bluuebunny/crossref_metadata_2025 huggingface dataset:
PMIP4/CMIP6 last interglacial simulations using three different versions of MIROC: importance of vegetation
Authors: O'ishi Ryouta , Chan Wing-Le , Abe-Ouchi Ayako , Sherriff-Tadano Sam , Ohgaito Rumi , Yoshimori Masakazu
Published: March 2021

We carry out three sets of last interglacial (LIG) experiments, named lig127k, and of pre-industrial experiments, named piControl, both as part of PMIP4/CMIP6 using three versions of the MIROC model: MIROC4m, MIROC4m-LPJ, and MIROC-ES2L. The results are compared with reconstructions from climate proxy data. All models show summer warming over northern high-latitude land, reflecting the differences between the distributions of the LIG and present-day solar irradiance. Globally averaged temperature changes are −0.94 K (MIROC4m), −0.39 K (MIROC4m-LPJ), and −0.43 K (MIROC-ES2L).
Only MIROC4m-LPJ, which includes dynamical vegetation feedback from the change in vegetation distribution, shows annual mean warming signals at northern high latitudes, as indicated by proxy data. In contrast, the latest Earth system model (ESM) of MIROC, MIROC-ES2L, which considers only a partial vegetation effect through the leaf area index, shows no change or even annual cooling over large parts of the Northern Hemisphere. Results from the series of experiments show that the inclusion of full vegetation feedback is necessary for the reproduction of the strong annual warming over land at northern high latitudes. The LIG experimental results show that the warming predicted by models is still underestimated, even with dynamical vegetation, compared to reconstructions from proxy data, suggesting that further investigation and improvement to the climate feedback mechanism are needed.
Attribution of the accelerating increase in atmospheric methane during 2010–2018 by inverse analysis of GOSAT observations
Authors: Zhang Yuzhong , Jacob Daneil J. , Lu Xiao , Maasakkers Joannes D. , Scarpelli Tia R. , Sheng Jian-Xiong , Shen Lu , Qu Zhen , Sulprizio Melissa P. , Chang Jinfeng , Bloom A. Anthony , Ma Shuang , Worden John , Parker Robert J. , Boesch Hartmut
Published: March 2021

We conduct a global inverse analysis of 2010–2018 GOSAT satellite observations to better understand the factors controlling atmospheric methane and its accelerating increase over the 2010–2018 period. The inversion optimizes anthropogenic methane emissions and their 2010–2018 trends on a 4º×5º grid, monthly regional wetland emissions, and annual hemispheric concentrations of tropospheric OH (the main sink of methane). We use an analytical solution to the Bayesian optimization problem that provides closed-form estimates of error covariances and information content for the solution. We verify our inversion results with independent methane observations from the TCCON and NOAA networks. Our inversion successfully reproduces the interannual variability of the methane growth rate inferred from NOAA background sites. We find that prior estimates of fuel-related emissions reported by individual countries to the United Nations are too high for China (coal) and Russia (oil/gas), and too low for Venezuela (oil/gas) and the U.S. (oil/gas). We show large 2010–2018 increases in anthropogenic methane emissions over South Asia, tropical Africa, and Brazil, coincident with rapidly growing livestock populations in these regions. We do not find a significant trend in anthropogenic emissions over regions with large production or use of fossil methane, including the U.S., Russia, and Europe. Our results indicate that the peak methane growth rates in 2014–2015 are driven by low OH concentrations (2014) and high fire emissions (2015), while strong emissions from tropical (Amazon and tropical Africa) and boreal (Eurasia) wetlands combined with increasing anthropogenic emissions drive high growth rates in 2016–2018. Our best estimate is that OH did not contribute significantly to the 2010–2018 methane trend other than the 2014 spike, though error correlation with global anthropogenic emissions limits confidence in this result.
Effects of spatial resolution and temporal offset of air-sea boundary-layer variables on turbulent heat flux estimates
Authors: Lee Tong , Centemann Chelle , Clayson Carol Anne , Bourassa Mark , Brown Shannon , Farrar Tom , Lombardo Kelly , Gille Sarah , Parfitt Rhys , Seo Hyodae , Subramanian Aneesh , Zlotnicki Victor
Published: March 2021

