julilili42/papers huggingface dataset:
Drought effects on whole-tree C dynamics in an enclosed tropical rainforest
2022-03-28

&amp;lt;p&amp;gt;Drought exerts a major control on the carbon (C) cycle of terrestrial ecosystems worldwide. However, the mechanisms and processes underpinning ecosystem responses remain uncertain, in particular in diverse, tall-growing ecosystems like tropical rainforests. In such ecosystems, trees are a predominant driver of ecosystem C cycling, as they link the major ecosystem fluxes, photosynthesis and ecosystem respiration through allocation and utilisation of recent assimilated C. Trees respond dynamically to drought, generally by reducing C assimilation and altering investments of recent C into metabolism, defence, growth and storage, which has consequences for the fate of C in the system. However, to date most of our understanding is derived from experiments on small trees and we lack an understanding of how whole-tree C allocation responds in diverse, stratified forest ecosystems.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;To address this knowledge gap, we implemented a 9.5-week experimental drought in the world&amp;amp;#8217;s largest controlled growth facility, the Biosphere 2 Tropical Rainforest in Arizona, US. We continuously measured isotopic CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fluxes of leaves, stem and soil as well as leaf and phloem non-structural carbohydrates across a range of canopy and understory forming trees during pre-drought and drought conditions. To study drought effects on the fate of recent photoassimilates, we labelled the entire ecosystem with a &amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; pulse during pre-drought and drought conditions and traced the carbon flow in leaf, stem and soil fluxes and non-structural carbohydrates of leaves and phloem.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Across all studied trees, drought generally reduced CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; uptake and metabolic activity in leaves, stems and soil. The phloem transport rates slowed down and the turnover of recent photoassimilates declined. As drought progressed respiration was increasingly fuelled by C reserves, as indicated by isotopic flux dynamics and a depletion of starch pools, particularly in leaves. Drought response patterns of fluxes, carbohydrate pools and C allocation dynamics were highly variable among trees. Interestingly, response diversity was not primarily explained by species identity, but likely related to a combination of functional and structural traits and the trees&amp;amp;#8217; microenvironment within the forest. We conclude that the structural and functional composition of a forest is an important driver for tree C allocation and needs to be considered for understanding the mechanisms underpinning forest C dynamics in response to drought.&amp;lt;/p&amp;gt;
Explainable community detection of extreme rainfall events using the tangles algorithmic framework
2022-03-28

&amp;lt;p&amp;gt;Climate networks have helped to uncover complex structures in climatic observables from large time series data sets. For instance, climate networks were used to reduce rainfall data to relevant patterns that can be linked to geophysical processes.&amp;amp;#160;However, the identification of regions that show similar behavior with respect to the timing and spatial distribution of extreme rainfall events (EREs) remains challenging.&amp;amp;#160;&amp;lt;br&amp;gt;To address this, we apply a recently developed algorithmic framework based on tangles [1] to discover community structures in the spatial distribution of EREs and to obtain inherently interpretable communities as an output.&amp;amp;#160;First, we construct a climate network using time-delayed event synchronization and create a collection of cuts (bipartitions) from the EREs data. By using these cuts, the tangles algorithmic framework allows us to both exploit the climate network structure and incorporate prior knowledge from the data.&amp;amp;#160;Applying tangles enables us to create a hierarchical tree representation of communities including the likelihood that spatial locations belong to a community. Each tree layer can be associated to an underlying cut, thus making the division of different communities transparent.&amp;amp;#160;&amp;lt;br&amp;gt;Applied to global precipitation data, we show that tangles is a promising tool to quantify community structures and to reveal underlying geophysical processes leading to these structures.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;[1] S. Klepper, C. Elbracht, D. Fioravanti, &amp;amp;#160;J. Kneip, L. Rendsburg, M. Teegen, and U. von Luxburg. Clustering with Tangles: Algorithmic Framework and Theoretical Guarantees. CoRR, abs/2006.14444v2, 2021. URL https://arxiv.org/abs/2006.14444v2.&amp;lt;/p&amp;gt;
Bayesian updating despite model errors? A sliding time-window approach to rescue&#160;
2022-03-28

