bluuebunny/crossref_metadata_2025 huggingface dataset:
 Implementation of mycorrhizal mechanism into a soil carbon model improves the prediction of long-term processes of plant litter decomposition
Authors: Huang Weilin , van Bodegom Peter , Viskari Toni , Liski Jari , Soudzilovskaia Nadejda
Published: March 2021

Mycorrhizae, a plant-fungal symbiosis, is an important contributor to below ground-microbial interactions, and hypothesized to play a paramount role in soil carbon (C) sequestration. Ectomycorrhizae (EM) and arbuscular mycorrhizae (AM) are the two dominant forms of mycorrhizae featured by nearly all Earth plant species. However, the difference in the nature of their contributions to the processes of plant litter decomposition is still understood poorly. Current soil carbon models treat mycorrhizal impacts on the processes of soil carbon transformation as a black box. This retards scientific progress in mechanistic understanding of soil C dynamics.

We examined four alternative conceptualizations of the mycorrhizal impact on plant litter C transformations, by integrating AM and EM fungal impacts on litter C pools of different recalcitrance into the soil carbon model Yasso15. The best performing concept featured differential impacts of EM and AM on a combined pool of labile C, being quantitatively distinct from impacts of AM and EM on a pool of recalcitrant C.

Analysis of time dynamics of mycorrhizal impacts on soil C transformations demonstrated that these impacts are larger at the long-term (>2.5yrs) litter decomposition processes, compared to the short-term processes. We detected that arbuscular mycorrhizae controls shorter term decomposition of labile carbon compounds, while ectomycorrhizae dominate the long term decomposition processes of highly recalcitrant carbon elements. Overall, adding our mycorrhizal module into the Yasso model greatly improved the accuracy of the temporal dynamics of carbon sequestration.

A sensitivity analysis of litter decomposition to climate and mycorrhizal factors indicated that ignoring the mycorrhizal impact on the decomposition leads to an overestimation of climate impacts. This suggests that being co-linear with climate impacts, mycorrhizal impacts could be partly hidden within climate factors in soil carbon models, reducing the capability of such models to mechanistically predict impacts of climate vs vegetation change on soil carbon dynamics.

Our results provide a benchmark to mechanistic modelling of microbial impacts on soil C dynamics. This work opens new pathways to examining the impacts of land-use change and climate change on plant-microbial interactions and their role in soil C dynamics, allowing the integration of microbial processes into global vegetation models used for policy decisions on terrestrial carbon monitoring.
Investigation of ambient noise seismological methods on a bridge model
Authors: Liao Chun-Man , Mehrkens Franziska , Hadziioannou Celine , Niederleithinger Ernst
Published: March 2021

The aim of this work is to investigate the application of seismological noise-based monitoring for bridge structures. A large-scale two-span concrete bridge model with a build-in post-tensioning system, which is exposed to environmental conditions, is chosen as our experimental test structure. Ambient seismic noise measurements were carried out under different pre-stressed conditions. Using the seismic interferometry technique, which is applied to the measurement data in the frequency domain, we reconstruct waveforms that relate to wave propagation in the structure. The coda wave interferometry technique is then implemented by comparing two waveforms recorded in two pre-stress states. Any relative seismic velocity changes are identified by determining the correlation coefficients and reveal the influence of the pre-stressing force. The decrease of the wave propagation velocity indicates the loss of the pre-stress and weakening stiffness due to opening or event extension of cracks. We conclude that the seismological methods used to estimate velocity change can be a promising tool for structural health monitoring of civil structures.
Global modeled sinking characteristics of biofouled microplastic
Authors: Lobelle Delphine , Kooi Merel , Koelmans Albert A. , Laufkotter Charlotte , Jongedijk Cleo E. , Kehl Christian , van Sebille Erik
Published: March 2021

Microplastic debris ending up at the sea surface has become a known major environmental issue. However, how microplastic particles move and when they sink in the ocean remains largely unknown. Here, we model microplastic subject to biofouling (algal growth on a substrate) to estimate sinking timescales and the time to reach the depth where particles stops sinking. We combine NEMO-MEDUSA 2.0 output, that represents hydrodynamic and biological properties of seawater, with a particle-tracking framework. Different sizes and densities of particles (for different types of plastic) are simulated, showing that the global distribution of sinking timescales is largely size-dependent as opposed to density-dependent. The smallest particles we simulate (0.1 μm) start sinking almost immediately around the globe and their trajectories produce the longest time to reach their first sinking depth (almost 40 days as a global median). In oligotrophic subtropical gyres with low algal concentrations, particles between 1 mm and 10 μm do not sink within the 90-day simulation time. This suggests that in addition to the comparatively well-known physical processes, biological processes might also contribute to the accumulation of floating plastic (of 1 mm to 10 μm) in subtropical gyres. Particles of 1 μm in the gyres start sinking largely due to vertical advection, whereas 0.1 μm particles sink both due to biofouling and advection. The qualitative impacts of seasonality on sinking timescales are small, however, localised sooner sinking due to spring algal blooms is seen. This study maps processes that affect the sinking of virtual microplastic globally, which could ultimately impact the ocean plastic budget.
Short lived peaks of stem methane emissions in temperate black alder forest - irrelevant for ecosystem methane budgets?
Authors: Köhn Daniel , Günther Anke , Jurasinski Gerald
Published: March 2021