Air-sea turbulent heat fluxes and their spatial gradients are important to the ocean, climate, weather, and their interactions. Satellite-based estimation of air-sea latent and sensible fluxes, providing broad coverage, require measurements of sea surface temperature, ocean-surface wind speed, and air temperature and humidity above sea surface. Because no single satellite has been able to provide simultaneous measurements of these input variables, they typically come from various satellites with different spatial resolutions and sampling times that can be offset by hours. These factors introduce errors in the estimated heat fluxes and their gradients that are not well documented. As a model-based assessment of these errors, we performed a simulation using a Weather Research and Forecasting (WRF) model forced by high-resolution blended satellite SST for the Gulf Stream extension region with a 3-km resolution and with 30-minute output. Latent and sensible heat fluxes were first computed from input variables with the original model resolutions and at coincident times. We then computed the heat fluxes by (1) decimating the input variables to various resolutions from 12.5 to 50 km, and (2) offsetting the “sampling” times of some input variables from others by 3 hours. The resultant estimations of heat fluxes and their gradients from (1) and (2) were compared with the counterparts without reducing resolution and without temporal offset of the input variables. The results show that reducing input-variable resolutions from 12.5 to 50 km weakened the magnitudes of the time-mean and instantaneous heat fluxes and their gradients substantially, for example, by a factor of two for the time-mean gradients. The temporal offset of input variables substantially impacted the instantaneous fluxes and their gradients, although not their time-mean values. The implications of these effects on scientific and operational applications of heat flux products will be discussed. Finally, we highlight a mission concept for providing simultaneous, high-resolution measurements of boundary-layer variables from a single satellite to improve air-sea turbulent heat flux estimation.
Enhanced soot particle ice nucleation ability induced by aggregate compaction
Authors: Gao Kunfeng , Zhou Chong-Wen , Kanji Zamin
Published: March 2021

Cirrus clouds have an important influence on the climate since the ice crystal size, concentration and distribution of the clouds determine their radiation properties and effects in the atmosphere. Aviation activities in the high troposphere impact cirrus cloud formation indirectly and significantly, due to aviation contrail evolution and aviation soot particles acting as potential ice nucleating particles (INPs). Soot particles have varying ice nucleation (IN) abilities. In cirrus cloud formation conditions, pore condensation and freezing (PCF) is an important ice formation pathway for soot particles, which requires the particle to have appropriate morphology properties and mesoporous structures. In this study, the morphology and pore size of two kinds of soot were changed by a physical agitation method without any chemical modification. The IN activities of both fresh and agitated soot particles with aggregate sizes, 60, 100, 200 and 400 nm, were tested by the Horizontal Ice Nucleation Chamber (HINC) under mixed phase and cirrus cloud conditions.

In general, the IN results show clear size dependence for particles with the same agitation degree both tested soot samples at all tested temperatures (T) from 218 K to 243 K with a step of 5 K. In addition, all soot particles do not form ice at T > 235 K (homogeneous nucleation temperature, HNT) but ice nucleation was observed well below homogeneous freezing relative humidity (RH) for T < HNT, suggesting PCF as the dominating mechanism rather than deposition nucleation. Furthermore, there are significant differences between agitated and fresh soot particles for both soot samples studied. We observed that all agitated soot particles reach a higher particle activation fraction (AF) value at the same T and RH condition, compared to the same size fresh soot particles. Moreover, 200 and 400 nm agitated soot particles require much lower ice saturation values to reach AF = 0.001 than their fresh counterparts. The enhanced IN abilities of agitated soot particles are attributed to soot aggregate structure compaction thus increasing mesopore occurrence probability induced by physical agitation. Preliminary evidence obtained from the mass measurements of the single aggregates show that agitated soot particles are more dense than fresh soot particles of the same size. Furthermore, soot aggregate morphology comparisons from HR-TEM (high resolution transmission electron microscopy) images, soot-water interaction ability results from DVS (dynamic vapor sorption) tests and micro-pore size distribution results from argon desorption tests will be used to explain the soot particle IN ability promotion induced by compaction.
Seesaw of Precipitation Variability over Anatolian Peninsula between LGM and Future Projections: A Possible Role of Wind Direction Change
Authors: boza burcu , ezber yasemin , şen ömer l.
Published: March 2021

Turkey is a part of Eastern Mediterranean and located between 36-42° North latitudes and 26-45° East longitudes, where Europe meets Asia. The country, which mostly comprises the Anatolian Peninsula, is unique in terms of geographical position and topography and occupies a region which is highly sensitive to climate change. Considering that the region is prone to drying as a result of climate change, inferences about future precipitation patterns is of value.

Studies conducted by cosmogenic surface dating of boulder moraines revealed that, during Last Glacial Maximum (LGM; 21 Ka), the precipitation at the southwest of Anatolian Peninsula was higher than today, and at the northeast it was lower than today, which implies a regional heterogeneity. On the other hand, future projections of precipitation point out reverse conditions. That is, there will be lower (higher) than today precipitation at the southwest (northeast) of the country. Namely, a seesaw of precipitation variability prevails between cold climate of LGM and warm climate of future.

As a highland located at mid-latitudes, Anatolian Peninsula takes most of the precipitation during winter. What mainly drives the changes in winter precipitation is the changes in atmospheric circulation. Model simulations reveal a southward and northward displacement of polar jet stream and consistent shifts of storm tracks during LGM and in the future respectively. Knowing this fact, we investigated directions of winds which carry precipitation into Anatolian Peninsula, for the sake of explaining the dominant regional mechanism related to abovementioned seesaw pattern of precipitation.

