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Preceramic human skeletal remains preserved in submerged caves near Tulum in the Mexican state of Quintana Roo, Mexico, reveal conflicting results regarding C-14 dating. Here we use U-series techniques for dating a stalagmite overgrowing the pelvis of a human skeleton discovered in the submerged Chan Hol cave. The oldest closed system U/Th age comes from around 21 mm above the pelvis defining the terminus ante quem for the pelvis to 11311 +/- 370 y BP. However, the skeleton might be considerable older, probably as old as 13 ky BP as indicated by the speleothem stable isotope data. The Chan Hol individual confirms a late Pleistocene settling of Mesoamerica and represents one of the oldest human osteological remains in America.
Large-scale commercial cropping of soybeans expanded in the tropical Amazon and Cerrado biomes of Brazil after 1990. More recently, cropping intensified from single-cropping of soybeans to double-cropping of soybeans with corn or cotton. Cropland expansion and intensification, and the accompanying use of mineral fertilizers, raise concerns about whether nutrient runoff and impacts to surface waters will be similar to those experienced in commercial cropland regions at temperate latitudes. We quantified water infiltration through soils, water yield, and streamwater chemistry in watersheds draining native tropical forest and single-and double-cropped areas on the level, deep, highly weathered soils where cropland expansion and intensification typically occurs. Although water yield increased four-fold from croplands, streamwater chemistry remained largely unchanged. Soil characteristics exerted important control over the movement of nitrogen (N) and phosphorus (P) into streams. High soil infiltration rates prevented surface erosion and movement of particulate P, while P fixation in surface soils restricted P movement to deeper soil layers. Nitrogen retention in deep soils, likely by anion exchange, also appeared to limit N leaching and export in streamwater from both single-and double-cropped watersheds that received nitrogen fertilizer. These mechanisms led to lower streamwater P and N concentrations and lower watershed N and P export than would be expected, based on studies from temperate croplands with similar cropping and fertilizer application practices.
Understanding how Earth-surface processes respond to past climatic perturbations is crucial for making informed predictions about future impacts of climate change on sediment "uxes. Sedimentary records provide the archives for inferring these processes, but their interpretation is compromised by our incomplete understanding of how sediment-routing systems respond to millennial-scale climate cycles. We analyzed seven sediment cores recovered from marine turbidite depositional sites along the Chile continental margin. The sites span a pronounced arid-to-humid gradient with variable relief and related sediment connectivity of terrestrial and marine environments. These sites allowed us to study event related depositional processes in different climatic and geomorphic settings from the Last Glacial Maximum to the present day. The three sites reveal a steep decline of turbidite deposition during deglaciation. High rates of sea-level rise postdate the decline in turbidite deposition. Comparison with paleoclimate proxies documents that the spatio-temporal sedimentary pattern rather mirrors the deglacial humidity decrease and concomitant warming with no resolvable lag times. Our results let us infer that declining deglacial humidity decreased "uvial sediment supply. This signal propagated rapidly through the highly connected systems into the marine sink in north-central Chile. In contrast, in south-central Chile, connectivity between the Andean erosional zone and the "uvial transfer zone probably decreased abruptly by sediment trapping in piedmont lakes related to deglaciation, resulting in a sudden decrease of sediment supply to the ocean. Additionally, reduced moisture supply may have contributed to the rapid decline of turbidite deposition. These different causes result in similar depositional patterns in the marine sinks. We conclude that turbiditic strata may constitute reliable recorders of climate change across a wide range of climatic zones and geomorphic conditions. However, the underlying causes for similar signal manifestations in the sinks may differ, ranging from maintained high system connectivity to abrupt connectivity loss. (C) 2017 Elsevier B.V. All rights reserved.
Fluvial fill terraces in intermontane basins are valuable geomorphic archives that can record tectonically and/or climatically driven changes of the Earth-surface process system. However, often the preservation of fill terrace sequences is incomplete and/or they may form far away from their source areas, complicating the identification of causal links between forcing mechanisms and landscape response, especially over multi-millennial timescales. The intermontane Toro Basin in the southern Central Andes exhibits at least five generations of fluvial terraces that have been sculpted into several-hundred-meter-thick Quaternary valley-fill conglomerates. New surface-exposure dating using nine cosmogenic Be-10 depth profiles reveals the successive abandonment of these terraces with a 100 kyr cyclicity between 75 +/- 7 and 487 +/- 34 ka. Depositional ages of the conglomerates, determined by four Al-26/Be-10 burial samples and U-Pb zircon ages of three intercalated volcanic ash beds, range from 18 +/- 141 to 936 +/- 170 ka, indicating that there were multiple cut-and-fill episodes. Although the initial onset of aggradation at similar to 1 Ma and the overall net incision since ca. 500 ka can be linked to tectonic processes at the narrow basin outlet, the superimposed 100 kyr cycles of aggradation and incision are best explained by eccentricity-driven climate change. Within these cycles, the onset of river incision can be correlated with global cold periods and enhanced humid phases recorded in paleoclimate archives on the adjacent Bolivian Altiplano, whereas deposition occurred mainly during more arid phases on the Altiplano and global interglacial periods. We suggest that enhanced runoff during global cold phases - due to increased regional precipitation rates, reduced evapotranspiration, or both - resulted in an increased sediment-transport capacity in the Toro Basin, which outweighed any possible increases in upstream sediment supply and thus triggered incision. Compared with two nearby basins that record precessional (21-kyr) and long-eccentricity (400-kyr) forcing within sedimentary and geomorphic archives, the recorded cyclicity scales with the square of the drainage basin length. (C) 2017 Elsevier B.V. All rights reserved.
Climate change is expected to exacerbate the current threats to freshwater ecosystems, yet multifaceted studies on the potential impacts of climate change on freshwater biodiversity at scales that inform management planning are lacking. The aim of this study was to fill this void through the development of a novel framework for assessing climate change vulnerability tailored to freshwater ecosystems. The three dimensions of climate change vulnerability are as follows: (i) exposure to climate change, (ii) sensitivity to altered environmental conditions and (iii) resilience potential. Our vulnerability framework includes 1685 freshwater species of plants, fishes, molluscs, odonates, amphibians, crayfish and turtles alongside key features within and between catchments, such as topography and connectivity. Several methodologies were used to combine these dimensions across a variety of future climate change models and scenarios. The resulting indices were overlaid to assess the vulnerability of European freshwater ecosystems at the catchment scale (18 783 catchments). The Balkan Lakes Ohrid and Prespa and Mediterranean islands emerge as most vulnerable to climate change. For the 2030s, we showed a consensus among the applied methods whereby up to 573 lake and river catchments are highly vulnerable to climate change. The anthropogenic disruption of hydrological habitat connectivity by dams is the major factor reducing climate change resilience. A gap analysis demonstrated that the current European protected area network covers <25% of the most vulnerable catchments. Practical steps need to be taken to ensure the persistence of freshwater biodiversity under climate change. Priority should be placed on enhancing stakeholder cooperation at the major basin scale towards preventing further degradation of freshwater ecosystems and maintaining connectivity among catchments. The catchments identified as most vulnerable to climate change provide preliminary targets for development of climate change conservation management and mitigation strategies.
Arctic and alpine treelines worldwide differ in their reactions to climate change. A northward advance of or densification within the treeline ecotone will likely influence climate-vegetation feedback mechanisms. In our study, which was conducted in the Taimyr Depression in the North Siberian Lowlands, w present a combined field-and model-based approach helping us to better understand the population processes involved in the responses of the whole treeline ecotone, spanning from closed forest to single-tree tundra, to climate warming. Using information on stand structure, tree age, and seed quality and quantity from seven sites, we investigate effects of intra-specific competition and seed availability on the specific impact of recent climate warming on larch stands. Field data show that tree density is highest in the forest-tundra, and average tree size decreases from closed forest to single-tree tundra. Age-structure analyses indicate that the trees in the closed forest and forest-tundra have been present for at least similar to 240 yr. At all sites except the most southerly ones, past establishment is positively correlated with regional temperature increase. In the single-tree tundra, however, a change in growth form from krummholz to erect trees, beginning similar to 130 yr ago, rather than establishment date has been recorded. Seed mass decreases from south to north, while seed quantity increases. Simulations with LAVESI (Larix Vegetation Simulator) further suggest that relative density changes strongly in response to a warming signal in the forest-tundra while intra-specific competition limits densification in the closed forest and seed limitation hinders densification in the single-tree tundra. We find striking differences in strength and timing of responses to recent climate warming. While forest-tundra stands recently densified, recruitment is almost non-existent at the southern and northern end of the ecotone due to autecological processes. Palaeo-treelines may therefore be inappropriate to infer past temperature changes at a fine scale. Moreover, a lagged treeline response to past warming will, via feedback mechanisms, influence climate change in the future.
