TY - JOUR A1 - Walther, Sophia A1 - Guanter, Luis A1 - Heim, Birgit A1 - Jung, Martin A1 - Duveiller, Gregory A1 - Wolanin, Aleksandra A1 - Sachs, Torsten T1 - Assessing the dynamics of vegetation productivity in circumpolar regions with different satellite indicators of greenness and photosynthesis JF - Biogeosciences N2 - High-latitude treeless ecosystems represent spatially highly heterogeneous landscapes with small net carbon fluxes and a short growing season. Reliable observations and process understanding are critical for projections of the carbon balance of the climate-sensitive tundra. Space-borne remote sensing is the only tool to obtain spatially continuous and temporally resolved information on vegetation greenness and activity in remote circumpolar areas. However, confounding effects from persistent clouds, low sun elevation angles, numerous lakes, widespread surface inundation, and the sparseness of the vegetation render it highly challenging. Here, we conduct an extensive analysis of the timing of peak vegetation productivity as shown by satellite observations of complementary indicators of plant greenness and photosynthesis. We choose to focus on productivity during the peak of the growing season, as it importantly affects the total annual carbon uptake. The suite of indicators are as follows: (1) MODIS-based vegetation indices (VIs) as proxies for the fraction of incident photosynthetically active radiation (PAR) that is absorbed (fPAR), (2) VIs combined with estimates of PAR as a proxy of the total absorbed radiation (APAR), (3) sun-induced chlorophyll fluorescence (SIF) serving as a proxy for photosynthesis, (4) vegetation optical depth (VOD), indicative of total water content and (5) empirically upscaled modelled gross primary productivity (GPP). Averaged over the pan-Arctic we find a clear order of the annual peak as APAR <= GPP < SIF < VIs/VOD. SIF as an indicator of photosynthesis is maximised around the time of highest annual temperatures. The modelled GPP peaks at a similar time to APAR. The time lag of the annual peak between APAR and instantaneous SIF fluxes indicates that the SIF data do contain information on light-use efficiency of tundra vegetation, but further detailed studies are necessary to verify this. Delayed peak greenness compared to peak photosynthesis is consistently found across years and land-cover classes. A particularly late peak of the normalised difference vegetation index (NDVI) in regions with very small seasonality in greenness and a high amount of lakes probably originates from artefacts. Given the very short growing season in circumpolar areas, the average time difference in maximum annual photosynthetic activity and greenness or growth of 3 to 25 days (depending on the data sets chosen) is important and needs to be considered when using satellite observations as drivers in vegetation models. Y1 - 2018 U6 - https://doi.org/10.5194/bg-15-6221-2018 SN - 1726-4170 SN - 1726-4189 VL - 15 IS - 20 SP - 6221 EP - 6256 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Kaboth-Bahr, Stefanie A1 - Bahr, André A1 - Zeeden, Christian A1 - Yamoah, Kweku A. A1 - Lone, Mahjoor Ahmad A1 - Chuang, Chih-Kai A1 - Löwemark, Ludvig A1 - Wei, Kuo-Yen T1 - A tale of shifting relations BT - East Asian summer and winter monsoon variability during the Holocene JF - Scientific Reports N2 - Understanding the dynamics between the East Asian summer (EASM) and winter monsoon (EAWM) is needed to predict their variability under future global warming scenarios. Here, we investigate the relationship between EASM and EAWM as well as the mechanisms driving their variability during the last 10,000 years by stacking marine and terrestrial (non-speleothem) proxy records from the East Asian realm. This provides a regional and proxy independent signal for both monsoonal systems. The respective signal was subsequently analysed using a linear regression model. We find that the phase relationship between EASM and EAWM is not time-constant and significantly depends on orbital configuration changes. In addition, changes in the Atlantic Meridional Overturning circulation, Arctic sea-ice coverage, El Niño-Southern Oscillation and Sun Spot numbers contributed to millennial scale changes in the EASM and EAWM during the Holocene. We also argue that the bulk signal of monsoonal activity captured by the stacked non-speleothem proxy records supports the previously argued bias of speleothem climatic archives to moisture source changes and/or seasonality. KW - Environmental sciences KW - Ocean sciences KW - Solid Earth sciences Y1 - 2020 U6 - https://doi.org/10.1038/s41598-021-85444-7 SN - 2045-2322 VL - 11 PB - Macmillan Publishers Limited, part of Springer Nature CY - London ER - TY - JOUR A1 - Pourteau, Amaury A1 - Scherer, Erik E. A1 - Schorn, Simon A1 - Bast, Rebecca A1 - Schmidt, Alexander A1 - Ebert, Lisa T1 - Thermal evolution of an ancient subduction interface revealed by Lu-Hf garnet geochronology, Halilbagi Complex (Anatolia) JF - Geoscience Frontiers N2 - The thermal structure of subduction zones exerts a major influence on deep-seated mechanical and chemical processes controlling arc magmatism, seismicity, and global element cycles. Accretionary complexes exposed inland may comprise tectonic blocks with contrasting pressure-temperature (P-T) histories, making it possible to investigate the dynamics and thermal evolution of former subduction interfaces. With this aim, we present new Lu-Hf geochronological results for mafic rocks of the Halilbagi Complex (Anatolia) that evolved along different thermal gradients. Samples include a lawsonite-epidote blueschist, a lawsonite-epidote eclogite, and an epidote eclogite (all with counter-clockwise P-T paths), a prograde lawsonite blueschist with a "hairpin"-type P-T path, and a garnet amphibolite from the overlying sub-ophiolitic metamorphic sole. Equilibrium phase diagrams suggest that the garnet amphibolite formed at similar to 0.6-0.7 GPa and 800-850 degrees C, whereas the prograde lawsonite blueschist records burial from 2.1 GPa and 420 degrees C to 2.6 GPa and 520 degrees C. Well-defined Lu-Hf isochrons were obtained for the epidote eclogite (92.38 +/- 0.22 Ma) and the lawsonite-epidote blueschist (90.19 +/- 0.54 Ma), suggesting rapid garnet growth. The lawsonite-epidote eclogite (87.30 +/- 0.39 Ma) and the prograde lawsonite blueschist (ca. 86 Ma) are younger, whereas the garnet amphibolite (104.5 +/- 3.5 Ma) is older. Our data reveal a consistent trend of progressively decreasing geothermal gradient from granulite-facies conditions at similar to 104 Ma to the epidote-eclogite facies around 92 Ma, and the lawsonite blueschist-facies between 90 Ma and 86 Ma. Three Lu-Hf garnet dates (between 92 Ma and 87 Ma) weighted toward the growth of post-peak rims (as indicated by Lu distribution in garnet) suggest that the HP/LT rocks were exhumed continuously and not episodically. We infer that HP/LT metamorphic rocks within the Halilbagi Complex were subjected to continuous return flow, with "warm" rocks being exhumed during the tectonic burial of "cold" ones. Our results, combined with regional geological constraints, allow us to speculate that subduction started at a transform fault near a mid-oceanic spreading centre. Following its formation, this ancient subduction interface evolved thermally over more than 15 Myr, most likely as a result of heat dissipation rather than crustal underplating. (C) 2018, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. KW - Subduction KW - Lu/Hf dating of garnet KW - Metamorphic sole KW - Eclogite KW - Blueschist KW - Lawsonite Y1 - 2019 U6 - https://doi.org/10.1016/j.gsf.2018.03.004 SN - 1674-9871 VL - 10 IS - 1 SP - 127 EP - 148 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Pauly, Maren A1 - Helle, Gerhard A1 - Miramont, Cecile A1 - Buentgen, Ulf A1 - Treydte, Kerstin A1 - Reinig, Frederick A1 - Guibal, Frederic A1 - Sivan, Olivier A1 - Heinrich, Ingo A1 - Riedel, Frank A1 - Kromer, Bernd A1 - Balanzategui, Daniel A1 - Wacker, Lukas A1 - Sookdeo, Adam A1 - Brauer, Achim T1 - Subfossil trees suggest enhanced Mediterranean hydroclimate variability at the onset of the Younger Dryas JF - Scientific reports N2 - Nearly 13,000 years ago, the warming trend into the Holocene was sharply interrupted by a reversal to near glacial conditions. Climatic causes and ecological consequences of the Younger Dryas (YD) have been extensively studied, however proxy archives from the Mediterranean basin capturing this period are scarce and do not provide annual resolution. Here, we report a hydroclimatic reconstruction from stable isotopes (delta O-18, delta C-13) in subfossil pines from southern France. Growing before and during the transition period into the YD (12 900-12 600 cal BP), the trees provide an annually resolved, continuous sequence of atmospheric change. Isotopic signature of tree sourcewater (delta O-18(sw)) and estimates of relative air humidity were reconstructed as a proxy for variations in air mass origin and precipitation regime. We find a distinct increase in inter-annual variability of sourcewater isotopes (delta O-18(sw)), with three major downturn phases of increasing magnitude beginning at 12 740 cal BP. The observed variation most likely results from an amplified intensity of North Atlantic (low delta O-18(sw)) versus Mediterranean (high delta O-18(sw)) precipitation. This marked pattern of climate variability is not seen in records from higher latitudes and is likely a consequence of atmospheric circulation oscillations at the margin of the southward moving polar front. Y1 - 2018 U6 - https://doi.org/10.1038/s41598-018-32251-2 SN - 2045-2322 VL - 8 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Huck, Stefan A1 - Wohlwend, Stephan A1 - Coimbra, Rute A1 - Christ, Nicolas A1 - Weissert, Helmut T1 - Disentangling shallow-water bulk carbonate carbon isotope archives with evidence for multi-stage diagenesis BT - an in-depth component-specific petrographic and geochemical study from Oman (mid-Cretaceous) JF - The depositional record N2 - Disentangling shallow‐water bulk carbonate carbon isotope archives into primary and diagenetic components is a notoriously difficult task and even diagenetically screened records often provide chemostratigraphic patterns that significantly differ from global signals. This is mainly caused by the polygenetic nature of shallow‐water carbonate substrates, local carbon cycle processes causing considerable neritic–pelagic isotope gradients and the presence of hiatal surfaces resulting in extremely low carbonate preservation rates. Provided here is an in‐depth petrographic and geochemical evaluation of different carbonate phases of a mid‐Cretaceous (Barremian–Aptian) shallow‐water limestone succession (Jabal Madar section) deposited on the tropical Arabian carbonate platform in Oman. The superposition of stable isotope signatures of identified carbonate phases causes a complex and often noisy bulk carbon isotope pattern. Blocky sparite cements filling intergranular pores and bioclastic voids evidence intermediate to (arguably) deep burial diagenetic conditions during their formation, owing to different timing or differential faulting promoting the circulation of fluids from variable sources. In contrast, sparite cements filling sub‐vertical veins reveal a rock‐buffered diagenetic fluid composition with an intriguing moderate enrichment in 13C, probably due to fractionation during pressure release in the context of the Miocene exhumation of the carbonate platform under study. The presence of abundant, replacive dedolomite in mud‐supported limestone samples forced negative carbon and oxygen isotope changes that are either associated with the thermal breakdown of organic matter in the deep burial realm or the expulsion of buried meteoric water in the intermediate burial realm. Notwithstanding the documented stratigraphically variable and often facies‐related impact of different diagenetic fluids on the bulk‐rock stable isotope signature, the identification of diagenetic end‐members defined δ13C and δ18O threshold values that allowed the most reliable ‘primary’ bulk carbon isotope signatures to be extracted. Most importantly, this approach exemplifies how to place regional shallow‐water stable isotope patterns with evidence for a complex multi‐stage diagenetic history into a supraregional or even global context. KW - Arabian carbonate platform KW - Barremian-Aptian KW - multi-stage diagenesis KW - shallow-water chemostratigraphy Y1 - 2017 U6 - https://doi.org/10.1002/dep2.35 SN - 2055-4877 VL - 3 SP - 233 EP - 257 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Wickert, Andrew D. A1 - Schildgen, Taylor F. T1 - Long-profile evolution of transport-limited gravel-bed rivers JF - Earth surface dynamics N2 - Alluvial and transport-limited bedrock rivers constitute the majority of fluvial systems on Earth. Their long profiles hold clues to their present state and past evolution. We currently possess first-principles-based governing equations for flow, sediment transport, and channel morphodynamics in these systems, which we lack for detachment-limited bedrock rivers. Here we formally couple these equations for transport-limited gravel-bed river long-profile evolution. The result is a new predictive relationship whose functional form and parameters are grounded in theory and defined through experimental data. From this, we produce a power-law analytical solution and a finite-difference numerical solution to long-profile evolution. Steady-state channel concavity and steepness are diagnostic of external drivers: concavity