most suitable proxy for further upscaling. Second, we upscale derived spatial relations from the first scaling stage to the entire river system of the Elbe River using a satellite-based analysis. In this way, we derived area-weighted CO2 emissions from exposed river sediments of 56.6 ± 64.8 tC day−1 (corrected distance proxy) and 52.9 ± 44.6 tC day−1 (land cover proxy), respectively, for 1 day during the 2018 extreme drought. Given the intensification of droughts in terms of length and reoccurrence frequency, this result not only highlights the importance of drought-induced exposition of river sediment as a source of atmospheric CO2 but also underscores the ability to monitor CO2 emissions over an entire river system on a regular basis using remote sensing.
    Keywords: 551.48 ; carbon dioxide emission ; chamber measurements ; hydrological drought ; Sentinel-2 ; upscaling
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  • 142
    Publication Date: 2021-09-27
    Description: Abstract In mixed bedrock–alluvial rivers, the response of the system to a flood event can be affected by a number of factors, including coarse sediment availability in the channel, sediment supply from the hillslopes and upstream, flood sequencing and coarse sediment grain size distribution. However, the impact of along-stream changes in channel width on bedload transport dynamics remains largely unexplored. We combine field data, theory and numerical modelling to address this gap. First, we present observations from the Daan River gorge in western Taiwan, where the river flows through a 1 km long 20–50 m wide bedrock gorge bounded upstream and downstream by wide braidplains. We documented two flood events during which coarse sediment evacuation and redeposition appear to cause changes of up to several metres in channel bed elevation. Motivated by this case study, we examined the relationships between discharge, channel width and bedload transport capacity, and show that for a given slope narrow channels transport bedload more efficiently than wide ones at low discharges, whereas wider channels are more efficient at high discharges. We used the model sedFlow to explore this effect, running a random sequence of floods through a channel with a narrow gorge section bounded upstream and downstream by wider reaches. Channel response to imposed floods is complex, as high and low discharges drive different spatial patterns of erosion and deposition, and the channel may experience both of these regimes during the peak and recession periods of each flood. Our modelling suggests that width differences alone can drive substantial variations in sediment flux and bed response, without the need for variations in sediment supply or mobility. The fluctuations in sediment transport rates that result from width variations can lead to intermittent bed exposure, driving incision in different segments of the channel during different portions of the hydrograph. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd
    Keywords: 551.3 ; bedload transport ; discharge variability ; bedrock–alluvial channels ; channel width ; hysteresis
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  • 143
    Publication Date: 2021-09-27
    Description: A new global climate model setup using FESOM2.0 for the sea ice-ocean component and ECHAM6.3 for the atmosphere and land surface has been developed. Replacing FESOM1.4 by FESOM2.0 promises a higher efficiency of the new climate setup compared to its predecessor. The new setup allows for long-term climate integrations using a locally eddy-resolving ocean. Here it is evaluated in terms of (1) the mean state and long-term drift under preindustrial climate conditions, (2) the fidelity in simulating the historical warming, and (3) differences between coarse and eddy-resolving ocean configurations. The results show that the realism of the new climate setup is overall within the range of existing models. In terms of oceanic temperatures, the historical warming signal is of smaller amplitude than the model drift in case of a relatively short spin-up. However, it is argued that the strategy of “de-drifting” climate runs after the short spin-up, proposed by the HighResMIP protocol, allows one to isolate the warming signal. Moreover, the eddy-permitting/resolving ocean setup shows notable improvements regarding the simulation of oceanic surface temperatures, in particular in the Southern Ocean.
    Keywords: 551.6 ; FESOM ; ocean model ; climate model ; unstructured mesh ; Finite Volume
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  • 144
    Publication Date: 2021-09-27
    Description: Detailed organic geochemical and carbon isotopic (δ13C and Δ14C) analyses are performed on permafrost deposits affected by coastal erosion (Herschel Island, Canadian Beaufort Sea) and adjacent marine sediments (Herschel Basin) to understand the fate of organic carbon in Arctic nearshore environments. We use an end-member model based on the carbon isotopic composition of bulk organic matter to identify sources of organic carbon. Monte Carlo simulations are applied to quantify the contribution of coastal permafrost erosion to the sedimentary carbon budget. The models suggest that ~40% of all carbon released by local coastal permafrost erosion is efficiently trapped and sequestered in the nearshore zone. This highlights the importance of sedimentary traps in environments such as basins, lagoons, troughs, and canyons for the carbon sequestration in previously poorly investigated, nearshore areas.
    Keywords: 551 ; permafrost ; coastal erosion ; biomarker ; radiocarbon ; carbon flux ; carbon burial
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  • 145
    Publication Date: 2021-10-07
    Description: Volcanic eruptions are an important climate driver. The impact of Pinatubo-sized eruptions has been observed and is well constrained. The magnitude and duration of volcanic winter effects after supereruptions such as Toba remain disputed due to disagreement between the strong cooling predicted by models and much milder climate perturbations according to the paleodata. Here we present a reevaluated climate impact of a Toba-sized supereruption based on up-to-date GISS ModelE simulations. In this study, we account for all known primary mechanisms that govern the evolution of the volcanic plume and their nonlinear interactions. The SO 2 radiative effects are evaluated for the first time in coupled climate simulations with the interactive atmospheric chemistry module. We found that SO 2 effects on photochemistry, dynamics, and radiative forcing are especially prominent. Due to strong absorption in ultraviolet, SO 2 feedback on photochemistry partially offsets the limiting effect associated with aerosol microphysical processes. SO 2 greenhouse warming soothes the radiative cooling exerted by sulfate aerosols. SO 2 absorption in the shortwave and longwave causes radiative heating and lofting of the volcanic plume, and boosts the efficiency of SO 2 impact on photochemistry. Our analysis shows that SO 2 lifetime and magnitude of effects scale up and increase with the amount of emitted material. For a Pinatubo-sized eruption, SO 2 feedbacks on chemistry and dynamics are relevant only during the initial stage of the volcanic plume evolution, while local SO 2 concentrations are high. For a Toba-sized eruption, SO 2 effects are as important as sulfate aerosols and produce a less extreme volcanic winter.
    Keywords: 551.5 ; supereruption ; Toba ; volcanic winter ; sulfate aerosols ; climate impact ; sulfur dioxide
    Language: English
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  • 146
    Publication Date: 2021-10-07
    Description: X-ray fluorescence (XRF) core scanning of marine and lake sediments has been extensively used to study changes in past environmental and climatic processes over a range of timescales. The interpretation of XRF-derived element ratios in paleoclimatic and paleoceanographic studies primarily considers differences in the relative abundances of particular elements. Here we present new XRF core scanning data from two long sediment cores in the Andaman Sea in the northern Indian Ocean and show that sea level related processes influence terrigenous inputs based proxies such as Ti/Ca, Fe/Ca, and elemental concentrations of the transition metals (e.g., Mn). Zr/Rb ratios are mainly a function of changes in median grain size of lithogenic particles and often covary with changes in Ca concentrations that reflect changes in biogenic calcium carbonate production. This suggests that a common process (i.e., sea level) influences both records. The interpretation of lighter element data (e.g., Si and Al) based on low XRF counts is complicated as variations in mean grain size and water content result in systematic artifacts and signal intensities not related to the Al or Si content of the sediments. This highlights the need for calibration of XRF core scanning data based on discrete sample analyses and careful examination of sediment properties such as porosity/water content for reliably disentangling environmental signals from other physical properties. In the case of the Andaman Sea, reliable extraction of a monsoon signal requires accounting for the sea level influence on the XRF data.
    Keywords: 552.5 ; marine sediments ; lake sediments ; core scanning ; X‐ray fluorescence (XRF ; sediment properties
    Language: English
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  • 147
    Publication Date: 2021-10-07
    Description: Land use and climate changes both affect terrestrial ecosystems. Here, we used three combinations of Shared Socioeconomic Pathways and Representative Concentration Pathways (SSP1xRCP26, SSP3xRCP60, and SSP5xRCP85) as input to three dynamic global vegetation models to assess the impacts and associated uncertainty on several ecosystem functions: terrestrial carbon storage and fluxes, evapotranspiration, surface albedo, and runoff. We also performed sensitivity simulations in which we kept either land use or climate (including atmospheric CO2) constant from year 2015 on to calculate the isolated land use versus climate effects. By the 2080–2099 period, carbon storage increases by up to 87 ± 47 Gt (SSP1xRCP26) compared to present day, with large spatial variance across scenarios and models. Most of the carbon uptake is attributed to drivers beyond future land use and climate change, particularly the lagged effects of historic environmental changes. Future climate change typically increases carbon stocks in vegetation but not soils, while future land use change causes carbon losses, even for net agricultural abandonment (SSP1xRCP26). Evapotranspiration changes are highly variable across scenarios, and models do not agree on the magnitude or even sign of change of the individual effects. A calculated decrease in January and July surface albedo (up to −0.021 ± 0.007 and −0.004 ± 0.004 for SSP5xRCP85) and increase in runoff (+67 ± 6 mm/year) is largely driven by climate change. Overall, our results show that future land use and climate change will both have substantial impacts on ecosystem functioning. However, future changes can often not be fully explained by these two drivers and legacy effects have to be considered.
    Keywords: 333.7 ; 551.6 ; land use change ; climate change projections ; terrestrial ecosystems ; vegetation modeling ; ecosystem service indicators ; legacy effects
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  • 148
    Publication Date: 2021-10-07
    Description: The transition from the Pliocene to the Pleistocene was accompanied by major tectonic reorganizations of key oceanic gateways. In particular, the gradual closure of the Panama Gateway and the constriction of the Indonesian Gateway significantly affected the structure of the Pacific thermocline. In the East Pacific, the thermocline shoaled from an early Pliocene El Niño-like depth to its modern state, which had significant implications for global climate. Here we use Mg/Ca temperature estimates from subsurface and thermocline dwelling foraminifera to reconstruct the meridional Plio-Pleistocene evolution of the Southeast Pacific thermocline, in relation to atmospheric circulation changes. In combination with similar reconstructions from the north-equatorial Pacific, our data indicate a change in the thermocline, responding to the northward displacement of the Intertropical Convergence Zone/South Pacific High system between ~3.8 and 3.5 Ma. After 3.5 Ma, we record a second major phase of thermocline shoaling, which points to the Intertropical Convergence Zone/South Pacific High-system movement toward its modern position along with the gradual cooling of the Northern Hemisphere and its associated glaciation. These findings highlight that a warming globe may affect equatorial regions more intensively due to the potential temperature-driven movement of the Intertropical Convergence Zone/South Pacific High and their associated oceanic systems.