Tree stems can be a source of the greenhouse gas methane (CH4) and locally as regionally important to the overall GHG budget. Stem emissions even hold the potential of narrowing down knowledge gap in the global methane budget. However, assessments of the global importance of stem CH4 emissions are complicated by a lack of research and high variability between individual ecosystems. Here, we determined the contribution of emissions from stems of mature black alder (Alnus glutinosa (L.) Gaertn.) to overall CH4 exchange in two temperate peatlands. We measured emissions from stems and soils using closed chambers in a drained and an undrained alder forest over 2 years. Furthermore, we studied the importance of alder leaves as substrate for methanogenesis in an incubation experiment. Stem CH4 emissions at the undrained alder forest were very variable in time and only persisted for a few weeks during the year. Generally the drained alder forest did not soil nor stem CH4 emissions. Different upscaling approaches were assessed and all approaches showed that stem CH4 emissions contributed less than 0.3 % to the total ecosystem CH4 budget. However, stem CH4 seem to depend strongly on the hydrological regime and therefore vary strongly between ecosystems. Hence, every ecosystem must be consdidered attentively with respect to their stem CH4 emissions.
How much Arctic fresh water participates in the subpolar overturning circulation?
Authors: Le Bras Isabela , Straneo Fiamma , Muilwijk Morven , Smedsrud Lars Henrik , Li Feili , Lozier Susan , Holliday Penny
Published: March 2021

Fresh Arctic waters flowing into the Atlantic are thought to have two primary fates. They may be mixed into the deep ocean as part of the overturning circulation, or flow alongside regions of deep water formation without impacting overturning. Climate models suggest that as increasing amounts of fresh water enter the Atlantic, the overturning circulation will be disrupted, yet we lack an understanding of how much fresh water is mixed into the overturning circulation's deep limb in the present day. To constrain these fresh water pathways, we build steady-state volume, salt, and heat budgets east of Greenland that are initialized with observations and closed using inverse methods. Fresh water sources are split into oceanic Polar Waters from the Arctic and surface fresh water fluxes, which include net precipitation, runoff, and ice melt, to examine how they imprint the circulation differently. We find that 65 mSv of the total 110 mSv of surface fresh water fluxes that enter our domain participate in the overturning circulation, as do 0.6 Sv of the total 1.2 Sv of Polar Waters that flow through Fram Strait. Based on these results, we hypothesize that the overturning circulation is more sensitive to future changes in Arctic fresh water outflow and precipitation, while Greenland runoff and iceberg melt are more likely to stay along the coast of Greenland.
A geodetic approach to Mapping and Parametrization of Argo Temperature and Salinity Profiles
Authors: Yakhontova Alisa , Rietbroek Roelof , Stolzenberger Sophie , Jonas Nadja
Published: March 2021

This study addresses mapping of Argo temperature and salinity profiles onto arbitrary positions using physically advanced statistical information from model fields, and their subsequent parametrization as function of depth. Argo suffers from spatio-temporal sampling problems, and some signals are not well captured, e.g. in the deeper ocean below 2000m, around the boundary currents, in the Arctic or in the shelf/coastal regions which are not frequently visited by floats. Mapping of Argo data into sparsely sampled areas would greatly benefit from additional physical information of coherent T/S behavior in form of covariance functions. Outputs from global general ocean circulation model FESOM1.4 provide covariance information for least squares collocation and also complement the spatially undersampled Argo data in high latitudes and in deep ocean. Additionally, model covariances are used to identify areas of strong correlation with interpolation points, so that only Argo measurements inside these areas are included in the mapping procedure. Parametrization of T/S profiles is performed with b-splines where the choice of knot locations is a trade-off between accuracy and overfitting. Proposed methodology is tested in South Atlantic, but can be extended to other regions.
Anisotropy of out-of-phase magnetic susceptibility: an approach for magnetic subfabrics determination
Authors: Cruz Cláudia , Sant'Ovaia Helena , McCarthy William , Noronha Fernando
Published: March 2021