We utilized monthly 850 hPa wind and precipitation data from the outputs of CCSM4.0 model of CMIP5 project and analyzed winds for past (LGM), present time and future conditions. Considering that it produces opposite conditions with comparable magnitudes with LGM, we used the RCP8.5 scenario. We found out that the 850 hPa winds entering from west into the peninsula are becoming more zonal (less tilted) as time passes from LGM to future. In other words, southwesterly winds evolve into westerly ones with a slight clockwise change of wind direction. This change considered together with orography of the peninsula explains the seesaw of precipitation variability over Anatolian Peninsula between cold and warm phases of global climate.
Realised added value in dynamical downscaling of Australian climate change
Authors: Di Virgilio Giovanni , Evans Jason P. , Di Luca Alejandro , Grose Michael R. , Round Vanessa , Thatcher Marcus
Published: March 2021

Coarse resolution global climate models (GCM) cannot resolve fine-scale drivers of regional climate, which is the scale where climate adaptation decisions are made. Regional climate models (RCMs) generate high-resolution projections by dynamically downscaling GCM outputs. However, evidence of where and when downscaling provides new information about both the current climate (added value, AV) and projected climate change signals, relative to driving data, is lacking. Seasons and locations where CORDEX-Australasia ERA-Interim and GCM-driven RCMs show AV for mean and extreme precipitation and temperature are identified. A new concept is introduced, ‘realised added value’, that identifies where and when RCMs simultaneously add value in the present climate and project a different climate change signal, thus suggesting plausible improvements in future climate projections by RCMs. ERA-Interim-driven RCMs add value to the simulation of summer-time mean precipitation, especially over northern and eastern Australia. GCM-driven RCMs show AV for precipitation over complex orography in south-eastern Australia during winter and widespread AV for mean and extreme minimum temperature during both seasons, especially over coastal and high-altitude areas. RCM projections of decreased winter rainfall over the Australian Alps and decreased summer rainfall over northern Australia are collocated with notable realised added value. Realised added value averaged across models, variables, seasons and statistics is evident across the majority of Australia and shows where plausible improvements in future climate projections are conferred by RCMs. This assessment of varying RCM capabilities to provide realised added value to GCM projections can be applied globally to inform climate adaptation and model development.
Lattice preferred orientation and seismic anisotropy of chloritoid in subduction zone
Authors: Lee Jungjin , Mookherjee Mainak , Kim Taehwan , Jung Haemyeong , Klemd Reiner
Published: March 2021

Subduction zones are often characterized by the presence of strong trench-parallel seismic anisotropy and large delay times. Hydrous minerals, owing to their large elastic anisotropy and strong lattice preferred orientations (LPOs) are often invoked to explain these observations. However, the elasticity and LPO of chloritoid, which is one such hydrous phases relevant in subduction zone settings, is poorly understood. In this study, we measured the LPO of polycrystalline chloritoid in natural rock samples and obtained the LPO-induced seismic anisotropy and evaluated the thermodynamic stability field of chloritoid in subduction zones. The LPO of chloritoid aggregates displayed a strong alignment of the [001] axes subnormal to the rock foliation, with a girdle distribution of the [100] axes and the (010) poles subparallel to the foliation. New elasticity data of single-crystal chloritoid showed a strong elastic anisotropy of chloritoid with 47% for S-waves (VS) and 22% for P-waves (VP), respectively. The combination of the LPO and the elastic anisotropy of the chloritoid aggregates produced a strong S-wave anisotropy of AVS = 18% and a P-wave anisotropy of AVP = 10%. Our results indicate that the strong LPO of chloritoid along the hydrated slab-mantle interface and in subducting slabs can influence trench-parallel seismic anisotropy in subduction zones with “cold” geotherms.
Societal vision vs. farmers’ reality: an approach to evaluate if agricultural intensification is sustainable
Authors: Helfenstein Julian , Bürgi Matthias , Diogo Vasco , Mohr Franziska , Schüpbach Beatrice , Swart Rebecca , Szerencsits Erich , Verburg Peter , Herzog Felix
Published: March 2021

There is broad agreement that agriculture has to become more sustainable in order to provide enough healthy food at minimal economic, environmental and social costs. But what is “more sustainable”? More often than not, different stakeholders have opposing opinions on what a more sustainable future should look like. In this study, we present an approach to assess the sustainability of agricultural development based on societal visions. We illustrate the approach by linking observed changes in agricultural land use intensity in a Swiss case study area with desired change according to three contrasting visions. The three visions, from a liberal think-tank, the Swiss Farmer Association, and the agroecological movement, cover a wide spectrum of sociopolitical interest groups in Swiss agriculture. The observed developments aligned most closely with desired developments of the liberal think-tank. Farmer interviews revealed that farms increased in size (+ 57%), became more specialized, and more productive (+ 223%) over the past 20 years. In addition, interpretation of aerial photographs indicated that farming became more rationalized at the landscape level, with increasing field sizes (+ 34%) and removal of solitary field trees (-18%). The case study example highlights the potential of societal visions to assess changes in land use intensity and outcomes in various sustainability dimensions. The main advantages are that the approach accommodates multiple stakeholder goals, while explicitly addressing their narratives and respective systems of values and norms, thus being more informative to the wider public. For these reasons, we argue that future assessments of sustainability should focus on contrasting observed developments with desired change by various stakeholder groups. This could help identify mismatches between desired and actual development and pave the way for designing appropriate new policies.
Atmospheric transport of micro and nanoplastics and fluorescence detection of particles < 20 µm
Authors: Bianco Angelica , Sordello Fabrizio , Ehn Mikael , Vione Davide Vittorio , Passananti Monica
Published: March 2021