decreases with increasing uplift rate, and steepness increases with an increasing sediment-to-water supply ratio. Constraining free parameters explains common observations of river form: to match observed channel concavities, gravel-sized sediments must weather and fine - typically rapidly - and valleys typically should widen gradually. To match the empirical square-root width-discharge scaling in equilibrium-width gravel-bed rivers, downstream fining must occur. The ability to assign a cause to such observations is the direct result of a deductive approach to developing equations for landscape evolution. Y1 - 2019 U6 - https://doi.org/10.5194/esurf-7-17-2019 SN - 2196-6311 SN - 2196-632X VL - 7 IS - 1 SP - 17 EP - 43 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Uber, Magdalena A1 - Vandervaere, Jean-Pierre A1 - Zin, Isabella A1 - Braud, Isabelle A1 - Heistermann, Maik A1 - Legout, Cedric A1 - Molinie, Gilles A1 - Nord, Guillaume T1 - How does initial soil moisture influence the hydrological response? A case study from southern France JF - Hydrology and earth system sciences : HESS N2 - The phi(ev) is calculated from high-resolution discharge and precipitation data for several rain events with a cumulative precipitation P-cum ranging from less than 5mm to more than 80 mm. Because of the high uncertainty of phi(ev) associated with the hydrograph separation method, phi(ev) is calculated with several methods, including graphical methods, digital filters and a tracer-based method. The results indicate that the hydrological response depends on (theta) over bar (ini): during dry conditions phi(ev) is consistently below 0.1, even for events with high and intense precipitation. Above a threshold of (theta) over bar (ini) = 34 vol % phi(ev) can reach values up to 0.99 but there is a high scatter. Some variability can be explained with a weak correlation of phi(ev) with P-cum and rain intensity, but a considerable part of the variability remains unexplained. It is concluded that threshold-based methods can be helpful to prevent overestimation of the hydrological response during dry catchment conditions. The impact of soil moisture on the hydrological response during wet catchment conditions, however, is still insufficiently understood and cannot be generalized based on the present results. Y1 - 2018 U6 - https://doi.org/10.5194/hess-22-6127-2018 SN - 1027-5606 SN - 1607-7938 VL - 22 IS - 12 SP - 6127 EP - 6146 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Milewski, Robert A1 - Chabrillat, Sabine A1 - Behling, Robert T1 - Analyses of Recent Sediment Surface Dynamic of a Namibian Kalahari Salt Pan Based on Multitemporal Landsat and Hyperspectral Hyperion Data JF - Remote Sensing N2 - This study combines spaceborne multitemporal and hyperspectral data to analyze the spatial distribution of surface evaporite minerals and changes in a semi-arid depositional environment associated with episodic flooding events, the Omongwa salt pan (Kalahari, Namibia). The dynamic of the surface crust is evaluated by a change-detection approach using the Iterative-reweighted Multivariate Alteration Detection (IR-MAD) based on the Landsat archive imagery from 1984 to 2015. The results show that the salt pan is a highly dynamic and heterogeneous landform. A change gradient is observed from very stable pan border to a highly dynamic central pan. On the basis of hyperspectral EO-1 Hyperion images, the current distribution of surface evaporite minerals is characterized using Spectral Mixture Analysis (SMA). Assessment of field and image endmembers revealed that the pan surface can be categorized into three major crust types based on diagnostic absorption features and mineralogical ground truth data. The mineralogical crust types are related to different zones of surface change as well as pan morphology that influences brine flow during the pan inundation and desiccation cycles. These combined information are used to spatially map depositional environments where the more dynamic halite crust concentrates in lower areas although stable gypsum and calcite/sepiolite crusts appear in higher elevated areas. KW - salt pan KW - playa KW - hyperspectral KW - multitemporal KW - change detection KW - evaporite minerals Y1 - 2016 U6 - https://doi.org/10.3390/rs9020170 SN - 2072-4292 VL - 9 IS - 2 PB - MDPI CY - Basel ER - TY - JOUR A1 - Knudsen, Erlend Moster A1 - Heinold, Bernd A1 - Dahlke, Sandro A1 - Bozem, Heiko A1 - Crewell, Susanne A1 - Gorodetskaya, Irina V. A1 - Heygster, Georg A1 - Kunkel, Daniel A1 - Maturilli, Marion A1 - Mech, Mario A1 - Viceto, Carolina A1 - Rinke, Annette A1 - Schmithusen, Holger A1 - Ehrlich, Andre A1 - Macke, Andreas A1 - Lüpkes, Christof A1 - Wendisch, Manfred T1 - Meteorological conditions during the ACLOUD/PASCAL field campaign near Svalbard in early summer 2017 JF - Atmospheric chemistry and physics N2 - The two concerted field campaigns, Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) and the Physical feedbacks of Arctic planetary boundary level Sea ice, Cloud and AerosoL (PASCAL), took place near Svalbard from 23 May to 26 June 2017. They were focused on studying Arctic mixed-phase clouds and involved observations from two airplanes (ACLOUD), an icebreaker (PASCAL) and a tethered balloon, as well as ground-based stations. Here, we present the synoptic development during the 35-day period of the campaigns, using near-surface and upper-air meteorological observations, as well as operational satellite, analysis, and reanalysis data. Over the campaign period, short-term synoptic variability was substantial, dominating over the seasonal cycle. During the first campaign week, cold and dry Arctic air from the north persisted, with a distinct but seasonally unusual cold air outbreak. Cloudy conditions with mostly low-level clouds prevailed. The subsequent 2 weeks were characterized by warm and moist maritime air from the south and east, which included two events of warm air advection. These synoptical disturbances caused lower cloud cover fractions and higher-reaching cloud systems. In the final 2 weeks, adiabatically warmed air from the west dominated, with cloud properties strongly varying within the range of the two other periods. Results presented here provide synoptic information needed to analyze and interpret data of upcoming studies from ACLOUD/PASCAL, while also offering unprecedented measurements in a sparsely observed region. Y1 - 2018 U6 - https://doi.org/10.5194/acp-18-17995-2018 SN - 1680-7316 SN - 1680-7324 VL - 18 IS - 24 SP - 17995 EP - 18022 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Runge, Alexandra A1 - Grosse, Guido T1 - Mosaicking Landsat and Sentinel-2 Data to Enhance LandTrendr Time Series Analysis in Northern High Latitude Permafrost Regions JF - Remote Sensing N2 - Permafrost is warming in the northern high latitudes, inducing highly dynamic thaw-related permafrost disturbances across the terrestrial Arctic. Monitoring and tracking of permafrost disturbances is important as they impact surrounding landscapes, ecosystems and infrastructure. Remote sensing provides the means to detect, map, and quantify these changes homogeneously across large regions and time scales. Existing Landsat-based algorithms assess different types of disturbances with similar spatiotemporal requirements. However, Landsat-based analyses are restricted in northern high latitudes due to the long repeat interval and frequent clouds, in particular at Arctic coastal sites. We therefore propose to combine Landsat and Sentinel-2 data for enhanced data coverage and present a combined annual mosaic workflow, expanding currently available algorithms, such as LandTrendr, to achieve more reliable time series analysis. We exemplary test the workflow for twelve sites across the northern high latitudes in Siberia. We assessed the number of images and cloud-free pixels, the spatial mosaic coverage and the mosaic quality with spectral comparisons. The number of available images increased steadily from 1999 to 2019 but especially from 2016 onward with the addition of Sentinel-2 images. Consequently, we have an increased number of cloud-free pixels even under challenging environmental conditions, which then serve as the input to the mosaicking process. In a comparison of annual mosaics, the Landsat+Sentinel-2 mosaics always fully covered the study areas (99.9–100 %), while Landsat-only mosaics contained data-gaps in the same years, only reaching coverage percentages of 27.2 %, 58.1 %, and 69.7 % for Sobo Sise, East Taymyr, and Kurungnakh in 2017, respectively. The spectral comparison of Landsat image, Sentinel-2 image, and Landsat+Sentinel-2 mosaic showed high correlation between the input images and mosaic bands (e.g., for Kurungnakh 0.91–0.97 between Landsat and Landsat+Sentinel-2 mosaic and 0.92–0.98 between Sentinel-2 and Landsat+Sentinel-2 mosaic) across all twelve study sites, testifying good quality mosaic results. Our results show that especially the results for northern, coastal areas was substantially improved with the Landsat+Sentinel-2 mosaics. By combining Landsat and Sentinel-2 data we accomplished to create reliably high spatial resolution input mosaics for time series analyses. Our approach allows to apply a high temporal continuous time series analysis to northern high latitude permafrost regions for the first time, overcoming substantial data gaps, and assess permafrost disturbance dynamics on an annual scale across large regions with algorithms such as LandTrendr by deriving the location, timing and progression of permafrost thaw disturbances KW - time series analysis KW - data fusion KW - disturbance tracking KW - permafrost KW - permafrost thaw Y1 - 2020 U6 - https://doi.org/10.3390/rs12152471 SN - 2072-4292 VL - 12 IS - 15 PB - MDPI CY - Basel ER - TY - JOUR A1 - Weisshuhn, Peter A1 - Reckling, Moritz A1 - Stachow, Ulrich A1 - Wiggering, Hubert T1 - Supporting Agricultural Ecosystem Services through the Integration of Perennial Polycultures into Crop Rotations JF - Sustainability N2 - This review analyzes the potential role and long-term effects of field perennial polycultures (mixtures) in agricultural systems, with the aim of reducing the trade-offs between provisioning and regulating ecosystem services. First, crop rotations are identified as a suitable tool for the assessment of the long-term effects of perennial polycultures on ecosystem services, which are not visible at the single-crop level. Second, the ability of perennial polycultures to support ecosystem services when used in crop rotations is quantified through eight agricultural ecosystem services. Legume-grass mixtures and wildflower mixtures are used as examples of perennial polycultures, and compared with silage maize as a typical crop for biomass production. Perennial polycultures enhance soil fertility, soil protection, climate regulation, pollination, pest and weed control, and landscape aesthetics compared with maize. They also score lower for biomass production compared with maize, which confirms the trade-off between provisioning and regulating ecosystem services. However, the additional positive factors provided by perennial polycultures, such as reduced costs for mineral fertilizer, pesticides, and soil tillage, and a significant preceding crop effect that increases the yields of subsequent crops, should be taken into account. However, a full assessment of agricultural ecosystem services requires a more holistic analysis that is beyond the capabilities of current frameworks. KW - agroecosystem KW - assessment KW - legume-grass mixture KW - wildflower mixture KW - perennial crop KW - mixed cropping Y1 - 2017 U6 - https://doi.org/10.3390/su9122267 SN - 2071-1050 VL - 9 PB - MDPI CY - Basel ER - TY - JOUR A1 - Tofelde, Stefanie A1 - Bufe, Aaron A1 - Turowski, Jens M. T1 - Hillslope Sediment Supply Limits Alluvial Valley Width JF - AGU Advances N2 - River-valley morphology preserves information on tectonic and climatic conditions that shape landscapes. Observations suggest that river discharge and valley-wall lithology are the main controls on valley width. Yet, current models based on these observations fail to explain the full range of cross-sectional valley shapes in nature, suggesting hitherto unquantified controls on valley width. In particular, current models cannot explain the existence of paired terrace sequences that form under cyclic climate forcing. Paired river terraces are staircases of abandoned floodplains on both valley sides, and hence preserve past valley widths. Their formation requires alternating phases of predominantly river incision and predominantly lateral planation, plus progressive valley narrowing. While cyclic Quaternary climate changes can explain shifts between incision and lateral erosion, the driving mechanism of valley narrowing is unknown. Here, we extract valley geometries from climatically formed, alluvial river-terrace sequences and show that across our dataset, the total cumulative terrace height (here: total valley height) explains 90%–99% of the variance in valley width at the terrace sites. This finding suggests that valley height, or a parameter that scales linearly with valley height, controls valley width in addition to river discharge and lithology. To explain this valley-width-height relationship, we reformulate existing valley-width models and suggest that, when adjusting to new boundary conditions, alluvial valleys evolve to a width at which sediment removal from valley walls matches lateral sediment supply from hillslope erosion. Such a hillslope-channel coupling is not captured in current valley-evolution