The Anisotropy of Magnetic Susceptibility (AMS) represents the contribution of all minerals in rock samples (paramagnetic, diamagnetic, and/or ferromagnetic minerals). An intermediate AMS tensor may be recorded in rocks where a composite fabric is present, due to the presence of both paramagnetic and ferromagnetic minerals, being possible to be resolved into two distinct subfabrics using techniques as out-of-phase AMS (opAMS). The magnetic susceptibility measured in alternating field can be resolved into in-phase and out-of-phase components. In-phase AMS (ipAMS) measures the bulk response of all minerals in a sample however, opAMS is only sensitive to selected ferromagnetic minerals such as hematite, titanomagnetite, and ultrafine magnetite. The opAMS can be harnessed as a tool for direct determination of magnetic subfabrics defined by ferromagnetic minerals. This work focuses on three Portuguese plutons: Lamas de Olo, Lavadores-Madalena, and Santa Eulália. The preliminary results show that magnetic susceptibility is lower in opAMS, the degree of magnetic anisotropy is much higher in opAMS and the ellipsoid shape parameter has no significant differences in opAMS or ipAMS. The ipAMS and opAMS tensors are in general coaxial, pointing out that standard AMS fabric is parallel to the subfabric of minerals like hematite, titanomagnetite, and ultrafine magnetite. Two sites from Lamas de Olo Pluton with low in-phase magnetic susceptibility (ipKm) values were also measured, showing two different scenarios: (i) the coaxially is present in one site, pointing out the presence of minerals like hematite (after magnetite) but with the same orientation as the matrix; (ii) different orientation of K1 and K3 in ipAMS and opAMS suggesting the presence of a ferromagnetic oxide like hematite (after magnetite) but with a different orientation from the paramagnetic minerals. Nevertheless, it should be noted that in samples with low Km values, the presence of ferromagnetic minerals is scarce (or absent) and the opAMS has minor accuracy (the associated error is greater). The opAMS findings attain similar results to the anisotropy of anhysteretic remanent magnetization (AARM) studies, once both are related to the presence of ferromagnetic minerals, and their magnetic properties. However, the opAMS does not require the permanent magnetization of samples and is measured simultaneously with the ipAMS. With further works, a larger number of samples will be measured to accomplish more information, and AARM measurements will be performed on the same samples to compare the ipAMS, opAMS, and AARM tensors.

Acknowledgements: This work was funded by the Fundação para a Ciência e a Tecnologia (FCT) under UIDB/04683/2020 project.
The open-ended, high cadence, Kp-like geomagnetic Hp30 and Hp60 indices
Authors: Kervalishvili Guram , Matzka Jürgen , Stolle Claudia , Rauberg Jan
Published: March 2021

The new planetary open-ended Hpo index family (consisting of the half-hourly Hp30 and hourly Hp60) has been developed within the Space Weather Atmosphere Models and Indices (SWAMI) project (see http://swami-h2020.eu/) of the H2020 European Union research activity. These new indices resemble the Kp index by having a similar derivation scheme and a nearly identical frequency distribution of index values for events with values < 9. However, they have provided a better temporal resolution than the 3-hourly Kp index. Additionally, the events with values > 9- are further subdivided using an open-ended scale (9o, 9+, 10-, 10o, 10+, 11-, ...) to better represent different levels of strong geomagnetic activity. In this study, the advantages and integrity of Hp30 and Hp60 indices are analysed and discussed. The comparison of these indices with the 3-hourly Kp index in terms of frequency distribution and correlation and with other geophysical parameters are also presented.

Near real-time indices and archive indices back to 1995 are available from GFZ under the CC BY 4.0 license including linear versions of the Hp30 and Hp60 indices, the ap30 and ap60 indices (see https://www.gfz-potsdam.de/en/section/geomagnetism/data-products-services/hpo-index/). Near real-time plots of the Hp30, Hp60 and Kp indices for the current day and the previous six days are also provided.
Indication of high basal melting at EastGRIP drill site on the Northeast Greenland Ice Stream
Authors: Zeising Ole , Humbert Angelika
Published: March 2021

The origin of Greenland’s largest ice stream – the Northeast Greenland Ice Stream (NEGIS) – is located far inland of the Greenland Ice Sheet. High surface flow velocities in the center of NEGIS are attributed to the lubrication of the ice sheet base facilitated by basal melt water. In order to derive basal melt rates at the EastGRIP drill site (~2668 m thick ice), we performed in-situ measurements with an autonomous phase-sensitive radar (ApRES; Brennan et al., 2014; Nicholls et al., 2015) in two consecutive years. The precise processing method (Stewart et al., 2019 and Vankova et al., 2020) detects englacial and basal vertical displacements, but it is limited due to noisy data in the lower half of the ice column. Thus, we made assumptions for the vertical strain in the lower half and adapted simulation results (Rückamp et al., 2020). We found melt rates ranging from 0.16 to 0.22 m/a, which is extremely large for inland ice. However, our results are only slightly above melt rates from previous studies (Fahnestock et al., 2001 and MacGregor et al., 2016) which found melt rates of 0.10 m/a and more through airborne radar measurements (evaluated using radiostratigraphy methods) in the vicinity of EastGRIP. Melt rates of >0.16 m/a require a heat flux into the ice of >1.55 W/m2 which is not exclusively the geothermal heat flux, as also the subglacial hydrological system may supply a significant heat flux into the ice.
Past, present and future aerosol forcing derived from CMIP6
Authors: Smith Christopher , Harris Glen , Palmer Matthew , Bellouin Nicolas , Collins William , Schulz Michael , Myhre Gunnar , Golaz Jean-Christophe , Ringer Mark , Storelvmo Trude , Forster Piers
Published: March 2021

Aerosol forcing remains the most uncertain component of the total climate forcing on the Earth system. RFMIP and AerChemMIP contained experiments that allow us to determine time-slice present day (2014 minus 1850) from 17 CMIP6 models, and transient (1850 to 2014, or 2100) aerosol forcing from 11 models. In CMIP6, aerosol present-day aerosol forcing is -1.01 (full range -1.37 to -0.63) W m-2, a range considerably narrower than comprehensive assessments of aerosol forcing from multiple lines of evidence such as AR5 (-1.9 to -0.1 W m-2) or Bellouin et al. 2020 (-2.0 to -0.35 W m-2). The transient experiments also show a diversity in time histories, with most models showing a peak negative aerosol forcing at some time between 1975 and 2010, and recent trends varying from strongly recovering to slightly strengthening aerosol forcing. Models that were run to 2100 under SSP2-4.5 all show a projected weakening aerosol forcing.