The Weather Research and Forecasting (WRF) model is used to simulate the spatiotemporal distribution of precipitation over central Asia over the year April 2005 through March 2006. Experiments are performed at 6.7 km horizontal grid spacing, with an emphasis on winter and summer precipitation over the Himalaya. The model and the Tropical Rainfall Measuring Mission show a similar inter-seasonal cycle of precipitation, from extratropical cyclones to monsoon precipitation, with agreement also in the diurnal cycle of monsoon precipitation. In winter months, WRF compares better in timeseries of daily precipitation to stations below than above 3-km elevation, likely due to inferior measurement of snow than rain by the stations, highlighting the need for reliable snowfall measurements at high elevations in winter. In summer months, the nocturnal precipitation cycle in the foothills and valleys of the Himalaya is captured by this 6.7-km WRF simulation, while coarser simulations with convective parameterization show near zero nocturnal precipitation. In winter months, higher resolution is less important, serving only to slightly increase precipitation magnitudes due to steeper slopes. However, even in the 6.7-km simulation, afternoon precipitation is overestimated at high elevations, which can be reduced by even higher-resolution (2.2-km) simulations. These results indicate that WRF provides skillful simulations of precipitation relevant for studies of water resources over the complex terrain in the Himalaya.
Early agriculture can be detected in palaeovegetation records, but quantification of the relative importance of climate and land use in influencing regional vegetation composition since the onset of agriculture is a topic that is rarely addressed. We present a novel approach that combines pollen-based REVEALS estimates of plant cover with climate, anthropogenic land-cover and dynamic vegetation modelling results. This is used to quantify the relative impacts of land use and climate on Holocene vegetation at a sub-continental scale, i.e. northern and western Europe north of the Alps. We use redundancy analysis and variation partitioning to quantify the percentage of variation in vegetation composition explained by the climate and land-use variables, and Monte Carlo permutation tests to assess the statistical significance of each variable. We further use a similarity index to combine pollen based REVEALS estimates with climate-driven dynamic vegetation modelling results. The overall results indicate that climate is the major driver of vegetation when the Holocene is considered as a whole and at the sub-continental scale, although land use is important regionally. Four critical phases of land-use effects on vegetation are identified. The first phase (from 7000 to 6500 BP) corresponds to the early impacts on vegetation of farming and Neolithic forest clearance and to the dominance of climate as a driver of vegetation change. During the second phase (from 4500 to 4000 BP), land use becomes a major control of vegetation. Climate is still the principal driver, although its influence decreases gradually. The third phase (from 2000 to 1500 BP) is characterised by the continued role of climate on vegetation as a consequence of late-Holocene climate shifts and specific climate events that influence vegetation as well as land use. The last phase (from 500 to 350 BP) shows an acceleration of vegetation changes, in particular during the last century, caused by new farming practices and forestry in response to population growth and industrialization. This is a unique signature of anthropogenic impact within the Holocene but European vegetation remains climatically sensitive and thus may continue to respond to ongoing climate change. (C) 2017 Elsevier Ltd. All rights reserved.
Retrogressive thaw slumps (RTSs) are among the most active landforms in the Arctic; their number has increased significantly over the past decades. While processes initiating discrete RTSs are well identified, the major terrain controls on the development of coastal RTSs at a regional scale are not yet defined. Our research reveals the main geomorphic factors that determine the development of RTSs along a 238km segment of the Yukon Coast, Canada. We (1) show the current extent of RTSs, (2) ascertain the factors controlling their activity and initiation, and (3) explain the spatial differences in the density and areal coverage of RTSs. We mapped and classified 287 RTSs using high-resolution satellite images acquired in 2011. We highlighted the main terrain controls over their development using univariate regression trees model. Coastal geomorphology influenced both the activity and initiation of RTSs: active RTSs and RTSs initiated after 1972 occurred primarily on terrains with slope angles greater than 3.9 degrees and 5.9 degrees, respectively. The density and areal coverage of RTSs were constrained by the volume and thickness of massive ice bodies. Differences in rates of coastal change along the coast did not affect the model. We infer that rates of coastal change averaged over a 39year period are unable to reflect the complex relationship between RTSs and coastline dynamics. We emphasize the need for large-scale studies of RTSs to evaluate their impact on the ecosystem and to measure their contribution to the global carbon budget. Plain Language Summary Retrogressive thaw slumps, henceforth slumps are a type of landslides that occur when permafrost thaws. Slumps are active landforms: they develop quickly and extend over several hectares. Satellite imagery allows to map such slumps over large areas. Our research shows where slumps develop along a 238 km segment of the Yukon Coast in Canada and explains which environments are most suitable for slump occurrence. We found that active and newly developed slumps were triggered where coastal slopes were greater than 3.9 degrees and 5.9 degrees, respectively. We explain that coastal erosion influences the development of slumps by modifying coastal slopes. We found that the highest density of slumps as well as the largest slumps occurred on terrains with high amounts of ice bodies in the ground. This study provides tools to better identify areas in the Arctic that are prone to slump development.
Permafrost is a distinct feature of the terrestrial Arctic and is vulnerable to climate warming. Permafrost degrades in different ways, including deepening of a seasonally unfrozen surface and localized but rapid development of deep thaw features. Pleistocene ice-rich permafrost with syngenetic ice-wedges, termed Yedoma deposits, are widespread in Siberia, Alaska, and Yukon, Canada and may be especially prone to rapid-thaw processes. Freeze-locked organic matter in such deposits can be re-mobilized on short time-scales and contribute to a carbon-cycle climate feedback. Here we synthesize the characteristics and vulnerability of Yedoma deposits by synthesizing studies on the Yedoma origin and the associated organic carbon pool. We suggest that Yedoma deposits accumulated under periglacial weathering, transport, and deposition dynamics in non-glaciated regions during the late Pleistocene until the beginning of late glacial warming. The deposits formed due to a combination of aeolian, colluvial, nival, and alluvial deposition and simultaneous ground ice accumulation. We found up to 130 gigatons organic carbon in Yedoma, parts of which are well-preserved and available for fast decomposition after thaw. Based on incubation experiments, up to 10% of the Yedoma carbon is considered especially decomposable and may be released upon thaw. The substantial amount of ground ice in Yedoma makes it highly vulnerable to disturbances such as thermokarst and thermo-erosion processes. Mobilization of permafrost carbon is expected to increase under future climate warming. Our synthesis results underline the need of accounting for Yedoma carbon stocks in next generation Earth-System-Models for a more complete representation of the permafrost-carbon feedback.