    Keywords: 551 ; ITCZ ; South Pacific High ; Plio-Pleistocene ; El Niño ; thermocline
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  • 149
    Publication Date: 2021-10-07
    Description: The brittle-ductile transition is a domain of finite extent characterized by high differential stress where both brittle and ductile deformation are likely to occur. Understanding its depth location, extent, and stability through time is of relevance for diverse applications including subduction dynamics, mantle-surface interactions, and, more recently, proper targeting of high-enthalpy unconventional geothermal resources, where local thermal conditions may activate ductile creep at shallower depths than expected. In this contribution, we describe a thermodynamically consistent physical framework and its numerical implementation, therefore extending the formulation of the companion paper Jacquey and Cacace (2020, https://doi.org/10.1029/2019JB018474) to model thermo-hydro-mechanical coupled processes responsible for the occurrence of transitional semi-brittle, semi-ductile behavior in porous rocks. We make use of a damage rheology to account for the macroscopic effects of microstructural processes leading to brittle-like material weakening and of a rate-dependent plastic model to account for ductile material behavior. Our formulation additionally considers the role of porosity and its evolution during loading in controlling the volumetric mechanical response of a stressed rock. By means of dedicated applications, we discuss how our damage poro-visco-elasto-viscoplastic rheology can effectively reconcile the style of localized deformation under different confining pressure conditions as well as the bulk macroscopic material response as recorded by laboratory experiments under full triaxial conditions.
    Keywords: 551 ; lithosphere ; brittle-ductile transition ; modeling
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  • 150
    Publication Date: 2021-10-07
    Description: To investigate transient dynamics of soil water redistribution during infiltration, we conducted horizontal borehole and surface ground penetrating radar measurements during a 4-day infiltration experiment at the rhizontron facility in Selhausen, Germany. Zero-offset ground penetrating radar profiling in horizontal boreholes was used to obtain soil water content information at specific depths (0.2, 0.4, 0.6, 0.8 and 1.2 m). However, horizontal borehole ground penetrating radar measurements do not provide accurate soil water content estimates of the top soil (0–0.1 m depth) because of interference between direct and critically refracted waves. Therefore, surface ground penetrating radar data were additionally acquired to estimate soil water content of the top soil. Due to the generation of electromagnetic waveguides in the top soil caused by infiltration, a strong dispersion in the ground penetrating radar data was observed in 500 MHz surface ground penetrating radar data. A dispersion inversion was thus performed with these surface ground penetrating radar data to obtain soil water content information for the top 0.1 m of the soil. By combining the complementary borehole and surface ground penetrating radar data, vertical soil water content profiles were obtained, which were used to investigate vertical soil water redistribution. Reasonable consistency was found between the ground penetrating radar results and independent soil water content data derived from time domain reflectometry measurements. Because of the improved spatial representativeness of the ground penetrating radar measurements, the soil water content profiles obtained by ground penetrating radar better matched the known water storage changes during the infiltration experiment. It was concluded that the combined use of borehole and surface ground penetrating radar data convincingly revealed spatiotemporal soil water content variation during infiltration. In addition, this setup allowed a better quantification of water storage, which is a prerequisite for future applications, where, for example, the soil hydraulic properties will be estimated from ground penetrating radar data.
    Keywords: 550.724 ; Ground-penetrating radar ; Hydrogeophysics ; Data processing
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  • 151
    Publication Date: 2021-10-07
    Description: Abstract Although the core velocity of the Atlantic North Equatorial Undercurrent (NEUC) is low (0.1−0.3 m s−1), it has been suggested to act as an important oxygen supply route towards the oxygen minimum zone in the eastern tropical North Atlantic. For the first time, the intraseasonal to interannual NEUC variability and its impact on oxygen are investigated based on shipboard and moored velocity observations around 5°N, 23°W. In contrast to previous studies that were mainly based on models or hydrographic data, we find hardly any seasonal cycle of NEUC transports in the central Atlantic. The NEUC transport variability is instead dominated by sporadic intraseasonal events. Only some of these events are associated with high oxygen levels suggesting an occasional eastward oxygen supply by NEUC transport events. Nevertheless, they likely contribute to the local oxygen maximum in the mean shipboard section along 23°W at the NEUC core position.
    Keywords: 551.46 ; Atlantic North Equatorial Undercurrent (NEUC)
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  • 152
    Publication Date: 2021-10-07
    Description: Abstract One of the most intriguing facets of the climate system is that it exhibits variability across all temporal and spatial scales; pronounced examples are temperature and precipitation. The structure of this variability, however, is not arbitrary. Over certain spatial and temporal ranges, it can be described by scaling relationships in the form of power laws in probability density distributions and autocorrelation functions. These scaling relationships can be quantified by scaling exponents which measure how the variability changes across scales and how the intensity changes with frequency of occurrence. Scaling determines the relative magnitudes and persistence of natural climate fluctuations. Here, we review various scaling mechanisms and their relevance for the climate system. We show observational evidence of scaling and discuss the application of scaling properties and methods in trend detection, climate sensitivity analyses, and climate prediction.
    Keywords: 551.6 ; scaling ; climate variability ; memory ; scaling mechanisms ; paleoclimate ; power law
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  • 153
    Publication Date: 2021-10-07
    Description: This paper presents evidence for a limnological response to the Laacher See eruption (LSE) as detected in lake sediments from Nahe, northern Germany. The sediment section of the Allerød period dating to between 13 422 and 12 708 cal. a BP is preserved in annual laminations. Within this section, the LSE was identified as a cryptotephra layer (12 944±44 cal. a BP). Microfacies analysis, continuous high-resolution geochemical measurements and pollen analyses enabled a high-resolution reconstruction of environmental change. The older part of the Allerød (c. 13 422 to 12 943 cal. a BP) was characterized by relatively stable sedimentation conditions. Evidence for windier conditions dating to c. 13 160 to 13 080 cal. a BP probably reflects the Gerzensee oscillation. Pronounced changes of the lake sedimentation followed the LSE. Four unusually thick varves with increased amounts of allochthonous material indicate serious disturbance of the local environment immediately after the LSE, related to increased storminess and/or the occurrence of high intensity rainfall events. A pronounced reduction of biogenic silica accumulation for c. 60 years after the LSE could reflect a period of acidification. Indications of a simultaneous lake level increase until c. 60 years after the LSE are in line with the supposed reduced evapotranspiration associated with cooler conditions. About 120 years after the LSE, increased oxygen access at the lake bottom, allochthonous input and Cl fluxes point to an onset of increasingly stronger westerly winds, probably as a long-term response to the LSE. This supports the idea of a southward shift of the mid-latitude westerlies wind system within the interval between the LSE and the beginning of the Younger Dryas. The pace of the southwards shift of this wind system decreased from 10 km a−1 in the initial phase (40–120 years after LSE) to 6 km a−1 in the later phase (120–200 years after LSE).
    Keywords: 551 ; Laacher See eruption (LSE) ; lake sediments
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  • 154
    Publication Date: 2021-10-07
    Description: We reconstructed the variability of the Earth's strongest hydrological system, the Indian monsoon, over the interval 6.24 to 4.91 Ma at International Ocean Discovery Program (IODP) Expedition 353 Site U1448 in the Andaman Sea. We integrated high-resolution benthic and planktic foraminiferal carbon and oxygen isotopes with Mg/Ca measurements of the mixed layer foraminifer Trilobatus sacculifer to reconstruct the isotopic composition of seawater (δ18Osw) and the gradient between planktic and benthic foraminiferal δ13C. A prominent increase in mixed layer temperatures of ~4°C occurred between 5.55 and 5.28 Ma, accompanied by a change from precession- to obliquity-driven variability in planktic δ18O and δ18Osw. We suggest that an intensified cross-equatorial transport of heat and moisture, paced by obliquity, led to increased summer monsoon precipitation during warm stages after 5.55 Ma. Transient cold stages were characterized by reduced mixed layer temperatures and summer monsoon failure, thus resembling late Pleistocene stadials. In contrast, an overall cooler background climate state with a strengthened biological pump prevailed prior to 5.55 Ma. These findings highlight the importance of internal feedback processes for the long-term evolution of the Indian monsoon.
    Keywords: 551.6 ; Indian monsoon ; Miocene-Pliocene transition ; Bay of Bengal ; Mg/Ca paleothermometry ; stable isotopes ; orbital forcing
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  • 155
    Publication Date: 2021-10-07
    Description: High-quality single-crystal X-ray diffraction measurements are a prerequisite for obtaining precise and reliable structure data and electron densities. The single crystal should therefore fulfill several conditions, of which a regular defined shape is of particularly high importance for compounds consisting of heavy elements with high X-ray absorption coefficients. The absorption of X-rays passing through a 50 µm-thick LiNbO3 crystal can reduce the transmission of Mo Kα radiation by several tens of percent, which makes an absorption correction of the reflection intensities necessary. In order to reduce ambiguities concerning the shape of a crystal, used for the necessary absorption correction, a method for preparation of regularly shaped single crystals out of large samples is presented and evaluated. This method utilizes a focused ion beam to cut crystals with defined size and shape reproducibly and carefully without splintering. For evaluation, a single-crystal X-ray diffraction study using a laboratory diffractometer is presented, comparing differently prepared LiNbO3 crystals originating from the same macroscopic crystal plate. Results of the data reduction, structure refinement and electron density reconstruction indicate qualitatively similar values for all prepared crystals. Thus, the different preparation techniques have a smaller impact than expected. However, the atomic coordinates, electron densities and atomic charges are supposed to be more reliable since the focused-ion-beam-prepared crystal exhibits the smallest extinction influences. This preparation technique is especially recommended for susceptible samples, for cases where a minimal invasive preparation procedure is needed, and for the preparation of crystals from specific areas, complex material architectures and materials that cannot be prepared with common methods (breaking or grinding).