&amp;lt;p&amp;gt;Bayesian mechanistic modeling often suffers from overconfident and biased posterior distributions for parameters and predictions. This phenomenon arises because the fundamental assumption of Bayesian Model Analysis is violated: the underlying model is assumed to be true, but in fact, it is a simplification of reality with structural errors that show at least during some periods of the modeled time span. As a result, a compromise solution in parameter space is identified that can formally fit the full data set best, but this parameter set will not be representative of the true system state. Neither will it be representative of the &amp;amp;#8220;compensation mode&amp;amp;#8221; in which the model is whenever structural error kicks in. As a logical consequence, predictions will be biased and their intervals too narrow. The longer the data set used for calibration, the stronger the misleading effect. Typical sources of severe structural deficits that produce dynamically occurring errors are missing or misspecified processes in the model.&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;We propose a formal time-windowed Bayesian analysis to overcome this general problem. When performing Bayesian updating on shorter time windows, the assumption of a (quasi-) true model becomes more plausible, and by sliding this window through the calibration time series, we let the model adjust its posterior parameter distributions according to the current strength of error. These time-shifting parameter distributions allow us to (1) identify periods of statistically significant model error occurrence via measuring time-varying Bayesian model evidence, (2) diagnose potential sources of model error by understanding the time-varying parameter compensation mechanisms, and (3) predict with more realistic uncertainty intervals by distribution averaging.&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;We demonstrate the proposed method on a set of synthetic and real-world scenarios of soil moisture modeling. With this example, we also highlight its usefulness to analyze dynamic systems in a wide range of disciplines, such as water quality modeling, decision support, and risk assessment. Results show that the time sequence of posterior parameter distributions (and dependent model mechanisms such as water retention curves and unsaturated hydraulic conductivity functions) provides valuable insights into the model&amp;amp;#8217;s weaknesses, and it also provides guidance for model improvement.&amp;lt;/p&amp;gt;
Bayesian Inference of Climate Parameters Using Multibox EBMs
2022-03-28

&amp;lt;div&amp;gt; &amp;lt;p&amp;gt;Reliable climate projections in face of global warming require a firm and detailed understanding of&amp;amp;#160;climate variability. Variations in climate can be externally-forced, for example by anthropogenic emissions, or internally-generated, for example from chaotic atmosphere&amp;amp;#160;and&amp;amp;#160;ocean dynamics. To investigate the climatic response to radiative forcing, a common concept is the equilibrium climate sensitivity (ECS). Many studies estimate the ECS by fitting&amp;amp;#160;simple energy balance models&amp;amp;#160;(EBMs) to observational data. This approach has benefitted from advances in numerical analysis and statistics, enabling a fully Bayesian analysis. Via Bayes theorem, it quantifies the probability of certain climate parameters given observations, for example of surface temperature. To this end, it combines the goodness of the model fit with assumptions on measurement errors and climate variability as well as prior information. Here, we&amp;amp;#160;analyse&amp;amp;#160;and discuss Bayesian inference of climate parameters such as ECS from global mean temperatures using&amp;amp;#160;multibox&amp;amp;#160;EBMs. We therefore present an R package which relies on the Markov Chain Monte Carlo algorithm and includes an extension of the one-box model with a time-dependent feedback parameter. Using&amp;amp;#160;measurements from the instrumental period as well as temperature reconstructions and model data from the last millennium, we validate and demonstrate the package.&amp;amp;#160;We find that the two-box model performs significantly better in fitting the observations than the one-box model, and generates 21&amp;lt;span&amp;gt;st&amp;lt;/span&amp;gt; century projections that agree&amp;amp;#160;more closely with&amp;amp;#160;AR5 estimates. Further, we evaluate the robustness of the estimate against uncertainties in temperature and forcing data through synthetic experiments. To this end, we quantify how estimation errors depend on the strength of noise in temperature data and compare the influence of dating and amplitude uncertainties in forcing reconstructions.&amp;amp;#160;In summary, we provide an effective tool for Bayesian estimation of climate parameters and elaborate its potential for studying the response to external forcing.&amp;amp;#160;&amp;lt;span&amp;gt;&amp;amp;#160;&amp;lt;/span&amp;gt;&amp;lt;/p&amp;gt; &amp;lt;/div&amp;gt;
Modern hotspot-influenced MORBs reveal anoxic conditions during deposition and subduction of recycled Proterozoic sediments in their source
2022-03-28