Inherited rheological structures in the lithosphere are expected to have large impact on the architecture of continental rifts. The Turkana depression in the East African Rift connects the Main Ethiopian Rift to the north with the Kenya rift in the south. This region is characterized by a NW-SE trending band of thinned crust inherited from a Mesozoic rifting event, which is cutting the present-day N-S rift trend at high angle. In striking contrast to the narrow rifts in Ethiopia and Kenya, extension in the Turkana region is accommodated in subparallel deformation domains that are laterally distributed over several hundred kilometers. We present both analog experiments and numerical models that reproduce the along-axis transition from narrow rifting in Ethiopia and Kenya to a distributed deformation within the Turkana depression. Similarly to natural observations, our models show that the Ethiopian and Kenyan rifts bend away from each other within the Turkana region, thus forming a right-lateral step over and avoiding a direct link to form a continuous N-S depression. The models reveal five potential types of rift linkage across the preexisting basin: three types where rifts bend away from the inherited structure connecting via a (1) wide or (2) narrow rift or by (3) forming a rotating microplate, (4) a type where rifts bend towards it, and (5) straight rift linkage. The fact that linkage type 1 is realized in the Turkana region provides new insights on the rheological configuration of the Mesozoic rift system at the onset of the recent rift episode. Plain Language Summary The Turkana depression in the Kenya/Ethiopia borderland is most famous for its several million years old human fossils, but it also holds a rich geological history of continental separation. The Turkana region is a lowland located between the East African and Ethiopian domes because its crust and mantle have been stretched in a continent-wide rift event during Cretaceous times about 140-120 Ma ago. This thin lithosphere exerted paramount control on the dynamics of East African rifting in this area, which commenced around 15 Ma ago and persists until today. Combining analog "sandbox" experiments with numerical geodynamic modeling, we find that inherited rift structures explain the dramatic change in rift style from deep, narrow rift basins north and south of the Turkana area to wide, distributed deformation within the Turkana depression. The failed Cretaceous rift is also responsible for the eastward bend of the Ethiopian rift and the westward bend of the Kenyan rift when entering the Turkana depression, which generated the characteristic hook-shaped form of present-day Lake Turkana. Combing two independent modeling techniques-analog and numerical experiments-is a very promising approach allowing to draw robust conclusions about the processes that shape the surface of our planet.
Biofilm formation in bacteria is considered to be one strategy to avoid protozoan grazing. However, this assumption is largely based on experiments with suspension-feeding protozoans. Here we test the hypothesis that grazing resistance depends on both the grazers’ feeding trait and the bacterial phenotype, rather than being a general characteristic of bacterial biofilms. We combined batch experiments with mathematical modelling, considering the bacterium Pseudomonas putida and either a suspension-feeding (i.e. the ciliate Paramecium tetraurelia) or a surface-feeding grazer (i.e. the amoeba Acanthamoeba castellanii). We find that both plankton and biofilm phenotypes were consumed, when exposed to their specialised grazer, whereas the other phenotype remained grazing-resistant. This was consistently shown in two experiments (starting with either only planktonic bacteria or with additional pre-grown biofilms) and matches model predictions. In the experiments, the plankton feeder strongly stimulated the biofilm biomass. This stimulation of the resistant prey phenotype was not predicted by the model and it was not observed for the biofilm feeders, suggesting the existence of additional mechanisms that stimulate biofilm formation besides selective feeding. Overall, our results confirm our hypothesis that grazing resistance is a matter of the grazers’ trait (i.e. feeding type) rather than a biofilm-specific property.
Silicon stable isotopes have emerged as a powerful proxy to investigate weathering because Si uptake from solution by secondary minerals or by the vegetation causes significant shifts in the isotope composition. In this study, we determined the Si isotope compositions of the principle Si pools within two small catchments located on sandstone and paragneiss, respectively, in the temperate Black Forest (Germany). At both settings, clay formation is dominated by mineral transformation preserving largely the signature of parental minerals with delta Si-30 values of around -0.7%. Bulk soils rich in primary minerals are similar to bulk parental material with delta Si-30 values close to -0.4%. Topsoils are partly different because organic matter degradation has promoted intense weathering leading to delta Si-30 values as low as -1.0%. Water samples expose highly dynamic weathering processes in the soil zone: 1) after spring snowmelt, increased release of DOC and high water fluxes trigger clay mineral dissolution which leads to delta Si-30 values down to -0.7% and 2) in course of the summer, Si uptake by the vegetation and secondary mineral formation drives dissolved Si to typical positive delta Si-30 values up to 1.1%. Groundwater with delta Si-30 values of around 0.4% records steady processes in bedrock reflecting plagioclase weathering together with kaolinite precipitation. An isotope mass balance approach reveals incongruent weathering conditions where denudation of Si is largely driven by physical erosion. Erosion of phytoliths contributes 3 to 21% to the total Si export flux, which is in the same order as the dissolved Si flux. These results elucidate the Si dynamics during weathering on catchments underlain of sedimentary origin, prevailing on the Earth surface and provide therefore valuable information to interpret the isotope signature of large river systems.
Highly regulated induction systems enabling dose-dependent and reversible fine-tuning of protein expression output are beneficial for engineering complex biosynthetic pathways. To address this, we developed PhiReX, a novel red/far-red light-regulated protein expression system for use in Saccharomyces cerevisiae. PhiReX is based on the combination of a customizable synTALE DNA-binding domain, the VP64 activation domain and the light-sensitive dimerization of the photoreceptor PhyB and its interacting partner PIF3 from Arabidopsis thaliana. Robust gene expression and high protein levels are achieved by combining genome integrated red light-sensing components with an episomal high-copy reporter construct. The gene of interest as well as the synTALE DNA-binding domain can be easily exchanged, allowing the flexible regulation of any desired gene by targeting endogenous or heterologous promoter regions. To allow low-cost induction of gene expression for industrial fermentation processes, we engineered yeast to endogenously produce the chromophore required for the effective dimerization of PhyB and PIF3. Time course experiments demonstrate high-level induction over a period of at least 48 h.
Normally in paleoseismology, the study of the tectonic slip-rate is performed in trenches on the fault scarp, or by the estimation of fault movements from the geomorphic features. In this work, we have carried out a paleoseismic analysis of the Benis Fault, located in southeast Spain, combined with a geothermal analysis inside a deep cave related to the fault (-350 m). Thus, we have estimated the last earthquake magnitude and time of occurrence from evidence of ceiling collapse and displaced carbonate blocks inside a cave, which is developed across the fault. The magnitude was obtained from the application of the empirical relationship of the fault parameters and coseismic vertical displacement, yielding a value ranging between M 5.9 and M 6.5. Moreover, we dated this paleoearthquake by the paleontological record of a "Lynx pardinus spelaea", with an age of 65 +/- 18 ka BP. Additionally, we have measured the thermal profile of the Benis Cave (-350 m of depth), from single rock point temperature measurements during 2 years. The temperature profile shows three different parts inside the cave, the shallow heterogeneous thermal zone till 50 m depth; the homogeneous thermal zone 150 m till with constant temperature and the hetero-thermal deep zone, deeper than 150 m and till the deepest zone (350 m). Furthermore, we have estimated the Vertical Geothermal Gradient, 1.85 degrees C/100 m for the deepest zone (-150; -290 m). The temperature increases with depth, showing a reverse thermal profile in comparison with normal gradients in deep caves. Finally, we have calculated the heat flux of 0.46 mWm(2). (C) 2016 Elsevier Ltd and INQUA. All rights reserved.
role of subducted slabs
(2017)
Long-term estimates of the dissolution of silicate rock are generally derived from a range of isotopic proxies, such as the radiogenic strontium isotope ratio (Sr-87/Sr-86), which are preserved in sediment archives. For these systems to fairly represent silicate weathering, the changes in isotopic ratios in terrestrial surface waters should correspond to changes in the overall silicate dissolution. This assumes that the silicate mineral phases that act as sources of a given isotope dissolve at a rate that is proportional to the overall silicate weathering. Bedrock landsliding exhumes large quantities of fresh rock for weathering in transient storage, and rapid weathering in these deposits is controlled primarily by dissolution of the most reactive phases. In this study, we test the hypothesis that preferential weathering of these labile minerals can decouple the dissolution of strontium sources from the actual silicate weathering rates in the rapidly eroding Western Southern Alps (WSA) of New Zealand. We find that rapid dissolution of relatively radiogenic calcite and biotite in landslides leads to high local fluxes in strontium with isotopic ratios that offer no clear discrimination between sources. These higher fluxes of radiogenic strontium are in contrast to silicate weathering rates in landslides that are not systematically elevated. On a mountain belt scale, radiogenic strontium fluxes are not coupled to volumes of recent landslides in large (>100 km(2)) catchments, but silicate weathering fluxes are. Such decoupling is likely due first to the broad variability in the strontium content of carbonate minerals, and second to the combination of radiogenic strontium released from both biotite and carbonate in recent landslides. This study supports previous work suggesting the limited utility of strontium isotopes as a system to study silicate weathering in the WSA. Crucially however, in settings where bedrock landsliding is a dominant erosive process there is potential for both random and systematic bias in isotope proxies if the most reactive phases exposed for dissolution by landslides disproportionately contribute to the proxy of choice. This clearly suggests that the isotopic composition of marine Sr is a proxy for periods of rapid mountain uplift and erosion rather than for the associated enhanced silicate weathering. (C) 2017 Elsevier Ltd. All rights reserved.