    Keywords: 548 ; X-ray diffraction ; sample preparation ; focused ion beams
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  • 156
    Publication Date: 2021-10-07
    Description: The joint effect of droplet sedimentation and wind shear on cloud top entrainment in stratocumulus is investigated with direct numerical simulations. Although it is well understood that droplet sedimentation weakens entrainment while wind shear enhances entrainment, there is no consensus on the magnitude of each process. We find that the entrainment reduction by droplet sedimentation is sufficiently strong to completely compensate the entrainment enhancement by wind shear, and thus, droplet sedimentation and wind shear effects can be equally important for cloud top entrainment. For instance, for the subtropical conditions considered here, droplet sedimentation weakens entrainment by up to 40% while wind shear enhances entrainment by up to 40%. This result implies that the droplet size distribution can substantially affect cloud lifetimes not only because of its effect on rain formation but also because of its effect on cloud top entrainment, which emphasizes the need for a better characterization of droplet size distributions in stratocumulus. A second implication is that entrainment velocity parametrizations should pay equal attention to droplet sedimentation and to wind shear effects.
    Keywords: 551.5 ; stratocumulus ; entrainment ; wind shear ; droplet sedimentation ; turbulence ; evaporative cooling
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  • 157
    Publication Date: 2021-10-07
    Description: Weirs are barriers built across rivers for a wide range of other purposes than hydropower production. Like hydropower installations, weirs can negatively impact fish migrations. Downstream migration and mortality of Atlantic salmon smolts were studied during passage of a weir and power station by tagging 227 smolts with radio transmitters. Extra loss of smolts due to the weir and adjacent reservoir was 5.2%. Mortality was likely related to physical damage imposed to the smolts and/or increased predation risk. Extra loss of smolts did not differ between the weir and the power station (7.2%). Migration speeds were reduced at the power station but not at the weir. We conclude that mortality at one power station site may differ considerably among years, because the mortality was more than four times higher in a previous year than in this study. Increased river discharge seemed to decrease mortality and increase migration speeds at the power station.
    Keywords: 551.483 ; downstream migration ; migration speed ; mortality ; power station ; radio telemetry ; salmon smolt ; weir
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  • 158
    Publication Date: 2021-10-07
    Description: The quantification of factors leading to harmfully high levels of particulate matter (PM) remains challenging. This study presents a novel approach using a statistical model that is trained to predict hourly concentrations of particles smaller than 10  μm (PM10) by combining satellite-borne aerosol optical depth (AOD) with meteorological and land-use parameters. The model is shown to accurately predict PM10 (overall R 2 = 0.77, RMSE = 7.44  μg/m 3) for measurement sites in Germany. The capability of satellite observations to map and monitor surface air pollution is assessed by investigating the relationship between AOD and PM10 in the same modeling setup. Sensitivity analyses show that important drivers of modeled PM10 include multiday mean wind flow, boundary layer height (BLH), day of year (DOY), and temperature. Different mechanisms associated with elevated PM10 concentrations are identified in winter and summer. In winter, mean predictions of PM10 concentrations 〉35  μg/m 3 occur when BLH is below ∼500 m. Paired with multiday easterly wind flow, mean model predictions surpass 40  μg/m 3 of PM10. In summer, PM10 concentrations seemingly are less driven by meteorology, but by emission or chemical particle formation processes, which are not included in the model. The relationship between AOD and predicted PM10 concentrations depends to a large extent on ambient meteorological conditions. Results suggest that AOD can be used to assess air quality at ground level in a machine learning approach linking it with meteorological conditions.
    Keywords: 551.5 ; aerosol optical depth ; air quality ; PM10 ; machine learning ; drivers of air pollution ; MAIAC
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  • 159
    Publication Date: 2021-10-07
    Description: Forest canopies present irregular surfaces that alter both the quantity and spatiotemporal variability of precipitation inputs. The drop size distribution (DSD) of rainfall varies with rainfall event characteristics and is altered substantially by the forest stand properties. Yet, the influence of two major European tree species, European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) H. karst), on throughfall DSD is largely unknown. In order to assess the impact of these two species with differing canopy structures on throughfall DSD, two optical disdrometers, one above and one below the canopy of each European beech and Norway spruce, measured DSD of both incident rainfall and throughfall over 2 months at a 10-s resolution. Fractions of different throughfall categories were analysed for single-precipitation events of different intensities. While penetrating the canopies, clear shifts in drop size and temporal distributions of incoming rainfall were observed. Beech and spruce, however, had different DSD, behaved differently in their effect on diameter volume percentiles as well as width of drop spectrum. The maximum drop sizes under beech were higher than under spruce. The mean ± standard deviation of the median volume drops size (D50) over all rain events was 2.7 ± 0.28 mm for beech and 0.80 ± 0.04 mm for spruce, respectively. In general, there was a high-DSD variability within events indicating varying amounts of the different throughfall fractions. These findings help to better understand the effects of different tree species on rainfall partitioning processes and small-scale variations in subcanopy rainfall inputs, thereby demonstrating the need for further research in high-resolution spatial and temporal properties of rainfall and throughfall.
    Keywords: 551.6 ; canopy drip ; canopy interaction ; disdrometer ; droplets ; interception ; rain intensity ; rain rate ; splash droplets
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  • 160
    Publication Date: 2021-10-07
    Description: Precipitation extremes with devastating socioeconomic consequences within the South American Monsoon System (SAMS) are expected to become more frequent in the near future. The complexity in SAMS behavior, however, poses severe challenges for reliable future projections. Thus, robust paleomonsoon records are needed to constrain the high spatiotemporal variability in the response of SAMS rainfall to different climatic drivers. This study uses Ti/Ca ratios from X-ray fluorescence scanning of a sediment core retrieved off eastern Brazilian to trace precipitation changes over the past 322 Kyr. The results indicate that despite the spatiotemporal complexity of the SAMS, insolation forcing is the primary pacemaker of variations in the monsoonal system. Additional modulation by atmospheric pCO2 suggests that SAMS intensity over eastern Brazil will be suppressed by rising CO2 emissions in the future. Lastly, our record reveals an unprecedented strong and persistent wet period during Marine Isotope Stage 6 driven by anomalously strong trade winds.
    Keywords: 551.6 ; South American Monsoon System (SAMS)
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  • 161
    Publication Date: 2021-10-15
    Description: A new microphysical cirrus model to simulate ice crystal nucleation, depositional growth, and gravitational settling is described. The model tracks individual simulation ice particles in a vertical column of air and allows moisture and heat profiles to be affected by turbulent diffusion. Ice crystal size- and supersaturation-dependent deposition coefficients are employed in a one-dimensional model framework. This enables the detailed simulation of microphysical feedbacks influencing the outcome of ice nucleation processes in cirrus. The use of spheroidal water vapor fluxes enables the prediction of primary ice crystal shapes once microscopic models describing the vapor uptake on the surfaces of cirrus ice crystals are better constrained. Two applications addressing contrail evolution and cirrus formation demonstrate the potential of the model for advanced studies of aerosol-cirrus interactions. It is shown that supersaturation in, and microphysical and optical properties of, cirrus are affected by variable deposition coefficients. Vertical variability in ice supersaturation, ice crystal sedimentation, and high turbulent diffusivity all tend to decrease homogeneously nucleated ice number mixing ratios over time, but low ice growth efficiencies counteract this tendency. Vertical mixing induces a tendency to delay the onset of homogeneous freezing. In situations of sustained large-scale cooling, natural cirrus clouds may often form in air surrounding persistent contrails.
    Keywords: 551.5 ; cirrus ; cloud model ; microphysics
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  • 162
    Publication Date: 2021-10-15
    Description: Upwelling ocean currents associated with oxygen minimum zones (OMZs) supply nutrients fuelling intense marine productivity. Perturbations in the extent and intensity of OMZs are projected in the future, but it is currently uncertain how this will impact fluxes of redox-sensitive trace metal micronutrients to the surface ocean. Here we report seawater concentrations of Fe, Mn, Co, Cd, and Ni alongside the redox indicator iodide/iodate in the Peruvian OMZ during the 2015 El Niño event. The El Niño drove atypical upwelling of oxygen-enriched water over the Peruvian Shelf, resulting in oxidized iodine and strongly depleted Fe (II), total dissolved Fe, and reactive particulate Fe concentrations relative to non-El Niño conditions. Observations of Fe were matched by the redox-sensitive micronutrients Co and Mn, but not by non-redox-sensitive Cd and Ni. These observations demonstrate that oxygenation of OMZs significantly reduces water column inventories of redox-sensitive micronutrients, with potential impacts on ocean productivity.
    Keywords: 551 ; iron ; trace metals ; oxygen minimum zone ; El Niño ; eastern tropical south pacific ; shelf source
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  • 163
    Publication Date: 2021-10-15
    Description: Heat transport in natural porous media, such as aquifers or streambeds, is generally modeled assuming local thermal equilibrium (LTE) between the fluid and solid phases. Yet, the mathematical and hydrogeological conditions and implications of this simplification have not been fully established for natural porous media. To quantify the occurrence and effects of local thermal disequilibrium during heat transport, we systematically compared thermal breakthrough curves from a LTE with those calculated using a local thermal nonequilibrium (LTNE) model, explicitly allowing for different temperatures in the fluid and solid phases. For the LTNE model, we developed a new correlation for the heat transfer coefficient representative of the conditions in natural porous aquifers using six published experimental results. By conducting an extensive parameter study (〉50,000 simulations), we show that LTNE effects do not occur for grain sizes smaller than 7 mm or for groundwater flow velocities that are slower than 1.6 m day−1. The limits of LTE are likely exceeded in gravel aquifers or in the vicinity of pumped bores. For such aquifers, the use of a LTE model can lead to an underestimation of the effective thermal dispersion by a factor of up to 30 or higher, while the advective thermal velocity remains unaffected for most conditions. Based on a regression analysis of the simulation results, we provide a criterion which can be used to determine if LTNE effects are expected for particular conditions.