By fitting a simple relationship of how globally integrated emissions of black carbon, organic carbon and SO2 relate to effective radiative forcing from aerosol-radiation interactions (ERFari) and aerosol-cloud interactions (ERFaci), an emissions to forcing relationship can be determined for these 11 RFMIP and AerChemMIP models. Using a 100,000 member Monte Carlo ensemble of historical aerosol time series, where coefficients are drawn from these model-derived distributions, and total 1850 to 2014 aerosol forcing is taken from the wider distributions of Bellouin et al. (2020), we create a best estimate historical time series for aerosol forcing (with uncertainty) that is constrained to historical warming and observed ocean heat uptake using a simple climate model. This method can also be used to predict aerosol forcing from future emissions scenarios, such as the SSPs and those derived from integrated assessment models, and provides estimates of the likely ranges for equilibrium climate sensitivity and transient climate response based on the historical aerosol forcing.
The role of tropopause polar vortices in the intensification of Summer Arctic cyclones
Authors: Gray Suzanne L. , Hodges Kevin , Vautrey Jonathan , Methven John
Published: March 2021

Human activity in the Arctic is expected to increase as new regions become accessible, with a consequent need for reliable forecasts of hazardous weather. Arctic cyclones are synoptic-scale cyclones developing within or moving into the Arctic region. Meso- to synoptic-scale tropopause-based coherent vortices called tropopause polar vortices (TPVs) are frequently observed in polar regions and are a proposed mechanism for Arctic cyclone genesis and intensification. While the importance of pre-existing tropopause-level features for cyclone development, and their existence as part of the three-dimensional mature cyclone structure, is well established in the mid-latitudes, evidence of the importance of pre-existing TPVs for Arctic cyclone development is more limited. Here we present a climatology and characteristics of summer Arctic cyclones and TPVs, produced by tracking them in the latest global ECMWF reanalysis (ERA5), and determine the role of pre-existing TPVs in the initiation and intensification of these cyclones.
Evolution of the Solar Wind Direction through the Heliosphere
Authors: Němeček Zdeněk , Ďurovcová Tereza , Šafránková Jana , Richardson John D. , Šimůnek Jiří , Stevens Michael L.
Published: March 2021

The solar wind non-radial velocity components observed beyond the Alfvén point are usually attributed to waves, the interaction of different streams, or other transient phenomena. However, Earth-orbiting spacecraft as well as monitors at L1 indicate systematic deviations of the wind velocity from the radial direction. Since these deviations are of the order of several degrees, the calibration of the instruments is often questioned. This paper investigates for the first time the evolution of non-radial components of the solar wind flow along the path from ≈ 0.17 to 10 AU. A comparison of observations at 1 AU with those closer to or farther from the Sun based on measurements of many spacecraft at different locations in the heliosphere (Parker Solar Probe, Helios 1 and 2, Wind, ACE, Spektr-R, ARTEMIS probes, MAVEN, Voyagers 1and 2) shows that (i) the average values of non-radial components are not zero and vary in a systematic manner with the distance from the Sun, (ii) their values significantly depend on the solar wind radial velocity, (iii) the deviation from radial direction well correlates with the cross-helicity, and (iv) the values of non-radial components peaks at 0.25 AU and gradually decreases toward zero in the outer heliosphere. Our results suggest that the difference in the propagation direction between the faster and slower winds is already established in the solar corona and is connected with the forces emitting solar wind plasma from the coronal magnetic field. The correlation with cross-helicity probably points to outward propagating Alfven waves generated in outer corona as the most probable source of observed deviations.
ENSO response to changes in the tropical Indian ocean temperature
Authors: Ferster Brady , Fedorov Alexey , Mignot Juliette , Guilyardi Eric
Published: March 2021

