ALBERT

Beschreibung: Lateglacial and Holocene faunal and stable-isotope records from benthic foraminifers in the eastern Mediterranean Sea (EMS) suggest a high spatiotemporal variability of deep-water oxygenation and biogeochemical processes at the sea floor during that time. Changes in the oxygenation and food availability of the deep-sea ecosystems are closely linked to the hydrology of the EMS borderlands; they reflect orbital and suborbital climate variations of the high northern latitudes and the African monsoon system. During the last glacial maximum, cool surface waters and high evaporation resulted in maximum convection and oxic deep-waters in all sub-basins. Strong wind-induced mixing fostered surface-water production with seasonal phytodetritus fluxes. During the glacial termination and the Holocene, oxygenation and food availability of deep-sea benthic ecosystems were characterized by a pronounced regional differentiation. Local deep-water formation and trophic conditions were particularly variable in the northern Aegean Sea as a response to changes in riverine runoff and Black Sea outflow. During the interval of sapropel S1 formation in the early Holocene, average oxygen levels decreased exponentially with increasing water depth, suggesting a basin-wide shallowing of vertical convection superimposed by local signals. In the northernmost Aegean Sea, deep-water ventilation persisted during the early period of S1 formation, owing to temperature-driven local convection and the absence of low-salinity Black Sea outflow. At the same time, severe temporary anoxia occurred in the eastern Levantine basin at water depths as shallow as 900 m. This area was likely influenced by enhanced nutrient input of the Nile river that resulted in high organic matter fluxes and related high oxygen-consumption rates in the water column. In the southern Aegean and Levantine Seas, we observe a gradual increase in deep-water residence times, preceding S1 formation by approximately 1–1.5 kyr. Once oxygen levels fell below a critical threshold, the benthic ecosystems collapsed almost synchronously with the onset of S1 deposition. The recovery of benthic ecosystems during the terminal phase of S1 formation is controlled by subsequently deeper convection and re-ventilation over a period of approximately 1500 years. After the re-ventilation of the various sub-basins had been completed during the middle and late Holocene, deep-water renewal was more or less similar to recent rates. During that time, deep-sea ecosystem variability was driven by short-term changes in food quantity and quality as well as in seasonality, all of which are linked to millennial-scale changes in riverine runoff and associated nutrient input.

Beschreibung: We present a new interface between the geochemical simulator PHREEQC and the open source language R. It represents a tool to flexibly and efficiently program and automate every aspect of geochemical modelling. The interface helps particularly to setup and run large numbers of simulations and visualise the results. Also profiting of numberless high-quality R extension packages, performing sensitivity analysis or Monte Carlo simulations becomes straightforward. Further, an algorithm to speedup reactive transport simulations starting from homogeneous or zone- homogeneous state is programmed and successfully evaluated through the interface. It proved effective and could therefore be included in any reactive transport simulator.

Beschreibung: Rare earth element distribution of mineral, geothermal and surface waters are discussed. The causes of the evidently natural Ce, Eu, and Y anomalies as well as the anthropogenic Gd anomaly are described. For crustal waters it is suggested to apply the REE/Ca abundance ratios rather than the REE abundances because of the less scatter of patterns achieved. The rock-normalised patterns show rock-specific signatures of the waters. The Gd anomaly can be applied as a conservative tracer in hydrological studies.