One of the most significant Late Holocene climate shifts occurred around 2800 years ago, when cooler and wetter climate conditions established in western Europe. This shift coincided with an abrupt change in regional atmospheric circulation between 2760 and 2560 cal years BP, which has been linked to a grand solar minimum with the same duration (the Homeric Minimum). We investigated the temporal sequence of hydroclimatic and vegetation changes across this interval of climatic change (Homeric climate oscillation) by using lipid biomarker stable hydrogen isotope ratios (ED values) and pollen assemblages from the annually-laminated sediment record from lake Meerfelder Maar (Germany). Over the investigated interval (3200-2000 varve years BP), terrestrial lipid biomarker ED showed a gradual trend to more negative values, consistent with the western Europe long-term climate trend of the Late Holocene. At ca. 2640 varve years BP we identified a strong increase in aquatic plants and algal remains, indicating a rapid change in the aquatic ecosystem superimposed on this long-term trend. Interestingly, this aquatic ecosystem change was accompanied by large changes in ED values of aquatic lipid biomarkers, such as nC(21) and nC(23) (by between 22 and 30%(0)). As these variations cannot solely be explained by hydroclimate changes, we suggest that these changes in the Wag value were influenced by changes in n-alkane source organisms. Our results illustrate that if ubiquitous aquatic lipid biomarkers are derived from a limited pool of organisms, changes in lake ecology can be a driving factor for variations on sedimentary lipid MN values, which then could be easily misinterpreted in terms of hydro climatic changes. (C) 2017 Elsevier Ltd. All rights reserved.
Accurate time series representation of paleoclimatic proxy records is challenging because such records involve dating errors in addition to proxy measurement errors. Rigorous attention is rarely given to age uncertainties in paleoclimatic research, although the latter can severely bias the results of proxy record analysis. Here, we introduce a Bayesian approach to represent layer-counted proxy records - such as ice cores, sediments, corals, or tree rings - as sequences of probability distributions on absolute, error-free time axes. The method accounts for both proxy measurement errors and uncertainties arising from layer-counting-based dating of the records. An application to oxygen isotope ratios from the North Greenland Ice Core Project (NGRIP) record reveals that the counting errors, although seemingly small, lead to substantial uncertainties in the final representation of the oxygen isotope ratios. In particular, for the older parts of the NGRIP record, our results show that the total uncertainty originating from dating errors has been seriously underestimated. Our method is next applied to deriving the overall uncertainties of the Suigetsu radiocarbon comparison curve, which was recently obtained from varved sediment cores at Lake Suigetsu, Japan. This curve provides the only terrestrial radiocarbon comparison for the time interval 12.5-52.8 kyr BP. The uncertainties derived here can be readily employed to obtain complete error estimates for arbitrary radiometrically dated proxy records of this recent part of the last glacial interval.
The aim of this paper is to investigate the ability of various site-condition proxies (SCPs) to reduce ground-motion aleatory variability and evaluate how SCPs capture nonlinearity site effects. The SCPs used here are time-averaged shear-wave velocity in the top 30 m (V-S30), the topographical slope (slope), the fundamental resonance frequency (f(0)) and the depth beyond which V-s exceeds 800 m/s (H800). We considered first the performance of each SCP taken alone and then the combined performance of the 6 SCP pairs [V-S30-f(0)], [V-S30-H-800], [f(0)-slope], [H-800-slope], [V-S30-slope] and [f(0)-H-800]. This analysis is performed using a neural network approach including a random effect applied on a KiK-net subset for derivation of ground-motion prediction equations setting the relationship between various ground-motion parameters such as peak ground acceleration, peak ground velocity and pseudo-spectral acceleration PSA (T), and Mw, RJB, focal depth and SCPs. While the choice of SCP is found to have almost no impact on the median groundmotion prediction, it does impact the level of aleatory uncertainty. VS30 is found to perform the best of single proxies at short periods (T < 0.6 s), while f(0) and H-800 perform better at longer periods; considering SCP pairs leads to significant improvements, with particular emphasis on [V-S30-H-800] and [f(0)-slope] pairs. The results also indicate significant nonlinearity on the site terms for soft sites and that the most relevant loading parameter for characterising nonlinear site response is the "stiff" spectral ordinate at the considered period.
High precipitation quantiles tend to rise with temperature, following the so-called Clausius-Clapeyron (CC) scaling. It is often reported that the CC-scaling relation breaks down and even reverts for very high temperatures. In our study, we investigate this reversal using observational climate data from 142 stations across Germany. One of the suggested meteorological explanations for the breakdown is limited moisture supply. Here we argue that, instead, it could simply originate from undersampling. As rainfall frequency generally decreases with higher temperatures, rainfall intensities as dictated by CC scaling are less likely to be recorded than for moderate temperatures. Empirical quantiles are conventionally estimated from order statistics via various forms of plotting position formulas. They have in common that their largest representable return period is given by the sample size. In small samples, high quantiles are underestimated accordingly. The small-sample effect is weaker, or disappears completely, when using parametric quantile estimates from a generalized Pareto distribution (GPD) fitted with L moments. For those, we obtain quantiles of rainfall intensities that continue to rise with temperature.
Climatic and limnological changes at Lake Karakul (Tajikistan) during the last similar to 29 cal ka
(2017)
We present results of analyses on a sediment core from Lake Karakul, located in the eastern Pamir Mountains, Tajikistan. The core spans the last similar to 29 cal ka. We investigated and assessed processes internal and external to the lake to infer changes in past moisture availability. Among the variables used to infer lake-external processes, high values of grain-size end-member (EM) 3 (wide grain-size distribution that reflects fluvial input) and high Sr/Rb and Zr/Rb ratios (coinciding with coarse grain sizes), are indicative of moister conditions. High values in EM1, EM2 (peaks of small grain sizes that reflect long-distance dust transport or fine, glacially derived clastic input) and TiO2 (terrigenous input) are thought to reflect greater influence of dry air masses, most likely of Westerly origin. High input of dust from distant sources, beginning before the Last Glacial Maximum (LGM) and continuing to the late glacial, reflects the influence of dry Westerlies, whereas peaks in fluvial input suggest increased moisture availability. The early to early-middle Holocene is characterised by coarse mean grain sizes, indicating constant, high fluvial input and moister conditions in the region. A steady increase in terrigenous dust and a decrease in fluvial input from 6.6 cal ka BP onwards points to the Westerlies as the predominant atmospheric circulation through to present, and marks a return to drier and even arid conditions in the area. Proxies for productivity (TOC, TOC/TN, TOCBr), redox potential (Fe/Mn) and changes in the endogenic carbonate precipitation (TIC, delta(18) OCarb) indicate changes within the lake. Low productivity characterised the lake from the late Pleistocene until 6.6 cal ka BP, and increased rapidly afterwards. Lake level remained low until the LGM, but water depth increased to a maximum during the late glacial and remained high into the early Holocene. Subsequently, the water level decreased to its present stage. Today the lake system is mainly climatically controlled, but the depositional regime is also driven by internal limnogeological processes.