models. Our model can explain the existence of paired terrace sequences under cyclic climate forcing and relates valley width to measurable field parameters. Therefore, it facilitates the reconstruction of past climatic and tectonic conditions from valley topography. Y1 - 2022 U6 - https://doi.org/10.1029/2021AV000641 SN - 2576-604X PB - American Geophysical Union (AGU); Wiley CY - Hoboken, New Jersey, USA ER - TY - JOUR A1 - Xiong, Chao A1 - Stolle, Claudia A1 - Park, Jaeheung T1 - Climatology of GPS signal loss observed by Swarm satellites JF - Annales geophysicae N2 - By using 3-year global positioning system (GPS) measurements from December 2013 to November 2016, we provide in this study a detailed survey on the climatology of the GPS signal loss of Swarm onboard receivers. Our results show that the GPS signal losses prefer to occur at both low latitudes between +/- 5 and +/- 20 degrees magnetic latitude (MLAT) and high latitudes above 60 degrees MLAT in both hemispheres. These events at all latitudes are observed mainly during equinoxes and December solstice months, while totally absent during June solstice months. At low latitudes the GPS signal losses are caused by the equatorial plasma irregularities shortly after sunset, and at high latitude they are also highly related to the large density gradients associated with ionospheric irregularities. Additionally, the high-latitude events are more often observed in the Southern Hemisphere, occurring mainly at the cusp region and along nightside auroral latitudes. The signal losses mainly happen for those GPS rays with elevation angles less than 20 degrees, and more commonly occur when the line of sight between GPS and Swarm satellites is aligned with the shell structure of plasma irregularities. Our results also confirm that the capability of the Swarm receiver has been improved after the bandwidth of the phase-locked loop (PLL) widened, but the updates cannot radically avoid the interruption in tracking GPS satellites caused by the ionospheric plasma irregularities. Additionally, after the PLL bandwidth increased larger than 0.5 Hz, some unexpected signal losses are observed even at middle latitudes, which are not related to the ionospheric plasma irregularities. Our results suggest that rather than 1.0 Hz, a PLL bandwidth of 0.5 Hz is a more suitable value for the Swarm receiver. KW - Ionosphere KW - equatorial ionosphere KW - ionospheric irregularities KW - radio science KW - radio wave propagation Y1 - 2018 U6 - https://doi.org/10.5194/angeo-36-679-2018 SN - 0992-7689 SN - 1432-0576 VL - 36 IS - 2 SP - 679 EP - 693 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Coesfeld, Jacqueline A1 - Kuester, Theres A1 - Kuechly, Helga U. A1 - Kyba, Christopher C. M. T1 - Reducing variability and removing natural light from nighttime satellite imagery: A case study using the VIIRS DNB JF - Sensors N2 - Temporal variation of natural light sources such as airglow limits the ability of night light sensors to detect changes in small sources of artificial light (such as villages). This study presents a method for correcting for this effect globally, using the satellite radiance detected from regions without artificial light emissions. We developed a routine to define an approximate grid of locations worldwide that do not have regular light emission. We apply this method with a 5 degree equally spaced global grid (total of 2016 individual locations), using data from the Visible Infrared Imaging Radiometer Suite (VIIRS) Day-Night Band (DNB). This code could easily be adapted for other future global sensors. The correction reduces the standard deviation of data in the Earth Observation Group monthly DNB composites by almost a factor of two. The code and datasets presented here are available under an open license by GFZ Data Services, and are implemented in the Radiance Light Trends web application. KW - airglow KW - artificial light KW - calibration KW - VIIRS DNB KW - nightlights KW - remote sensing Y1 - 2020 VL - 20 PB - MDPI CY - Basel ER - TY - JOUR A1 - Zeeden, Christian A1 - Obreht, Igor A1 - Veres, Daniel A1 - Kaboth-Bahr, Stefanie A1 - Hošek, Jan A1 - Marković, Slobodan B. A1 - Bösken, Janina A1 - Lehmkuhl, Frank A1 - Rolf, Christian A1 - Hambach, Ulrich T1 - Smoothed millennial-scale palaeoclimatic reference data as unconventional comparison targets: Application to European loess records JF - Scientific Reports N2 - Millennial-scale palaeoclimate variability has been documented in various terrestrial and marine palaeoclimate proxy records throughout the Northern Hemisphere for the last glacial cycle. Its clear expression and rapid shifts between different states of climate (Greenland Interstadials and Stadials) represents a correlation tool beyond the resolution of e.g. luminescence dating, especially relevant for terrestrial deposits. Usually, comparison of terrestrial proxy datasets and the Greenland ice cores indicates a complex expression of millennial-scale climate variability as recorded in terrestrial geoarchives including loess. Loess is the most widespread terrestrial geoarchive of the Quaternary and especially widespread over Eurasia. However, loess often records a smoothed representation of millennial-scale variability without all fidelity when compared to the Greenland data, this being a relevant limiting feature in integrating loess with other palaeoclimate records. To better understand the loess proxy-response to millennial-scale climate variability, we simulate a proxy signal smoothing by natural processes through application of low-pass filters of delta O-18 data from Greenland, a high-resolution palaeoclimate reference record, alongside speleothem isotope records from the Black Sea-Mediterranean region. We show that low-pass filters represent rather simple models for better constraining the expression of millennial-scale climate variability in low sedimentation environments, and in sediments where proxy-response signals are most likely affected by natural smoothing (by e.g. bioturbation). Interestingly, smoothed datasets from Greenland and the Black Sea-Mediterranean region are most similar in the last similar to 15 ka and between similar to 50-30 ka. Between similar to 30-15 ka, roughly corresponding to the Last Glacial Maximum and the deglaciation, the records show dissimilarities, challenging the construction of robust correlative time-scales in this age range. From our analysis it becomes apparent that patterns of palaeoclimate signals in loess-palaeosol sequences often might be better explained by smoothed Greenland reference data than the original high-resolution Greenland dataset, or other reference data. This opens the possibility to better assess the temporal resolution and palaeoclimate potential of loess-palaeosol sequences in recording supra-regional climate patterns, as well as to securely integrate loess with other chronologically better-resolved palaeoclimate records. KW - last glacial period KW - Western Interior Basin KW - high-resolution record KW - Greenland ice cores KW - paleosol sequence KW - time-scale KW - Chinese loess KW - astronomical calibration KW - chronology (AICC2012) KW - Antarctic ice Y1 - 2020 VL - 10 IS - 1 PB - Springer Nature CY - Berlin ER - TY - JOUR A1 - Naliboff, John B. A1 - Glerum, Anne A1 - Brune, Sascha A1 - Péron-Pinvidic, G. A1 - Wrona, Thilo T1 - Development of 3-D rift heterogeneity through fault network evolution JF - Geophysical Research Letters N2 - Observations of rift and rifted margin architecture suggest that significant spatial and temporal structural heterogeneity develops during the multiphase evolution of continental rifting. Inheritance is often invoked to explain this heterogeneity, such as preexisting anisotropies in rock composition, rheology, and deformation. Here, we use high-resolution 3-D thermal-mechanical numerical models of continental extension to demonstrate that rift-parallel heterogeneity may develop solely through fault network evolution during the transition from distributed to localized deformation. In our models, the initial phase of distributed normal faulting is seeded through randomized initial strength perturbations in an otherwise laterally homogeneous lithosphere extending at a constant rate. Continued extension localizes deformation onto lithosphere-scale faults, which are laterally offset by tens of km and discontinuous along-strike. These results demonstrate that rift- and margin-parallel heterogeneity of large-scale fault patterns may in-part be a natural byproduct of fault network coalescence. KW - magma-poor KW - continental lithosphere KW - extension KW - insights KW - margins KW - architecture KW - systems KW - models KW - sea KW - reactivation Y1 - 2019 VL - 47 IS - 13 PB - John Wiley & Sons, Inc. CY - New Jersey ER - TY - JOUR A1 - Lara, Mark J. A1 - Nitze, Ingmar A1 - Grosse, Guido A1 - Martin, Philip A1 - McGuire, A. David T1 - Reduced arctic tundra productivity linked with landform and climate change interactions JF - Scientific reports N2 - Arctic tundra ecosystems have experienced unprecedented change associated with climate warming over recent decades. Across the Pan-Arctic, vegetation productivity and surface greenness have trended positively over the period of satellite observation. However, since 2011 these trends have slowed considerably, showing signs of browning in many regions. It is unclear what factors are driving this change and which regions/landforms will be most sensitive to future browning. Here we provide evidence linking decadal patterns in arctic greening and browning with regional climate change and local permafrost-driven landscape heterogeneity. We analyzed the spatial variability of decadal-scale trends in surface greenness across the Arctic Coastal Plain of northern Alaska (similar to 60,000 km(2)) using the Landsat archive (1999-2014), in combination with novel 30 m classifications of polygonal tundra and regional watersheds, finding landscape heterogeneity and regional climate change to be the most important factors controlling historical greenness trends. Browning was linked to increased temperature and precipitation, with the exception of young landforms (developed following lake drainage), which will likely continue to green. Spatiotemporal model forecasting suggests carbon uptake potential to be reduced in response to warmer and/or wetter climatic conditions, potentially increasing the net loss of carbon to the atmosphere, at a greater degree than previously expected. Y1 - 2018 U6 - https://doi.org/10.1038/s41598-018-20692-8 SN - 2045-2322 VL - 8 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Goodwin, Guillaume C. H. A1 - Mudd, Simon M. A1 - Clubb, Fiona J. T1 - Unsupervised detection of salt marsh platforms BT - a topographic method JF - Earth surface dynamics N2 - Salt marshes filter pollutants, protect coastlines against storm surges, and sequester carbon, yet are under threat from sea level rise and anthropogenic modification. The sustained existence of the salt marsh ecosystem depends on the topographic evolution of marsh platforms. Quantifying marsh platform topography is vital for improving the management of these valuable landscapes. The determination of platform boundaries currently relies on supervised classification methods requiring near-infrared data to detect vegetation, or demands labour-intensive field surveys and digitisation. We propose a novel, unsupervised method to reproducibly isolate salt marsh scarps and platforms from a digital elevation model (DEM), referred to as Topographic Identification of Platforms (TIP). Field observations and numerical models show that salt marshes mature into subhorizontal platforms delineated by subvertical scarps. Based on this premise, we identify scarps as lines of local maxima on a slope raster, then fill landmasses from the scarps upward, thus isolating mature marsh platforms. We test the TIP method using lidar-derived DEMs from six salt marshes in England with varying tidal ranges and geometries, for which topographic platforms were manually isolated from tidal flats. Agreement between manual and unsupervised classification exceeds 94% for DEM resolutions of 1 m, with all but one site maintaining an accuracy superior to 90% for resolutions up to 3 m. For resolutions of 1 m, platforms detected with the TIP method are comparable in surface area to digitised platforms and have similar elevation distributions. We also find that our method allows for the accurate detection of local block failures as small as 3 times the DEM resolution. Detailed inspection reveals that although tidal creeks were digitised as part of the marsh platform, unsupervised classification categorises them as part of the tidal flat, causing an increase in false negatives and overall platform perimeter. This suggests our method may benefit from combination with existing creek detection algorithms. Fallen blocks and high tidal flat portions, associated with potential pioneer zones, can also lead to differences between our method and supervised mapping. Although pioneer zones prove difficult to classify using a topographic method, we suggest that these transition areas should be considered when analysing erosion and accretion processes, particularly in the case of incipient marsh platforms. Ultimately, we have shown that unsupervised classification of marsh platforms from high-resolution topography is possible and sufficient to monitor and analyse topographic evolution. Y1 - 2018 U6 - https://doi.org/10.5194/esurf-6-239-2018 SN - 2196-6311 SN - 2196-632X VL - 6 IS - 1 SP - 239 EP - 255 