Beschreibung: We studied 40 artesian wells (AWs) in the Amu Darya Delta. These wells include high-salinity (∼ 52 g/l) and saline (5 – 24 g/l) waters but are mostly low-salinity waters (1.3 – 2.9 g/l). The low-salinity AWs cluster into three types, reflecting the variable mixing of different end-member solutes: (residual) brines and solutes deriving from silicate alteration, dissolution of limestone and dissolution of gypsum. The solutes are all undersaturated in calcite and gypsum, contain a substantial cation excess against dissolved inorganic carbon and are characterised by low Ca/SO4 ratios. On the basis of the hydrochemical mass budgets of model cases, we demonstrate that Na-rich Cl-brines (45-48%) and a Na2SO4-brine (30-47%) are the dominant solute components. The solutes derived from aluminium silicate alteration are minor components (7.3 – 19.4%). Even less important are solutes from limestone or gypsum dissolution (0.05 – 3.7%). These waters are unlikely to have originated from sediments hosting gypsum. The low-salinity AWs must have acquired their dominant hydrochemical signatures under non-equilibrium conditions between their remote (unknown) seepage areas and their discharge locations. This acquisition may have begun during the early hydrochemical groundwater evolution when meteoric or surface water passed the critical zone under an arid climate regime. Warmer saline AWs (∼40°C) hosted in deeper Cretaceous formations contain a high portion of NaCl-rich brine (85%) and some are saturated in gypsum. These waters were derived from fluids rising along faults from pre-Cretaceous strata. The high-salinity and relatively cold AWs discharge close to the retreating Aral Sea south of its western basin. These AWs are suboxic, and Si concentrations are very low. The AW hydrochemical signatures reflect the dissolution of halite and gypsum. We observed positive correlations between temperature, Br, B and Si. The temperature correlation with bromide likely documents the transformation of organically bound Br. The silica concentrations in low-salinity AWs southeast of the Aral Sea (eastern basin) are close to quartz saturation and define a chemical Si-geothermometer.

Beschreibung: The use of stable isotopes as climate proxies is widely accepted for climate reconstruction. Re-establishing climate signals, e.g. temperature, from isotope values of biological materials requires some knowledge of the system’s response behaviour. The related problems are discussed in conjunction with stable isotopes of two different terrestrial archives: carbon isotope data of tree rings from southern Germany and oxygen isotope data of diatoms from Lake Holzmaar, Germany. Carbon isotope temperature coefficients (Δδ13C/ΔT) derived from tree rings were chosen as an example for non-linear transformation of environmental signals through biological systems explaining negative and positive temperature coefficients. Thin radial tree ring sections taken from tree rings of different species (poplar, beech and oak) show carbon isotope variations of up to 3‰ with a characteristic, annually recurring isotope pattern. This behaviour is discussed in view of time resolution, isotope signature conservation and the question of storage and remobilisation of photosynthates with time. For Lake Holzmaar it is shown that isotope proxy signals derived from diatoms may not be unambiguously translated into abiotic environmental forcing factors, such as for example temperature. Corresponding measurements reveal that the isotopic input signal varies considerably and nonlinearly with temperature.

Beschreibung: We applied scaled physical analogue experiments to investigate the early development of salt diapirs induced by differential sedimentary loading in an intra-continental basin realm (e.g. the North German Basin). During the experiments, deformation in a salt-analogue viscous layer was initiated by variations in the thickness of an overlying brittle material and subsequent accumulation of the brittle material further sustained deformation. A 2D optical image correlation system was used to monitor the strain evolution in the salt analogue material. Our models indicate that the formation of salt pillow structures can be achieved by minimum variations in the overburden loading. The increase of differential loading by adding synkinematic layers in the subsided areas causes not only an active piercing of the viscous layer through the brittle overburden but also an additional uplift in the adjacent areas. These elevations, named “secondary structures”, act as origins for a successive generation of diapirs. Consequently, an initial perturbation of the salt–sediment-interface can lead to a lateral propagation temporally shifted diapirs. The linkage between primary and secondary structures is reflected in the synkinematic overburden layers such as overlapping peripheral sinks in the transition zone between two diapirs. These sinks, in turn, are a frequently observable phenomenon around salt structures of the North German basin indicating that “secondary diapirism” is an underestimated process – besides regional tectonic stresses – influencing the evolution of salt structures.