Since the start of the 21st century, El Niño-Southern Oscillation (ENSO) variability has changed, supporting generally weaker Central Pacific El Niño events. Recent studies suggest that stronger trade winds in the equatorial Pacific could be a key driving force contributing to this shift. One possible mechanism to drive such changes in the mean tropical Pacific climate state is the enhanced warming trends in the tropical Indian Ocean (TIO) relative to the rest of the tropics. TIO warming can affect the Walker circulation in both the Pacific and Atlantic basins by inducing quasi-stationary Kelvin and Rossby wave patterns. Using the latest coupled-model from Insitut Pierre Simon Laplace (IPSL-CM6), ensemble experiments are conducted to investigate the effect of TIO sea surface temperature (SST) on ENSO variability. Applying a weak SST nudging over the TIO region, in four ensemble experiments we change mean Indian ocean SST by -1.4°C, -0.7°C, +0.7°C, and +1.4°C and find that TIO warming changes the magnitude of the mean equatorial Pacific zonal wind stress proportionally to the imposed forcing, with stronger trades winds corresponding to a warmer TIO. Surprisingly, ENSO variability increases in both TIO cooling and warming experiments, relative to the control. While a stronger ENSO for weaker trade winds, associated with TIO cooling, is expected from previous studies, we argue that the ENSO strengthening for stronger trade winds, associated with TIO cooling, is related to the induced changes in ocean stratification. We illustrate this effect by computing different contributions to the Bjerknes stability index. Thus, our results suggest that the tropical Indian ocean temperatures are an important regulator of TIO mean state and ENSO dynamics.
Foreshock ULF fluctuations near the Moon: THEMIS observations
Authors: Salohub Anna , Šafránková Jana , Němeček Zdeněk
Published: March 2021

The foreshock is a region filled with a turbulent plasma located upstream the Earth’s bow shock where interplanetary magnetic field (IMF) lines are connected to the bow shock surface. In this region, ultra-low frequency (ULF) waves are generated due to the interaction of the solar wind plasma with particles reflected from the bow shock back into the solar wind. It is assumed that excited waves grow and they are convected through the solar wind/foreshock, thus the inner spacecraft (close to the bow shock) would observe larger wave amplitudes than the outer (far from the bow shock) spacecraft. The paper presents a statistical analysis of excited ULF fluctuations observed simultaneously by two closely separated THEMIS spacecraft orbiting the Moon under a nearly radial IMF. We found that ULF fluctuations (in the plasma rest frame) can be characterized as a mixture of transverse and compressional modes with different properties at both locations. We discuss the growth and/or damping of ULF waves during their propagation.
Assessing water doses, water use efficiency and tomato quality under greenhouse conditions in Natabuela-Ecuador
Authors: Colimba Limaico Javier Ezcequiel , Zubelzu Minguez Sergio , Rodriguez Sinobas Leonor
Published: March 2021

In Ecuador, tomato (Solanum lycopersicum L.) is a main crop which production has been increase in the latest decade. The crop is grown throughout the country, although it is in the Sierra region where locate the greenhouse production areas. Tomato manufacturers face the water scarcity problems and in addition, the small and medium producers have little knowledge regarding the amount of water they should apply to the crop, and how they should manage. Considering this framework, this study first is aimed at determining the optimal water doses for tomato crop cultivated under greenhouse conditions in the Sierra region and second, it is aimed at establishing the best irrigation frequency. The experimental study was carried out from June to December 2020, in a metallic greenhouse with plastic cover, located in the Natabuela’s parish which belong to the city of Antonio Ante in the Imbabura province. The variables studied were:  two water doses (100% and 120% of the of the evapotraspiration, ET) and four irrigation frequencies (two irrigations and one irrigation a day, one irrigation every other day and one irrigation every two days). In total, eight treatments were evaluated in an 2 x 4 factorial design, under a completely random block distribution, with four repetitions. The results show that the 120% ET irrigation dose produces the highest plant vigor and total and commercial production, while the 100% ET irrigation dose presents a higher citric acid percentage and total soluble solids content. Likewise, both doses do not showed significant differences in their water use efficiency and pH. Therefore, if the increase in production is searching then, it would be advisable to apply the 120% ET dose, although if the search is for the production quality it would be better to apply 100% ET. Regarding the irrigation frequency, one or two irrigations a day produced higher plant vigor as well as higher production and water use efficiency. None of the irrigation frequencies studied had significant differences in plant height and fruit quality variables.

 
Changes in leaf nitrogen and phosphorus content from observations and a land surface model: evidence for increasing nutrient imbalance in Europe
Authors: Caldararu Silvia , Fleischer Katrin , Yu Lin , Zaehle Sönke
Published: March 2021

Increasing atmospheric CO2 concentrations can be a driver for higher ecosystem productivity across the globe but nutrient availability may limit subsequent biomass growth. Concurrently, increased anthropogenic nitrogen (N) deposition introduces a relatively large amount of N into the system, thus potentially alleviating N limitation. However, this new N input could push ecosystems into being limited by other resources, most importantly phosphorus (P) in mid- and high-latitude systems, leading to what has been termed an NP imbalance. While the ecological theory behind the processes described above has been discussed on many occasions, it is yet unclear what the actual spatial and temporal patterns of such an imbalance are, as well as the ecpological processes and drivers behind such observed patterns.

Here, we use leaf N and P data from a large European monitoring network, ICP forests, in conjunction with a land surface model, QUINCY (QUantifying Interactions between terrestrial Nutrient CYcles and the climate system), to explore the patterns and drivers behind nutrient limitation at European forest sites. The overall trend in observed leaf N and P content as well as N:P ratio show an increasing nutrient limitation from 1990 to 2015, as well as a shift towards P limitation. However, the observed spatial patterns of change in leaf nutrient content vary strongly with soil nutrient availability, N deposition and leaf habit. The effect of leaf habit suggests that leaf growth strategies  play an important role in dealing with nutrient availability and controlling observed ecosystem responses. 