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Fuchs, Matthias A1 - Grosse, Guido A1 - Strauss, Jens A1 - Günther, Frank A1 - Grigoriev, Mikhail N. A1 - Maximov, Georgy M. A1 - Hugelius, Gustaf T1 - Carbon and nitrogen pools in thermokarst-affected permafrost landscapes in Arctic Siberia JF - Biogeosciences N2 - Ice-rich yedoma-dominated landscapes store considerable amounts of organic carbon (C) and nitrogen (N) and are vulnerable to degradation under climate warming. We investigate the C and N pools in two thermokarst-affected yedoma landscapes - on Sobo-Sise Island and on Bykovsky Peninsula in the north of eastern Siberia. Soil cores up to 3m depth were collected along geomorphic gradients and analysed for organic C and N contents. A high vertical sampling density in the profiles allowed the calculation of C and N stocks for short soil column intervals and enhanced understanding of within-core parameter variability. Profile-level C and N stocks were scaled to the landscape level based on landform classifications from 5 m resolution, multispectral RapidEye satellite imagery. Mean landscape C and N storage in the first metre of soil for Sobo-Sise Island is estimated to be 20.2 kg C m(-2) and 1.8 kg N m(-2) and for Bykovsky Peninsula 25.9 kg C m(-2) and 2.2 kg N m(-2). Radiocarbon dating demonstrates the Holocene age of thermokarst basin deposits but also suggests the presence of thick Holoceneage cover layers which can reach up to 2 m on top of intact yedoma landforms. Reconstructed sedimentation rates of 0.10-0.57 mm yr(-1) suggest sustained mineral soil accumulation across all investigated landforms. Both yedoma and thermokarst landforms are characterized by limited accumulation of organic soil layers (peat). We further estimate that an active layer deepening of about 100 cm will increase organic C availability in a seasonally thawed state in the two study areas by similar to 5.8 Tg (13.2 kg C m(-2)). Our study demonstrates the importance of increasing the number of C and N storage inventories in ice-rich yedoma and thermokarst environments in order to account for high variability of permafrost and thermokarst environments in pan-permafrost soil C and N pool estimates. Y1 - 2018 U6 - https://doi.org/10.5194/bg-15-953-2018 SN - 1726-4170 SN - 1726-4189 VL - 15 IS - 3 SP - 953 EP - 971 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Taffarello, Denise A1 - Srinivasan, Raghavan A1 - Samprogna Mohor, Guilherme A1 - Bittencourt Guimaraes, Joao Luis A1 - Calijuri, Maria do Carmo A1 - Mendiondo, Eduardo Mario T1 - Modeling freshwater quality scenarios with ecosystem-based adaptation in the headwaters of the Cantareira system, Brazil JF - Hydrology and earth system sciences : HESS N2 - Although hydrologic models provide hypothesis testing of complex dynamics occurring at catchments, fresh-water quality modeling is still incipient at many subtropical headwaters. In Brazil, a few modeling studies assess freshwater nutrients, limiting policies on hydrologic ecosystem services. This paper aims to compare freshwater quality scenarios under different land-use and land-cover (LULC) change, one of them related to ecosystem-based adaptation (EbA), in Brazilian headwaters. Using the spatially semi-distributed Soil and Water Assessment Tool (SWAT) model, nitrate, total phosphorous (TP) and sediment were modeled in catchments ranging from 7.2 to 1037 km(2). These head-waters were eligible areas of the Brazilian payment for ecosystem services (PES) projects in the Cantareira water supply system, which had supplied water to 9 million people in the Sao Paulo metropolitan region (SPMR). We considered SWAT modeling of three LULC scenarios: (i) recent past scenario (S1), with historical LULC in 1990; (ii) current land-use scenario (S2), with LULC for the period 2010-2015 with field validation; and (iii) future land-use scenario with PES (S2 + EbA). This latter scenario proposed forest cover restoration through EbA following the river basin plan by 2035. These three LULC scenarios were tested with a selected record of rainfall and evapotranspiration observed in 2006-2014, with the occurrence of extreme droughts. To assess hydrologic services, we proposed the hydrologic service index (HSI), as a new composite metric comparing water pollution levels (WPL) for reference catchments, related to the grey water footprint (greyWF) and water yield. On the one hand, water quality simulations allowed for the regionalization of greyWF at spatial scales under LULC scenarios. According to the critical threshold, HSI identified areas as less or more sustainable catchments. On the other hand, conservation practices simulated through the S2 + EbA scenario envisaged not only additional and viable best management practices (BMP), but also preventive decision-making at the headwaters of water supply systems. Y1 - 2018 U6 - https://doi.org/10.5194/hess-22-4699-2018 SN - 1027-5606 SN - 1607-7938 VL - 22 IS - 9 SP - 4699 EP - 4723 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Marcisz, Katarzyna A1 - Jassey, Vincent E. J. A1 - Kosakyan, Anush A1 - Krashevska, Valentyna A1 - Lahr, Daniel J. G. A1 - Lara, Enrique A1 - Lamentowicz, Lukasz A1 - Lamentowicz, Mariusz A1 - Macumber, Andrew A1 - Mazei, Yuri A1 - Mitchell, Edward A. D. A1 - Nasser, Nawaf A. A1 - Patterson, R. Timothy A1 - Roe, Helen M. A1 - Singer, David A1 - Tsyganov, Andrey N. A1 - Fournier, Bertrand T1 - Testate amoeba functional traits and their use in paleoecology JF - Frontiers in Ecology and Evolution N2 - This review provides a synthesis of current knowledge on the morphological and functional traits of testate amoebae, a polyphyletic group of protists commonly used as proxies of past hydrological changes in paleoecological investigations from peatland, lake sediment and soil archives. A trait-based approach to understanding testate amoebae ecology and paleoecology has gained in popularity in recent years, with research showing that morphological characteristics provide complementary information to the commonly used environmental inferences based on testate amoeba (morpho-)species data. We provide a broad overview of testate amoeba morphological and functional traits and trait-environment relationships in the context of ecology, evolution, genetics, biogeography, and paleoecology. As examples we report upon previous ecological and paleoecological studies that used trait-based approaches, and describe key testate amoebae traits that can be used to improve the interpretation of environmental studies. We also highlight knowledge gaps and speculate on potential future directions for the application of trait-based approaches in testate amoeba research. KW - protists KW - functional traits KW - morphological traits KW - ecology KW - peatlands KW - lakes KW - soils KW - trait-based approaches Y1 - 2020 U6 - https://doi.org/10.3389/fevo.2020.575966 SN - 2296-701X VL - 8 PB - Frontiers Media CY - Lausanne ER - TY - JOUR A1 - Tutu, Anthony Osei A1 - Steinberger, Bernhard A1 - Sobolev, Stephan Vladimir A1 - Rogozhina, Irina A1 - Popov, Anton A. T1 - Effects of upper mantle heterogeneities on the lithospheric stress field and dynamic topography JF - Solid earth N2 - The orientation and tectonic regime of the observed crustal/lithospheric stress field contribute to our knowledge of different deformation processes occurring within the Earth's crust and lithosphere. In this study, we analyze the influence of the thermal and density structure of the upper mantle on the lithospheric stress field and topography. We use a 3-D lithosphere–asthenosphere numerical model with power-law rheology, coupled to a spectral mantle flow code at 300 km depth. Our results are validated against the World Stress Map 2016 (WSM2016) and the observation-based residual topography. We derive the upper mantle thermal structure from either a heat flow model combined with a seafloor age model (TM1) or a global S-wave velocity model (TM2). We show that lateral density heterogeneities in the upper 300 km have a limited influence on the modeled horizontal stress field as opposed to the resulting dynamic topography that appears more sensitive to such heterogeneities. The modeled stress field directions, using only the mantle heterogeneities below 300 km, are not perturbed much when the effects of lithosphere and crust above 300 km are added. In contrast, modeled stress magnitudes and dynamic topography are to a greater extent controlled by the upper mantle density structure. After correction for the chemical depletion of continents, the TM2 model leads to a much better fit with the observed residual topography giving a good correlation of 0.51 in continents, but this correction leads to no significant improvement of the fit between the WSM2016 and the resulting lithosphere stresses. In continental regions with abundant heat flow data, TM1 results in relatively small angular misfits. For example, in western Europe the misfit between the modeled and observation-based stress is 18.3°. Our findings emphasize that the relative contributions coming from shallow and deep mantle dynamic forces are quite different for the lithospheric stress field and dynamic topography. Y1 - 2018 U6 - https://doi.org/10.5194/se-9-649-2018 SN - 1869-9510 SN - 1869-9529 VL - 9 IS - 3 SP - 649 EP - 668 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Kaboth-Bahr, Stefanie A1 - Bahr, André A1 - Stepanek, Christian A1 - Catunda, Maria Carolina Amorim A1 - Karas, Cyrus A1 - Ziegler, Martin A1 - García-Gallardo, Ángela A1 - Grunert, Patrick T1 - Mediterranean heat injection to the North Atlantic delayed the intensification of Northern Hemisphere glaciations JF - Communications Earth & Environment N2 - The intensification of Northern Hemisphere glaciations at the end of the Pliocene epoch marks one of the most substantial climatic shifts of the Cenozoic. Despite global cooling, sea surface temperatures in the high latitude North Atlantic Ocean rose between 2.9–2.7 million years ago. Here we present sedimentary geochemical proxy data from the Gulf of Cadiz to reconstruct the variability of Mediterranean Outflow Water, an important heat source to the North Atlantic. We find evidence for enhanced production of Mediterranean Outflow from the mid-Pliocene to the late Pliocene which we infer could have driven a sub-surface heat channel into the high-latitude North Atlantic. We then use Earth System Models to constrain the impact of enhanced Mediterranean Outflow production on the northward heat transport in the North Atlantic. In accord with the proxy data, the numerical model results support the formation of a sub-surface channel that pumped heat from the subtropics into the high latitude North Atlantic. We further suggest that this mechanism could have delayed ice sheet growth at the end of the Pliocene. Y1 - 2021 U6 - https://doi.org/10.1038/s43247-021-00232-5 SN - 2662-4435 SP - 1 EP - 9 PB - Springer Nature CY - London ER - TY - JOUR A1 - Lu, Yin A1 - Dewald, Nico A1 - Koutsodendris, Andreas A1 - Kaboth-Bahr, Stefanie A1 - Rösler, Wolfgang A1 - Fang, Xiaomin A1 - Pross, Jörg A1 - Appel, Erwin A1 - Friedrich, Oliver T1 - Sedimentological evidence for pronounced glacial-interglacial climate fluctuations in NE Tibet in the latest Pliocene to early Pleistocene JF - Paleoceanography and Paleoclimatology N2 - The intensification of Northern Hemisphere glaciation (iNHG) and uplift of the Tibetan Plateau have been argued to be among the main drivers of climate change in midlatitude Central Asia during the Pliocene/Pleistocene. While most proxy records that support this hypothesis are from regions outside the Tibetan Plateau (such as from the Chinese Loess Plateau), detailed paleoclimatic information for the plateau itself during that time has yet remained elusive. Here we present a temporally highly resolved (similar to 500 years) sedimentological record from the Qaidam Basin situated on the northeastern Tibetan Plateau that shows pronounced glacial-interglacial climate variability during the interval from 2.7 to 2.1 Ma. Glacial (interglacial) intervals are generally characterized by coarser (finer) grain size, minima (maxima) in organic matter content, and maxima (minima) in carbonate content. Comparison of our results with Earth's orbital parameters and proxy records from the Chinese Loess Plateau suggests that the observed climate fluctuations were mainly driven by changes in the Siberian High/East Asian winter monsoon system as a response to the iNHG. They are further proposed to be enhanced by the topography of the Tibetan Plateau and its impact on the position and intensity of the westerlies. KW - Western Qaidam Basin KW - grain-size distribution KW - lake Donggi Cona KW - Chinese loess KW - Central-Asia KW - transport processes KW - Qilian mountains KW - dust sources KW - plateau KW - record Y1 - 2020 VL - 35 IS - 5 PB - John Wiley & Sons, Inc. CY - New Jersey ER - TY - JOUR A1 - Ehrlich, Elias A1 - Gaedke, Ursula T1 - Not attackable or not crackable BT - How pre- and post-attack defenses with different competition costs affect prey coexistence and population dynamics JF - Ecology and evolution N2 - It is well-known that prey species often face trade-offs between defense against predation and competitiveness, enabling predator-mediated coexistence. However, we lack an understanding of how the large variety of different defense traits with different competition costs affects coexistence and population dynamics. Our study focusses on two general defense mechanisms, that is, pre-attack (e.g., camouflage) and post-attack defenses (e.g., weaponry) that act at different phases of the predator—prey interaction. We