Beschreibung: Calibration is a fundamental stage of the radiocarbon (14C) dating process if one is to derive meaningful calendar ages from samples’ 14C measurements. For the first time, the IntCal09 calibration curve (Reimer et al. 2009) provided an internationally ratified calibration data set across almost the complete range (0 to 50,000 cal BP) of the 14C timescale. However, only the last 12,550 cal yr of this record are composed of terrestrial data, leaving approximately three quarters of the 14C timescale necessarily calibrated via less secure, marine records (incorporating assumptions pertaining to the temporally variable “marine reservoir effect”). The predominantly annually laminated (varved) sediment profile of Lake Suigetsu, central Japan, offers an ideal opportunity to derive an extended terrestrial record of atmospheric 14C across the entire range of the method, through pairing of 14C measurements of terrestrial plant macrofossil samples (extracted from the sediment) with the independent chronology provided through counting of its annual laminations. This paper presents new data (182 14C determinations) from the upper (largely non-varved) 15 m of the Lake Suigetsu (SG06) sediment strata. These measurements provide evidence of excellent coherence between the Suigetsu 14C data and the IntCal09 calibration curve across the last ~12,000 cal yr (i.e. the portion of IntCal based entirely on terrestrial data). Such agreement demonstrates that terrestrial plant material picked from the Lake Suigetsu sediment provides a reliable archive of atmospheric 14C, and therefore supports the site as being capable of providing a high-resolution extension to the “wholly terrestrial” (i.e. non-reservoir-corrected) calibration curve beyond its present 12,550 cal BP limit.

Beschreibung: Scaled analogue experiments are used to investigate the indentation of two basement blocks into a sedimentary basin and the formation of a fold-and-thrust belt. The experimental set-up has two adjacent indenters moving in parallel with a velocity difference. The slow indenter moves with a relative velocity ranging from 40 to 80% of that of the fast one. In a first experimental series, quartz sand and low-friction glass beads represent the sediment stack and its basal detachment, respectively; silicone oil simulates a viscous detachment in the second series of experiments. The surface evolution and the spatio-temporal strain distribution are derived from particle image velocimetry (PIV). Together with the 3D finite structure derived by cutting the models at the end of each experiment, this allows the analysis of the structural evolution of the experimental wedges. Thrusting wedge development depends crucially on the relative velocity: when the slow indenter moves with a velocity of more than 55% of the fast indenter, a single curved thrust wedge develops. The wedge becomes decoupled along strike-slip zone at large velocity differences, i.e. when the slow indenter moves slower than 55% of the faster indenter. Consequently the thrust front is strongly curved at high (55–60%) and smoothly curved at low velocity differences (70–80%); in all cases curvature increases during indentation. Along the most strongly curved portion of the thrust wedge, the transfer zone rises, particle rotation and material transport oblique to the indentation direction occur directed toward the front of the slow indenter. Thrusting cycles are timed by the fast indenter and influence thrusting in front of the slow indenter. Thrusts nucleate in front of the fast indenter wedge and propagate laterally to the slow indenter front. This implies distant effects of wedge growth active hundreds of kilometres along-strike of orogens. Silicone oil as a detachment induces a low-angle wedge, which is less curved than in the glass beads experiments, and shows variable thrust vergence with fore- and back-thrusts. We compare our experimental results with the curved fold-and-thrust belts of the Tajik basin in front of the Hindu-Kush and Pamir indenters; our results are able to explain several first-order features.