Atmospheric plastic pollution is now a global problem. Microplastics (MP) have been detected in urban atmospheres as well as in remote and pristine environments, showing that suspension, deposition and aeolian transport of MP should be included and considered as a major transport pathway in the plastic life cycle. Due to the limitations in sampling and instrumental methodology, little is known about MP and nanoplastics (NP) with sizes lower than 50 µm, which is the current limit for FT-IR and Raman microscopy. In our recent work [Bianco et al. 2020], we describe how NP could be transported for longer distances than MP, making them globally present and potentially more concentrated than MP. We highlight that it is crucial to explore new methodologies to collect and analyse NP.

Small MPs can be detected by fluorescence spectroscopy: for example, particles can be efficiently stained using Nile Red, as described by Erni-Cassola et al. [2017]. This hydrophobic dye shows fluorescence in green and yellow range of the electromagnetic spectrum and can be easily detected also at low concentration. We are developing a new method, based on this principle, to detect MPs in natural matrices. These are, for instance, surface and atmospheric waters, containing dissolved organic matter and suspended organic particles. Preliminary results on polyethylene, polystyrene and polyvinylchloride are promising for particles in the range 1-25 µm suspended in MilliQ water. We are currently testing the method on river water and snow.

 

Bianco, A.; Passananti, M. Atmospheric Micro and Nanoplastics: An Enormous Microscopic Problem. Sustainability 2020, 12, 7327.

Erni-Cassola, G.; Gibson, M.; Thompson, R.; Christie-Oleza, J. Lost, but Found with Nile Red: A Novel Method for Detecting and Quantifying Small Microplastics (1 mm to 20 μm) in Environmental Samples. Environ. Sci. Technol. 2017, 51, 23, 13641–13648
Motion of masses with asymmetric and symmetric friction. Application to fault sliding
Authors: Wong Rui Xiang , Pasternak Elena , Dyskin Arcady
Published: March 2021

This study analyses a situation when a geological fault contains a section of anisotropic gouge with inclined symmetry axes (e.g. inclined layering), Bafekrpour et al. [1]. Such gouge in a constrained environment induces, under compression, asymmetric friction (different friction forces resisting sliding in the opposite directions). The rest of the gouge produces conventional symmetric friction. A mass-spring model of the gouge with asymmetric and symmetric friction sections is proposed consisting of a mass with asymmetric friction connected through a spring to another mass with symmetric friction. These masses are set on a base subjected to vibration. A parametric analysis is performed on this system. Two distinct characteristic regimes were observed: recurrent movement resembling stick-slip motion similar to predicted by [2] and sub-frictional movement. Recurrent movement arises when the inertial force is sufficient to overcome frictional force of a block with symmetric friction. Sub-frictional movement occurs when the inertial force is not sufficient to overcome frictional force of an equivalent system with only symmetric friction. The sub-frictional movement is produced by the force in the connecting spring increased due to the movement of the asymmetric friction block in the direction characterised by low friction. We formulate the criterion at which sub-frictional movement occurs. The occurrence of sub-frictional depends upon the relative mass of the symmetric and asymmetric friction sections, as well as the amplitude and driving frequency of the excitation. Power spectra of the produced vibrations are determined for both regimes. The results can shed light on mechanisms of sliding over pre-existing discontinuities and their effect on seismic event generation and propagation of hydraulic fractures in the presence of discontinuities.

[1] Bafekrpour, E., A.V. Dyskin, E. Pasternak, A. Molotnikov and Y. Estrin (2015), Internally architectured materials with directionally asymmetric friction. Scientific Reports, 5, Article 10732.

[2] Pasternak, E. A.V. Dyskin and I. Karachevtseva, 2020. Oscillations in sliding with dry friction. Friction reduction by imposing synchronised normal load oscillations. International Journal of Engineering Science, 154, 103313.

Acknowledgement. AVD and EP acknowledge support from the Australian Research Council through project DP190103260.
Interferometric Synthetic Aperture Sonar as a tool for seafloor geological mapping on the Grand Banks offshore Atlantic Canada: preliminary results.
Authors: Gini Caroline , Robert Katleen , Jamieson John , Dillon Jeremy
Published: March 2021

With less than 20% of the seafloor mapped at a sufficiently high resolution for geological and biological studies (<50m), there is a need for new technological approaches to map and characterize the seafloor environment at higher resolutions. Here, we present preliminary results of an investigation into the use of interferometric synthetic aperture sonar (InSAS) as a new approach to help fill this gap. InSAS can provide very high-resolution acoustic imagery (3cm/pixel) and bathymetry (25 cm/pixel) as well as large coverage area (up to 150m across track per side while flying at a 15m altitude, at 6 knots). Compared to traditional sidescan sonars, high-resolution imagery in both along and across track directions is achieved by the synthetic aperture of the sonar array, which uses a large number of receiver arrays and a cm-size spacing between individual elements. This technique has so far mostly been used for military and industrial purposes.