The SEIS (Seismic Experiment for Interior Structure) instrument onboard the InSight mission will be the first seismometer directly deployed on the surface of Mars. From studies on the Earth and the Moon, it is well known that site amplification in low-velocity sediments on top of more competent rocks has a strong influence on seismic signals, but can also be used to constrain the subsurface structure. Here we simulate ambient vibration wavefields in a model of the shallow sub-surface at the InSight landing site in Elysium Planitia and demonstrate how the high-frequency Rayleigh wave ellipticity can be extracted from these data and inverted for shallow structure. We find that, depending on model parameters, higher mode ellipticity information can be extracted from single-station data, which significantly reduces uncertainties in inversion. Though the data are most sensitive to properties of the upper-most layer and show a strong trade-off between layer depth and velocity, it is possible to estimate the velocity and thickness of the sub-regolith layer by using reasonable constraints on regolith properties. Model parameters are best constrained if either higher mode data can be used or additional constraints on regolith properties from seismic analysis of the hammer strokes of InSight’s heat flow probe HP3 are available. In addition, the Rayleigh wave ellipticity can distinguish between models with a constant regolith velocity and models with a velocity increase in the regolith, information which is difficult to obtain otherwise.
One of the major challenges in understanding the evolution of our own species is identifying the role climate change has played in the evolution of hominin species. To clarify the influence of climate, we need long and continuous high-resolution paleoclimate records, preferably obtained from hominin-bearing sediments, that are well-dated by tephro- and magnetostratigraphy and other methods. This is hindered, however, by the fact that fossil-bearing outcrop sediments are often discontinuous, and subject to weathering, which may lead to oxidation and remagnetization. To obtain fresh, unweathered sediments, the Hominin Sites and Paleolakes Drilling Project (HSPDP) collected a ∼216-meter core (WTK13) in 2013 from Early Pleistocene Paleolake Lorenyang deposits in the western Turkana Basin (Kenya). Here, we present the magnetostratigraphy of the WTK13 core, providing a first age model for upcoming HSPDP paleoclimate and paleoenvrionmental studies on the core sediments. Rock magnetic analyses reveal the presence of iron sulfides carrying the remanent magnetizations. To recover polarity orientation from the near-equatorial WTK13 core drilled at 5°N, we developed and successfully applied two independent drill-core reorientation methods taking advantage of (1) the sedimentary fabric as expressed in the Anisotropy of Magnetic Susceptibility (AMS) and (2) the occurrence of a viscous component oriented in the present day field. The reoriented directions reveal a normal to reversed polarity reversal identified as the top of the Olduvai Subchron. From this excellent record, we find no evidence for the ‘Vrica Subchron’ previously reported in the area. We suggest that outcrop-based interpretations supporting the presence of the Vrica Subchron have been affected by the oxidation of iron sulfides initially present in the sediments -as evident in the core record- and by subsequent remagnetization. We discuss the implications of the observed geomagnetic record for human evolution studies.
Competing hypotheses suggest that Himalayan topography is sustained and the plate convergence is accommodated either solely along the basal decollement, the Main Himalayan thrust (MHT), or more broadly, across multiple thrust faults. In the past, structural, geomorphic, and geodetic data of the Nepalese Himalaya have been used to constrain the geometry of the MHT and its shallow frontal thrust fault, known as Main Frontal thrust (MFT). The MHT flattens at depth and connects to a hinterland mid-crustal, steeper thrust ramp, located similar to 100 km north of the deformation front. There, the present-day convergence across the Himalaya is mostly accommodated by slip along the MFT. Despite a general agreement that in Nepal most of the shortening is accommodated along the MHT, some researchers have suggested the occurrence of persistent out-of-sequence shortening on interior faults near the Main Central thrust (MCT). Along the northwest Himalaya, in contrast, some of these characteristics of central Nepal are missing, suggesting along-strike variation of wedge deformation and MHT fault geometry. Here we present new field observations and seven zircon (U-Th)/He (ZHe) cooling ages combined with existing low-temperature data sets. In agreement with our previous findings, we suggest that the transect of cooling age patterns across the frontal Dhauladhar Range reveals that the Main Boundary thrust (MBT) is a primary fault, which has uplifted and sustained this spectacular mountain front since at least the late Miocene. Our results suggest that the MBT forms an similar to 40-km-long fault ramp before it soles into the MHT, and motion along it has exhumed rocks from depth of similar to 8-10 km. New three-dimensional thermokinematic modeling (using Pecube finite-element code) reveals that the observed ZHe and apatite fission track cooling ages can only be explained by sustained mean MBT slip rates between similar to 2.6 and 3.5 mm a(-1) since at least 8 Ma, which corresponds to a horizontal shortening rate of similar to 1.7-2.4 mm a(-1). We propose that the MBT is active today, despite a lack of definitive field or seismogenic evidence, and continues to accommodate crustal shorting by out-of-sequence faulting. Assuming that present-day geodetic shorting rates (similar to 14 +/- 2 mm a(-1)) across the northwest Himalaya have been sustained over geologic time scales, this implies that the MBT accommodated similar to 15% of the total Himalayan convergence since its onset. Furthermore, our modeling results imply that the MHT is missing a hinterland mid-crustal ramp further north.
Presentation and Analysis of a Worldwide Database of Earthquake-Induced Landslide Inventories
(2017)
Earthquake-induced landslide (EQIL) inventories are essential tools to extend our knowledge of the relationship between earthquakes and the landslides they can trigger. Regrettably, such inventories are difficult to generate and therefore scarce, and the available ones differ in terms of their quality and level of completeness. Moreover, access to existing EQIL inventories is currently difficult because there is no centralized database. To address these issues, we compiled EQIL inventories from around the globe based on an extensive literature study. The database contains information on 363 landslide-triggering earthquakes and includes 66 digital landslide inventories. To make these data openly available, we created a repository to host the digital inventories that we have permission to redistribute through the U.S. Geological Survey ScienceBase platform. It can grow over time as more authors contribute their inventories. We analyze the distribution of EQIL events by time period and location, more specifically breaking down the distribution by continent, country, and mountain region. Additionally, we analyze frequency distributions of EQIL characteristics, such as the approximate area affected by landslides, total number of landslides, maximum distance from fault rupture zone, and distance from epicenter when the fault plane location is unknown. For the available digital EQIL inventories, we examine the underlying characteristics of landslide size, topographic slope, roughness, local relief, distance to streams, peak ground acceleration, peak ground velocity, and Modified Mercalli Intensity. Also, we present an evaluation system to help users assess the suitability of the available inventories for different types of EQIL studies and model development.
Modeling loss-propagation in the global supply network: The dynamic agent-based model acclimate
(2017)
World markets are highly interlinked and local economies extensively rely on global supply and value chains. Consequently, local production disruptions, for instance caused by extreme weather events, are likely to induce indirect losses along supply chains with potentially global repercussions. These complex loss dynamics represent a challenge for comprehensive disaster risk assessments. Here, we introduce the numerical agent-based model acclimate designed to analyze the cascading of economic losses in the global supply network. Using national sectors as agents, we apply the model to study the global propagation of losses induced by stylized disasters. We find that indirect losses can become comparable in size to direct ones, but can be efficiently mitigated by warehousing and idle capacities. Consequently, a comprehensive risk assessment cannot focus solely on first-tier suppliers, but has to take the whole supply chain into account. To render the supply network climate-proof, national adaptation policies have to be complemented by international adaptation efforts. In that regard, our model can be employed to assess reasonable leverage points and to identify dynamic bottlenecks inaccessible to static analyses. (C) 2017 Elsevier B.V. All rights reserved.