&amp;lt;p&amp;gt;Significant Mo mobility and isotope (&amp;amp;#948;&amp;lt;sup&amp;gt;98/95&amp;lt;/sup&amp;gt;Mo) fractionation is induced during prograde metamorphism at present-day subduction zones. Depending on the redox conditions during early subduction and accompanied slab dehydration, isotopically heavy Mo is released towards the overlying mantle wedge, leaving behind a depleted, and isotopically light subducted slab. This isotopically light Mo signature has been detected in slab-melt influenced volcanic rocks and potentially will be traceable in ocean-island basalts, if their geochemical signatures are affected by previously subducted lithologies (i.e. slab and overlying sediments). Thus, the isotope composition of mantle plume-influenced volcanic rocks might reveal the nature of subducted and re-incorporated lithologies and possibly redox conditions during subduction.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;In this study, we present new Mo isotope data for South-Mid Atlantic Ridge basalts that partly interacted with the enriched Discovery and Shona mantle plumes. Isotopically heavier Mo isotope ratios (&amp;amp;#948;&amp;lt;sup&amp;gt;98/95&amp;lt;/sup&amp;gt;Mo &amp;gt; ambient depleted mantle) are observed in samples tapping a more enriched mantle source. Furthermore, &amp;amp;#948;&amp;lt;sup&amp;gt;98/95&amp;lt;/sup&amp;gt;Mo correlates with radiogenic isotopes (Sr, Nd, Hf) indicating recycling of a Proterozoic sedimentary components with a Mo isotopic composition that was not modified during and before subduction by Mo mobility under oxidising conditions. Rather, the new Mo isotope data supports and expands on previous stable Se and S isotope evidence that suggests the incorporation of subducted anoxic Proterozoic deep-sea sediments into the mantle of the South-Mid Atlantic Ridge basalts.&amp;lt;/p&amp;gt;
What is driving the isotopic composition of surface snow in East Antarctica? - Insights from a multi-year time series of surface snow at Dome C
2022-03-28

&amp;lt;p&amp;gt;The isotopic composition (d&amp;lt;sup&amp;gt;18&amp;lt;/sup&amp;gt;O, dD) of surface snow on an ice sheet is primarily seen as a recorder of the air temperature and is used to reconstruct past climatic conditions from ice cores. The second order parameters d-excess and &amp;lt;sup&amp;gt;17&amp;lt;/sup&amp;gt;O-excess can preserve climatic signals from the moisture origin and are indicative for kinetic fractionation processes in the water cycle between the source and the deposition site. Fractionation is especially important for the surface snow which can exposed to the atmosphere for a long time during periods without snowfall. The resulting effect of this process on the isotopic composition and the second order parameters in the interior of Antarctica is, however, unclear. In order to better understand the contribution of secondary processes on the isotopic signature and to disentangle the climate characteristics at the moisture source region and at the ice core site, we study both the isotopic composition and the second order parameters of surface and subsurface snow at Dome C on the East Antarctic Plateau. For this, we make use of an extensive data set of isotopic data (d&amp;lt;sup&amp;gt;18&amp;lt;/sup&amp;gt;O, dD, dexcess and &amp;lt;sup&amp;gt;17&amp;lt;/sup&amp;gt;O-excess) from surface (0 - 1.5 cm) and subsurface snow (1.5 - 4.5 cm) covering continuously the period from 2016 to 2020. This data set is complemented with previously published isotopic data of surface snow and precipitation data back to 2011. For additional comparisons and analyses, we use data from a nearby weather station, the ERA5 reanalysis data set, a satellite-derived grain index estimate and simulations from the detailed snowpack model CROCUS.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;We observe a good (weak) correlation between the ambient temperature and the surface (subsurface) layer. Most years are characterised by a strong increase in the isotopic composition towards the summer and a gentle decrease towards winter while d-excess shows a contrary behaviour. We suggest that the strength of the summer increase is related to the amount of precipitation and the magnitude of metamorphism at the surface. The degree of metamorphism can (to some degree) be approximated from observational data (e.g. the grain index) or from model output (e.g. latent heat flux from CROCUS). In addition to presenting possible mechanisms leading to strong or weak increases in the isotopic composition in summer, we developed a simple model using temperature and snowfall data from ERA5 to analyse the contribution of temperature and other parameters to the observed isotopic signals.&amp;lt;/p&amp;gt;
Holocene silt-clay overbank sedimentation between climate change and human activitiy within the fragile loess-covered Wei&#223;e Elster catchment in Central Germany
2022-03-28