Onboard the Atlantic Kingfisher in October 2020, we used Kraken Robotic Systems’ InSAS system on a Katfish towed vehicle to survey 85 km2 of the Tail of the Grand Banks, the southernmost extremity of the continental shelf offshore Newfoundland, Canada. During a survey, the sonar is set at a center frequency of 337 kHz and survey planning included data coverage overlap for 140% coverage of the seafloor. Kraken Robotic’s processing algorithm and the towing optic cable allowed for real-time processing of the data and initial post processing using Caris Onboard.

We show one of the first applications of InSAS for geological studies. This system is excellent for identifying fine-scale geological features as well as variations of seabed texture and composition at a large scale on flat seafloor. We identified distinct seafloor sedimentary textures on the imagery, such as relatively homogeneously spaced alternations of high and low backscatter (BS) strength corresponding to well-defined ripple marks, as well as multiple 1-10m wide circular depressions of high BS strength surrounding individual rocks and a lower BS strength on the seafloor surrounding depressions. With high coverage, speed and resolution, InSAS represents an effective tool for environmental, biological and geohazard monitoring.
Parsimonious representation of plant water use strategies via non-dimensional parameter groups
Authors: Bassiouni Maoya , Manzoni Stefano , Vico Giulia
Published: March 2021

Process-based models are needed to improve estimates of water and carbon cycles in variable climatic conditions. Yet, their utility is often limited by our inability to directly measure plant stomatal and hydraulic traits at scales suitable to quantify characteristics of whole ecosystems. Inferring such parameters from ecosystem-scale data with parsimonious models offers an avenue to address this limitation. To this aim, we use a simple representation of the water flux through the soil-plant-atmosphere continuum (SPAC) and derive a parameterization of Feddes-type soil water-limitation constraints on transpiration (expressed via a soil moisture dependent function β). This parameterization explicitly accounts for community-effective plant eco-physiological traits as encoded in the SPAC model parameters. We express analytically the fractional loss of conductivity in well-watered conditions and the soil saturation thresholds at which transpiration is down-regulated from its well-watered rate and at which transpiration ceases, as a function of non-dimensional parameter groups. These non-dimensional groups combine plant stomatal and hydraulic traits, soil texture and climate. We implement the theoretical β function into a soil water balance and infer distributions of plant traits which best-match FLUXNET observations in a range of biomes. Finally, we analyze the resulting non-dimensional groups to explore patterns in plant water use strategies. Our results indicate that non-dimensional groups reflect combinations of plant traits which are adapted to growing season environmental conditions and these groups may be more meaningful model parameters than individual traits at ecosystem scales. Additionally, using non-dimensional groups instead of focusing on individual parameters reduces risks of equifinality and provides future opportunities to exploit satellite data to quantify robust ecosystem-scale parameters. This analysis provides a parsimonious and functionally accurate alternative to account for ecosystem hydraulic controls and feedbacks and can help overcome limitations of commonly used empirical water-limitation constraints.
Short-lived, long-lived and periodic flat slab subduction
Authors: Schellart Wouter P. , Strak Vincent
Published: March 2021

Flat slab subduction occurs when the subducted slab lies flat below the base of the overriding plate for up to several hundred kilometres before bending into the deeper mantle. It has been ascribed to a variety of causes, including subduction of buoyant ridges/plateaus and forced trench retreat. Ridge/plateau subduction, however, shows irregular spatial correlations with flat slabs, while forced trench retreat has required external forcing in geodynamic subduction models, which might be insufficient or absent in nature. Here we present buoyancy-driven numerical geodynamic models and aim to investigate flat slab subduction in the absence of external forcing. Furthermore, we test the influence of a variety of subduction zone parameters, including overriding plate strength and subducting plate thickness, on flat slab formation and its evolution. Flat slab subduction is reproduced during normal oceanic subduction in the absence of ridge/plateau subduction and without externally forced plate motion. Flat slab subduction only commences after a prolonged period of upper mantle slab dip angle reduction during lower mantle slab penetration. The flat slab is supported by mantle wedge suction, vertical compressive stresses at the base of the slab and upper mantle slab buckling stresses. Our models demonstrate three modes of flat slab subduction, namely short-lived (transient) flat slab subduction, long-lived flat slab subduction, and periodic flat slab subduction, which occur for different model parameter combinations. Most models demonstrate slab folding at the 660 km discontinuity, which produces periodic changes in the upper mantle slab dip angle. With relatively high overriding plate strength, such folding results in periodic changes in the dip angle of the flat slab segment, which can lead to periodic flat slab subduction, providing a potential explanation for periodic arc migration. Flat slab subduction ends due to the local overriding plate shortening and thickening it produces, which forces mantle wedge opening and a reduction in mantle wedge suction. As overriding plate strength controls the shortening rate, it has a strong control on the duration of flat slab subduction, which lasts only ~6 Myr for the weakest plate and exceeds 75 Myr for the strongest plate. Progressive overriding plate shortening during flat slab subduction might explain why flat slab subduction terminated in the Eocene in western North America and in the Jurassic in South China.
Inverse modeling of halocarbons: sensitivity to the baseline definition
Authors: Vojta Martin , Thompson Rona , Groot Zwaaftink Christine , Stohl Andreas
Published: March 2021

