Beschreibung: The vertical distributions of early developmental stages of oceanic fishes were investigated across the tropical and equatorial Atlantic, from oligotrophic waters close to the Brazilian coast to more productive waters close to the Mauritanian Upwelling Region. Stratification of the water column was observed throughout the study region. Fishes were caught with a MOCNESS-1 net with mouth area of 1 m2 at 11 stations. Each station was sampled both during the day and at night within a single 24-h period. The investigation covered both larvae and transforming stages from the surface to 800 m depth. Distribution patterns were analysed, and weighted mean depths for the larvae and transforming stages of each species were calculated for day and night conditions. Forty-seven different species were found. The highest number of species occurred in the three stations south of Cape Verde Islands, characterized by a mixture of South Atlantic Central Water (SACW) and Eastern North Atlantic Central Water (ENACW). There was a marked drop in species richness in the three stations closer to the African upwelling, dominated by ENACW. The highest abundances occurred in the families Myctophidae, Sternoptychidae, Gonostomatidae and Phosichthyidae. Day and night vertical distributions of larvae and transforming stages showed contrasting patterns, both in the depths of the main concentration layers in the water column, and in the diel migration patterns (where these were observed). Larvae generally showed a preference for the upper mixed layer (ca. 0–50 m) and upper thermocline (ca. 50–100 m), except for sternoptychids, which were also abundant in the lower thermocline layer (100–200 m) and even extended into the mesopelagic zone (down to 500 m). Transforming stages showed a more widespread distribution, with main concentrations in the mesopelagic zone (200–800 m). Larvae showed peak concentrations in the more illuminated and zooplankton-rich upper mixed layers during the day and a wider distribution through the upper 100 m during the night. For most species, transforming stages were concentrated in the mesopelagic layers both day and night, although in some species (Diaphus cf. vanhoeffeni and Vinciguerria nimbaria), the transforming stages displayed vertical migration into the upper 100 m at night, in a manner similar to their adult stages.

Beschreibung: Highlights • Method and application to improve digital soil maps of silt and clay in China • Within the framework of a DSM approach we derived spatial uncertainties. • Spatial uncertainty is based on randomized decision trees. • Model calibration set is refined by purposive sampling in area of high uncertainty. • Method and map refinement is approved using accuracy and uncertainty measures. Digital soil mapping (DSM) products represent estimates of spatially distributed soil properties. These estimations comprise an element of uncertainty that is not evenly distributed over the area covered by DSM. If we quantify the uncertainty spatially explicit, this information can be used to improve the quality of DSM by optimizing the sampling design. This study follows a DSM approach using a Random Forest regression model, legacy soil samples, and terrain covariates to estimate topsoil silt and clay contents in a small catchment of 4.2 km2 in the Three Gorges Reservoir Area, Central China. We aim (i) to introduce a method to derive spatial uncertainty, and (ii) to improve the initial DSM approaches by additional sampling that is guided by the spatial uncertainty. The proposed uncertainty measure is based on multiple realizations of individual and randomized decision tree models. We used the spatial uncertainty of the initial DSM approaches to stratify the study area and thereby to identify potential sampling areas of high uncertainties. Further, we tested how precisely available legacy samples cover the variability of the covariates within each potential sampling area to define the final sampling area and to apply a purposive sampling design. For the final Random Forest model calibration, we combined the legacy sample set with the additional samples. This uncertainty-driven DSM refinement was evaluated by comparing it to a second approach. In this second approach, the additional samples were replaced by a random sample set of the same size, obtained from the entire study area. For the comparative analysis, external, bootstrap-, and cross-validation was applied. The DSM approach using the uncertainty-driven refinement performed best. The averaged spatial uncertainty was reduced by 31% for silt and by 27% for clay compared to the initial DSM approach. Using external validation, the accuracy increased by the same proportions, while showing an overall accuracy of R2 = 0.59 for silt and R2 = 0.56 for clay.