    Keywords: 551 ; local thermal nonequilibrium ; thermal dispersion ; modeling advective heat transport ; local thermal equilibrium ; porous aquifer
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  • 164
    Publication Date: 2021-10-15
    Description: Lake Victoria is a shared water resource between Kenya, Uganda, and Tanzania, which is the second largest freshwater lake in the world. It has long since suffered from the consequences of overexploitation of its resources, mainly fish stocks, and increasingly high pollution. The closure of 58% of the fish processing plants (FPPs) is attributed to the declining fish stocks due to overfishing and pollution in particular. The installation and operation of a pilot membrane bioreactor (MBR) in Kisumu, Kenya, adopts an integrated approach by providing an integral, sustainable, cost-effective, and robust solution for water sanitation, which also meets the demand for clean water in the fish processing industry, aquaculture, and irrigation. The innovative system comprises a pilot MBR coupled with a recirculation aquaculture system (RAS). The RAS is able to recirculate 90% to 95% of its water volume; only the water loss through evaporation and drum filter back flushing has to be replaced. To compensate for this water deficit, the MBR treats domestic wastewater for further reuse. Additionally, excess purified water is used for irrigating a variety of local vegetables and could also be used in FPPs. The pilot-scale MBR plant with around 6 m2 submerged commercial polyethersulfone (PES) membranes provides treated water in basic agreement with Food and Agriculture Organization (FAO) standards for irrigation and aquaculture, showing no adverse effects on tilapia fingerlings production. A novel membrane module with a low-fouling coating is operating stably but has not yet shown improved performance compared to the commercial one. Integr Environ Assess Manag 2020;16:942–954. © 2020 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC)
    Keywords: 333.9 ; Membrane bioreactor ; Low-fouling membrane coating ; Recirculating aquaculture system ; Domestic wastewater ; Water reuse
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  • 165
    Publication Date: 2021-10-15
    Description: In this study we demonstrate the potential of a kinetic energy backscatter scheme for use in global ocean simulations. Ocean models commonly employ (bi)harmonic eddy viscosities causing excessive dissipation of kinetic energy in eddy-permitting simulations. Overdissipation not only affects the smallest resolved scales but also the generation of eddies through baroclinic instabilities, impacting the entire wave number spectrum. The backscatter scheme returns part of this overdissipated energy back into the resolved flow. We employ backscatter in the FESOM2 multiresolution ocean model with a quasi-uniform 1/4° mesh. In multidecadal ocean simulations, backscatter increases eddy activity by a factor 2 or more, moving the simulation closer to observational estimates of sea surface height variability. Moreover, mean sea surface height, temperature, and salinity biases are reduced. This amounts to a globally averaged bias reduction of around 10% for each field, which is even larger in the Antarctic Circumpolar Current. However, in some regions such as the coastal Kuroshio, backscatter leads to a slight overenergizing of the flow and, in the Antarctic, to an unrealistic reduction of sea ice. Some of the bias increases can be reduced by a retuning of the model, and we suggest related adjustments to the backscatter scheme. The backscatter simulation is about 2.5 times as expensive as a simulation without backscatter. Most of the increased cost is due to a halving of the time step to accommodate higher simulated velocities.
    Keywords: 551.46 ; ocean kinetic energy backscatter ; subgrid eddy parametrization ; inverse energy cascade ; viscosity closure ; eddy-permitting resolution
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  • 166
    Publication Date: 2021-10-15
    Description: Wetlands such as bogs, swamps, or freshwater marshes are hotspots of biodiversity. For 5.1 million km2 of inland wetlands, the dynamics of area and water storage, which strongly impact biodiversity and ecosystem services, were simulated using the global hydrological model WaterGAP. For the first time, the impacts of both human water use and man-made reservoirs (WUR) and future climate change (CC) on wetlands around the globe were quantified. WUR impacts are concentrated in arid/semiarid regions, where WUR decreased mean wetland water storage by more than 5% on 8.2% of the mean wetland area during 1986–2005 (Am), with highest decreases in groundwater depletion area. Using output of three climate models, CC impacts on wetlands were quantified, distinguishing unavoidable impacts [i.e., at 2 °C global warming (GW)] from avoidable impacts (difference between 3 °C and 2 °C impacts). Even unavoidable CC impacts are projected to be much larger than WUR impacts, also in arid/semiarid regions. On most wetland area with reliable estimates, avoidable CC impacts are more than twice as large as unavoidable impacts. In case of 2 °C GW, half of Am is estimated to be unaffected by mean storage changes of more than 5%, but only one third in case of 3 °C GW. Temporal variability of water storage will increase for most wetlands. Wetlands in dry regions will be affected the most, particularly by water storage decreases in the dry season. Different from wealthier countries, low-income countries will dominantly suffer from a decrease in wetland water storage due to CC.
    Keywords: 333.7 ; climate change ; water storage ; water use ; wetland ; reservoirs ; global
    Language: English
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  • 167
    Publication Date: 2021-10-15
    Description: Many soil types in the federal state of Schleswig-Holstein (North Germany) are naturally compacted in the subsoil due to pedo- or geogenic processes (42% of the area) but, due to anthropogenic impacts, the percentage of subsoil compaction has increased further. To determine the overall subsoil compaction status of seven representative soil types in Schleswig-Holstein (≤ 60 cm depth), air capacity (AC), saturated hydraulic conductivity (Ks) and effective bulk density (ρBeff) of 342 soil profiles from the database of the State Agency for Agriculture, Environment and Rural Areas of Schleswig-Holstein (LLUR) were evaluated with respect to critical threshold values (AC 〈 5 Vol.-%, Ks 〈 10 cm day−1, ρBeff 〉 1.7 g cm−3). The compaction status was classified into Classes I–IV, where a harmful subsoil compaction was assumed if both values of AC and Ks simultaneously exceeded (are smaller than) their threshold value (Class IV). Subsoils of (Stagnic) Luvisols and Stagnosols derived from glacial till, as well as those of Fluvic Gleyic Stagnosols of the marshlands, showed a high degree of natural compaction (46%–65% in Class IV). In contrast, sandy subsoil horizons of Podzols and Brunic Arenosols derived from glacifluvial sediments were rarely compacted (〈 13% in Class IV), and possessed the lowest ρBeff, which were similar to Anthrosols. Only 5%–18% of their subsoil horizons exceeded the critical value of 1.7 g cm−3. Additionally, anthropogenic subsoil compaction of at least 6%–10% was verified for (Stagnic) Luvisols and Stagnosols.
    Keywords: 631.4 ; air capacity ; hydraulic conductivity ; soil database ; subsoil compaction
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  • 168
    Publication Date: 2021-10-15
    Description: As the Arctic coast erodes, it drains thermokarst lakes, transforming them into lagoons, and, eventually, integrates them into subsea permafrost. Lagoons represent the first stage of a thermokarst lake transition to a marine setting and possibly more saline and colder upper boundary conditions. In this research, borehole data, electrical resistivity surveying, and modeling of heat and salt diffusion were carried out at Polar Fox Lagoon on the Bykovsky Peninsula, Siberia. Polar Fox Lagoon is a seasonally isolated water body connected to Tiksi Bay through a channel, leading to hypersaline waters under the ice cover. The boreholes in the center of the lagoon revealed floating ice and a saline cryotic bed underlain by a saline cryotic talik, a thin ice-bearing permafrost layer, and unfrozen ground. The bathymetry showed that most of the lagoon had bedfast ice in spring. In bedfast ice areas, the electrical resistivity profiles suggested that an unfrozen saline layer was underlain by a thick layer of refrozen talik. The modeling showed that thermokarst lake taliks can refreeze when submerged in saltwater with mean annual bottom water temperatures below or slightly above 0°C. This occurs, because the top-down chemical degradation of newly formed ice-bearing permafrost is slower than the refreezing of the talik. Hence, lagoons may precondition taliks with a layer of ice-bearing permafrost before encroachment by the sea, and this frozen layer may act as a cap on gas migration out of the underlying talik.
    Keywords: 551.48 ; thermokarst lake ; talik ; lagoon ; subsea permafrost ; salt diffusion ; Siberia
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  • 169
    Publication Date: 2021-10-15
    Description: The concept of ecosystem services (ES) creates understanding of the value of ecosystems for human well-being. With regard to soils, it provides a framework for assessments of soil contributions and soil management impacts. However, a lack of standardization impedes comparisons between assessment studies and the building of synthesis information. The Common International Classification of Ecosystem Services (CICES) is an important step forward, although its application to soils is not without difficulty. CICES version 5.1 defines 83 ES classes, of which only some are relevant for soils. We compiled two subsets of CICES classes: one set of soil-related ES comprising 29 services defined as directly and quantifiably controlled by soils and their properties, processes and functions, and another set of 40 ES defined as being affected by agricultural soil management. Additionally, we conducted a systematic literature review, searching for published lists of soil-related ES that claim completeness. We identified 11 relevant lists. Of all CICES classes, 12 were included in more than 75% of the lists, whereas another 36 classes were included in 25–75% of them. Regarding the suitability of the CICES classification for addressing ES in the context of soils and their agricultural management, we identified constraints, such as overlaps, gaps, and highly specific or very broad class definitions. Close cooperation between the soil research and ES communities could ensure better consideration of soils in future CICES updates. A shortlist of 25 service classes affected by agricultural soil management facilitates a standardized approach and may function as checklists in impact assessments. Highlights: Standardized definitions are needed to allow meta-analysis of ecosystem service studies and improve assessments. CICES defines 83 detailed classes of ecosystem services, suggested as a “default list”. We identified 29 classes as soil related and 40 classes as affected by agricultural soil management. Both subsets facilitate ecosystem service assessments in soil research and comparability of results.