consider a food web model with one predator, two prey types and one resource. One prey type is undefended, while the other one is pre- or post-attack defended paying costs either by a higher half-saturation constant for resource uptake or a lower maximum growth rate. We show that post-attack defenses promote prey coexistence and stabilize the population dynamics more strongly than pre-attack defenses by interfering with the predator's functional response: Because the predator spends time handling “noncrackable” prey, the undefended prey is indirectly facilitated. A high half-saturation constant as defense costs promotes coexistence more and stabilizes the dynamics less than a low maximum growth rate. The former imposes high costs at low resource concentrations but allows for temporally high growth rates at predator-induced resource peaks preventing the extinction of the defended prey. We evaluate the effects of the different defense mechanisms and costs on coexistence under different enrichment levels in order to vary the importance of bottom-up and top-down control of the prey community. KW - coexistence KW - competition-defense trade-off KW - defense against predation KW - functional response KW - indirect facilitation KW - predator-prey cycles Y1 - 2018 U6 - https://doi.org/10.1002/ece3.4145 SN - 2045-7758 VL - 8 IS - 13 SP - 6625 EP - 6637 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Filipovic, Vilim A1 - Gerke, Horst H. A1 - Filipovic, Lana A1 - Sommer, Michael T1 - Quantifying subsurface lateral flow along sloping horizon boundaries in soil profiles of a hummocky ground moraine JF - Vadose zone journal N2 - Subsurface lateral flow in hillslope soils depends on lower permeability or texture-contrasting soil horizons. In the arable hummocky soil landscape, erosion processes caused glacial till appearance closer to the soil surface at upslope positions. The objective of this work was to quantify the potential for subsurface lateral flow depending on the erosion-affected spatial hydropedological complexity. The eroded Haplic Luvisol profile was studied due to the presence of a relatively dense C horizon that varied in depth, thickness, and sloping angle. A two-dimensional numerical modeling and sensitivity analysis for the saturated hydraulic conductivity (K-s) of the C horizon and the depth to C horizon (i.e., soil solum thickness) was performed for rainstorms in 2011 and 2012 using HYDRUS-2D. A K-s value of <2.5 cm d(-1) for the C horizon was required for lateral flow initiation. Lateral flow was (i) increasing with decreasing solum thickness, indicating an erosion-induced feedback on subsurface lateral flow, and (ii) dependent on the soil moisture regime prior to rainstorms. The effect of lateral flow on the movement of a conservative tracer was simulated in the form of a "virtual experiment". Simulation scenarios revealed only a relatively small lateral shift of the tracer plume caused by a local decoupling of water (already lateral) from subsequent tracer movement (still vertical). Longer term simulations suggested that, for the present conditions, lateral flow was limited mostly to occasional summer storm events. Even without considering preferential flow contribution to lateral flow, highly complex hydropedologic interactions are present in erosion-affected heterogeneous soil profiles. Y1 - 2016 U6 - https://doi.org/10.2136/vzj2017.05.0106 SN - 1539-1663 VL - 17 IS - 1 PB - Soil Science Society of America CY - Madison ER - TY - JOUR A1 - Casado, Mathieu A1 - Landais, Amaelle A1 - Picard, Ghislain A1 - Münch, Thomas A1 - Laepple, Thomas A1 - Stenni, Barbara A1 - Dreossi, Giuliano A1 - Ekaykin, Alexey A1 - Arnaud, Laurent A1 - Genthon, Christophe A1 - Touzeau, Alexandra A1 - Masson-Delmotte, Valerie A1 - Jouzel, Jean T1 - Archival processes of the water stable isotope signal in East Antarctic ice cores JF - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union N2 - The oldest ice core records are obtained from the East Antarctic Plateau. Water isotopes are key proxies to reconstructing past climatic conditions over the ice sheet and at the evaporation source. The accuracy of climate reconstructions depends on knowledge of all processes affecting water vapour, precipitation and snow isotopic compositions. Fractionation processes are well understood and can be integrated in trajectory-based Rayleigh distillation and isotope-enabled climate models. However, a quantitative understanding of processes potentially altering snow isotopic composition after deposition is still missing. In low-accumulation sites, such as those found in East Antarctica, these poorly constrained processes are likely to play a significant role and limit the interpretability of an ice core's isotopic composition. By combining observations of isotopic composition in vapour, precipitation, surface snow and buried snow from Dome C, a deep ice core site on the East Antarctic Plateau, we found indications of a seasonal impact of metamorphism on the surface snow isotopic signal when compared to the initial precipitation. Particularly in summer, exchanges of water molecules between vapour and snow are driven by the diurnal sublimation-condensation cycles. Overall, we observe in between precipitation events modification of the surface snow isotopic composition. Using high-resolution water isotopic composition profiles from snow pits at five Antarctic sites with different accumulation rates, we identified common patterns which cannot be attributed to the seasonal variability of precipitation. These differences in the precipitation, surface snow and buried snow isotopic composition provide evidence of post-deposition processes affecting ice core records in low-accumulation areas. Y1 - 2018 U6 - https://doi.org/10.5194/tc-12-1745-2018 SN - 1994-0416 SN - 1994-0424 VL - 12 IS - 5 SP - 1745 EP - 1766 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Lehr, Christian A1 - Dannowski, Ralf A1 - Kalettka, Thomas A1 - Merz, Christoph A1 - Schröder, Boris A1 - Steidl, Jörg A1 - Lischeid, Gunnar T1 - Detecting dominant changes in irregularly sampled multivariate water quality data sets JF - Hydrology and earth system sciences : HESS N2 - Time series of groundwater and stream water quality often exhibit substantial temporal and spatial variability, whereas typical existing monitoring data sets, e.g. from environmental agencies, are usually characterized by relatively low sampling frequency and irregular sampling in space and/or time. This complicates the differentiation between anthropogenic influence and natural variability as well as the detection of changes in water quality which indicate changes in single drivers. We suggest the new term "dominant changes" for changes in multivariate water quality data which concern (1) multiple variables, (2) multiple sites and (3) long-term patterns and present an exploratory framework for the detection of such dominant changes in data sets with irregular sampling in space and time. Firstly, a non-linear dimension-reduction technique was used to summarize the dominant spatiotemporal dynamics in the multivariate water quality data set in a few components. Those were used to derive hypotheses on the dominant drivers influencing water quality. Secondly, different sampling sites were compared with respect to median component values. Thirdly, time series of the components at single sites were analysed for long-term patterns. We tested the approach with a joint stream water and groundwater data set quality consisting of 1572 samples, each comprising sixteen variables, sampled with a spatially and temporally irregular sampling scheme at 29 sites in northeast Germany from 1998 to 2009. The first four components were interpreted as (1) an agriculturally induced enhancement of the natural background level of solute concentration, (2) a redox sequence from reducing conditions in deep groundwater to post-oxic conditions in shallow groundwater and oxic conditions in stream water, (3) a mixing ratio of deep and shallow groundwater to the streamflow and (4) sporadic events of slurry application in the agricultural practice. Dominant changes were observed for the first two components. The changing intensity of the first component was interpreted as response to the temporal variability of the thickness of the unsaturated zone. A steady increase in the second component at most stream water sites pointed towards progressing depletion of the denitrification capacity of the deep aquifer. Y1 - 2018 U6 - https://doi.org/10.5194/hess-22-4401-2018 SN - 1027-5606 SN - 1607-7938 VL - 22 IS - 8 SP - 4401 EP - 4424 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Brune, Sascha A1 - Williams, Simon E. A1 - Müller, R. Dietmar T1 - Oblique rifting: the rule, not the exception JF - Solid earth N2 - Movements of tectonic plates often induce oblique deformation at divergent plate boundaries. This is in striking contrast with traditional conceptual models of rifting and rifted margin formation, which often assume 2-D deformation where the rift velocity is oriented perpendicular to the plate boundary. Here we quantify the validity of this assumption by analysing the kinematics of major continent-scale rift systems in a global plate tectonic reconstruction from the onset of Pangea breakup until the present day. We evaluate rift obliquity by joint examination of relative extension velocity and local rift trend using the script-based plate reconstruction software pyGPlates. Our results show that the global mean rift obliquity since 230 Ma amounts to 34 degrees with a standard deviation of 24 degrees, using the convention that the angle of obliquity is spanned by extension direction and rift trend normal. We find that more than similar to 70 % of all rift segments exceeded an obliquity of 20 degrees demonstrating that oblique rifting should be considered the rule, not the exception. In many cases, rift obliquity and extension velocity increase during rift evolution (e.g. Australia-Antarctica, Gulf of California, South Atlantic, India-Antarctica), which suggests an underlying geodynamic correlation via obliquity-dependent rift strength. Oblique rifting produces 3-D stress and strain fields that cannot be accounted for in simplified 2-D plane strain analysis. We therefore highlight the importance of 3-D approaches in modelling, surveying, and interpretation of most rift segments on Earth where oblique rifting is the dominant mode of deformation. Y1 - 2018 U6 - https://doi.org/10.5194/se-9-1187-2018 SN - 1869-9510 SN - 1869-9529 VL - 9 IS - 5 SP - 1187 EP - 1206 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Coesfeld, Jacqueline A1 - Anderson, Sharolyn J. A1 - Baugh, Kimberly A1 - Elvidge, Christopher D. A1 - Schernthanner, Harald A1 - Kyba, Christopher C. M. T1 - Variation of Individual Location Radiance in VIIRS DNB Monthly Composite Images JF - Remote sensing N2 - With the growing size and use of night light time series from the Visible Infrared Imaging Radiometer Suite Day/Night Band (DNB), it is important to understand the stability of the dataset. All satellites observe differences in pixel values during repeat observations. In the case of night light data, these changes can be due to both environmental effects and changes in light emission. Here we examine the stability of individual locations of particular large scale light sources (e.g., airports and prisons) in the monthly composites of DNB data from April 2012 to September 2017. The radiances for individual pixels of most large light emitters are approximately normally distributed, with a standard deviation of typically 15-20% of the mean. Greenhouses and flares, however, are not stable sources. We observe geospatial autocorrelation in the monthly variations for nearby sites, while the correlation for sites separated by large distances is small. This suggests that local factors contribute most to the variation in the pixel radiances and furthermore that averaging radiances over large areas will reduce the total variation. A better understanding of the causes of temporal variation would improve the sensitivity of DNB to lighting changes. KW - artificial light at night KW - light pollution KW - night lights KW - VIIRS DNB Y1 - 2018 U6 - https://doi.org/10.3390/rs10121964 SN - 2072-4292 VL - 10 IS - 12 PB - MDPI CY - Basel ER - TY - JOUR A1 - Latimer, Andrew M. A1 - Jacobs, Brooke S. A1 - Gianoli, Ernesto A1 - Heger, Tina A1 - Salgado-Luarte, Cristian T1 - Parallel functional differentiation of an invasive annual plant on two continents JF - AoB PLANTS N2 - Rapid local adaptation frequently occurs during the spread of invading species. It remains unclear, however, how consistent, and therefore potentially predictable, such patterns of local adaptation are. One approach to this question is to measure patterns of local differentiation in functional traits and plasticity levels in invasive species in multiple regions. Finding consistent patterns of local differentiation in replicate regions suggests that these patterns are adaptive. Further, this outcome indicates that the invading species likely responds predictably to selection along environmental gradients, even though standing genetic variation is likely to have been reduced during introduction. We studied local differentiation in the invasive annual plant Erodium cicutarium in two invaded regions, California and Chile. We collected seeds from across strong gradients in precipitation and temperature in Mediterranean-climate parts of the two regions (10 populations per region). We grew seeds from maternal families from these populations through two