Beschreibung: Highlights • We modeled landslide susceptibility with statistical and machine learning techniques. • We evaluate performance, predictor importance, and visual appearance of susceptibility maps. • Differences in model prediction performance were for the majority non-significant. • Consequently, landslide modelers may consider selecting modeling techniques based on additional practical criteria. Statistical and now machine learning prediction methods have been gaining popularity in the field of landslide susceptibility modeling. Particularly, these data driven approaches show promise when tackling the challenge of mapping landslide prone areas for large regions, which may not have sufficient geotechnical data to conduct physically-based methods. Currently, there is no best method for empirical susceptibility modeling. Therefore, this study presents a comparison of traditional statistical and novel machine learning models applied for regional scale landslide susceptibility modeling. These methods were evaluated by spatial k-fold cross-validation estimation of the predictive performance, assessment of variable importance for gaining insights into model behavior and by the appearance of the prediction (i.e. susceptibility) map. The modeling techniques applied were logistic regression (GLM), generalized additive models (GAM), weights of evidence (WOE), the support vector machine (SVM), random forest classification (RF), and bootstrap aggregated classification trees (bundling) with penalized discriminant analysis (BPLDA). These modeling methods were tested for three areas in the province of Lower Austria, Austria. The areas are characterized by different geological and morphological settings. Random forest and bundling classification techniques had the overall best predictive performances. However, the performances of all modeling techniques were for the majority not significantly different from each other; depending on the areas of interest, the overall median estimated area under the receiver operating characteristic curve (AUROC) differences ranged from 2.9 to 8.9 percentage points. The overall median estimated true positive rate (TPR) measured at a 10% false positive rate (FPR) differences ranged from 11 to 15pp. The relative importance of each predictor was generally different between the modeling methods. However, slope angle, surface roughness and plan curvature were consistently highly ranked variables. The prediction methods that create splits in the predictors (RF, BPLDA and WOE) resulted in heterogeneous prediction maps full of spatial artifacts. In contrast, the GAM, GLM and SVM produced smooth prediction surfaces. Overall, it is suggested that the framework of this model evaluation approach can be applied to assist in selection of a suitable landslide susceptibility modeling technique.

Beschreibung: Large-scale spatial heterogeneity in fisheries production is predominantly controlled by the availability of zooplankton and benthic organisms, which have a complex relationship with primary production. To investigate how cross-ecosystem differences in these drivers determine fish assemblages and productivity, we constructed a spatially explicit mechanistic model of three fish functional types: forage, large pelagic, and demersal fishes. The model is based on allometric scaling principles, includes basic life cycle transitions, and has trophic interactions between the fishes and with their pelagic and benthic food resources. The model was applied to the global ocean, with plankton food web estimates and ocean conditions from a high-resolution earth system model. Further, a simple representation of fishing was included, and led to moderate matches with total, large pelagic, and demersal catches, including re-creation of observed variations in fish catch spanning two orders of magnitude. Our results highlight several ecologically meaningful model sensitivities. First, coexistence between forage and large pelagic fish in productive regions occurred when forage fish survival is promoted via both favorable metabolic allometry and enhanced predator avoidance in adult forage fish. Second, the prominence of demersal fish is highly sensitive to the efficiency of energy transfer to benthic invertebrates. Third, the latitudinal distribution of the total catch is modulated by the temperature dependence of metabolic rates, with increased sensitivity pushing fish biomass toward the poles. Fourth, forage fish biomass is suppressed by strong top-down controls on temperate and subpolar shelves, where mixed assemblages of large pelagic and demersal fishes exerted high predation rates. Last, spatial differences in the dominance of large pelagics vs. demersals is strongly related to the ratio of pelagic zooplankton production to benthic production. We discuss the potential linkages between model misfits and unresolved processes including movement, spawning phenology, seabird and marine mammal predators, and socioeconomically driven fishing pressure, which are identified as priorities for future model development. Ultimately, the model and analyses herein are intended as a baseline for a robust, mechanistic tool to understand, quantify, and predict global fish biomass and yield, now and in a future dominated by climate change and improved fishing technology.

Beschreibung: The properties, formation, and dissipation of the North Pacific Eastern Subtropical Mode Water (ESTMW), their interannual variability, and impact on spiciness anomalies in the upper permanent pycnocline were investigated using Argo profiling float data in 2005–2015. The core temperature and salinity of ESTMWs were horizontally compensated to a constant density, and core potential density concentrates in a range of 24.5–25.2 kg m−3 with two distinct peaks. ESTMWs showed different spatial distribution and persistence for its core potential density. Denser ESTMWs with a potential density of 24.9–25.2 kg m−3 were formed in winter mixed layer depth maximum centered at 30°N, 140°W and lighter ESTMWs of 24.5–24.9 kg m−3 were formed south and east of it. After formation through shoaling of the winter mixed layer, the former persisted until the following autumn and a small part of it subducted in winter, while the latter dissipated in summer. The formation region of ESTMW corresponded to the summer sea surface density maximum resulting from its poleward sea surface salinity front. Sea surface density maximum maintains weak stratification during summer, preconditioning the deepening of the winter mixed layer and hence the formation of ESTMWs. A relationship between the ESTMW formation region and the summer sea surface density maximum was also found in the North Atlantic and the South Pacific, implying the importance of sea surface salinity fronts and the associated summer sea surface density maximum to ESTMW formation. Interannual variations of ESTMW reflected that of the winter mixed layer in its formation region, and the thickness of ESTMW was related to the Pacific decadal oscillation. ESTMW contributed to the occurrence of spice injection and affected spiciness anomalies in the upper permanent pycnocline through its formation and dissipation.