The identification of the baseline is an important task in inverse modeling of greenhouse gases, as it represents the influence of atmospheric chemistry and transport and surface fluxes from outside the inversion domain, or flux contributions prior to the length of the backward calculation for Lagrangian models. When modeling halocarbons, observation-based approaches are often used to calculate the baseline, although model-based approaches are an alternative. Model-based methods need global unbiased fields of mixing ratios of the observed species, which are not always easy to get and which need to be interfaced with the model used for the inversion. To find the best way to identify the baseline and to investigate whether the usage of observation-based approaches is suitable for inverse modeling of halocarbons, we use and analyze a model-based and two frequently used observation-based methods to determine the baseline and investigate their influence on inversion results. The model-based method couples global fields of mixing ratios with backwards-trajectories at their point of termination. We simulate those global fields with a Lagrangian particle dispersion model, FLEXPART_CTM, that uses a nudging routine to relax model data to observed values. The second method under investigation is the robust estimation of baseline signal (REBS) method, that is purely based on statistical analysis of observations. The third analyzed method is also primarily observation-based, but uses model information to subtract prior simulated mixing ratios from selected observations. We apply those three methods to sulfur hexafluoride (SF6) and use the Bayesian inversion framework FLEXINVERT for the inverse modeling and the Lagrangian particle dispersion model FLEXPART to calculate the source-receptor-relationship used in the inversion.
Identifying drivers controlling the synchronicity of Heinrich-type ice sheet surges from the European and North American ice sheets
Authors: Schannwell Clemens , Kapsch Marie-Luise , Mikolajewicz Uwe , Ziemen Florian
Published: March 2021

Heinrich-type ice sheet surge events are among the most prominent signals in the paleoclimate data records. Even though these events have previously been intensely studied, it still remains an open question whether the cyclic ice sheet surges are triggered by internal ice dynamics, climate forcing, or a combination of the two. In simulations of the last deglaciation using the fully-coupled Max Planck Institute Earth System Model, surges from the European and North American ice sheets often occur in synchronicity. This model behaviour is in agreement with observations from sediment cores that find a similar pattern in the isotopic fingerprint of the deposited ice-rafted detritus. The synchronicity indicates that climate forcing is playing an important role in initiating ice sheet surges. In this study, we use the coupled ice-sheet-solid earth model PISM-VILMA in a northern hemispheric setup to investigate the modelled synchronicity of the surge events. More specifically, we perform an ensemble of simulations to study if the modelled synchronicity is a direct result of one of the surge locations causing other surge locations to be a activated as well. Moreover, we aim to investigate whether previously suggested trigger mechanisms such as regional changes in sea level or ocean temperatures are indeed key processes in controlling the synchronicity of these surge events.
Evaluating a land surface model at a water-limited site: implications for land surface contributions to droughts and heatwaves
Authors: Mu Mengyuan , De Kauwe Martin , Ukkola Anna , Pitman Andy , Gimeno Teresa , Medlyn Belinda , Or Dani , Yang Jinyan , Ellsworth David
Published: March 2021

Land surface models underpin coupled climate model projections of droughts and heatwaves. However, the lack of simultaneous observations of individual components of evapotranspiration, concurrent with root-zone soil moisture, has limited previous model evaluations. Here, we use a comprehensive set of observations from a water-limited site in southeastern Australia including both evapotranspiration and soil moisture to a depth of 4.5 m to evaluate the Community Atmosphere-Biosphere Land Exchange (CABLE) land surface model. We demonstrate that alternative process representations within CABLE had the capacity to improve simulated evapotranspiration, but not necessarily soil moisture dynamics - highlighting problems of model evaluations against water fluxes alone. Our best simulation was achieved by resolving a soil evaporation bias; a more realistic initialisation of the groundwater aquifer state; higher vertical soil resolution informed by observed soil properties; and further calibrating soil hydraulic conductivity. Despite these improvements, the role of the empirical soil moisture stress function in influencing the simulated water fluxes remained important: using a site calibrated function reduced the soil water stress on plants by 36 % during drought and 23 % at other times. These changes in CABLE not only improve the seasonal cycle of evapotranspiration, but also affect the latent and sensible heat fluxes during droughts and heatwaves. The range of parameterisations tested led to differences of ~150 W m-2 in the simulated latent heat flux during a heatwave, implying a strong impact of parameterisations on the capacity for evaporative cooling and feedbacks to the boundary layer (when coupled). Overall, our results highlight the opportunity to advance the capability of land surface models to capture water cycle processes, particularly during meteorological extremes, when sufficient observations of both evapotranspiration fluxes and soil moisture profiles are available.
Transient Climate Simulations of Orbital Effects on Mesozoic Climates
Authors: Landwehrs Jan , Feulner Georg , Willeit Matteo , Sames Benjamin , Wagreich Michael
Published: March 2021

The Mesozoic era (~252—66 Ma) is traditionally considered as a prolonged greenhouse period, witnessing the breakup of the Pangaean supercontinent. Orbital cycles have, for example, been invoked as drivers of e.g. Pangaean „Megamonsoon“ variability and eustatic sea level cycles in the Mesozoic.