    Keywords: 631.4 ; agriculture ; arable ; CICES ; impact area ; impact assessment ; soil functions ; soil management ; soil properties ; standardization
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  • 170
    Publication Date: 2021-10-15
    Description: The biogeochemical functioning of soils (e.g., soil carbon stabilization and nutrient cycling) is determined at the interfaces of specific soil structures (e.g., aggregates, particulate organic matter (POM) and organo-mineral associations). With the growing accessibility of spectromicroscopic techniques, there is an increase in nano- to microscale analyses of biogeochemical interfaces at the process scale, reaching from the distribution of elements and isotopes to the localization of microorganisms. A widely used approach to study intact soil structures is the fixation and embedding of intact soil samples in resin and the subsequent analyses of soil cross-sections using spectromicroscopic techniques. However, it is still challenging to link such microscale approaches to larger scales at which normally bulk soil analyses are conducted. Here we report on the use of laboratory imaging Vis–NIR spectroscopy on resin embedded soil sections and a procedure for supervised image classification to determine the microscale soil structure arrangement, including the quantification of soil organic matter fractions. This approach will help to upscale from microscale spectromicroscopic techniques to the centimetre and possibly pedon scale. Thus, we demonstrate a new approach to integrate microscale soil analyses into pedon-scale conceptual and experimental approaches. Highlights: Quantification of soil constituents using Vis-NIR spectroscopy. New approach to use resin embedded soil core sections with intact structure. Reproducible quantification of soil constituents important for soil carbon storage. Vis-NIR as promising tool for upscaling from microscale to pdeon scale.
    Keywords: 631.4 ; Alaska ; HySpex ; mineral associated organic matter ; occluded particulate organic matter ; particulate organic matter ; pedogenic iron oxides ; supervised image classification
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  • 171
    Publication Date: 2021-10-15
    Description: Nowadays, national and international requirements and laws emphasize the “natural” development of river-floodplain systems. One goal is to increase the connectivity between the river and its floodplains and thus reactivate floodplains as flooding areas, which potentially increases the mobility of fine sediments. The objective of this study is to analyze the long-term effects of reactivated floodplains on the mobility of floodplain deposits of small rivers based on two river restoration scenarios: elevating the riverbed or lowering the floodplains. Past channel fixation and degradation as well as the subsequent increase in the floodplain elevation led to the decoupling of the channel and floodplain morphodynamics associated with the reduction of the habitat connectivity. Here, the floodplain sedimentation rates were determined using a numerical model based on the Delft3D software. The novelty of these numerical investigations is the morphological long-term analysis over timescales of decades, which is not comparable to other short-term hydrodynamic and morphodynamic studies for small meandering lowland rivers. The results of 11 river restoration scenarios show that lowering the floodplain and raising the riverbed elevation both lead to an increase in the fine sediment deposition on the floodplain. However, lowering the floodplain elevation is generally more effective. Based on the numerical model results and the assumption of a fixed river channel, only anthropogenic activity might have increased the amount of fine sediments deposited on floodplains and has accelerated the decoupling of the floodplains from the riverbed in the past centuries.
    Keywords: 551.48 ; Reactivation of floodplain sediment deposits ; Numerical modelling ; River restorations
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  • 172
    Publication Date: 2021-10-15
    Description: Winter chill is expected to decrease in many of the suitable growing regions for deciduous trees. Argentinean North Patagonia hosts extensive fruit tree cultivation, which provides an important contribution to both local and global food security. Using historic records from 11 weather stations from North Patagonia, we evaluate the possible impacts of climate change on fruit tree cultivation. We assess winter chill and seasonal heat availability, and the risk of spring frost events based on outputs from 15 Global Climate Models (GCMs) for two Representative Concentration Pathway (RCP) scenarios and two future time periods (represented by central years 2050 and 2085). Metrics were estimated for 47 years of records from the weather stations, as well as typical conditions for 10 past scenarios and 60 future GCM and RCP projections. Scenarios consisted of 100 plausible annual temperature records produced by a weather generator. Results suggest that fruit tree dormancy in Argentinean North Patagonia will not be strongly affected by climate change. Compared to the past, winter chill may only decrease by 9% in the RCP4.5 scenario by 2050 in the northeastern and eastern subregion, while in the central-south and west the reduction seems unlikely to exceed 6% by the same RCP scenario and year. Our models project stable high growing season heat in the northeastern and eastern regions, and major increases in the south by 2085 in both RCP scenarios. Projections of spring frost events varied between 0 and about 25 hours below 0°C depending on the site. Increasing heat availability may create opportunities for fruit and nut growers to introduce new species and cultivars to the region. Our results provide a basis for planning such introductions and for enabling growers to exploit new opportunities for producing temperate orchard crops beyond their traditional ranges.
    Keywords: 551.6 ; chill models ; chill requirement ; heat requirement ; Prunus sp. ; spring frost risk ; temperate trees ; warm winters
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  • 173
    Publication Date: 2021-10-15
    Description: Cities are the drivers of socioeconomic innovation and are also forced to address the accelerating risk of failure in providing essential services such as water supply today and in the future. Here, we investigate the resilience of urban water supply security, which is defined in terms of the services that citizens receive. The resilience of services is determined by the availability and robustness of critical system elements or “capitals” (water resources, infrastructure, finances, management efficacy, and community adaptation). We translate quantitative information about this portfolio of capitals from seven contrasting cities on four continents into parameters of a coupled system dynamics model. Water services are disrupted by recurring stochastic shocks, and we simulate the dynamics of impact and recovery cycles. Resilience emerges under various constraints, expressed in terms of each city's capital portfolio. Systematic assessment of the parameter space produces the urban water resilience landscape, and we determine the position of each city along a continuous gradient from water insecure and nonresilient to secure and resilient systems. In several cities stochastic disturbance regimes challenge steady-state conditions and drive system collapse. While water insecure and nonresilient cities risk being pushed into a poverty trap, cities which have developed excess capitals risk being trapped in rigidity and crossing a tipping point from high to low services and collapse. Where public services are insufficient, community adaptation improves water security and resilience to varying degrees. Our results highlight the need for resilience thinking in the governance of urban water systems under global change pressures.
    Keywords: 333.9 ; systems dynamics modeling ; coupled natural-human-engineered systems (CNHES) ; adaptive capacity ; water management ; stochastic shocks ; Capital Portfolio Approach (CPA)
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  • 174
    Publication Date: 2021-10-15
    Description: Tunnel valleys are assumed to form near the margin of ice sheets. Hence, they can be used to reconstruct the dynamics of former ice margins. The detailed formation and infill of tunnel valleys, however, are still not well understood. Here, we present a dense grid of high-resolution 2D multi-channel reflection seismic data from the German sector of the southeastern North Sea imaging tunnel valleys in very great detail. Three tunnel valley systems were traced over distances ranging between 11 and 21 km. All tunnel valleys are completely filled and buried. They differ in incision depth, incision width and number of incisions. The tunnel valleys cut 130–380 m deep into Neogene, Palaeogene and Cretaceous sediments; they show a lower V-shaped and an upper U-shaped morphology. For individual tunnel valleys, the overall incision direction ranges from east–west to northeast–southwest. Two tunnel valleys intersect at an oblique angle without reuse of the thalweg. These valleys incise into a pre-existing glaciotectonic complex consisting of thrust sheets in the northwest of the study area. The analysis of the glaciotectonic complex and the tunnel valleys leads us to assume that we identified several marginal positions of (pre-)Elsterian ice lobes in the southeastern North Sea.
    Keywords: 551 ; 622.15 ; glaciogenic unconformity ; glaciotectonic complex ; ice margin ; Quaternary succession ; tunnel valleys
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  • 175
    Publication Date: 2021-10-15
    Description: Within a rapidly changing Arctic climate system, snow on sea ice is an important climate parameter. A common method to derive snow depth on an Arctic-wide scale is based on passive microwave satellite observations. However, the uncertainties of this method are not well constrained. In this study, we estimate the influence of geophysical parameters, including ice, snow, and atmospheric properties on passive microwave snow depth retrievals using a Monte Carlo uncertainty estimation. The results are based on model simulations from the Microwave Emission Model for Layered Snowpacks, the SNOWPACK model, and from the Passive and Active Microwave TRAnsfer model. All simulations are based on in situ observations obtained during the N-ICE2015 campaign. The average uncertainty in potential snow depth retrievals is between 11% and 19%, depending on the microwave frequencies used and increases with increasing snow depth. For lower-frequency retrievals (including 6.9 GHz), unknown snow properties are the strongest source of uncertainty while for higher-frequency retrievals (including 36.5 GHz), the contribution of ice, snow properties, and clouds is equally strong.
    Keywords: 551.5 ; snow ; remote sensing ; modeling ; Arctic
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  • 176
    Publication Date: 2021-10-15
    Description: A full-vector paleomagnetic record, comprising directional data and relative paleointensity (rPI), was derived from 16 sediment cores recovered from the southeastern Black Sea. The obtained data were used to create a stack covering the time window between 68.9 and 14.5 ka. Age models are based on radiocarbon dating and correlations of warming/cooling cycles monitored by high-resolution X-ray fluorescence (XRF) elementary ratios and by ice-rafted debris (IRD) in Black Sea sediments to the sequence of “Dansgaard-Oeschger” (D-O) events defined from the Greenland ice core oxygen isotope stratigraphy. The reconstructed prominent lows in paleointensity at about 64.5, 41.2, and 34.5 ka are coeval with the Norwegian-Greenland Sea, the Laschamps, and the Mono Lake excursions, respectively. For a further analysis, the stacked Black Sea paleomagnetic record was converted into one component being parallel to the direction expected from a geocentric axial dipole (GAD) and two components perpendicular to it (EW, inclined NS), representing definitely only non-GAD components of the geomagnetic field. Discussions of the field configurations at the Black Sea site are focused on the three excursional events. The Norwegian-Greenland Sea excursion was dominated by a decaying axial dipole and persisting weak nondipole field, with directional variations still within the range of normal secular variations. The Laschamps excursion comprises two full polarity transitions and a short stable interval of reversed polarity in between. The Mono Lake excursion was mostly dominated by a nondipole field, though with a less pronounced weakening of the axial dipole component.