&amp;lt;p&amp;gt;The role of climatic or human forcing for Holocene silt-clay overbank sedimentation in Central Europe has been debated for decades. To date, former studies were often limited by rather low chronological resolutions of the fluvial stratigraphies, and especially by records of human activity in the studied catchments with rather fragmentary spatial and chronological resolutions.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Within the frame of an interdisciplinary geoarchaeological project carried out in the Wei&amp;amp;#223;e Elster catchment in Central Germany, using drill cores, geophysical measurements, sedimentological and micromorphological analyses as well as numerical dating along three transects, we build up a highly resolved record of fine-grained fluvial sedimentation along the middle river reach. Complementarily, based on archaeological data stored in local area files of the State Offices of Archaeology as well as on historical and onomastic data, we build up a catchment-wide record of human activity from the Early Neolithic period until the High Middle Ages with a so far unprecedented high spatial and chronological resolution in Central Europe. Comparing these geomorphologic and archeological/historic datasets with highly resolved paleoclimatic records allows a large step forward in understanding the intricate interplay of the Holocene geomorphodynamics with climate changes and human activity with an exceptional spatial and chronological resolution. So far, first results demonstrate a significant impact of climatic events such as the Little Ice Age on river activity that were linked with fine-grained sedimentation also after the start of intensive human activity in the catchment since the Early Neolithic period ca. 7.5 ka.&amp;lt;/p&amp;gt;
Upper Pleistocene dust dynamics reconstructed by isotope fingerprinting and the magnetic fabric of Loess-Palaeosol-Sequences&#160;
2022-03-28

&amp;lt;p&amp;gt;Loess-Palaeosol-Sequences (LPS) are the most widespread aeolian sedimentary deposits providing climatic- and environmental records across continents. As dust sinks, they may archive information on dust source dynamics, if targeted source signals survived processes operating during production, transport, and syn- and post-depositional alteration of particles and sediments. Yet, our knowledge about such dynamics through palaeoenvironmental changes during the Upper Pleistocene remains vague. This limits our understanding of thresholds that may have (de-) activated dust sources causing major environmental changes in prevalent areas. We thus combine results of isotope- (&amp;lt;sup&amp;gt;87/86&amp;lt;/sup&amp;gt;Sr, &amp;lt;sup&amp;gt;143/144&amp;lt;/sup&amp;gt;Nd) and major element (Si/Al) provenance proxies that react differently to pre-, syn- and post depositional alteration processes, with granulometry (U-ratio) and the anisotropy of magnetic susceptibility (AMS). Granulometry is recognised as an indicator for wind strengths and the primary magnetic fabric of loess deposits has been successfully used to reconstruct surface near wind directions. We apply our approach on the RP1 profile of the Schwalbenberg LPS that covers the late OIS 3 and the OIS 2 in centennial-scale resolution. The site is embedded in the Middle Rhine Valley (Germany) dividing the Rhenish Massif in its western and eastern part. Consequently, the Schwalbenberg seems appropriate to trace provenance shifts as it is linked to a distal dust source via the Rhine and as it is surrounded by potential local dust sources of the Rhenish Massif. Our results indicate shifts in source areas NNE-SSW off the site, contemporary with increasing frost dynamics and aridification. Both factors seem to enhance dust inputs from the Rhine system up to a threshold where the Rhenish Massif gets activated as a dominant source. Geochemical fingerprinting and AMS at the Schwalbenberg RP1 LPS reveal insights into dust source dynamics that allow for estimating their emission potential during Upper Pleistocene palaeoenvironmental changes. &amp;amp;#160;&amp;lt;/p&amp;gt;
Exploring the effect of instream boulders on large wood transport combining numerical modelling and field experiments
2022-03-28