We aim to contribute to a more comprehensive understanding of orbital effects on Mesozoic climates by employing the newly developed CLIMBER-X Earth System Model. Here, we primarily use its coupled atmosphere, ocean, sea ice and vegetation modules, but also include preliminary tests with dynamic carbon cycle and ice-sheets. We present first results from a set of transient climate simulations of four Mesozoic timeslices representative for Triassic, Jurassic, Early Cretaceous and Late Cretaceous boundary conditions (e.g. paleogeography and solar luminosity). The simulations each cover ~100,000 years and are driven by changing precession, obliquity, and eccentricity.

We would like to use the opportunity to discuss this approach and associated questions with the community. For example: Would changing paleogeography and climate background state have modified the response to orbital forcings? Could eustatic sea level cycles have been caused by orbitally-driven redistribution of water between the ocean and land water storages or should orbitally-forced ice sheets also have played a role in the alleged Mesozoic greenhouse? Which connections can be established to proxy records?
Structural characterization of soil organic matter individual fractions (fulvic acids, humic acids and humins) in relation to potential sorption of organic contaminants 
Authors: Ukalska-Jaruga Aleksandra , Bejger Romualda , Debaene Guillaume , Smreczak Bozena
Published: March 2021

The objective of this paper was to investigate the molecular characterization of individual humic substances ( fulvic acids-FAs, humic ascids-HAs, and humins-HNs), which are the most reactive soil components and exhibit high sorption capacity in relation to various groups of organic contaminants. A wide spectrum of spectroscopic (UV-VIS, VIS-nearIR), as well as electrochemical (zeta potential, particle size diameter, polidyspersity index), methods were applied to find the relevant differences in the behavior, formation, composition and sorption properties of HS fractions derived from various mineral soils.

Soil material (n = 30) used for the study were sampled from the surface layer (0–30 cm) of agricultural soils. FAs and HAs were isolated by sequential extraction in alkaline and acidic solutions, according to the International Humic Substances Society method, while HNs was determined in the soil residue (after FAs and HAs extraction) by mineral fraction digestion using a 0.1M HCL/0.3M HF mixture and DMSO.

Our study showed that significant differences in the molecular structures of FAs, HAs and HNs occurred. Optical analysis confirmed the lower molecular weight of FAs with high amount of lignin-like compounds and the higher weighted aliphatic–aromatic structure of HAs. The HNs were characterized by a very pronounced and strong condensed structure associated with the highest molecular weight. HAs and HNs molecules exhibited an abundance of acidic, phenolic and amine functional groups at the aromatic ring and aliphatic chains, while FAs mainly showed the presence of methyl, methylene, ethenyl and carboxyl reactive groups. HS was characterized by high polydispersity related with their structure. FAs were characterized by ellipsoidal shape as being associated to the long aliphatic chains, while HAs and HNs revealed a smaller particle diameter and a more spherical shape caused by the higher intermolecular forcing between the particles.  

The observed trends directly indicate that individual HS fractions differ in behavior, formation, composition and sorption properties, which reflects their binding potential to different group of organic contaminants, but the general properties of individual fractions are similar and do not depend on the type of soil.

Acknowledgement: The studies were supported from the National Science Centre project No. 2018/29/N/ST10/01320 “Analysis of the fractional composition and sorption properties of humic substances in relation to various groups of organic contaminants”
Variability across scales - exploring methods for predicting soil properties from multiple sources
Authors: Zeitfogel Hanna , Feigl Moritz , Schulz Karsten
Published: March 2021

To assess future groundwater recharge rates in Austria under climate change conditions, detailed spatial soil information is required.  Different data sources such as global soil maps (SoilGrids), regional soil maps of arable land (eBOD) and local soil profiles are available. However, they differ in scale and degree of data aggregation, as well as in spatial coverage.

Soil properties are characterized by a high spatial variability at all scales and it is well known that averaging will cause biases in the statistical relationships between different soil data sets, and between soil and landscape physio-geographical properties. Aiming for a best quality Austrian-wide soil map synthesizing all information, scale dependent multi-level relations between soil data bases are examined following two approaches:

Firstly, a linear relationship of soil variables at different scales is assumed. The statistical and geostatistical characteristics are analyzed at different aggregation levels to explore the scale-related behavior of our data. Secondly, machine learning algorithms (random forests and boosting methods) are applied to predict soil characteristics of existing regional soil maps by using all other available data sources as input features. Additional locally available variables such as elevation, slope, aspect, vegetation and climate data are evaluated for significance when predicting the missing soil information.  