generations and exposed the second generation to contrasting levels of water and nutrient availability. We measured growth, flowering time and leaf functional traits across these treatments to obtain trait means and plasticity measures. We found strong differentiation among populations in all traits. Plants from drier environments flowered earlier, were less plastic in flowering time and reached greater size in all treatments. Correlations among traits within regions suggested a coordinated evolutionary response along environmental gradients associated with growing season length. There was little divergence in traits and trait intercorrelations between regions, but strongly parallel divergence in traits within regions. Similar, statistically consistent patterns of local trait differentiation across two regions suggest that local adaptation to environmental gradients has aided the spread of this invasive species, and that the formation of ecotypes in newly invaded environments has been relatively consistent and predictable. KW - Erodium cicutarium KW - flowering time KW - functional trait correlations KW - invasive species KW - life-history strategy KW - local adaptation KW - parallel evolution KW - phenotypic plasticity Y1 - 2019 U6 - https://doi.org/10.1093/aobpla/plz010 SN - 2041-2851 VL - 11 IS - 2 PB - Oxford University Press CY - Oxford ER - TY - JOUR A1 - Javhar, Aminov A1 - Chen, Xi A1 - Bao, Anming A1 - Jamshed, Aminov A1 - Yunus, Mamadjanov A1 - Jovid, Aminov A1 - Latipa, Tuerhanjiang T1 - Comparison of Multi-Resolution Optical Landsat-8, Sentinel-2 and Radar Sentinel-1 Data for Automatic Lineament Extraction BT - A Case Study of Alichur Area, SE Pamir JF - Remote sensing N2 - Lineament mapping, which is an important part of any structural geological investigation, is made more efficient and easier by the availability of optical as well as radar remote sensing data, such as Landsat and Sentinel with medium and high spatial resolutions. However, the results from these multi-resolution data vary due to their difference in spatial resolution and sensitivity to soil occupation. The accuracy and quality of extracted lineaments depend strongly on the spatial resolution of the imagery. Therefore, the aim of this study was to compare the optical Landsat-8, Sentinel-2A, and radar Sentinel-1A satellite data for automatic lineament extraction. The framework of automatic approach includes defining the optimal parameters for automatic lineament extraction with a combination of edge detection and line-linking algorithms and determining suitable bands from optical data suited for lineament mapping in the study area. For the result validation, the extracted lineaments are compared against the manually obtained lineaments through the application of directional filtering and edge enhancement as well as to the lineaments digitized from the existing geological maps of the study area. In addition, a digital elevation model (DEM) has been utilized for an accuracy assessment followed by the field verification. The obtained results show that the best correlation between automatically extracted lineaments, manual interpretation, and the preexisting lineament map is achieved from the radar Sentinel-1A images. The tests indicate that the radar data used in this study, with 5872 and 5865 lineaments extracted from VH and VV polarizations respectively, is more efficient for structural lineament mapping than the Landsat-8 and Sentinel-2A optical imagery, from which 2338 and 4745 lineaments were extracted respectively. KW - image enhancement KW - automatic lineament extraction KW - Landsat-8 KW - Sentinel-1 KW - Sentinel-2 KW - structural mapping Y1 - 2019 U6 - https://doi.org/10.3390/rs11070778 SN - 2072-4292 VL - 11 IS - 7 PB - MDPI CY - Basel ER - TY - JOUR A1 - Cordonnier, Guillaume A1 - Bovy, Benoit A1 - Braun, Jean T1 - A versatile, linear complexity algorithm for flow routing in topographies with depressions JF - Earth surface dynamics N2 - We present a new algorithm for solving the common problem of flow trapped in closed depressions within digital elevation models, as encountered in many applications relying on flow routing. Unlike other approaches (e.g., the Priority-Flood depression filling algorithm), this solution is based on the explicit computation of the flow paths both within and across the depressions through the construction of a graph connecting together all adjacent drainage basins. Although this represents many operations, a linear time complexity can be reached for the whole computation, making it very efficient. Compared to the most optimized solutions proposed so far, we show that this algorithm of flow path enforcement yields the best performance when used in landscape evolution models. In addition to its efficiency, our proposed method also has the advantage of letting the user choose among different strategies of flow path enforcement within the depressions (i.e., filling vs. carving). Furthermore, the computed graph of basins is a generic structure that has the potential to be reused for solving other problems as well, such as the simulation of erosion. This sequential algorithm may be helpful for those who need to, e.g., process digital elevation models of moderate size on single computers or run batches of simulations as part of an inference study. Y1 - 2019 U6 - https://doi.org/10.5194/esurf-7-549-2019 SN - 2196-6311 SN - 2196-632X VL - 7 IS - 2 SP - 549 EP - 562 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Masson, Torsten A1 - Bamberg, Sebastian A1 - Stricker, Michael A1 - Heidenreich, Anna T1 - "We can help ourselves": does community resilience buffer against the negative impact of flooding on mental health? JF - Natural hazards and earth system sciences N2 - Empirical evidence of the relationship between social support and post-disaster mental health provides support for a general beneficial effect of social support (main-effect model; Wheaton, 1985). From a theoretical perspective, a buffering effect of social support on the negative relationship between disaster-related stress and mental health also seems plausible (stress-buffering model; Wheaton, 1985). Previous studies, however, (a) have paid less attention to the buffering effect of social support and (b) have mainly relied on interpersonal support (but not collective-level support such as community resilience) when investigating this issue. This previous work might have underestimated the effect of support on post-disaster mental health. Building on a sample of residents in Germany recently affected by flooding (N = 118), we show that community resilience to flooding (but not general interpersonal social support) buffered against the negative effects of flooding on post-disaster mental health. The results support the stress-buffering model and call for a more detailed look at the relationship between support and resilience and post-disaster adjustment, including collective-level variables. Y1 - 2019 U6 - https://doi.org/10.5194/nhess-19-2371-2019 SN - 1561-8633 SN - 1684-9981 VL - 19 IS - 11 SP - 2371 EP - 2384 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Totz, Sonja Juliana A1 - Petri, Stefan A1 - Lehmann, Jascha A1 - Peukert, Erik A1 - Coumou, Dim T1 - Exploring the sensitivity of Northern Hemisphere atmospheric circulation to different surface temperature forcing using a statistical-dynamical atmospheric model JF - Nonlinear processes in geophysics N2 - Climate and weather conditions in the mid-latitudes are strongly driven by the large-scale atmosphere circulation. Observational data indicate that important components of the large-scale circulation have changed in recent decades, including the strength and the width of the Hadley cell, jets, storm tracks and planetary waves. Here, we use a new statistical-dynamical atmosphere model (SDAM) to test the individual sensitivities of the large-scale atmospheric circulation to changes in the zonal temperature gradient, meridional temperature gradient and global-mean temperature. We analyze the Northern Hemisphere Hadley circulation, jet streams, storm tracks and planetary waves by systematically altering the zonal temperature asymmetry, the meridional temperature gradient and the global-mean temperature. Our results show that the strength of the Hadley cell, storm tracks and jet streams depend, in terms of relative changes, almost linearly on both the global-mean temperature and the meridional temperature gradient, whereas the zonal temperature asymmetry has little or no influence. The magnitude of planetary waves is affected by all three temperature components, as expected from theoretical dynamical considerations. The width of the Hadley cell behaves nonlinearly with respect to all three temperature components in the SDAM. Moreover, some of these observed large-scale atmospheric changes are expected from dynamical equations and are therefore an important part of model validation. Y1 - 2019 U6 - https://doi.org/10.5194/npg-26-1-2019 SN - 1023-5809 SN - 1607-7946 VL - 26 IS - 1 SP - 1 EP - 12 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Gailleton, Boris A1 - Mudd, Simon M. A1 - Clubb, Fiona J. A1 - Peifer, Daniel A1 - Hurst, Martin D. T1 - A segmentation approach for the reproducible extraction and quantification of knickpoints from river long profiles JF - Earth surface dynamics N2 - Changes in the steepness of river profiles or abrupt vertical steps (i.e. waterfalls) are thought to be indicative of changes in erosion rates, lithology or other factors that affect landscape evolution. These changes are referred to as knickpoints or knickzones and are pervasive in bedrock river systems. Such features are thought to reveal information about landscape evolution and patterns of erosion, and therefore their locations are often reported in the geomorphic literature. It is imperative that studies reporting knickpoints and knickzones use a reproducible method of quantifying their locations, as their number and spatial distribution play an important role in interpreting tectonically active landscapes. In this contribution we introduce a reproducible knickpoint and knickzone extraction algorithm that uses river profiles transformed by integrating drainage area along channel length (the so-called integral or chi method). The profile is then statistically segmented and the differing slopes and step changes in the elevations of these segments are used to identify knickpoints, knickzones and their relative magnitudes. The output locations of identified knickpoints and knickzones compare favourably with human mapping: we test the method on Santa Cruz Island, CA, using previously reported knickzones and also test the method against a new dataset from the Quadrilatero Ferrifero in Brazil. The algorithm allows for the extraction of varying knickpoint morphologies, including stepped, positive slope-break (concave upward) and negative slope-break knickpoints. We identify parameters that most affect the resulting knickpoint and knickzone locations and provide guidance for both usage and outputs of the method to produce reproducible knickpoint datasets. Y1 - 2019 U6 - https://doi.org/10.5194/esurf-7-211-2019 SN - 2196-6311 SN - 2196-632X VL - 7 IS - 1 SP - 211 EP - 230 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Rodriguez-Zuluaga, Juan A1 - Stolle, Claudia T1 - Interhemispheric field-aligned currents at the edges of equatorial plasma depletions JF - Scientific reports N2 - A comprehensive description of electromagnetic processes related to equatorial plasma depletions (EPDs) is essential for understanding their evolution and day-to-day variability. Recently, field-aligned currents (FACs) flowing at both western and eastern edges of EPDs were observed to be interhemispheric rather than anti-parallel about the dip equator, as suggested by previous theoretical studies. In this paper, we investigate the spatial and temporal variability of the FACs orientation using simultaneous measurements of electron density and magnetic field gathered by ESA’s Swarm constellation mission. By using empirical models, we assess the role of the Pedersen conductance in the preference of the FACs to close either in the northern or southern magnetic hemisphere. Here we show that the closure of the FACs agrees with an electrostatic regime determined by a hemispherical asymmetry of the Pedersen conductance. That is, the EPD-related FACs close at lower altitudes in the hemisphere with the highest conductivity. The evidence of this conclusion stands on the general agreement between the longitudinal and seasonal variability of both the conductivity and the FACs orientation. Y1 - 2019 U6 - https://doi.org/10.1038/s41598-018-37955-z SN - 2045-2322 VL - 9 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Reschke, Maria A1 - Rehfeld, Kira A1 - Laepple, Thomas T1 - Empirical estimate of the signal content of Holocene temperature proxy records JF - Climate of the past : an interactive open access journal of the European Geosciences Union N2 - Proxy records from climate archives provide evidence about past climate changes, but the recorded signal is affected by non-climate-related effects as well as time uncertainty. As proxy-based climate reconstructions are frequently used to test climate models and to quantitatively infer past climate, we need to improve our understanding of the proxy record signal content as well as the uncertainties involved. In this study, we empirically estimate signal-to-noise ratios (SNRs) of temperature proxy records used in global compilations of the middle to late Holocene (last 6000 years). This is achieved through