&amp;lt;p&amp;gt;Large and relatively immobile sediment particles (i.e., boulders, usually defined with a diameter greater than 256 mm) are naturally delivered to rivers from hillslopes, transported by extreme floods, or produced by processes such as bed armouring. Boulder placement is also used as an artifical method for stabilizing channel beds and banks in river restoration projects. Natural or reintroduced boulders are important elements with a significant influence on channel hydraulics, erosion and deposition dynamics, and morphology. Still, little is known about their effect on large wood transported as floats along the river.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;A field experiment was performed to track the mobility of cylindrical wood elements artificially placed in a reach of the Rienz River upstream from the city of Brunico, in South Tyrol (Northern Italy) and transported along a few kilometres over a period of three years. The Rienz River is a single thread sinuous gravel-bed river, characterized by the presence of several large boulders. Combining available field observations and 2D numerical modelling (coupling a 2D flow and a Lagrangian calculation of wood elements), this work aims to test the effect of boulders on both the river ecohydraulics and large wood transport. First, a detailed topography was obtained combining an available digital elevation model (2 m resolution) with topographical surveys. Second, the numerical model (i.e., Iber-Wood) has been calibrated with flow depths observations and the wood travel distances recorded during one high flow event were used for validation of the Lagrangian calculation. Finally, different scenarios with different boulder rearrangements are currently run to explore the effects of boulders size and location distribution on both wood transport and river ecohydraulics. This contribution will show preliminary results and discuss how boulder-rich channels differ from boulder-free channels in terms of large wood transport and deposition.&amp;lt;/p&amp;gt;
Temperature and precipitation distribution changes in response to global warming &#8211; results from transient simulations of the Last Deglaciation from a hierarchy of climate models
2022-03-28

&amp;lt;div&amp;gt; &amp;lt;p&amp;gt;Projections of anthropogenic climate change suggest possible surface temperature increases similar to those during past major shifts of the mean climate like the Last Deglaciation. Such shifts do not only affect the mean but rather the full probability distributions of climatic variables such as temperature and precipitation. Changes to their distributions can thus be expected for the future as well and need to be constrained. &amp;lt;span&amp;gt;&amp;amp;#160;&amp;lt;/span&amp;gt;&amp;lt;/p&amp;gt; &amp;lt;/div&amp;gt;&amp;lt;div&amp;gt; &amp;lt;p&amp;gt;To this end, we examine transient simulations of the Last Deglaciation from a hierarchy of climate models, ranging from an energy balance model to state-of-the-art Earth System Models. Besides the mean, we use the higher moments of variability &amp;amp;#8211; variance, skewness, and kurtosis &amp;amp;#8211; to characterize changes of the distribution. The analysis covers annual to millennial timescales and examines how patterns vary with timescale and region in response to warming. Furthermore, we evaluate how the changes of the distributions affect the occurrence of extremes.&amp;amp;#160;&amp;lt;span&amp;gt;&amp;amp;#160;&amp;lt;/span&amp;gt;&amp;lt;/p&amp;gt; &amp;lt;/div&amp;gt;&amp;lt;div&amp;gt; &amp;lt;p&amp;gt;To analyze the influence of forcings on the distributions, we compare the patterns of the fully-forced simulations to those in sensitivity experiments that isolate the effects of individual forcings. In particular, the effect of volcanism is examined across the hierarchy, as well as changes in ice cover, freshwater input, CO&amp;lt;sub&amp;gt;&amp;lt;span&amp;gt;2&amp;lt;/span&amp;gt;&amp;lt;/sub&amp;gt;, and orbit. While large-scale global patterns can be found, there are significant regional differences as well as differences between simulations, relating for example to differences in the modelling of ice cover changes and freshwater input. Finally, we investigate whether climate model projections show the same trends with respect to the change in moments as those found in the deglacial simulations and thus whether the patterns found might hold for future climate.&amp;lt;span&amp;gt;&amp;amp;#160;&amp;lt;/span&amp;gt;&amp;lt;/p&amp;gt; &amp;lt;/div&amp;gt;