Hydrochemistry,origin and evolution of sedimentary subsurface fluids: I. Early diagenetic pore-water evolution in low-sedimentation rate offshore basins

Pore water studies enable (1) the detection of diagenetic reactions actively occurring in the sediment at the time of sampling,(2) the distinction between principal modes of solute transport, i.e., between advection (convection) and diffusion, and (3) the assessment of mineral-solution equilibria, Pore waters are, therefore, preferred diagnostic objects in the study of diagenesis, particularly early diagenesis. The single most important factor for pore-fluid evolution in modern offshore basins is sedimentation rate which is closely correlated with organtic matter content of the sediment. Organic matter represents the most reactive sediment constituent which, through bacterial decomposition, provides some of the main solutes involved in early diagenetic mineralization reactions. On the basis of sedimentation rate and organic matter content, it is convenient to distinguish two end-members of basins (environments) with respect to early diagenesis: I. Low to intermediate-sedimentation rate basins with convection or diffusion-controlled pore-water profiles and II. high-sedimentation rate basins with reaction-controlled pore-water profiles. The first group of basins or environments, which is the subject of this paper, is typically represented by pelagic sediments. Three principally different trends of pore-water evolution occur: 1. convection-controlled profiles with no pronounced vertical gradients for the dissolved species; 2. diffusion-controlled profiles with vertical gradients but linear correlations between major ions, especially Ca and Mg, and 3. profiles with gradients but no linear correlation between the major ions. The later are transitional to the trends seen in high-sedimentation rate basins. With respect to redox-potentials, the diagenetic environments of low-sedimentation rate basins are generally oxic to suboxic.     

Geodetic observations of ice flow velocities over the southern part of subglacial Lake Vostok, Antarctica, and their glaciological implications

In the austral summer seasons 2001/02 and 2002/03, Global Positioning System (GPS) data were collected in the vicinity of Vostok Station to determine ice flow velocities over Lake Vostok. Ten GPS sites are located within a radius of 30 km around Vostok Station on floating ice as well as on grounded ice to the east and to the west of the lake. Additionally, a local deformation network around the ice core drilling site 5G-1 was installed.
The derived ice flow velocity for Vostok Station is  2.00 m a⁻¹± 0.01 m a⁻¹  . Along the flowline of Vostok Station an extension rate of about 10⁻⁵ a⁻¹ (equivalent to 1 cm km⁻¹ a⁻¹) was determined. This significant velocity gradient results in a new estimate of 28 700 years for the transit time of an ice particle along the Vostok flowline from the bedrock ridge in the southwest of the lake to the eastern shoreline. With these lower velocities compared to earlier studies and, hence, larger transit times the basal accretion rate is estimated to be 4 mm a⁻¹ along a portion of the Vostok flowline. An assessment of the local accretion rate at Vostok Station using the observed geodetic quantities yields an accretion rate in the same order of magnitude. Furthermore, the comparison of our geodetic observations with results inferred from ice-penetrating radar data indicates that the ice flow may not have changed significantly for several thousand years.     

Warmer early instrumental measurements versus colder reconstructed temperatures: shooting at a moving target

Comparison of tree-ring-based warm-season temperature reconstructions and their instrumental target data reveals substantial divergence between (warmer) early instrumental measurements and (colder) proxy estimates. Here we detail this systematic misfit for the Northern Hemisphere before 1900 and the European Alps before 1850. Five hypotheses related to both proxy and target uncertainties are presented towards explaining this phenomenon. These include: (1) tree-ring detrending methods, (2) biological persistence in the proxy time-series, (3) uncertainties and instabilities in the growth response to given climatic parameters, (4) reduced instrumental station availability back in time, and (5) instrumental data homogeneity. We suggest that uncertainties in the choice of instrumental targets at the hemispheric scale, and instrumental data inhomogeneities at the Alpine and possibly also the hemispheric-scale are the most important factors in explaining this offset. Assessment of homogeneity at larger scales remains challenging. Attention is drawn to possible warm biases in early thermometer shelters and the relevance of proxy/target discrepancies for understanding and quantifying the amplitude of both recent anthropogenic and past natural forced climate fluctuations.     