We use the QUINCY model to explore the drivers behind the observed leaf nutrient trends. We perform simulations with fixed levels of atmospheric CO2 as well as in the absence of anthropogenic nitrogen deposition. We show that the decrease in leaf N and P content is attributable to increased atmospheric CO2, while the changes in N:P stoichiometry are reproducible with increased N deposition. Additionally, the model can only predict observed trends when representing physiologically-realistic responses of leaf stoichiometry to nutrient availability. The use of a process-based model allows us to attribute drivers to the observed changes in leaf nutrient content. This research helps the development of data-constrained, process-based models which can potentially be used to predict changes in ecosystem nutrient limitation, and implicitly growth and carbon storage, under future scenarios
Irrigation Estimates from Remote Sensing Soil Moisture: A District-Scale Analysis in Spain
Authors: Dari Jacopo , Quintana-Seguí Pere , Escorihuela María José , Stefan Vivien , Morbidelli Renato , Saltalippi Carla , Flammini Alessia , Brocca Luca
Published: March 2021

Irrigation represents a primary source of anthropogenic water consumption, whose effects impact on the natural distribution of water on the Earth’s surface and on food production. Over anthropized basins, irrigation often represents the missing variable to properly close the hydrological balance. Despite this, detailed information on the amounts of water actually applied for irrigation is lacking worldwide. In this study, a method to estimate irrigation volumes applied over a heavily irrigated area in the North East of Spain through high-resolution (1 km) remote sensing soil moisture is presented. Two DISPATCH (DISaggregation based on Physical And Theoretical scale CHange) downscaled data sets have been used: SMAP (Soil Moisture Active Passive) and SMOS (Soil Moisture and Ocean Salinity). The SMAP experiment covers the period from January 2016 to September 2017, while the SMOS experiment is referred to the time span from January 2011 to September 2017. The irrigation amounts have been retrieved through the SM2RAIN algorithm, in which the guidelines provided in the FAO (Food and Agriculture Organization) paper n.56 about the crop evapotranspiration have been implemented for a proper modeling of the crop evapotranspiration. A more detailed analysis has been performed in the context of the SMAP experiment. In fact, the spatial distribution and the temporal occurrence of the irrigation events have been investigated. Furthermore, the loss of accuracy of the irrigation estimates when using different sources for the evapotranspiration data has been assessed. In order to do this, the SMAP experiment has been repeated by forcing the SM2RAIN algorithm with several evapotranspiration data sets, both calculated and observed. Finally, the merging of the results obtained through the two experiments has produced a data set of almost 7 years of irrigation estimated from remote sensing soil moisture.
Overriding plate deformation and topography during slab rollback and slab rollover: insights from subduction experiments
Authors: Xue Kai , Schellart Wouter P. , Strak Vincent
Published: March 2021

Overriding plate deformation (OPD) and topography vary at different subduction zones, with some subduction zones showing mainly overriding plate extension and low topography (e.g. Mariana, Tonga, Izu-Bonin subduction zones), while some showing mainly shortening and elevated topography (e.g. Makran, southern Manila subduction zones). Here we investigate how different subduction modes, namely trench retreat and trench advance, affect OPD and generate corresponding topography with fully dynamic analogue models of time-evolving subduction in three-dimensional space. We conduct two sets of experiments, one of which is characterized by trench retreat and slab rollback, and the other characterized by trench advance and slab rollover. We compute the mantle flow, the overriding plate strain and topography during subduction using the particle image velocimetry technique (PIV). The overriding plate in the experiments showing continuous trench retreat experiences overall extension, while in the experiments with trench advance following trench retreat it experiences overall shortening. The overriding plate in both trench retreat and trench advance subduction modes present fore-arc shortening and intra-arc extension. Our experiments indicate that the overall OPD except in the fore-arc region is mainly driven by the horizontal mantle flow at the base of the OP inducing a viscous drag force (FD), and is determined by the gradient of the horizontal mantle flow velocity (dvx/dx). Furthermore, a large-scale trenchward overriding plate tilting and an overall subsidence of the overriding plate were observed in the experiments showing continuous trench retreat, while a landward tilting and an overall uplift of the overriding plate were observed during long-term trench advance. The two types of topography during the two different subduction modes can be ascribed to the large-scale trenchward and landward mantle flow, respectively, and thus represent forms of dynamic topography. Our models showing trench advance provide a possible mechanism for OPD in the Makran subduction zone, which has experienced overall trench-normal tectonic shortening in the overriding plate, but shows extension in a local region of the coastal Makran that is spatially comparable to that in our experiments.  In addition, these models might also provide an explanation for the regional topography at the Makran subduction zone, which shows a long-wavelength topographic high in the overriding plate near the trench that decreases northward.
Calibration of a frontal ablation parameterization applied to Greenland's peripheral calving glaciers
Authors: Recinos Beatriz , Maussion Fabien , Noël Brice , Möller Marco , Marzeion Ben
Published: March 2021