Beschreibung: Highlights • The Southern Hemisphere mid-latitudes are characterised by obliquity and semi-precession cycles during the Mi-1 deglaciation • The obliquity variability is attributed to polar influence and the semi-precessional variability to tropical influence • Semi-precession cycles do not appear until 23.01 Ma, corresponding to the onset of Antarctic deglaciation • The interaction between polar and tropical influence is related to the position and strength of the westerly wind belt Abstract It is well-known from geologic archives that Pleistocene and Holocene climate is characterised by cyclical variation on a wide range of timescales, and that these cycles of variation interact in complex ways. However, it is rarely possible to reconstruct sub-precessional (〈 20 kyr) climate variations for periods predating the oldest ice-core records (c. 800 ka). Here we present an investigation of orbital to potentially sub-precessional cyclicity from an annually resolved lake sediment core dated to a 100-kyr period in the earliest Miocene (23.03–22.93 Ma) and spanning a period of major Antarctic deglaciation associated with the second half of the Mi-1 event. Principal component analysis (PCA) of sediment bulk density, magnetic susceptibility (MS), and CIELAB L* and b* with a resolution of ~10 years indicates two major environmental processes governing the physical properties records, which we interpret as changes in wind strength and changes in precipitation. Spectral analysis of the principal components indicates that both processes are strongly influenced by obliquity (41 kyr). We interpret this 41-kyr cycle in wind strength and precipitation as related to the changing position and strength of the Southern Hemisphere westerly winds. Precipitation is also influenced by an 11-kyr cycle. The 11-kyr periodicity is potentially related to orbital cyclicity, representing the equatorial semi-precessional maximum insolation cycle. This semi-precession cycle has been identified in a number of records from the Pleistocene and Holocene and has recently been suggested to indicate that insolation in low-latitude regions may be an important driver of millennial-scale climate response to orbital forcing (Feretti et al., 2015). This is the first time this cycle has been identified in a mid-latitude Southern Hemisphere climate archive, as well as the first identification in pre-Pleistocene records. The 11-kyr cycle appears at around 23.01 Ma, which coincides with the initiation of a major phase of Antarctic deglaciation, and strengthens during the subsequent period of rapid ice decay. This pattern suggests that the westerly winds may have expanded north of 50°S at the height of Mi-1, excluding tropical influence from the Foulden Maar site, and subsequently contracted polewards in tandem with warming deep-sea temperatures and Antarctic deglaciation, allowing the advection of tropical waters further south.

Beschreibung: Highlights • Numerical model of sill intrusions in sedimentary basins. • Fracture and vent formation due to overpressure generation. • Methane fluxes through a single vent with upscaling to basin scales. • Additional regions in the NAIP required to correlate methane venting and the PETM. Abstract Vent structures are intimately associated with sill intrusions in sedimentary basins globally and are thought to have been formed contemporaneously due to overpressure generated by gas generation during thermogenic breakdown of kerogen or boiling of water. Methane and other gases generated during this process may have driven catastrophic climate change in the geological past. In this study, we present a 2D FEM/FVM model that accounts for ‘explosive’ vent formation by fracturing of the host rock based on a case study in the Harstad Basin, offshore Norway. Overpressure generated by gas release during kerogen breakdown in the sill thermal aureole causes fracture formation. Fluid focusing and overpressure migration towards the sill tips results in vent formation after only few tens of years. The size of the vent depends on the region of overpressure accessed by the sill tip. Overpressure migration occurs in self-propagating waves before dissipating at the surface. The amount of methane generated in the system depends on TOC content and also on the type of kerogen present in the host rock. Generated methane moves with the fluids and vents at the surface through a single, large vent structure at the main sill tip matching first-order observations. Violent degassing takes place within the first couple of hundred years and occurs in bursts corresponding to the timing of overpressure waves. The amount of methane vented through a single vent is only a fraction (between 5 and 16%) of the methane generated at depth. Upscaling to the Vøring and Møre Basins, which are a part of the North Atlantic Igneous Province, and using realistic host rock carbon content and kerogen values results in a smaller amount of methane vented than previously estimated for the PETM. Our study, therefore, suggests that the negative carbon isotope excursion (CIE) observed in the fossil record could not have been caused by intrusions within the Vøring and Møre Basins alone and that a contribution from other regions in the NAIP is also required to drive catastrophic climate change.