Receiver functions (RF) have been used for several decades to study structures beneath seismic stations. Although most available stations are deployed on shore, the number of ocean bottom station (OBS) experiments has increased in recent years. Almost all OBSs have to deal with higher noise levels and a limited deployment time (approximate to 1year), resulting in a small number of usable records of teleseismic earthquakes. Here we use OBSs deployed as midaperture array in the deep ocean (4.5-5.5km water depth) of the eastern mid-Atlantic. We use evaluation criteria for OBS data and beamforming to enhance the quality of the RFs. Although some stations show reverberations caused by sedimentary cover, we are able to identify the Moho signal, indicating a normal thickness (5-8km) of oceanic crust. Observations at single stations with thin sediments (300-400m) indicate that a probable sharp lithosphere-asthenosphere boundary (LAB) might exist at a depth of approximate to 70-80km which is in line with LAB depth estimates for similar lithospheric ages in the Pacific. The mantle discontinuities at approximate to 410km and approximate to 660km are clearly identifiable. Their delay times are in agreement with PREM. Overall the usage of beam-formed earthquake recordings for OBS RF analysis is an excellent way to increase the signal quality and the number of usable events.
Voluminous magmatism during the South Atlantic opening has been considered as a classical example for plume related continental breakup. We present a study of the crustal structure around Walvis Ridge, near the intersection with the African margin. Two wide-angle seismic profiles were acquired. One is oriented NNW–SSE, following the continent–ocean transition and crossing Walvis Ridge. A second amphibious profile runs NW–SE from the Angola Basin into continental Namibia. At the continent–ocean boundary (COB) the mafic crust beneath Walvis Ridge is up to 33 km thick, with a pronounced high-velocity lower crustal body. Towards the south there is a smooth transition to 20–25 km thick crust underlying the COB in the Walvis Basin, with a similar velocity structure, indicating a gabbroic lower crust with associated cumulates at the base. The northern boundary of Walvis Ridge towards the Angola Basin shows a sudden change to oceanic crust only 4–6 km thick, coincident with the projection of the Florianopolis Fracture Zone, one of the most prominent tectonic features of the South Atlantic ocean basin. In the amphibious profile the COB is defined by a sharp transition from oceanic to rifted continental crust, with a magmatic overprint landward of the intersection of Walvis Ridge with the Namibian margin. The continental crust beneath the Congo Craton is 40 km thick, shoaling to 35 km further SE. The velocity models show that massive high-velocity gabbroic intrusives are restricted to a narrow zone directly underneath Walvis Ridge and the COB in the south. This distribution of rift-related magmatism is not easily reconciled with models of continental breakup following the establishment of a large, axially symmetric plume in the Earth's mantle. Rift-related lithospheric stretching and associated transform faulting play an overriding role in locating magmatism, dividing the margin in a magma-dominated southern and an essentially amagmatic northern segment.
Passive continental margins offer the unique opportunity to study the processes involved in continental extension and break-up. Within the LISPWAL (Llthospheric Structure of the Namibian continental Passive margin at the intersection with the Walvis Ridge from amphibious seismic investigations) project, combined on- and offshore seismic experiments were designed to characterize the Southern African passive margin at the Walvis Ridge in northern Namibia. In addition to extensive analysis of the crustal structures, we carried out seismic investigations targeting the velocity structure of the upper mantle in the landfall region of the Walvis Ridge with the Namibian coast. Upper mantle P-n travel time tomography from controlled source, amphibious seismic data was used to investigate the sub-Moho upper mantle seismic velocity. We succeeded in imaging upper mantle structures potentially associated with continental break-up and/or the Tristan da Cunha hotspot track. We found mostly coast-parallel sub-Moho velocity anomalies, interpreted as structures which were created during Gondwana break-up. (C)2016 Published by Elsevier B.V.
The opening of the South Atlantic is a classical example for a plume related continental breakup. Flood basalts are present on both conjugate margins as well as aseismic ridges connecting them with the current plume location at Tristan da Cunha. To determine the effect of the proposed plume head on the continental crust, we acquired wide-angle seismic data at the junction of the Walvis Ridge with the African continent and modelled the P-wave velocity structure in a forward approach. The profile extends 430 km along the ridge and continues onshore to a length of 720 km. Crustal velocities beneath the Walvis Ridge vary between 5.5 km/s and 7.0 km/s, a typical range for oceanic crust. The crustal thickness of 22 km, however, is approximately three times larger than of normal oceanic crust. The continent-ocean transition is characterized by 30 km thick crust with strong lateral velocity variations in the upper crust and a high-velocity lower crust (HVLC), where velocities reach up to 7.5 km/s. The HVLC is 100 to 130 km wider at the Walvis Ridge than it is farther south, and impinges onto the continental crust of the Kaoko fold belt. Such high seismic velocities indicate Mg-rich igneous material intruded into the continental crust during the initial rifting stage. However, the remaining continental crust seems unaffected by intrusions and the root of the 40 km-thick crust of the Kaoko belt is not thermally abraded. We conclude that the plume head did not modify the continental crust on a large scale, but caused rather local effects. Thus, it seems unlikely that a plume drove or initiated the breakup process. We further propose that the plume already existed underneath the continent prior to the breakup, and ponded melt erupted at emerging rift structures providing the magma for continental flood basalts. (C) 2017 Elsevier B.V. All rights reserved.
In the last few years the method of cosmic-ray neutron sensing (CRNS) has gained popularity among hydrologists, physicists, and land-surface modelers. The sensor provides continuous soil moisture data, averaged over several hectares and tens of decimeters in depth. However, the signal still may contain unidentified features of hydrological processes, and many calibration datasets are often required in order to find reliable relations between neutron intensity and water dynamics. Recent insights into environmental neutrons accurately described the spatial sensitivity of the sensor and thus allowed one to quantify the contribution of individual sample locations to the CRNS signal. Consequently, data points of calibration and validation datasets are suggested to be averaged using a more physically based weighting approach. In this work, a revised sensitivity function is used to calculate weighted averages of point data. The function is different from the simple exponential convention by the extraordinary sensitivity to the first few meters around the probe, and by dependencies on air pressure, air humidity, soil moisture, and vegetation. The approach is extensively tested at six distinct monitoring sites: two sites with multiple calibration datasets and four sites with continuous time series datasets. In all cases, the revised averaging method improved the performance of the CRNS products. The revised approach further helped to reveal hidden hydrological processes which otherwise remained unexplained in the data or were lost in the process of overcalibration. The presented weighting approach increases the overall accuracy of CRNS products and will have an impact on all their applications in agriculture, hydrology, and modeling.
High Mountain Asia (HMA) – encompassing the Tibetan Plateau and surrounding mountain ranges – is the primary water source for much of Asia, serving more than a billion downstream users. Many catchments receive the majority of their yearly water budget in the form of snow, which is poorly monitored by sparse in situ weather networks. Both the timing and volume of snowmelt play critical roles in downstream water provision, as many applications – such as agriculture, drinking-water generation, and hydropower – rely on consistent and predictable snowmelt runoff. Here, we examine passive microwave data across HMA with five sensors (SSMI, SSMIS, AMSR-E, AMSR2, and GPM) from 1987 to 2016 to track the timing of the snowmelt season – defined here as the time between maximum passive microwave signal separation and snow clearance. We validated our method against climate model surface temperatures, optical remote-sensing snow-cover data, and a manual control dataset (n = 2100, 3 variables at 25 locations over 28 years); our algorithm is generally accurate within 3–5 days. Using the algorithm-generated snowmelt dates, we examine the spatiotemporal patterns of the snowmelt season across HMA. The climatically short (29-year) time series, along with complex interannual snowfall variations, makes determining trends in snowmelt dates at a single point difficult. We instead identify trends in snowmelt timing by using hierarchical clustering of the passive microwave data to determine trends in self-similar regions. We make the following four key observations. (1) The end of the snowmelt season is trending almost universally earlier in HMA (negative trends). Changes in the end of the snowmelt season are generally between 2 and 8 days decade−1 over the 29-year study period (5–25 days total). The length of the snowmelt season is thus shrinking in many, though not all, regions of HMA. Some areas exhibit later peak signal separation (positive trends), but with generally smaller magnitudes than trends in snowmelt end. (2) Areas with long snowmelt periods, such as the Tibetan Plateau, show the strongest compression of the snowmelt season (negative trends). These trends are apparent regardless of the time period over which the regression is performed. (3) While trends averaged over 3 decades indicate generally earlier snowmelt seasons, data from the last 14 years (2002–2016) exhibit positive trends in many regions, such as parts of the Pamir and Kunlun Shan. Due to the short nature of the time series, it is not clear whether this change is a reversal of a long-term trend or simply interannual variability. (4) Some regions with stable or growing glaciers – such as the Karakoram and Kunlun Shan – see slightly later snowmelt seasons and longer snowmelt periods. It is likely that changes in the snowmelt regime of HMA account for some of the observed heterogeneity in glacier response to climate change. While the decadal increases in regional temperature have in general led to earlier and shortened melt seasons, changes in HMA's cryosphere have been spatially and temporally heterogeneous.