In summary, this study analyzes the statistical behavior and patterns of variability of soil properties at different scales and derives a modelling approach that can be used to predict regional soil properties from data sources spanning a range of different scales.
Stabilization of organic carbon isolated from cryoconite holes in polar and mountain systems by 13С NMR spectroscopy
Authors: Polyakov Vjacheslav , Abakumov Evgeny
Published: March 2021

Black carbon is one of the short-lived climatically significant factors. This term refers to climate-forming substances that are located for a short amount of time in the atmosphere - from several days to several years. To identify the role of cryoconite in the conditions of a possible climatic crisis, the stabilization of organic matter isolated from cryoconite holes was assessed. Humic acids are part of the organic matter accumulating in soils and cryoconites and are heterogeneous systems of high-molecular condensed compounds formed as a result of the decomposition of organic remains of plants and animals in terrestrial and aquatic ecosystems. Climatic parameters, precursors of humification, and the local position in the landscape determine the diversity of the composition and properties of HAs. Stabilization of organic material is defined as the transformation of organic matter into a state inaccessible to soil microorganisms, and the very property of stabilization is a characteristic stage in the dynamics of carbon. Using 13C NMR spectroscopy, we determined the proportion of aromatic and aliphatic compounds in the composition of HAs in order to assess the stabilization of organic matter in cryoconites from Mount Elbrus (Caucasus Mountains, Russia), the Arctic (Severnaya Zemlya archipelago, Russia) and Antarctica (King George Island, West Antarctica).

Samples for qualitative analysis of carbon accumulated in cryoconites were carried out during fieldwork in 2020. The studied samples were analyzed at the Department of Applied Ecology, St. Petersburg State University. Humic acids (HAs) were extracted from each sample according to a published IHSS protocol. Solid-state CP/MAS 13C-NMR spectra of HAs were measured with a Bruker Avance 500 NMR spectrometer.

Thus, it follows from the obtained results that aliphatic fragments of humic acids predominate in all studied cryoconites. A similar composition of humic acids testifies to a single mechanism of accumulation and development of organic matter in glacier regions. Low biological activity and climatic features prevent condensation of high-molecular compounds in the organic matter of cryoconite holes. This is an essential prerequisite for high rates of carbon dioxide emissions into the atmosphere under the conditions of deglaciation of the studied regions. With the thawing of glaciers and the ingress of cryoconites into warmer conditions, an additional contribution of carbon dioxide to the atmosphere can occur and, therefore, increase the possible climate crisis on our planet.

This study was supported by Russian Foundation for Basic Research No. 19-05-50107.
Long-lasting impacts of a glacial lake outburst flood on the hydrology of a fjord-river system (Pascua River, Chilean Patagonia)
Authors: Piret Loic , Bertrand Sebastien , Nguyen Nhut , Hawkings Jon , Rodrigo Cristian , Wadham Jemma
Published: March 2021

Glacial Lake Outburst Floods (GLOFs) are an increasing threat to Patagonian environments and communities. Here, we investigate the geomorphological and hydrological impact of a recent GLOF from Pascua River, which discharges at the head of Baker Fjord (Chile, 48°S). To do so, a sediment core was taken ~4 km offshore of the Pascua River mouth at a water depth of 248 m. The coring site is located on the flank of a submarine channel incised trough the subaquatic delta of Pascua River, 30 m above the bottom of the channel. The sediment physical and chemical properties were analysed at high resolution with X-ray CT, MSCL and XRF core scanning, in combination with lower resolution grain-size and bulk organic geochemistry measurements, and a core chronology was established using downcore variations in 137Cs activity. In addition, historical maps and satellite imagery of the past century were examined in combination with multibeam bathymetry of Baker Fjord to aid the interpretation of the sediment record.

Results show that the sediments are composed of two distinct units separated by a 5-cm thick event deposit dated 1945±9 CE. Below the event, the sediment consists of coarse silt and fine sand, likely representing sediment deposition from turbidity currents. Above it, it consists of very fine silts, likely representing settling from the surficial sediment plume. Historical evidence shows that the event deposit corresponds to a ~256 106 m3 GLOF from Bergues Lake, the proglacial lake of Lucia Glacier that discharges directly into Pascua River. Before 1945, historical information shows that Pascua River drained via two active river branches that were most likely connected to the two submarine channels visible in the bathymetry of the subaquatic delta. After 1945, only the western river branch appears active, which likely caused the abandonment of the eastern submarine channel near which the sediment core was taken. Therefore, we hypothesize that the 1945 Bergues Lake GLOF caused the abandonment of the eastern river branch and submarine channel, which explains the absence of coarse-grained sediments in our sediment record after 1945±9 CE.

This study provides the first report of a GLOF from the northeastern part of the Southern Patagonian Icefield, and it demonstrates that GLOFs can have long-term impacts on the hydrology of fjord-river systems.