    Keywords: 538.7 ; Black Sea ; Norwegian-Greenland Sea excursion ; Laschamps excursion ; Mono Lake excursion ; paleosecular variations
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  • 177
    Publication Date: 2021-10-15
    Description: This paper introduces the software solution bingo-antidote for thermodynamic calculations at equilibrium based on iterative thermodynamic models. It describes a hybrid strategy combining the strength of Gibbs energy minimization (GEM) and inverse thermobarometry models based on the comparison between the modelled and observed mineral assemblage, modes and compositions. The overall technique relies on quantitative compositional maps acquired by electron probe micro-analyser for obtaining a mutually consistent set of observed data such as bulk rock and mineral compositions. Thus it offers the opportunity to investigate metamorphic rocks on a microscale. The scoring part bingo integrates three statistical model quality factors Qasm for the assemblage, Qvol for the mineral modes, Qcmp for the mineral compositions combined in a global evaluation criterion Qtotal that quantifies how the model reproduces the observations for the investigated volume. The input parameters of GEM affecting the model quality such as pressure, temperature and eventually some components of the bulk composition (e.g. the molar amount of hydrogen, carbon or oxygen) or activity variables of fluids and gases (e.g. aH2O, aCO2, f(O2)) can be optimized by inversion in antidote using several mapping stages followed by a direct search optimization. Examples of iterative models based on compositional maps processed with bingo-antidote demonstrate the utility of the program. In contrast to the qualitative interpretation of phase diagrams, the inversion maximizes the benefits of GEM and permits the derivation of statistically ‘optimal’ pressure–temperature conditions for well-equilibrated samples. In addition, bingo-antidote opens new avenues for petrological investigations such as the generation of chemical potential landscape maps.
    Keywords: 552 ; bingo-antidote ; compositional mapping ; inversion ; model evaluation ; phase equilibria
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  • 178
    Publication Date: 2021-10-15
    Description: The climate of the western Mediterranean was characterized by a strong precipitation gradient during the Holocene driven by atmospheric circulation patterns. The scarcity of terrestrial paleoclimate archives has precluded exploring this hydroclimate pattern during Marine Isotope Stages 5 to 3. Here we present stable carbon and oxygen isotope records from three flowstones from southeast Iberia, which show that Dansgaard/Oeschger events were associated with more humid conditions. This is in agreement with other records from the Iberian Peninsula, the Mediterranean, and western Europe, which all responded in a similar way to millennial-scale climate variability in Greenland. This general increase in precipitation during Dansgaard/Oeschger events cannot be explained by any present-day or Holocene winter atmospheric circulation pattern. Instead, we suggest that changes in sea surface temperature played a dominant role in determining precipitation amounts in the western Mediterranean.
    Keywords: 551 ; Spain ; last glacial ; Dansgaard/Oeschger ; speleothem ; Marine Isotope Stage 3 ; western Mediterranean climate
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  • 179
    Publication Date: 2021-10-15
    Description: Porosity and its distribution in impact craters has an important effect on the petrophysical properties of impactites: seismic wave speeds and reflectivity, rock permeability, strength, and density. These properties are important for the identification of potential craters and the understanding of the process and consequences of cratering. The Chicxulub impact structure, recently drilled by the joint International Ocean Discovery Program and International Continental scientific Drilling Program Expedition 364, provides a unique opportunity to compare direct observations of impactites with geophysical observations and models. Here, we combine small-scale petrographic and petrophysical measurements with larger-scale geophysical measurements and numerical simulations of the Chicxulub impact structure. Our aim is to assess the cause of unusually high porosities within the Chicxulub peak ring and the capability of numerical impact simulations to predict the gravity signature and the distribution and texture of porosity within craters. We show that high porosities within the Chicxulub peak ring are primarily caused by shock-induced microfracturing. These fractures have preferred orientations, which can be predicted by considering the orientations of principal stresses during shock, and subsequent deformation during peak ring formation. Our results demonstrate that numerical impact simulations, implementing the Dynamic Collapse Model of peak ring formation, can accurately predict the distribution and orientation of impact-induced microfractures in large craters, which plays an important role in the geophysical signature of impact structures.
    Keywords: 551.8 ; cratering ; porosity ; Chicxulub ; fractures
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  • 180
    Publication Date: 2021-10-15
    Description: Entangled embedded periodic nets and crystal frameworks are defined, along with their dimension type, homogeneity type, adjacency depth and periodic isotopy type. Periodic isotopy classifications are obtained for various families of embedded nets with small quotient graphs. The 25 periodic isotopy classes of depth-1 embedded nets with a single-vertex quotient graph are enumerated. Additionally, a classification is given of embeddings of n-fold copies of pcu with all connected components in a parallel orientation and n vertices in a repeat unit, as well as demonstrations of their maximal symmetry periodic isotopes. The methodology of linear graph knots on the flat 3-torus [0,1)3 is introduced. These graph knots, with linear edges, are spatial embeddings of the labelled quotient graphs of an embedded net which are associated with its periodicity bases.
    Keywords: 548 ; periodic nets ; embedded nets ; coordination polymers ; isotopy types ; crystallographic frameworks
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  • 181
    Publication Date: 2021-10-15
    Description: Geoarchives in ancient settlement sites and their environs bear valuable information about Holocene landscape evolution and human–environment interactions. During the last six millennia, sea-level and coastline changes have had a significant impact on coastal settlements, some of which even had to be relocated. This paper reveals new insights into the spatio-temporal development of the Lycian city of Limyra. Selected sediment cores were analyzed using a multiproxy approach, combining sedimentology, geochemistry, micropaleontology, and 14C dating. When the postglacial sea-level rise decelerated, a coastal barrier and a deep lake, presumably a lagoon, evolved after the mid-Holocene. The siltation history of the lake is complex: three coastal peat layers (mid-4th millennium BC, end of 3rd/beginning of 2nd millennium BC, beginning of 1st millennium BC), indicate periods of semiterrestrial conditions. That they are sandwiched by lake sediments is consistent with new expansion phases of the lake, most likely triggered by coseismic subsidence. There is evidence of a former lakeshore, dated to between 1400 and 1100 BC, with an intentionally deposited layer of anthropogenic remains, now at 5.5 m below the surface. In the mid-1st millennium BC, the lake silted up, river channels evolved, and people started to settle the area of the later city of Limyra.
    Keywords: 551.7 ; ancient city ; Eastern Mediterranean ; Finike plain ; landscape development ; paleogeography ; sea level
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  • 182
    Publication Date: 2021-10-15
    Description: This research conceptually and empirically summarizes multiple aspects of the association between corporate environmental performance and corporate environmental reporting in previous literature, addressing the questions of (a) whether disclosure is a reliable indicator of performance and (b) whether variable measurement characteristics influence empirical outcomes. Systematic literature review and meta-analytic techniques are employed to generate objective and valid summarized effects. The research covers a total of 251 effect sizes within 62 primary studies, representing a total of 56,387 observations. This study discovers a weak and negative association between environmental performance and environmental reporting, supporting the sociopolitical perspective that poor environmental performers have higher motivations to increase their level of disclosure than strong performers. At the same time, this research confirms the heterogeneity of previous studies in the field and verifies the effects of measurement methods on empirical outcomes.
    Keywords: 333.7 ; environmental disclosure ; environmental performance ; environmental reporting ; industrial ecology ; measurement characteristic ; meta-analysis
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  • 183
    Publication Date: 2021-10-15
    Description: The Middle Eocene Climatic Optimum (MECO) was a gradual warming event and carbon cycle perturbation that occurred between 40.5 and 40.1 Ma. A number of characteristics, including greater-than-expected deep-sea carbonate dissolution, a lack of globally coherent negative δ13C excursion in marine carbonates, a duration longer than the characteristic timescale of carbon cycle recovery, and the absence of a clear trigger mechanism, challenge our current understanding of the Earth system and its regulatory feedbacks. This makes the MECO one of the most enigmatic events in the Cenozoic, dubbed a middle Eocene “carbon cycle conundrum.” Here we use boron isotopes in planktic foraminifera to better constrain pCO2 changes over the event. Over the MECO itself, we find that pCO2 rose by only 0.55–0.75 doublings, thus requiring a much more modest carbon injection than previously indicated by the alkenone δ13C-pCO2 proxy. In addition, this rise in pCO2 was focused around the peak of the 400 kyr warming trend. Before this, considerable global carbonate δ18O change was asynchronous with any coherent ocean pH (and hence pCO2) excursion. This finding suggests that middle Eocene climate (and perhaps a nascent cryosphere) was highly sensitive to small changes in radiative forcing.
    Keywords: 551 ; boron isotopes ; pCO2 reconstruction ; Middle Eocene Climatic Optimum ; carbon cycle ; paleoclimate ; cryosphere
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  • 184
    Publication Date: 2021-10-15
    Description: Millennial-scale reductions in monsoon precipitation, so-called Weak Monsoon Intervals (WMIs), have been identified in numerous paleoclimate records across the Afro-Asian monsoon domain throughout the last glacial-interglacial cycle. These are considered the regional response to cooling during Heinrich events in the North Atlantic realm and several mechanisms have been suggested to explain this hemisphere-scale climatic teleconnection. In particular, reductions in Indian Ocean sea surface temperature (SST) have been proposed as the linking element between Heinrich events and WMIs. However, the validity of this relationship has only been demonstrated for the last ~20 kyr, leaving unresolved whether it also holds on longer time scales. Here we present a new paired record of planktonic foraminifera-based δ18Osw-ivc and UK'37-based SST from the northern Bay of Bengal, covering the last ~130 kyr. The δ18Osw-ivc record clearly reflects orbitally paced changes of Indian Summer Monsoon intensity superimposed by centennial- to millennial-scale WMIs that occurred synchronously to North Atlantic Heinrich events. Comparison with the UK'37-based SST reconstruction reveals, however, that WMIs in most cases were not paralleled by ocean surface cooling, questioning whether Indian Ocean SST lowering was the linking element between Heinrich events and reductions in monsoon precipitation in Asia also during the last glacial period.