Immune deficiency causes annual late summer brown trout (Salmo trutta) mortality in Austrian prealpine river systems

For several years, severe brown trout (Salmo trutta) mortality has been observed in different prealpine river systems of Austria, Southern Germany, and Switzerland during late summer and early autumn. Often, the skin of the effected fish shows a medium to intense black pigmentation, and therefore this phenomenon is called “Schwarze Bachforelle Phänomen” or “proliferative darkening syndrom”. The present study was conducted to gain insight about its presence. From middle of May to end of August, brown trout and rainbow trout were kept in experimental tanks supplied with water from an effected river system. In brown trout, samples for blood diagnostics and histological investigations were taken after 0, 47, 62, and 77 days, and in rainbow trout after 0 and 107 days. Brown trout from a wild population were investigated for comparative purposes. Brown trout showed no abnormalities till the end of June. All fish sampled in the second half of July suffered from severe immune deficiency as the numbers of peripheral blood granulocytes and lymphocytes, plasma lysozyme activity, and plasma immunoglobulin levels significantly decreased. During August, the number of erythrocytes decreased and the osmotic fragility of the erythrocytes increased. Senescent erythrocytes became more frequent and the hematopoietic tissue of spleen and kidney enlarged. Also, the cellular composition of the spleen changed as the number of hemoblasts and normal erythroblasts decreased while the number of atypical erythroblasts increased. In the pronephros and hematopoietic tissue of the mesonephros, aggregation of macrophages and tissue disintegration was frequently observed. This was similar for brown trout from the field experiment and from the wild population. High mortality occurred in the end of July and during August. Death of the fishes might have been caused by secondary infections with microorganisms. Almost similar changes were observed in rainbow trout, however, the mortality was lower.     

Depositional history of the Miocene Lake Sinj (Dinaride Lake System,Croatia): a long-lived hard-water lake in a pull-apart tectonic setting

Early Miocene transpressional wrenching yielded a series of NW–SE-elongated pull-apart basins in the Dinarides of Croatia and Bosnia and Herzegovina. They accommodated a huge lake system that gave rise to spectacular endemic mollusk radiation. Lake Sinj, moderately sized at 342 km², flooded the south-westernmost basin of this system. Due to the karstic environment, the hard-water, alkaline, long-lived lake developed a sediment infill with an average thickness of 370 m, dominated by authigenic limestone. The studied section represents the upper third of the basinal infill and provides detailed insights into the critical period of the lake and of the basinal evolution during the final stages of its filling. It comprises two large-scale, shallowing-upward cycles, both starting with fossil-poor limestones, gradually passing into coal-bearing carbonate rocks and coal seams. The fossil-poor intervals are interpreted as phases of repetitive acidification events due to changing lake level, which induced periodic drying and flooding of the uppermost littoral zone inhabited by starfruit (Damasonium) meadows. The flooding of the aerated, limy mud plain introduced H+ ions from organic-matter decay reactions into the shallow lake. This decreased its pH level, with catastrophic consequences for its biota. The ecosystem then stabilized during the orbitally-forced, dry climate phases. Based on the mollusk record, streams still influenced the marginal lake environment and rich organic-matter production created swamps and mires. The onset of mollusk radiation in the section correlates with stabilized lake alkalinity, as indicated by the disappearance of starfruits, ongoing authigenic carbonate production and by coal seams representing textbook examples for coal formation in alkaline environments. The inferred basinal setting fits well with the pull-apart basin model, pointing to the presence of an extended shallow ramp in front of a steep, fault-induced hillside of the hinterland.     

Tidal gravity variations revisited at Vostok Station, Antarctica

In 1969, prior to the discovery of the subglacial Lake Vostok, an Askania Gs-11 gravimeter was operated at Vostok Station (78.466°S, 106.832°E; 3478 m asl) to observe tidal gravity variations. To gain a better understanding of the lake's tidal dynamics, we reanalyzed these data using a Bayesian Tidal Analysis Program Grouping method (BAYTAP-G and -L programs). The obtained phase leads for the semidiurnal waves M2 (6.6 ± 2.1°) and S2 (10.1 ± 4.2°) are more pronounced than those of the diurnal waves, among which the largest phase lead (for K1) was 5.0 ± 0.5°. The obtained δ factor for M2 was 0.890 ± 0.032, significantly less than the theoretical value of 1.16. For three global ocean tide models (NAO99b, FES2004, and TPXO6.2), the estimated load tides on waves Q1, O1, P1, K1, M2, and S2 range from 0.1–0.2 μGal (Q1 and S2) to 0.6–0.7 μGal (K1). The difference in amplitude among the three models is less than 0.14 μGal (M2), and the difference in phase is generally less than 10°. In calculating the residual tide vectors using the ocean models, the TPXO6.2 model generally gave the smallest residual amplitudes. Our result for the K1 wave was anomalously large (1.36 ± 0.25 μGal), while that for the M2 wave was sufficiently small (0.37 ± 0.17 μGal). The associated uncertainty is half that reported in previous studies. It is interesting that the residual K1 tide is approximately 90° phase-leaded, while the M2 tide is approximately 180° phase-leaded (delayed). Importantly, a similar reanalysis of data collected at Asuka Station (71.5°S, 24.1°E) gave residual tides within 0.2–0.3 μGal for all major diurnal and semidiurnal waves, including the K1 wave. Therefore, the anomalous K1 residual tide observed at Vostok Station must be linked to the existence of the subglacial lake and the nature of solid–ice–water dynamics in the region.     