a comparison of the correlation of proxy time series from nearby sites of three compilations and model time series extracted at the proxy sites from two transient climate model simulations: a Holocene simulation of the ECHAM5/MPI-OM model and the Holocene part of the TraCE-21ka simulation. In all comparisons, we found the mean correlations of the proxy time series on centennial to millennial timescales to be low (R < 0.2), even for nearby sites, which resulted in low SNR estimates. The estimated SNRs depend on the assumed time uncertainty of the proxy records, the timescale analysed, and the model simulation used. Using the spatial correlation structure of the ECHAM5/MPI-OM simulation, the estimated SNRs on centennial timescales ranged from 0.05 - assuming no time uncertainty - to 0.5 for a time uncertainty of 400 years. On millennial timescales, the estimated SNRs were generally higher. Use of the TraCE-21ka correlation structure generally resulted in lower SNR estimates than for ECHAM5/MPI-OM. As the number of available high-resolution proxy records continues to grow, a more detailed analysis of the signal content of specific proxy types should become feasible in the near future. The estimated low signal content of Holocene temperature compilations should caution against over-interpretation of these multi-proxy and multisite syntheses until further studies are able to facilitate a better characterisation of the signal content in paleoclimate records. Y1 - 2019 U6 - https://doi.org/10.5194/cp-15-521-2019 SN - 1814-9324 SN - 1814-9332 VL - 15 IS - 2 SP - 521 EP - 537 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Petitgirard, Sylvian A1 - Sahle, C. J. A1 - Weis, C. A1 - Gilmore, K. A1 - Spiekermann, Georg A1 - Tse, J. S. A1 - Wilke, Max A1 - Cavallari, C. A1 - Cerantola, V A1 - Sternemann, Christian T1 - Magma properties at deep Earth’s conditions from electronic structure of silica JF - Geochemical perspectives letters N2 - SiO(2 )is the main component of silicate melts and thus controls their network structure and physical properties. The compressibility and viscosities of melts at depth are governed by their short range atomic and electronic structure. We measured the O K-edge and the Si L-2,L-3-edge in silica up to 110 GPa using X-ray Raman scattering spectroscopy, and found a striking match to calculated spectra based on structures from molecular dynamic simulations. Between 20 and 27 GPa, Si-[4] species are converted into a mixture of Si-[5] and Si-[6] species and between 60 and 70 GPa, Si-[6] becomes dominant at the expense of Si-[5] with no further increase up to at least 110 GPa. Coordination higher than 6 is only reached beyond 140 GPa, corroborating results from Brillouin scattering. Network modifying elements in silicate melts may shift this change in coordination to lower pressures and thus magmas could be denser than residual solids at the depth of the core-mantle boundary. Y1 - 2019 U6 - https://doi.org/10.7185/geochemlet.1902 SN - 2410-339X SN - 2410-3403 VL - 9 SP - 32 EP - 37 PB - Association of Geochemistry CY - Paris ER - TY - JOUR A1 - Zorn, Edgar Ulrich A1 - Le Corvec, Nicolas A1 - Varley, Nick R. A1 - Salzer, Jacqueline T. A1 - Walter, Thomas R. A1 - Navarro-Ochoa, Carlos A1 - Vargas-Bracamontes, Dulce M. A1 - Thiele, Samuel T. A1 - Arámbula Mendoza, Raúl T1 - Load stress controls on directional lava dome growth at Volcan de Colima, Mexico JF - Frontiers in Earth Science N2 - During eruptive activity of andesitic stratovolcanoes, the extrusion of lava domes, their collapse and intermittent explosions are common volcanic hazards. Many lava domes grow in a preferred direction, in turn affecting the direction of lava flows and pyroclastic density currents. Access to active lava domes is difficult and hazardous, so detailed data characterizing lava dome growth are typically limited, keeping the processes controlling the directionality of extrusions unclear. Here we combine TerraSAR-X satellite radar observations with high-resolution airborne photogrammetry to assess morphological changes, and perform finite element modeling to investigate the impact of loading stress on shallow magma ascent directions associated with lava dome extrusion and crater formation at Volcan de Colima, Mexico. The TerraSAR-X data, acquired in similar to 1-m resolution spotlight mode, enable us to derive a chronology of the eruptive processes from intensity-based time-lapse observations of the general crater and dome evolution. The satellite images are complemented by close-range airborne photos, processed by the Structure-from-Motion workflow. This allows the derivation of high-resolution digital elevation models, providing insight into detailed loading and unloading features. During the observation period from Jan-2013 to Feb-2016, we identify a dominantly W-directed dome growth and lava flow production until Jan-2015. In Feb-2015, following the removal of the active summit dome, the surface crater widened and elongated along a NE-SW axis. Later in May-2015, a new dome grew toward the SW of the crater while a separate vent developed in the NE of the crater, reflecting a change in the direction of magma ascent and possible conduit bifurcation. Finite element models show a significant stress change in agreement with the observed magma ascent direction changes in response to the changing surface loads, both for loading (dome growth) and unloading (crater forming excavation) cases. These results allow insight into shallow dome growth dynamics and the migration of magma ascent in response to changing volcano summit morphology. They further highlight the importance of detailed volcano summit morphology surveillance, as changes in direction or location of dome extrusion may have major implications regarding the directions of potential volcanic hazards, such as pyroclastic density currents generated by dome collapse. KW - lava dome KW - load stress KW - Volcan de Colima KW - TerraSAR-X KW - photogrammetry KW - finite element modeling Y1 - 2019 U6 - https://doi.org/10.3389/feart.2019.00084 SN - 2296-6463 VL - 7 PB - Frontiers Media CY - Lausanne ER - TY - JOUR A1 - Asgarimehr, Milad A1 - Wickert, Jens A1 - Reich, Sebastian T1 - Evaluating impact of rain attenuation on space-borne GNSS reflectometry wind speeds JF - Remote Sensing N2 - The novel space-borne Global Navigation Satellite System Reflectometry (GNSS-R) technique has recently shown promise in monitoring the ocean state and surface wind speed with high spatial coverage and unprecedented sampling rate. The L-band signals of GNSS are structurally able to provide a higher quality of observations from areas covered by dense clouds and under intense precipitation, compared to those signals at higher frequencies from conventional ocean scatterometers. As a result, studying the inner core of cyclones and improvement of severe weather forecasting and cyclone tracking have turned into the main objectives of GNSS-R satellite missions such as Cyclone Global Navigation Satellite System (CYGNSS). Nevertheless, the rain attenuation impact on GNSS-R wind speed products is not yet well documented. Evaluating the rain attenuation effects on this technique is significant since a small change in the GNSS-R can potentially cause a considerable bias in the resultant wind products at intense wind speeds. Based on both empirical evidence and theory, wind speed is inversely proportional to derived bistatic radar cross section with a natural logarithmic relation, which introduces high condition numbers (similar to ill-posed conditions) at the inversions to high wind speeds. This paper presents an evaluation of the rain signal attenuation impact on the bistatic radar cross section and the derived wind speed. This study is conducted simulating GNSS-R delay-Doppler maps at different rain rates and reflection geometries, considering that an empirical data analysis at extreme wind intensities and rain rates is impossible due to the insufficient number of observations from these severe conditions. Finally, the study demonstrates that at a wind speed of 30 m/s and incidence angle of 30 degrees, rain at rates of 10, 15, and 20 mm/h might cause overestimation as large as approximate to 0.65 m/s (2%), 1.00 m/s (3%), and 1.3 m/s (4%), respectively, which are still smaller than the CYGNSS required uncertainty threshold. The simulations are conducted in a pessimistic condition (severe continuous rainfall below the freezing height and over the entire glistening zone) and the bias is expected to be smaller in size in real environments. KW - GNSS Reflectometry KW - wind speed KW - rain effect KW - rain attenuation KW - DDM simulation Y1 - 2019 U6 - https://doi.org/10.3390/rs11091048 SN - 2072-4292 VL - 11 IS - 9 PB - MDPI CY - Basel ER - TY - JOUR A1 - Stich, Daniel A1 - Martin, Rosa A1 - Morales, Jose A1 - Lopez-Comino, Jose Angel A1 - Mancilla, Flor de Lis T1 - Slip partitioning in the 2016 Alboran Sea earthquake sequence (western Mediterranean) JF - Frontiers in Earth Science N2 - AM(W)= 5.1 earthquake on January 21st, 2016 marked the beginning of a significant seismic sequence in the southern Alboran Sea, culminating in aM(W)= 6.3 earthquake on January 25th, and continuing with further moderate magnitude earthquakes until March. We use data from 35 seismic broadband stations in Spain, Morocco and Portugal to relocate the seismicity, estimate seismic moment tensors, and isolate regional apparent source time functions for the main earthquake. Relocation and regional moment tensor inversion consistently yield very shallow depths for the majority of events. We obtain 50 moment tensors for the sequence, showing a mixture of strike-slip faulting for the foreshock and the main event and reverse faulting for the major aftershocks. The leading role of reverse focal mechanisms among the aftershocks may be explained by the geometry of the fault network. The mainshock nucleates at a bend along the left-lateral Al-Idrisi fault, introducing local transpression within the transtensional Alboran Basin. The shallow depths of the 2016 Alboran Sea earthquakes may favor slip-partitioning on the involved faults. Apparent source durations for the main event suggest a similar to 21 km long, asymmetric rupture that propagates primarily toward NE into the restraining fault segment, with fast rupture speed of similar to 3.0 km/s. Consistently, the inversion for laterally variable fault displacement situates the main slip in the restraining segment. The partitioning into strike-slip rupture and dip-slip aftershocks confirms a non-optimal orientation of this segment, and suggests that the 2016 event settled a slip deficit from previous ruptures that could not propagate into the stronger restraining segment. KW - slip partitioning KW - fault bend KW - moment tensor KW - source time function KW - shallow earthquakes Y1 - 2020 U6 - https://doi.org/10.3389/feart.2020.587356 SN - 2296-6463 VL - 8 PB - Frontiers Media CY - Lausanne ER - TY - JOUR A1 - Giarolla, Emanuel A1 - Veiga, Sandro F. A1 - Nobre, Paulo A1 - Silva, Manoel B. A1 - Capistrano, Vinicius B. A1 - Callegare, Andyara O. T1 - Sea surface height trends in the southern hemisphere oceans simulated by the Brazilian Earth System Model under RCP4.5 and RCP8.5 scenarios JF - Journal of southern hemisphere earth systems science N2 - The Brazilian Earth System Model (BESM-OA2.5), while simulating the historical period proposed by the fifth phase of the Coupled Model Intercomparison Project (CMIP5), detects an increasing trend in the sea surface height (SSH) on the southern hemisphere oceans relative to that of the pre-industrial era. The increasing trend is accentuated in the CMIP5 RCP4.5 and RCP8.5 future scenarios with higher concentrations of greenhouse gases in the atmosphere. This study sheds light on the sources of such trends in these regions. The results suggest an association with the thermal expansion of the oceans in the upper 700 m due to a gradual warming inflicted by those future scenarios. BESM-OA2.5 presents a surface height increase of 0.11 m in the historical period of 1850-2005. Concerning future projections, BESM-OA2.5 projects SSH increases of 0.14 and 0.23 m (relative to the historical 2005 value) for RCP4.5 and RCP8.5, respectively, by the end of 2100. These increases are predominantly in a band of latitude within 35-60 degrees S in the Atlantic and Indian oceans. The reproducibility of the trend signal detected in the BESM-OA2.5 simulations is confirmed by the results of three other CMIP5 models. KW - Brazilian Earth System Model KW - CMIP5 KW - IPCC AR5 scenarios KW - RCP4.5 KW - RCP8.5 KW - sea level trends KW - sea surface height KW - southern hemisphere oceans Y1 - 2020 U6 - https://doi.org/10.1071/ES19042 SN - 2206-5865 VL - 70 IS - 1 SP - 280 EP - 289 PB - CSIRO CY - Clayton ER - TY - JOUR A1 - Crisologo, Irene A1 - Heistermann, Maik T1 - Using ground radar overlaps to verify the retrieval of calibration bias estimates from spaceborne platforms JF - Atmospheric measurement techniques : an interactive open access journal of the European Geosciences Union N2 - Many institutions struggle to tap into the potential of their large archives of radar reflectivity: these data are often affected by miscalibration, yet the bias is typically unknown and temporally volatile. Still, relative calibration techniques can be used to correct the measurements a posteriori. For that purpose, the usage of spaceborne reflectivity observations from the Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Measurement (GPM) platforms has become increasingly popular: the calibration bias of a