Nitrogen lipid regulator (NlpR) is a pleiotropic regulator that positively controls genes associated with both nitrogen and lipid metabolism in the oleaginous bacterium Rhodococcus jostii RHA1. In this study, we investigated the effect of nlpR disruption and overexpression on the assimilation of C-13-labeled glucose as carbon source, during cultivation of cells under nitrogen-limiting and nitrogen-rich conditions, respectively. Label incorporation into the total lipid extract (TLE) fraction was about 30% lower in the mutant strain in comparison with the wild type strain under low-nitrogen conditions. Moreover, a higher C-13 abundance (similar to 60%) into the extracellular polymeric substance fraction was observed in the mutant strain, nlpR disruption also promoted a decrease in the label incorporation into several TLE-derivative fractions including neutral lipids (NL), glycolipids (GL), phospholipids (PL), triacylglycerols (TAG), diacylglycerols (DAG), and free fatty acids (FFA), with the DAG being the most affected. In contrast, the nlpR overexpression in RHA1 cells under nitrogen-rich conditions produced an increase of the label incorporation into the TLE and its derivative NL and PL fractions, the last one being the highest C-13 enriched. In addition, a higher C-13 enrichment occurred in the TAG, DAG, and FFA fractions after nlpR induction, with the FFA fraction being the most affected within the TLE. Isotopic-labeling experiments demonstrated that NlpR regulator is contributing in oleaginous phenotype of R. jostii RHA1 to the allocation of carbon into the different lipid fractions in response to nitrogen levels, increasing the rate of carbon flux into lipid metabolism.
The temporal dynamics of climate processes are spread across different timescales and, as such, the study of these processes at only one selected timescale might not reveal the complete mechanisms and interactions within and between the (sub-) processes. To capture the non-linear interactions between climatic events, the method of event synchronization has found increasing attention recently. The main drawback with the present estimation of event synchronization is its restriction to analysing the time series at one reference timescale only. The study of event synchronization at multiple scales would be of great interest to comprehend the dynamics of the investigated climate processes. In this paper, the wavelet-based multi-scale event synchronization (MSES) method is proposed by combining the wavelet transform and event synchronization. Wavelets are used extensively to comprehend multi-scale processes and the dynamics of processes across various timescales. The proposed method allows the study of spatio-temporal patterns across different timescales. The method is tested on synthetic and real-world time series in order to check its replicability and applicability. The results indicate that MSES is able to capture relationships that exist between processes at different timescales.
Erosion processes, aggravated by human activity, have a large impact on the spatial variation of soil and topographic properties. Knowledge of the topography prior to human-induced erosion (paleotopography) in naturally stable landscapes is valuable for identifying vulnerable landscape positions and is required as starting point for erosion modelling exercises. However, developing accurate reconstructions of paleotopography provide a major challenge for geomorphologists. Here, we present a set of paleotopographies for a closed kettle hole catchment in north-east Germany (4 ha), obtained through different reconstruction approaches. Current soil and colluvium thickness, estimated from a dataset of 264 soil descriptions using Ordinary Kriging, were used as input for a mass balance, or were compared with a set of undisturbed soil thicknesses to estimate the amount of erosion. The performance of the different approaches was assessed with cross-validation and the count of mispredicted eroded, depositional or stable landscape positions. The paleotopographic reconstruction approach based on the average thickness of undisturbed soils in the study area showed the best performance. This thickness (1.00 m) is comparable to the average undisturbed soil thickness in the region and in line with global correlations of soil thickness as a function of rainfall and initial CaCO3 content. The performance of the different approaches depended more on mispredictions of landscape position due to the assumption of a spatially constant initial soil depth than on small variations in this depth. To conclude, we mention several methodological and practical points of attention for future topography reconstruction studies, concerning data quality and availability, spatial configuration of data and other processes affecting topography. (C) 2017 Elsevier B.V. All rights reserved.
Regional snow-avalanche detection using object-based image analysis of near-infrared aerial imagery
(2017)
Snow avalanches are destructive mass movements in mountain regions that continue to claim lives and cause infrastructural damage and traffic detours. Given that avalanches often occur in remote and poorly accessible steep terrain, their detection and mapping is extensive and time consuming. Nonetheless, systematic avalanche detection over large areas could help to generate more complete and up-to-date inventories (cadastres) necessary for validating avalanche forecasting and hazard mapping. In this study, we focused on automatically detecting avalanches and classifying them into release zones, tracks, and run-out zones based on 0.25m near-infrared (NIR) ADS80-SH92 aerial imagery using an object-based image analysis (OBIA) approach. Our algorithm takes into account the brightness, the normalised difference vegetation index (NDVI), the normalised difference water index (NDWI), and its standard deviation (SDNDWI) to distinguish avalanches from other land-surface elements. Using normalised parameters allows applying this method across large areas. We trained the method by analysing the properties of snow avalanches at three 4km−2 areas near Davos, Switzerland. We compared the results with manually mapped avalanche polygons and obtained a user's accuracy of >0.9 and a Cohen's kappa of 0.79–0.85. Testing the method for a larger area of 226.3km−2, we estimated producer's and user's accuracies of 0.61 and 0.78, respectively, with a Cohen's kappa of 0.67. Detected avalanches that overlapped with reference data by >80% occurred randomly throughout the testing area, showing that our method avoids overfitting. Our method has potential for large-scale avalanche mapping, although further investigations into other regions are desirable to verify the robustness of our selected thresholds and the transferability of the method.
On trend detection
(2017)
A main obstacle to trend detection in time series occurs when they are autocorrelated. By reducing the effective sample size of a series, autocorrelation leads to decreased trend significance. Numerous recipes attempt to mitigate the effect of autocorrelation, either by adjusting for the reduced effective sample size or by removing the autocorrelated components of a series. This short note deals with the latter, also called prewhitening (PW). It is known that removal of autocorrelation also removes part of the trend, which may affect the signal-to-noise ratio. Two popular methods have dealt with this problem, the trend-free prewhitening (TFPW) and the iterative prewhitening. Although it is generally accepted that both methods reduce the adverse effects of PW on the trend magnitude, corresponding effects on statistical significance have not been clearly stated for TFPW. Using a Monte Carlo approach, it is demonstrated that both methods entail quite different Type-I error rates. The iterative prewhitening produces rates that are generally close to the nominal significance level. The TFPW, however, shows very high Type-I error rates with increasing autocorrelation. The corresponding rate of false trend detections is unacceptable for applications, so that published trends based on TFPW need to be reassessed.
The development of well-constrained palaeo-proxies that enable the reconstruction of past climate change is becoming an ever more important field of scientific enquiry within the palaeobotanical community, with the potential to deliver broader impacts linked to understanding of future anthropogenic climate change. One of the major uncertainties in predicting climate change is how the hydrological cycle will respond to future warming. Griener and Warny (2015, Review of Palaeobotany and Palynology 221,138-143) suggested that pollen size might be a useful proxy for tracking moisture availability, as pollen size appears to be negatively correlated with moisture. Given the long fossil record of pollen and spores such a proxy would have broad scope and the potential to deliver much needed information. Here we set out to fully evaluate and test the robustness of this proxy. We focus on a number of key issues: controls on pollen size, data analysis, and finally proxy validation. Using this approach we find that there is little theoretical or empirical support for the original relationship proposed by Griener and Warny. Consequently it is currently premature to use pollen size as a moisture availability proxy in the fossil record. However, we recognise that the technique may have potential and conclude by offering a series of recommendations that would rigorously assess and test for a relationship between pollen size and moisture availability. (c) 2017 Elsevier B.V. All rights reserved.