Greenland's Peripheral Glaciers (PGs) are glaciers that are weakly or not connected to the Ice Sheet. Many are tidewater, losing mass via frontal ablation. Without comprehensive regional observations or enough individual estimates of frontal ablation, constraining model parameters remains a challenging task in this region. We present three independent ways to calibrate the calving parameterization implemented in the Open Global Glacier Model (OGGM) and asses the impact of accounting for frontal ablation on the estimate of ice stored in PGs. We estimate an average regional frontal ablation flux for PGs of 7.94±4.15 Gtyr-1 after calibrating the model with two different satellite velocity products, and of 0.75±0.55 Gt yr-1 if the model is constrained using frontal ablation fluxes derived from independent modelled Surface Mass Balance (SMB) averaged over an equilibrium reference period (1961-1990). This second method is based on the assumption that most PGs during that time have an equilibrium between mass gain via SMB and mass loss via frontal ablation. This assumption can serve as a basis to assess the order of magnitude of dynamic mass loss of glaciers when compared to the SMB imbalance. By comparing the model output after applying both calibration methods, we find that the model is not able to predict individual tidewater glacier dynamics if it relies only on SMB estimates and the assumption of a closed budget to constrain the model. The differences between the results from both calibration methods serve as an indication of how strong the dynamic imbalance might have been for PGs during that reference period.
Quantifying heating biases in marine air temperature observations, ~1790 - present
Authors: Cropper Thomas , Kent Elizabeth , Berry David , Cornes Richard , Recinos-Rivas Beatriz
Published: March 2021

Accurate, long-term time series of near-surface air temperature (AT) are the fundamental datasets on which the magnitude of anthropogenic climate change is scientifically and societally addressed. Across the ocean, these (near-surface) climate records use Sea Surface Temperature (SST) instead of Marine Air Temperature (MAT) and blend the SST and AT over land to create datasets. MAT has often been overlooked as a data choice as daytime MAT observations from ships are known to contain warm biases due to the storage of accumulated solar energy. Two recent MAT datasets, CLASSnmat (1881 – 2019) and UAHNMAT (1900 – 2018), both use night-time MAT observations only. Daytime MAT observations in the International Comprehensive Ocean–Atmosphere Data Set (ICOADS) account for over half of the MAT observations in ICOADS, and this proportion increases further back in time (i.e. pre-1850s). If long-term MAT records over the ocean are to be extended, the use of daytime MAT is vital.

 

To adjust for the daytime MAT heating bias, and apply it to ICOADS, we present the application of a physics-based model, which accounts for the accumulated energy storage throughout the day. As the ‘true’ diurnal cycle of MAT over the ocean has not been, to-date, adequately quantified, our approach also removes the diurnal cycle from ICOADS observations and generates a night-time equivalent MAT for all observations. We fit this model to MAT observations from groups of ships in ICOADS that share similar heating biases and metadata characteristics. This enables us to use the empirically derived coefficients (representing the physical energy transfer terms of the heating model) obtained from the fit for use in removal of the heating bias and diurnal cycle from ship-based MAT observations throughout ICOADS which share similar characteristics (i.e. we can remove the diurnal cycle from a ship which only reports once daily at noon). This adjustment will create an MAT record of night-time-equivalent temperatures that will enable an extension of the marine surface AT record back into the 18th century.
Are ectomycorrhizal fungi actually adapting to 5 years of extreme summer drought in Middle European forests?
Authors: Weikl Fabian , Pritsch Karin
Published: March 2021

Middle Europe’s forests face an increasing risk of recurring summer droughts. To explore the impact of such conditions, trees in a mature spruce-beech forest were exposed to five successive years of extreme summer drought during the Kranzberg Roof Experiment located in Bavaria (Grams et al. 2021, DOI: 10.1002/ecs2.3399).

Those trees (Picea abies and Fagus sylvatica) heavily depend on their ectomycorrhizal fungal symbiosis partners (ECMf) belowground. Thus, we set out to identify modes of compositional and functional adaptation in these communities.

We monitored ECMf communities via metabarcoding and analysed the functionality of morphotyped ectomycorrhizae via testing their enzyme activities.

To our surprise, most effects were quantitative throughout the whole period. Total enzyme activities strongly declined alongside the numbers of vital root tips of drought treated trees, while enzyme activities per surviving root tip remained remarkably similar to controls. Likewise, ECMf communities only experienced minor shifts that only slightly increased during the years, although different capacities for drought tolerance in ECMf have previously been hypothesised.

Summed up: Along with most tree individuals, their fungal partners showed a strong ability to resist the applied extreme drought scenario, at the cost of severely diminished capacities at the ecosystems level.

Speculatively, individual root tips could be seen as surviving insulae whose fungal communities only experienced indirect and moderated drought effects. Therefore, the ECM system may rather show an inherent resistance to drought, with observable qualitative adaptation requiring a still longer time-frame.
Application of the complete CORINE land covers for modelling in WRF model
Authors: Breuer Hajnalka , Zempléni Zsuzsanna , Varga Ákos
Published: March 2021

Land use information is crucial in weather modelling as it determines the energy partitioning of the land surface. Based on the partitioning heating of near surface air and moisture supply of the planetary boundary layer is determined. These processes affect the general calculation of temperature, but it also has substantial effect on precipitation formation, especially on convective precipitation.