ground radar (GR) is estimated from its average reflectivity difference to the spaceborne radar (SR). Recently, Crisologo et al. (2018) introduced a formal procedure to enhance the reliability of such estimates: each match between SR and GR observations is assigned a quality index, and the calibration bias is inferred as a quality-weighted average of the differences between SR and GR. The relevance of quality was exemplified for the Subic S-band radar in the Philippines, which is greatly affected by partial beam blockage. The present study extends the concept of quality-weighted averaging by accounting for path-integrated attenuation (PIA) in addition to beam blockage. This extension becomes vital for radars that operate at the C or X band. Correspondingly, the study setup includes a C-band radar that substantially overlaps with the S-band radar. Based on the extended quality-weighting approach, we retrieve, for each of the two ground radars, a time series of calibration bias estimates from suitable SR overpasses. As a result of applying these estimates to correct the ground radar observations, the consistency between the ground radars in the region of overlap increased substantially. Furthermore, we investigated if the bias estimates can be interpolated in time, so that ground radar observations can be corrected even in the absence of prompt SR overpasses. We found that a moving average approach was most suitable for that purpose, although limited by the absence of explicit records of radar maintenance operations. Y1 - 2020 U6 - https://doi.org/10.5194/amt-13-645-2020 SN - 1867-1381 SN - 1867-8548 VL - 13 IS - 2 SP - 645 EP - 659 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Wieczorek, Mareike A1 - Herzschuh, Ulrike T1 - Compilation of relative pollen productivity (RPP) estimates and taxonomically harmonised RPP datasets for single continents and Northern Hemisphere extratropics JF - Earth system science data : ESSD N2 - Relative pollen productivity (RPP) estimates are fractionate values, often in relation to Poaceae, that allow vegetation cover to be estimated from pollen counts with the help of models. RPP estimates are especially used in the scientific community in Europe and China, with a few studies in North America. Here we present a comprehensive compilation of available northern hemispheric RPP studies and their results arising from 51 publications with 60 sites and 131 taxa. This compilation allows scientists to identify data gaps in need of further RPP analyses but can also aid them in finding an RPP set for their study region. We also present a taxonomically harmonised, unified RPP dataset for the Northern Hemisphere and subsets for North America (including Greenland), Europe (including arctic Russia), and China, which we generated from the available studies. The unified dataset gives the mean RPP for 55 harmonised taxa as well as fall speeds, which are necessary to reconstruct vegetation cover from pollen counts and RPP values. Data are openly available at https://doi.org/10.1594/PANGAEA.922661 (Wieczorek and Herzschuh, 2020). Y1 - 2020 U6 - https://doi.org/10.5194/essd-12-3515-2020 SN - 1866-3508 SN - 1866-3516 VL - 12 IS - 4 SP - 3515 EP - 3528 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Wetzel, Maria A1 - Kempka, Thomas A1 - Kühn, Michael T1 - Hydraulic and mechanical impacts of pore space alterations within a sandstone quantified by a flow velocity-dependent precipitation approach JF - Materials N2 - Geochemical processes change the microstructure of rocks and thereby affect their physical behaviour at the macro scale. A micro-computer tomography (micro-CT) scan of a typical reservoir sandstone is used to numerically examine the impact of three spatial alteration patterns on pore morphology, permeability and elastic moduli by correlating precipitation with the local flow velocity magnitude. The results demonstrate that the location of mineral growth strongly affects the permeability decrease with variations by up to four orders in magnitude. Precipitation in regions of high flow velocities is characterised by a predominant clogging of pore throats and a drastic permeability reduction, which can be roughly described by the power law relation with an exponent of 20. A continuous alteration of the pore structure by uniform mineral growth reduces the permeability comparable to the power law with an exponent of four or the Kozeny-Carman relation. Preferential precipitation in regions of low flow velocities predominantly affects smaller throats and pores with a minor impact on the flow regime, where the permeability decrease is considerably below that calculated by the power law with an exponent of two. Despite their complete distinctive impact on hydraulics, the spatial precipitation patterns only slightly affect the increase in elastic rock properties with differences by up to 6.3% between the investigated scenarios. Hence, an adequate characterisation of the spatial precipitation pattern is crucial to quantify changes in hydraulic rock properties, whereas the present study shows that its impact on elastic rock parameters is limited. The calculated relations between porosity and permeability, as well as elastic moduli can be applied for upscaling micro-scale findings to reservoir-scale models to improve their predictive capabilities, what is of paramount importance for a sustainable utilisation of the geological subsurface. KW - Bentheim sandstone KW - digital rock physics KW - micro-CT KW - elastic properties KW - permeability KW - precipitation Y1 - 2020 U6 - https://doi.org/10.3390/ma13143100 SN - 1996-1944 VL - 13 IS - 14 PB - MDPI CY - Basel ER - TY - JOUR A1 - Wetzel, Maria A1 - Kempka, Thomas A1 - Kühn, Michael T1 - Quantifying rock weakening due to decreasing calcite mineral content by numerical simulations JF - Materials N2 - The quantification of changes in geomechanical properties due to chemical reactions is of paramount importance for geological subsurface utilisation, since mineral dissolution generally reduces rock stiffness. In the present study, the effective elastic moduli of two digital rock samples, the Fontainebleau and Bentheim sandstones, are numerically determined based on micro-CT images. Reduction in rock stiffness due to the dissolution of 10% calcite cement by volume out of the pore network is quantified for three synthetic spatial calcite distributions (coating, partial filling and random) using representative sub-cubes derived from the digital rock samples. Due to the reduced calcite content, bulk and shear moduli decrease by 34% and 38% in maximum, respectively. Total porosity is clearly the dominant parameter, while spatial calcite distribution has a minor impact, except for a randomly chosen cement distribution within the pore network. Moreover, applying an initial stiffness reduced by 47% for the calcite cement results only in a slightly weaker mechanical behaviour. Using the quantitative approach introduced here substantially improves the accuracy of predictions in elastic rock properties compared to general analytical methods, and further enables quantification of uncertainties related to spatial variations in porosity and mineral distribution. KW - digital rock physics KW - micro-CT KW - elastic properties KW - numerical simulation KW - chemical-mechanical interaction KW - Code_Aster KW - composite properties Y1 - 2018 U6 - https://doi.org/10.3390/ma11040542 SN - 1996-1944 VL - 11 IS - 4 PB - MDPI CY - Basel ER - TY - JOUR A1 - Nakaten, Natalie Christine A1 - Kempka, Thomas T1 - Techno-Economic Comparison of Onshore and Offshore Underground Coal Gasification End-Product Competitiveness JF - Energies N2 - Underground coal gasification (UCG) enables utilization of coal reserves, currently not economically exploitable due to complex geological boundary conditions. Hereby, UCG produces a high-calorific synthesis gas that can be used for generation of electricity, fuels, and chemical feedstock. The present study aims to identify economically-competitive, site-specific end-use options for onshore- and offshore-produced UCG synthesis gas, taking into account the capture and storage (CCS) and/or utilization (CCU) of produced CO2. Modeling results show that boundary conditions favoring electricity, methanol, and ammonia production expose low costs for air separation, low compression power requirements, and appropriate shares of H-2/N-2. Hereby, a gasification agent ratio of more than 30% oxygen by volume is not favorable from the economic and CO2 mitigation viewpoints. Compared to the costs of an offshore platform with its technical equipment, offshore drilling costs are marginal. Thus, uncertainties related to parameters influenced by drilling costs are negligible. In summary, techno-economic process modeling results reveal that air-blown gasification scenarios are the most cost-effective ones, while offshore UCG-CCS/CCU scenarios are up to 1.7 times more expensive than the related onshore processes. Hereby, all investigated onshore scenarios except from ammonia production under the assumed worst-case conditions are competitive on the European market. KW - underground coal gasification (UCG) KW - economics KW - cost of electricity (COE) KW - techno-economic model KW - methanol KW - ammonia KW - carbon capture and storage (CCS) KW - carbon capture and utilization (CCU) KW - electricity generation KW - process simulation Y1 - 2019 U6 - https://doi.org/10.3390/en12173252 SN - 1996-1073 VL - 12 IS - 17 PB - MDPI CY - Basel ER - TY - JOUR A1 - Cheng, Chaojie A1 - Milsch, Harald T1 - Evolution of fracture aperture in quartz sandstone under hydrothermal conditions BT - mechanical and chemical effects JF - Minerals N2 - Fractures efficiently affect fluid flow in geological formations, and thereby determine mass and energy transport in reservoirs, which are not least exploited for economic resources. In this context, their response to mechanical and thermal changes, as well as fluid-rock interactions, is of paramount importance. In this study, a two-stage flow-through experiment was conducted on a pure quartz sandstone core of low matrix permeability, containing one single macroscopic tensile fracture. In the first short-term stage, the effects of mechanical and hydraulic aperture on pressure and temperature cycles were investigated. The purpose of the subsequent intermittent-flow long-term (140 days) stage was to constrain the evolution of the geometrical and hydraulic fracture properties resulting from pressure solution. Deionized water was used as the pore fluid, and permeability, as well as the effluent Si concentrations, were systematically measured. Overall, hydraulic aperture was shown to be significantly less affected by pressure, temperature and time, in comparison to mechanical aperture. During the long-term part of the experiment at 140 degrees C, the effluent Si concentrations likely reached a chemical equilibrium state within less than 8 days of stagnant flow, and exceeded the corresponding hydrostatic quartz solubility at this temperature. This implies that the pressure solution was active at the contacting fracture asperities, both at 140 degrees C and after cooling to 33 degrees C. The higher temperature yielded a higher dissolution rate and, consequently, a faster attainment of chemical equilibrium within the contact fluid. X-ray mu CT observations evidenced a noticeable increase in fracture contact area ratio, which, in combination with theoretical considerations, implies a significant decrease in mechanical aperture. In contrast, the sample permeability, and thus the hydraulic fracture aperture, virtually did not vary. In conclusion, pressure solution-induced fracture aperture changes are affected by the degree of time-dependent variations in pore fluid composition. In contrast to the present case of a quasi-closed system with mostly stagnant flow, in an open system with continuous once-through fluid flow, the activity of the pressure solution may be amplified due to the persistent fluid-chemical nonequilibrium state, thus possibly enhancing aperture and fracture permeability changes. KW - flow-through experiment KW - fracture aperture KW - pressure solution KW - mass KW - transfer KW - silica concentration KW - permeability KW - quartz sandstone Y1 - 2020 U6 - https://doi.org/10.3390/min10080657 SN - 2075-163X VL - 10 IS - 8 PB - MDPI CY - Basel ER - TY - JOUR A1 - Brendel, Nina A1 - Matzner, Nils A1 - Menzel, Max-Peter T1 - Geographisches Gezwitscher – Analyse von Twitter-Daten als Methode im GW-Unterricht JF - GW-Unterricht N2 - Soziale Medien sind ein wesentlicher Bestandteil des Alltags von Schüler*innen und gleichzeitig zunehmend wichtig in Wirtschaft, Politik und Wissenschaft. Am Beispiel von Twitter zeigt dieser Beitrag, dass soziale Medien im Unterricht auch für die Beantwortung geographischer Fragestellungen verwendet werden können. Hierfür eignen sich Twitter-Daten aufgrund ihrer Georeferenzierung und weiterer interessanter Inhalte besonders. Der Beitrag gibt einen Überblick über die Verwendung von Twitter für sozialwissenschaftliche und humangeographische Fragestellungen und reflektiert die Nutzung von Twitter im Unterricht. Für die Unterrichtspraxis werden Beispiele zu den Themen Braunkohle, Flutereignisse und Raumwahrnehmungen sowie Anleitungen zur Auswertung, Anwendung und Reflexion von Twitter-Analysen vorgestellt. KW - Twitter KW - Soziale Medien KW - Forschungsmethodik KW - Unterrichtsmethoden Y1 - 2021 U6 - https://doi.org/10.1553/gw-unterricht164s72 SN - 2414-4169 SP - 72 EP - 85 PB - Verlag der Österreichischen Akademie der Wissenschaften CY - Wien ER -