Northeastern (NE) India experiences extraordinarily pronounced seasonal climate, governed by the Indian summer monsoon (ISM). The vulnerability of this region to floods and droughts calls for detailed and highly resolved paleoclimate reconstructions to assess the recurrence rate and driving factors of ISM changes. We use stable oxygen and carbon isotope ratios (delta O-18 and delta C-13) from stalagmite MAW-6 from Mawmluh Cave to infer climate and environmental conditions in NE India over the last deglaciation (16-6ka). We interpret stalagmite delta O-18 as reflecting ISM strength, whereas delta C-13 appears to be driven by local hydroclimate conditions. Pronounced shifts in ISM strength over the deglaciation are apparent from the delta O-18 record, similarly to other records from monsoonal Asia. The ISM is weaker during the late glacial (LG) period and the Younger Dryas, and stronger during the BOlling-Allerod and Holocene. Local conditions inferred from the delta C-13 record appear to have changed less substantially over time, possibly related to the masking effect of changing precipitation seasonality. Time series analysis of the delta O-18 record reveals more chaotic conditions during the late glacial and higher predictability during the Holocene, likely related to the strengthening of the seasonal recurrence of the ISM with the onset of the Holocene.
River-bed disturbance and associated sedimentary processes such as particle mobility are central elements to assess river ecosystem functioning. Dams change river dynamics affecting the magnitude and frequency of biophysical elements that depend on them. This paper examines the effects of two dams different in size, management, and location, on the flow regime, flood competence, and bed disturbance in two contrasting Mediterranean rivers, the Esera and the Siurana. For this purpose, two reaches on each river were monitored upstream and downstream from reservoirs. Several monitoring and modeling techniques were used to characterize flow competence, particle entrainment, and the volumes of sediments eroded and deposited after floods. The flow regime of the Esera has been modified from nivo-pluvial regime, typical of humid mountainous environments, to that observed in dry semiarid regions, in which high magnitude but low frequency floods are the dominant processes. Conversely, the flow regime of the Siurana has changed from a typical Mediterranean stream to a regime observed in more temperate environments, with more permanent and stable flows. Both rivers show notably physical changes, with channels clearly less dynamic below the dams. The lack of competent flows together with the sediment deficit associated with the dams has led to less active fluvial environments (reduced particle mobility and bed scour dynamics), a fact that affects instream habitat structure (more uniform grain size distribution, less physical heterogeneity, more stable flows), overall contributing to the degradation of the stream corridor and the subsequent environmental deterioration of the whole fluvial landscape. Copyright (c) 2017 John Wiley & Sons, Ltd.
We have analyzed the recently developed pan-European strong motion database, RESORCE-2012: spectral parameters, such as stress drop (stress parameter, Delta sigma), anelastic attenuation (Q), near surface attenuation (kappa(0)) and site amplification have been estimated from observed strong motion recordings. The selected dataset exhibits a bilinear distance-dependent Q model with average kappa(0) value 0.0308 s. Strong regional variations in inelastic attenuation were also observed: frequency-independent Q(0) of 1462 and 601 were estimated for Turkish and Italian data respectively. Due to the strong coupling between Q and kappa(0), the regional variations in Q have strong impact on the estimation of near surface attenuation kappa(0). kappa(0) was estimated as 0.0457 and 0.0261 s for Turkey and Italy respectively. Furthermore, a detailed analysis of the variability in estimated kappa(0) revealed significant within-station variability. The linear site amplification factors were constrained from residual analysis at each station and site-class type. Using the regional Q(0) model and a site-class specific kappa(0), seismic moments (M-0) and source corner frequencies f (c) were estimated from the site corrected empirical Fourier spectra. Delta sigma did not exhibit magnitude dependence. The median Delta sigma value was obtained as 5.75 and 5.65 MPa from inverted and database magnitudes respectively. A comparison of response spectra from the stochastic model (derived herein) with that from (regional) ground motion prediction equations (GMPEs) suggests that the presented seismological parameters can be used to represent the corresponding seismological attributes of the regional GMPEs in a host-to-target adjustment framework. The analysis presented herein can be considered as an update of that undertaken for the previous Euro-Mediterranean strong motion database presented by Edwards and Fah (Geophys J Int 194(2):1190-1202, 2013a).
Sedimentary lipid biomarkers have become widely used tools for reconstructing past climatic and ecological changes due to their ubiquitous occurrence in lake sediments. In particular, the hydrogen isotopic composition (expressed as delta D values) of leaf wax lipids derived from terrestrial plants has been a focus of research during the last two decades and the understanding of competing environmental and plant physiological factors influencing the delta D values has greatly improved. Comparatively less attention has been paid to lipid biomarkers derived from aquatic plants, although these compounds are abundant in many lacustrine sediments. We therefore conducted a field and laboratory experiment to study the effect of salinity and groundwater discharge on the isotopic composition of aquatic plant biomarkers. We analyzed samples of the common submerged plant species, Potamogeton pectinatus (sago pondweed), which has a wide geographic distribution and can tolerate high salinity. We tested the effect of groundwater discharge (characterized by more negative delta D values relative to lake water) and salinity on the delta D values of n-alkanes from P. pectinatus by comparing plants (i) collected from the oligotrophic freshwater Lake Stechlin (Germany) at shallow littoral depth from locations with and without groundwater discharge, and (ii) plants grown from tubers collected from the eutrophic Lake Muggelsee in nutrient solution at four salinity levels. Isotopically depleted groundwater did not have a significant influence on the delta D values of n-alkanes in Lake Stechlin P. pectinatus and calculated isotopic fractionation factors epsilon(l/w) between lake water and n-alkanes averaged -137 +/- 9%(n-C-23), -136 +/- 7%(n-C-25) and -131 +/- 6%(n-C-27), respectively. Similar epsilon values were calculated for plants from Lake Muggelsee grown in freshwater nutrient solution (-134 +/- 11% for n-C-23), while greater fractionation was observed at increased salinity values of 10 (163 +/- 12%) and 15(-172 +/- 15%). We therefore suggest an average e value of -136 +/- 9% between source water and the major n-alkanes in P. pectinatus grown under freshwater conditions. Our results demonstrate that isotopic fractionation can increase by 30-40% at salinity values 10 and 15. These results could be explained either by inhibited plant growth at higher salinity, or by metabolic adaptation to salt stress that remain to be elucidated. A potential salinity effect on dD values of aquatic lipids requires further examination, since this would impact on the interpretation of downcore isotopic data in paleohydrologic studies. (C) 2017 Elsevier Ltd. All rights reserved.
The majority of original seismograms recorded at the very beginning of instrumental seismology (the early 1900s) did not survive till present. However, a number of books, bulletins, and catalogs were published including the seismogram reproductions of some, particularly interesting earthquakes. In case these reproductions contain the time and amplitude scales, they can be successfully analyzed the same way as the original records. Information about the Atushi (Kashgar) earthquake, which occurred on August 22, 1902, is very limited. We could not find any original seismograms for this earthquake, but 12 seismograms from 6 seismic stations were printed as example records in different books. These data in combination with macroseismic observations and different bulletins information published for this earthquake were used to determine the source parameters of the earthquake. The earthquake epicenter was relocated at 39.87A degrees N and 76.42A degrees E with the hypocenter depth of about 18 km. We could further determine magnitudes m (B) = 7.7 +/- 0.3, M (S) = 7.8 +/- 0.4, M (W) = 7.7 +/- 0.3 and the focal mechanism of the earthquake with strike/dip/rake - 260A degrees +/- 20/30A degrees +/- 10/90A degrees +/- 10. This study confirms that the earthquake likely had a smaller magnitude than previously reported (M8.3). The focal mechanism indicates dominant thrust faulting, which is in a good agreement with presumably responsible Tuotegongbaizi-Aerpaleike northward dipping thrust fault kinematic, described in previous studies.