Beschreibung: Comparing the organic matter (OM) composition of modern and past lake sediments contributes to the understanding of changes in lacustrine environments over time. We investigate modern plant and lake-water samples as well as modern and ancient sediment samples from the Tswaing Crater in South Africa using biomarker and stable carbon isotope analyses on bulk OM and specific biomarker compounds. The characteristic molecular markers for higher land plants (predominantly C3-type deciduous angiosperms) in Lake Tswaing are long-chain n-alkanes (n-C27−33), n-alkanols (n-C28+30), stigmasterol, β-sitosterol, β-amyrin, α-amyrin and lupeol. The C17 n-alkane, tetrahymanol, gammaceran-3-one and C29 sterols dominate the lipid fraction of autochthonously produced OM. By comparing stable carbon isotope analyses on bulk OM and the characteristic biomarkers, we follow the modern carbon cycle in the crater environment and find indications for methanotrophic activity in the lake from isotopically depleted moretene. A comparative study of core sediments reveals changes in the terrestrial (C3 versus C4) and aquatic bioproductivity and allows insights into the variability of the carbon cycle under the influence of changing climatic conditions for the time from the end of the last glacial (Termination I) to the late Holocene, ca. 14,000–2,000 calibrated years before present (years BP). The most pronounced changes occur in the aquatic realm after ca. 10,000 years BP when our results imply climate swings from more humid to more arid and after 7,500 years BP to gradually more humid conditions again, which can be related to a shift in the position of the Inter-Tropical Convergence Zone or to changes in the tropical atmosphere–ocean interaction. Long-chain alkenones (LCAs) have been identified in ancient lake sediments from Africa for the first time. They occur in samples older than 7,500 years BP and their distribution (dominance of C38 and of tri- over tetra-unsaturated LCAs) is distinctly different from other published records suggesting a to date unknown source organism.

Beschreibung: We study opportunities for CO2 sequestration in geological formations of the state North Rhine Westphalia in Germany. Simulations are performed for evaluating a potential site within the Bunter sandstone formation near the town of Minden in a depth of around 3,000 m using the numerical simulator TOUGHREACT. Our focus is on three CO2 storage mechanisms: (1) hydrodynamic trapping, (2) dissolution trapping, and (3) mineral trapping. The results show that due to buoyancy the injected CO2 phase initially migrates towards the top of the reservoir and is hydrodynamically trapped beneath the confining layer of the cap rock. Then, the CO2 spreads laterally and dissolves partially in the formation water. The dissolution of CO2 results in an increase of the density of the brine causing a downward migration until it settles after 10,000 years at the bottom of the reservoir. The simulations indicate that after 10,000 years, 15% (17 Mt) from a total of 114 Mt injected CO2 are trapped hydrodynamically, 20% (23 Mt) are trapped by dissolution, and 65% (74 Mt) are fixed in newly formed carbonates such as dawsonite, ankerite, and siderite. Within our study pressure increases near the injection well by a factor of 1.1 which is lower than the upper limit usually accepted in gas storage operations. The mineral reactions cause a net decrease of porosity and in turn a decrease of permeability down to 9% of the initial value in parts of the reservoir.

Beschreibung: Receiver functions are widely employed to detect P-to-S converted waves and are especially useful to image seismic discontinuities in the crust. In this study we used the P receiver function technique to investigate the velocity structure of the crust beneath the Northwest Zagros and Central Iran and map out the lateral variation of the Moho boundary within this area. Our dataset includes teleseismic data (Mb ≥ 5.5, epicentral distance from 30◦ to 95◦) recorded at 12 three component short-period stations of Kermanshah, Isfahan and Yazd telemetry seismic networks. Our results obtained from P receiver functions indicate clear Ps conversions at theMoho boundary. The Moho depths were firstly estimated from the delay time of the Moho converted phase relative to the direct P wave beneath each network. Then, we used the P receiver function inversion to find the properties of the Moho discontinuity such as depth and velocity contrast. Our results obtained from PRF are in good agreement with those obtained from the P receiver function modeling. We found an average Moho depth of about 42 km beneath the Northwest Zagros increasing toward the Sanandaj-Sirjan Metamorphic Zone and reaches 51 km, where two crusts (Zagros and Central Iran) are assumed to be superposed. The Moho depth decreases toward the Urmieh-Dokhtar Cenozoic volcanic belt and reaches 43 km beneath this area. We found a relatively flat Moho beneath the Central Iran where, the average crustal thickness is about 42 km. Our P receiver function modeling revealed a shear wave velocity of 3.6 km/s in the crust of Northwest Zagros and Central Iran increasing to 4.5 km/s beneath the Moho boundary. The average shear wave velocity in the crust of UDMA as SSZ is 3.6 km/s, which reaches to 4.0 km/s while in SSZ increases to 4.3 km/s beneath the Moho.