    Keywords: 551 ; Indian Summer Monsoon ; Weak Monsoon Intervals ; marine sediments ; Bay of Bengal ; foraminifera oxygen isotopes ; UK'37 sea surface temperature
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  • 185
    Publication Date: 2021-10-15
    Description: Despite facilitating transport by low-volume roads for multiple purposes, these roads also open corridors to the remote pristine forests and accelerate forest dynamics with deleterious consequences to the forest functionalities and indigenous inhabitants. We assessed the spatial variations of Hyrcanian forest loss, fragmentation, and degradation resulting from the expansion of rural, logging, and mine roads between 1966 and 2016 in northeast Iran. Various data were employed to generate a precise road network; the density of road segments was weighted on the basis of their carrying capacity during 1966–1986, 1986–2000, and 2000–2016. Three dimensions of forest changes were retrieved using the Landsat time-series and object-based image analysis. The spatial patterns of high rates of forest changes were clustered using spatial autocorrelation indicators. The spatial regression models were carried out to explore relationships between forest change and road expansion. The results showed that rural roads were upgraded but forest and mine roads remarkably expanded in recent decades. The spatial variations of forest-dynamic patterns have been changing from forest loss (1966–2000) to forest fragmentation and degradation (1986–2016). The high density of rural roads was significant on the high rates of forest loss and fragmentation during 1966–2000, and the expansion of forest and mine roads significantly intensified the rates of fragmentation and degradation during 1986–2016. Our findings suggest for mitigating destructive schemes over Hyrcanian forests, developing either protected areas or joining unprotected forests to the reserved areas should be prioritized.
    Keywords: 333.7 ; forest changes ; low-volume roads ; OBIA ; spatial indicators ; spatial models ; time series
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  • 186
    Publication Date: 2021-10-27
    Description: Vertical and horizontal components of GNSS displacements in the Long Valley Caldera and adjacent Sierra Nevada range show a clear correlation with hydrological trends at both multiyear and seasonal time scales. We observe a clear vertical and horizontal seasonal deformation pattern primarily attributable to the solid earth response to hydrological surface loading at large-to-regional (Sierra Nevada range) scales. Several GNSS sites, located at the eastern edge of the Sierra Nevada along the southwestern rim of Long Valley Caldera, also show significant horizontal deformation that cannot be explained by elastic deformation from surface loading. Due to the location of these sites and the strong correlation between their horizontal displacements and spring discharge, we hypothesize that this deformation reflects poroelastic processes related to snowmelt runoff water infiltrating into the Sierra Nevada slopes around Long Valley Caldera. Interestingly, this is also an area where water infiltrates to feed the local hydrothermal system, and where snowmelt-induced earthquake swarms have been recently detected.
    Keywords: 551 ; Long Valley Caldera ; GNSS observations ; transient signal ; nontectonic deformation
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  • 187
    Publication Date: 2021-10-27
    Description: On interannual timescales the growth rate of atmospheric CO2 is largely controlled by the response of the land and ocean carbon sinks to climate variability. Yet, it is unknown to what extent this variability limits the predictability of atmospheric CO2 variations. Using perfect-model Earth System Model simulations, we show that variations in atmospheric CO2 are potentially predictable for 3 years. We find a 2-year predictability horizon for global oceanic CO2 flux with longer regional predictability of up to 7 years. The 2-year predictability horizon of terrestrial CO2 flux originates in the tropics and midlatitudes. With the predictability of the isolated effects of land and ocean carbon sink on atmospheric CO2 of 5 and 12 years respectively, land dampens the overall predictability of atmospheric CO2 variations. Our research shows the potential of Earth System Model-based predictions to forecast multiyear variations in atmospheric CO2.
    Keywords: 551 ; decadal predictability ; atmospheric CO2 ; carbon fluxes ; internal variability ; Earth System Model
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  • 188
    Publication Date: 2021-10-27
    Description: Wheat production plays an important role in Morocco. Current wheat forecast systems use weather and vegetation data during the crop growing phase, thus limiting the earliest possible release date to early spring. However, Morocco's wheat production is mostly rainfed and thus strongly tied to fluctuations in rainfall, which in turn depend on slowly evolving climate dynamics. This offers a source of predictability at longer time scales. Using physically guided causal discovery algorithms, we extract climate precursors for wheat yield variability from gridded fields of geopotential height and sea surface temperatures which show potential for accurate yield forecasts already in December, with around 50% explained variance in an out-of-sample cross validation. The detected interactions are physically meaningful and consistent with documented ocean-atmosphere feedbacks. Reliable yield forecasts at such long lead times could provide farmers and policy makers with necessary information for early action and strategic adaptation measurements to support food security.
    Keywords: 551.6 ; causal discovery algorithms ; teleconnections ; seasonal forecast ; machine learning ; wheat forecast ; climate precursors
    Language: English
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  • 189
    Publication Date: 2021-10-27
    Description: Deforestation influences surface properties such as surface roughness, resulting in changes in the surface energy balance and surface temperature. Recent studies suggest that the biogeophysical effects are dominated by changing roughness, and it remains unclear whether this can be reconciled with earlier modeling studies that highlighted the importance of a reduction of evapotranspiration in the low latitudes and a reduction of net shortwave radiation at the surface in the high latitudes. To clarify this situation, we analyze the local effects of deforestation on surface energy balance and temperature in the MPI-ESM climate model by performing three separate experiments: switching from forest to grass all surface properties, only surface albedo, and only surface roughness. We find that the locally induced changes in surface temperature are dominated by changes in surface roughness for the annual mean, the response of the diurnal amplitude, and the seasonal response to deforestation. For these three quantities, the results of the MPI-ESM lie within the range of observation-based data sets. Deforestation-induced decreases in surface roughness contribute substantially to winter cooling in the boreal regions and to decreases in evapotranspiration in the tropics. By comparing the energy balance decompositions from the three experiments, the view that roughness changes dominate the biogeophysical consequences of deforestation can be reconciled with the earlier studies highlighting the relevance of evapotranspiration.
    Keywords: 551.5 ; deforestation ; land use change ; biogeophysical effects ; local effects ; surface roughness ; surface energy balance
    Language: English
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  • 190
    Publication Date: 2021-10-27
    Description: We show that there is a strong sensitivity of cloud microphysics to model time step in idealized convection-permitting simulations using the COnsortium for Small-scale MOdeling model. Specifically, we found a 53% reduction in precipitation when the time step is increased from 1 to 15 s, changes to the location of precipitation and hail reaching the surface, and changes to the vertical distribution of hydrometeors. The effect of cloud condensation nuclei perturbations on precipitation also changes both magnitude and sign with the changing model time step. The sensitivity arises because of the numerical implementation of processes in the model, specifically the so-called “splitting” of the dynamics (e.g., advection and diffusion) and the parameterized physics (e.g., microphysics scheme). Calculating one step at a time (sequential-update splitting) gives a significant time step dependence because large supersaturation with respect to liquid is generated in updraft regions, which strongly affect parameterized microphysical process rates—in particular, ice nucleation. In comparison, calculating both dynamics and microphysics using the same inputs of temperature and water vapor (hybrid parallel splitting) or adding an additional saturation adjustment within the dynamics reduces the time step sensitivity of surface precipitation by limiting the supersaturation seen by the microphysics, although sensitivity to time step remains for some processes.
    Keywords: 551.5 ; convection permitting ; microphysics ; time step ; parallel splitting ; saturation adjustment ; physics-dynamics coupling
    Language: English
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  • 191
    Publication Date: 2021-10-27
    Description: Rising global temperatures over the last decades have increased heat exposure among populations worldwide. An accurate estimate of the resulting impacts on human health demands temporally explicit and spatially resolved monitoring of near-surface air temperature (Ta). Neither ground-based nor satellite-borne observations can achieve this individually, but the combination of the two provides synergistic opportunities. In this study, we propose a two-stage machine learning-based hybrid model to estimate 1 × 1 km2 gridded intra-daily Ta from surface skin temperature (Ts) across the complex terrain of Israel during 2004–2016. We first applied a random forest (RF) regression model to impute missing Ts from the Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua and Terra satellites, integrating Ts from the geostationary Spinning Enhanced Visible and InfraRed Imager (SEVIRI) satellite and synoptic variables from European Centre for Medium-Range Weather Forecasts' (ECMWF) ERA5 reanalysis data sets. The imputed Ts are in turn fed into the Stage 2 RF-based model to estimate Ta at the satellite overpass hours of each day. We evaluated the model's performance applying out-of-sample fivefold cross validation. Both stages of the hybrid model perform very well with out-of-sample fivefold cross validated R2 of 0.99 and 0.96, MAE of 0.42°C and 1.12°C, and RMSE of 0.65°C and 1.58°C (Stage 1: imputation of Ts, and Stage 2: estimation of Ta from Ts, respectively). The newly proposed model provides excellent computationally efficient estimation of near-surface air temperature at high resolution in both space and time, which helps further minimize exposure misclassification in epidemiological studies.
    Keywords: 551.6 ; air temperature ; health 〈 6. application/context ; health exposure ; MODIS ; random forest ; remote sensing 〈 1. tools and methods ; statistical methods 〈 1. tools and methods ; surface skin temperature
    Language: English
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  • 192
    Publication Date: 2021-10-27
    Description: Understanding hemisphere-wide millennial-scale temperature variability during past glacials in response to ice sheet dynamics and orbital forcing is one of the key targets for Quaternary climate research. While an inland propagation of abrupt temperature changes into Eurasia from the North Atlantic realm during the last glacial (Weichselian) receives increasingly broad support, much less is known regarding the penultimate glacial (Saalian) temperature variability, especially from a continental interior perspective. Here, we present a TEX86-derived lake surface temperature (LST) record from the former Black Sea “Lake” covering nearly the entire Marine Isotope Stage (MIS) 6. While orbital-scale LST cooling likely relates to meltwater discharge from the retreating Eurasian Ice Sheet during insolation maxima, millennial-scale LST variability suggests interstadial warming in phase with Greenland and northern Mediterranean Sea temperature records during the first half of MIS 6. Although summer insolation reached an interglacial-like level during this period, we propose that the reduced extent of the Eurasian Ice Sheet associated with northward shifted atmospheric fronts was ultimately responsible for the inland propagation of Dansgaard-Oeschger-like temperature variability. During the second half of MIS 6, temperature patterns across the North Atlantic-Eurasian corridor were more variable and less comparable with each other, likely because of the larger continental ice sheet weakening northern hemisphere atmospheric teleconnections. Temperature records across the North Atlantic-Eurasian realm suggest a weaker atmospheric teleconnection during MIS 6 compared to MIS 3, likely related to a stronger imprint of the Eurasian Ice Sheet on the continental and regional climate.