Beschreibung: Highlights • Crustal structure of Walvis Ridge reveals high seismic velocities in the lower crust intruding the African continent. • This modified crust is localized to approx. 100 × 100 km within the continent. • No indication for a large plume head observed The opening of the South Atlantic is a classical example for a plume related continental breakup. Flood basalts are present on both conjugate margins as well as aseismic ridges connecting them with the current plume location at Tristan da Cunha. To determine the effect of the proposed plume head on the continental crust, we acquired wide-angle seismic data at the junction of the Walvis Ridge with the African continent and modelled the P-wave velocity structure in a forward approach. The profile extends 430. km along the ridge and continues onshore to a length of 720. km. Crustal velocities beneath the Walvis Ridge vary between 5.5. km/s and 7.0. km/s, a typical range for oceanic crust. The crustal thickness of 22. km, however, is approximately three times larger than of normal oceanic crust. The continent-ocean transition is characterized by 30. km thick crust with strong lateral velocity variations in the upper crust and a high-velocity lower crust (HVLC), where velocities reach up to 7.5. km/s. The HVLC is 100 to 130. km wider at the Walvis Ridge than it is farther south, and impinges onto the continental crust of the Kaoko fold belt. Such high seismic velocities indicate Mg-rich igneous material intruded into the continental crust during the initial rifting stage. However, the remaining continental crust seems unaffected by intrusions and the root of the 40. km-thick crust of the Kaoko belt is not thermally abraded. We conclude that the plume head did not modify the continental crust on a large scale, but caused rather local effects. Thus, it seems unlikely that a plume drove or initiated the breakup process. We further propose that the plume already existed underneath the continent prior to the breakup, and ponded melt erupted at emerging rift structures providing the magma for continental flood basalts.

Beschreibung: Highlights • Original 2D/3D seismic data present structural styles across the deformation front. • Dynamic process of the deformation front shifts as plate convergence moving westward. • Migration of submarine canyons is related to the incipient arc-continent collision. • Temporal changes in the stress regime leads to structural/sedimentary alterations. Abstract This study analyzes both 2D and 3D seismic images around the Palm Ridge area offshore of southwestern Taiwan to understand how the deformation front shifted westward and how tectonic activities interact with submarine canyon paths in the transition area between the active and passive margins. Palm Ridge is a submarine ridge that developed on the passive China continental margin by down-dip erosion of several tributaries of Penghu Canyon; it extends eastward across the deformation front into the submarine Taiwan accretionary wedge. The presence of proto-thrusts that are located west of the frontal thrust implies that the compressional stress field has advanced westward due to the convergence of the Philippine Sea Plate and Eurasian Plate. Since the deformation front is defined as the location of the most frontal contractional structure, no significant contractional structure should appear west of it. We thus suggest moving the location of the previously mapped deformation front farther west to where the westernmost proto-thrust lies. High-resolution seismic and bathymetric data reveal that the directions of the paleo-submarine canyons run transverse to the present slope dip, while the present submarine canyons head down slope in the study area. We propose that this might be the result of the westward migration of the deformation front that changed the paleo-bathymetry and thus the canyon path directions. The interactions of down-slope processes and active tectonics control the canyon paths in our study area.

Beschreibung: Highlights • We have tested a hypothesis where a sill intrusion is present at depth near Lusi. • We have calculated the CO2 generation following the emplacing a 150 m sill in an organic rich sequence at 4.5 km. • This scenario may provide the CO2 currently emitted from Lusi, and are consistent with geological information. Abstract The Lusi mud eruption started in 2006 and is located near the Arjuno-Welirang volcanic complex in Northeastern Java. Lusi is characterized by the eruption of aqueous vapor, CO2, and CH4 in addition to mud breccia and boiling water. However, the ultimate driving force for the eruption remains unclear. Here we investigate if Lusi could have been driven by the heat released from a deep-seated igneous sill originating from the neighboring volcanic arc. We have used a 1D thermal model to calculate the production of CO2 from thermally matured organic matter in the contact aureole of a hypothetical 150 m thick sill. The sill is tentatively emplaced at 1100 °C at 4.5 km depth within the organic-rich Eocene Ngimbang Formation. The carbon gas produced from the thermal perturbation reaches a peak of 1357 kg/m2/y CO2 equivalents shortly after sill emplacement, stressing the efficiency of organic matter transformation in contact aureoles. Our simulations show that during the first 1000 years after emplacement, 53.5 ton CO2/m2 is produced in the contact aureole. When scaled to a sill size of 150 m × 25 km2, i.e., a sill volume of 3.75 km3, the aureole has the potential to generate a total of 1350 Mt CO2 during the first 1000 years, with a peak generation of about 34 Mt CO2/y. We conclude that contact metamorphism in our hypothetical geological scenario generates CO2 in the gigaton range and represents a plausible source for the Lusi gas.