Determination of directions of horizontal principal stress and identification of active faults in Kachchh (India) by electromagnetic radiation (EMR)

The Kachchh basin in the western India is known for its recent high seismicity. This study presents an application of the geogenic Electromagnetic Radiation (EMR) technique for deciphering the directions of principal horizontal stress in the eastern Kachchh. The principal direction of horizontal stress obtained from EMR differs from those obtained from earthquake focal plane solutions. The major horizontal principal stress based on the EMR study shows an azimuth of N60°E ± 10°. The principal directions of EMR emissions are parallel to the acute bisector of conjugate microcracks. The azimuthal distribution of EMR signal and dimension of microcracks suggest that the EM emissions are transversely polarized.The study also deals with the first application of electromagnetic radiation emissions to identify active fracture planes in sandstones that could become potential active faults later, which might be seismogenic or nonseimogenic. This study is based on linear profiling at six different places across two major faults, the Kachchh Mainland Fault (KMF) and the South Wagad Fault (SWF) in the eastern Kachchh. Anomalously, high EMR emissions are observed in the eastern part of the KMF, indicating active surface deformation.     

Quantifying river incision into low‐relief surfaces using local and catchment‐wide 10Be denudation rates

Relief generation in non‐glaciated regions is largely controlled by river incision into bedrock but datable fluvial terraces that allow quantifying incision rates are not always present. Here we suggest a new method to determine river incision rates in regions where low‐relief surfaces are dissected by streams. The approach consists of three steps and requires the ¹⁰Be concentrations of a stream sediment sample and a regolith sample from the low‐relief surface. In the first step, the spatial distribution of ¹⁰Be surface concentrations in the given catchment is modelled by assuming that denudation rates are controlled by the local hillslope angles. The slope–denudation rate relation for this catchment is then quantified by adjusting the relation between slope angle and denudation rate until the average ¹⁰Be concentration in the model is equal to the one measured in the stream sediment sample. In the second step, curved swath profiles are used to measure hillslope angles adjacent to the main river channel. Third, the mean slope angle derived from these swath profiles and the slope–denudation relation are used to quantify the river incision rate (assuming that the incision rate equals the denudation rate on adjacent hillslopes). We apply our approach to two study areas in southern Tibet and central Europe (Black Forest). In both regions, local ¹⁰Be denudation rates on flat parts of the incised low‐relief surface are lower than catchment‐wide denudation rates. As the latter integrate across the entire landscape, river incision rates must exceed these spatially averaged denudation rates. Our approach yields river incision rates between ~15 and ~30 m/Ma for the Tibetan study area and incision rates of ~70 to ~100 m/Ma in the Black Forest. Taking the lowering of the low‐relief surfaces into account suggests that relief in the two study areas increases at rates of 10–20 and 40–70 m/Ma, respectively. Copyright © 2018 John Wiley & Sons, Ltd.     

Synthetic design hydrographs for ungauged catchments: a comparison of regionalization methods

Design flood estimates for a given return period are required in both gauged and ungauged catchments for hydraulic design and risk assessments. Contrary to classical design estimates, synthetic design hydrographs provide not only information on the peak magnitude of events but also on the corresponding hydrograph volumes together with the hydrograph shapes. In this study, we tested different regionalization approaches to transfer parameters of synthetic design hydrographs from gauged to ungauged catchments. These approaches include classical regionalization methods such as linear regression techniques, spatial methods, and methods based on the formation of homogeneous regions. In addition to these classical approaches, we tested nonlinear regression models not commonly used in hydrological regionalization studies, such as random forest, bagging, and boosting. We found that parameters related to the magnitude of the design event can be regionalized well using both linear and nonlinear regression techniques using catchment area, length of the main channel, maximum precipitation intensity, and relief energy as explanatory variables. The hydrograph shape, however, was found to be more difficult to regionalize due to its high variability within a catchment. Such variability might be better represented by looking at flood-type specific synthetic design hydrographs.