    Keywords: 551 ; lake surface temperature ; Black Sea ; MIS 6 ; Eurasia
    Language: English
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  • 193
    Publication Date: 2021-10-27
    Description: A common assumption in models of water flow from soil to root is that the soil can be described in terms of its representative or effective behavior. Microscale heterogeneity and structure are thereby replaced by effective descriptions, and their role in flow processes at the root-soil interface is neglected. Here the aim was to explore whether a detailed characterization of the microscale heterogeneity at the scale of a single root impacts the relation between flow rate and pressure gradient. Numerical simulations of water flow toward a root surface were carried out in a two-dimensional domain with a randomized configuration of spatially variable unsaturated hydraulic conductivities and varying boundary conditions, that is, increasing and decreasing root water uptake rates. By employing Matheron's method, the soil hydraulic properties were varied, while the effective hydraulic conductivity (corresponding to the geometric mean) remained unchanged. Results show that domains with a uniform conductivity could not capture important features of water flow and pressure distribution in spatially variable domains. Specifically, increasing heterogeneity at the root-soil interface allowed to sustain higher root water uptake rates but caused a slower recovery in xylem suction after transpiration ceased. The significance of this is that, under critical conditions, when pressure gradients and flow rates are high, microscale heterogeneity may become an important determinant and should not be neglected in adequate descriptions of water flow from soil to root in dry soil.
    Keywords: 631.4 ; effective soil hydraulic conductivity ; leaf water potential ; soil water potential ; root water uptake ; root-soil interface ; soil heterogeneity
    Language: English
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  • 194
    Publication Date: 2021-10-27
    Description: Using seven single-model ensembles and the two multimodel ensembles CMIP5 and CMIP6, we show that observed and simulated trends in sea surface temperature (SST) patterns are globally consistent when accounting for internal variability. Some individual ensemble members simulate trends in large-scale SST patterns that closely resemble the observed ones. Observed regional trends that lie at the outer edge of the models' internal variability range allow two nonexclusive interpretations: (a) Observed trends are unusual realizations of the Earth's possible behavior and/or (b) the models are systematically biased but large internal variability leads to some good matches with the observations. The existing range of multidecadal SST trends is influenced more strongly by large internal variability than by differences in the model formulation or the observational data sets.
    Keywords: 551.6 ; sea surface temperature patterns ; internal variability ; global climate models ; large ensembles ; model evaluation
    Language: English
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  • 195
    Publication Date: 2021-10-27
    Description: Forecasting and early warning systems are important investments to protect lives, properties, and livelihood. While early warning systems are frequently used to predict the magnitude, location, and timing of potentially damaging events, these systems rarely provide impact estimates, such as the expected amount and distribution of physical damage, human consequences, disruption of services, or financial loss. Complementing early warning systems with impact forecasts has a twofold advantage: It would provide decision makers with richer information to take informed decisions about emergency measures and focus the attention of different disciplines on a common target. This would allow capitalizing on synergies between different disciplines and boosting the development of multihazard early warning systems. This review discusses the state of the art in impact forecasting for a wide range of natural hazards. We outline the added value of impact-based warnings compared to hazard forecasting for the emergency phase, indicate challenges and pitfalls, and synthesize the review results across hazard types most relevant for Europe.
    Keywords: 550 ; impact forecasting ; natural hazards ; early warning
    Language: English
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  • 196
    Publication Date: 2021-11-01
    Description: Mapping spatial and temporal variability of urban microclimate is pivotal for an accurate estimation of the ever-increasing exposure of urbanized humanity to global warming. This particularly concerns cities in arid/semi-arid regions which cover two fifths of the global land area and are home to more than one third of the world's population. Focusing on the desert city of Be'er Sheva Israel, we investigate the spatial and temporal patterns of urban–rural and intra-urban temperature variability by means of satellite observation, vehicular traverse measurement, and computer simulation. Our study reveals a well-developed nocturnal canopy layer urban heat island in Be'er Sheva, particularly in the winter, but a weak diurnal cool island in the mid-morning. Near surface air temperature exhibits weak urban–rural and intra-urban differences during the daytime (〈1°C), despite pronounced urban surface cool islands observed in satellite images. This phenomenon, also recorded in some other desert cities, is explained by the rapid increase in surface skin temperature of exposed desert soils (in the absence of vegetation or moisture) after sunrise, while urban surfaces are heated more slowly. The study highlights differences among the three methods used for describing urban temperature variability, each of which may have different applications in fields such as urban planning, climate change mitigation, and epidemiological research.
    Keywords: 551.6 ; Israel ; desert city ; urban microclimate ; mapping methods
    Language: English
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  • 197
    Publication Date: 2021-11-01
    Description: Abstract We investigated the inventory of presolar silicate, oxide, and silicon carbide (SiC) grains of fine-grained chondrule rims in six Mighei-type (CM) carbonaceous chondrites (Banten, Jbilet Winselwan, Maribo, Murchison, Murray and Yamato 791198), and the CM-related carbonaceous chondrite Sutter's Mill. Sixteen O-anomalous grains (nine silicates, six oxides) were detected, corresponding to a combined matrix-normalized abundance of ~18 ppm, together with 21 presolar SiC grains (~42 ppm). Twelve of the O-rich grains are enriched in 17O, and could originate from low-mass asymptotic giant branch stars. One grain is enriched in 17O and significantly depleted in 18O, indicative of additional cool bottom processing or hot bottom burning in its stellar parent, and three grains are of likely core-collapse supernova origin showing enhanced 18O/16O ratios relative to the solar system ratio. We find a presolar silicate/oxide ratio of 1.5, significantly lower than the ratios typically observed for chondritic meteorites. This may indicate a higher degree of aqueous alteration in the studied meteorites, or hint at a heterogeneous distribution of presolar silicates and oxides in the solar nebula. Nevertheless, the low O-anomalous grain abundance is consistent with aqueous alteration occurring in the protosolar nebula and/or on the respective parent bodies. Six O-rich presolar grains were studied by Auger Electron Spectroscopy, revealing two Fe-rich silicates, one forsterite-like Mg-rich silicate, two Al-oxides with spinel-like compositions, and one Fe-(Mg-)oxide. Scanning electron and transmission electron microscopic investigation of a relatively large silicate grain (490 nm × 735 nm) revealed that it was crystalline åkermanite (Ca2Mg[Si2O7]) or a an åkermanite-diopside (MgCaSi2O6) intergrowth.
    Keywords: 549.112
    Language: English
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  • 198
    Publication Date: 2021-10-12
    Description: Surfaces exposed to atmospheric cold temperature and humid environments are prone to ice accretion. Airplanes, electrical power transmission cables, and wind turbines are typical examples for which icing has to be considered. The measurement of the resulting ice shapes is a challenging process. While macroscopic characteristics of the ice geometry can be observed using photography and optical scanning techniques, microscopic measurements are difficult to conduct because grooved surface partially occludes the geometry of chasms. To overcome this optical inaccessibility, we propose a method to carry out detailed high-resolution measurements of the accretion surface with micro-computed tomography. This approach provides a unique visualization of the empty spaces in the feather region. The information obtained by this technique can improve the understanding of ice accretion physics and its computational modeling.
    Keywords: 551.5 ; atmospheric icing ; ice feather ; icing wind tunnel ; micro-computed tomography
    Language: English
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  • 199
    Publication Date: 2021-10-12
    Description: Gravity waves (GWs) are important for coupling the mesosphere to the lower atmosphere during sudden stratospheric warmings (SSWs). Here, a minor SSW is internally generated in a simulation with the upper-atmosphere configuration of the ICOsahedral Nonhydrostatic model. At a horizontal resolution of 20 km the simulation uses no GW drag parameterizations but resolves large fractions of the GW spectrum explicitly, including orographic and nonorographic sources. Consistent with previous studies, the simulated zonal-mean stratospheric warming is accompanied by zonal-mean mesospheric cooling. During the course of the SSW the mesospheric GW momentum flux (GWMF) turns from mainly westward to mainly eastward. Waves of large phase speed (40–80 m s −1) dominate the eastward GWMF during the peak phase of the warming. The GWMF is strongest along the polar night jet axis. Parameterizations of GWs usually assume straight upward propagation, but this assumption is often not satisfied. In the case studied here, a substantial amount of the GWMF is significantly displaced horizontally between the source region and the dissipation region, implying that the local impact of GWs on the mesosphere does not need to be above their local transmission through the stratosphere. The simulation produces significant vertically misaligned anomalies between the stratosphere and mesosphere. Observations by the Microwave Limb Sounder confirm the poleward tilt with height of the polar night jet and horizontal displacements between mesospheric cooling and stratospheric warming patterns. Thus, lateral GW propagation may be required to explain the middle-atmosphere temperature evolution in SSW events with significant zonally asymmetric anomalies.
    Keywords: 551.5 ; Sudden Stratospheric Warming ; Gravity wave propagation ; Zonal asymmetries ; High-resolution climate model ; Microwave Limb Sounder ; Tilt of polar night jet
    Language: English
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  • 200
    Publication Date: 2021-10-12
    Description: Recent evidence shows that wind-driven ocean currents, like the western boundary currents, are strongly affected by global warming. However, due to insufficient observations both on temporal and spatial scales, the impact of climate change on large-scale ocean gyres is still not clear. Here, based on satellite observations of sea surface height and sea surface temperature, we find a consistent poleward shift of the major ocean gyres. Due to strong natural variability, most of the observed ocean gyre shifts are not statistically significant, implying that natural variations may contribute to the observed trends. However, climate model simulations forced with increasing greenhouse gases suggest that the observed shift is most likely to be a response of global warming. The displacement of ocean gyres, which is coupled with the poleward shift of extratropical atmospheric circulation, has broad impacts on ocean heat transport, regional sea level rise, and coastal ocean circulation.
    Keywords: 551.46 ; ocean gyre ; climate change ; poleward shift ; global warming ; ocean circulation ; sea level rise
    Language: English
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