In this study the CORINE 44 categories are integrated into the WRF model. Usually the 44 land cover types are recategorized into a standard USGS or MODIS land use types. Here we present a dataset and application with the complete integration of the 44 types.

One-year runs are created with the CORINE land cover compared to the standard USGS dataset. Along with the new land cover types vegetation parameters had be defined as well. Four runs refer to a USGS-reference, CORINE2USGS converted, CORINE-USGS parameter, CORINE-newparameters where the effect of land cover and parameter change is analyzed. The modelled area covers the whole European region with 50 km resolution using the WRF 4.2 model. Regionally, on a monthly average 5-30% difference in precipitation and around 1 °C differences occur.

The research was supported by the Hungarian National Research, Development and Innovation Office, Grant No. FK132014. Hajnalka Breuer's work was additionally financed by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences.
What controls probability distribution of local wave activity in the midlatitudes?
Authors: Nakamura Noboru , Valva Claire
Published: March 2021

We examine probability distributions of local wave activity (LWA), a measure of the jet stream's meander, and factors that control them.  The observed column-mean LWA distributions exhibit significant seasonal, interhemispheric, and regional variations but are always positively skewed in the extratropics, and their tail often involves disruptions of the jet stream.  A previously derived 1D traffic flow model driven by observed spectra of transient eddy forcing qualitatively reproduces the shape of the observed LWA distribution.  It is shown that the skewed distribution emerges from nonlinearity in the zonal advection of LWA even though the eddy forcing is symmetrically distributed.  A slower jet and stronger transient and stationary eddy forcings, when introduced independently, all broaden the LWA distribution and increase the probability of spontaneous jet disruption.  Quasigeostrophic two-layer model also simulates skewed LWA distributions in the upper layer.  However, in the two-layer model both transient eddy forcing and the jet speed increase with an increasing shear (meridional temperature gradient), and their opposing influence leaves the frequency of jet disruptions insensitive to the vertical shear.  When the model's nonlinearity in the zonal flux of potential vorticity is artificially suppressed, it hinders wave-flow interaction and virtually eliminates reversal of the upper-layer zonal wind.  The study underscores the importance of nonlinearity in the zonal transmission of Rossby waves to the frequency of jet disruptions and associated weather anomalies. 
Investigating hydrological model versatility to simulate extreme flood events 
Authors: Peredo Ramirez Daniela , Ramos Maria-Helena , Andréassian Vazken , Oudin Ludovic
Published: March 2021

High-impact flood events in the Mediterranean region are often the result of a combination of local climate and topographic characteristics of the region. Therefore, the way runoff generation processes are represented in hydrological models is a key factor to simulate and forecast floods. In this study, we adapt an existing model in order to increase its versatility to simulate flood events occurring under different conditions: during or after wet periods and after long and dry summer periods. The model adaptation introduces a dependency on rainfall intensity in the production function. The impact of this adaptation is analysed considering model performance over selected flood events and also over a continuous 10-year period of flows. The event-based assessment showed that the adapted model structure performs better than or equal to the original model structure in terms of differences in the timing of peak discharges, regardless of the season of the year when the flood occurs. The most important improvement was observed in the simulation of the magnitude of the flood peaks. A visualisation of model versatility is proposed, which allows detecting the time steps when the new model structure tends to behave more similarly or differently from the original model structure in terms of runoff production. Overall, the results show the potential of the model adaptation proposed to simulate floods originated by different hydrological processes and the value of increasing hydrological model versatility to simulate extreme events.
A Methodology for Attributing the Role of Climate Change in Extreme Events: A Global Spectrally Nudged Storyline
Authors: van Garderen Linda , Feser Frauke , Shepherd Theodore G.
Published: March 2021

Extreme weather events are generally associated with unusual dynamical conditions, yet the signal-to-noise ratio of the dynamical aspects of climate change that are relevant to extremes appears to be small, and the nature of the change can be highly uncertain. On the other hand, the thermodynamic aspects of climate change are already largely apparent from observations, and are far more certain since they are anchored in agreed-upon physical understanding. The storyline method of extreme event attribution, which has been gaining traction in recent years, quantitatively estimates the magnitude of thermodynamic aspects of climate change, given the dynamical conditions. There are different ways of imposing the dynamical conditions. Here we present and evaluate a method where the dynamical conditions are enforced through global spectral nudging towards reanalysis data of the large-scale vorticity and divergence in the free atmosphere, leaving the lower atmosphere free to respond. We simulate the historical extreme weather event twice: first in the world as we know it, with the events occurring on a background of a changing climate, and second in a ‘counterfactual’ world, where the background is held fixed over the past century. We describe the methodology in detail, and present results for the European 2003 heatwave and the Russian 2010 heatwave as a proof of concept. These show that the conditional attribution can be performed with a high signal-to-noise ratio on daily timescales and at local spatial scales. Our methodology is thus potentially highly useful for realistic stress testing of resilience strategies for climate impacts, when coupled to an impact model.