Composition and Equation of State of the Lower Mantle from the p VT Data of Perovskite

For the earth's lower mantle, a long-standing issue is whether it has a composition similar to that of the upper mantle represented by Ringwood's py-rolite model. Although a homogeneous mantle issupported by geophysical studies, and also used as an apriori assumption to estimate the composition of the bulk silicate earth (BSE) or primitive mantle( PM), it is inconsistent with a number of geochemi-cal observations.     

Solution-precipitation creep and fluid flow in halite: a case study of Zechstein (Z1) rocksalt from Neuhof salt mine (Germany)

Zechstein (Z1) rocksalt from the Fulda basin, from the immediate vicinity of the Hessen potash bed is folded into tight to isoclinal folds which are cut by an undeformed, 1 cm thick, coarse-grained halite vein. Microstructures were investigated in etched, gamma-irradiated thin sections from both the wall rock and the vein. The lack of synsedimentary dissolution structures and the widespread occurrence of plate-shaped and hopper grains in the wall-rock suggests that the sedimentary environment was perennial lake. Deformation microstructures are in good agreement with solution-precipitation creep process, and salt flow under very low differential stress. Strength contrast between anhydrite-rich and anhydrite-poor layers caused the small scale folding in the halite beds. The vein is completely sealed and composed mainly of euhedral to subhedral halite grains, which often overgrow the wall-rock grains. Those microstructures, together with the presence of occasional fluid inclusion bands, suggest that the crystals grew into a solution-filled open space. Based on considerations on the maximum value of in-situ differential stress, the dilatancy criteria, the amount of released fluids from the potash bed during metamorphism and the volume change, it is proposed that the crack was generated by hydrofracturing of the rocksalt due to the presence of the salt-metamorphic fluid at near-lithostatic pressure.     

High-resolution isotope records of early Holocene rapid climate change from two coeval stalagmites of Katerloch Cave,Austria

Two coeval stalagmites from Katerloch Cave show pronounced intervals of low δ¹⁸O values around 8.2, 9.1, and 10.0 kyr (all ages are reported before the year 2000 AD) and represent an inorganic U–Th dated climate archive from the southeast of the European Alps, a region where only very few well-dated climate records exist. The O isotope curves, providing near-annual resolution, allow a direct comparison to the Greenland ice core records, as temperature was the primary factor controlling the O isotopic composition of Katerloch speleothems.The 8.2 kyr climate anomaly lasted about one century, from 8196 to 8100 yr, with a maximum amplitude of 1.1‰ at 8175 yr. The event is characterized by a rapid onset and a more gradual demise and U–Th data as well as annual lamina counting support a rapid climate change towards cooler conditions within 10–20 yr. There is no strong evidence that the 8.2 kyr anomaly was superimposed on a pronounced longer-term cooling episode, nor do the new data support two separate cooling events within the 8.2 kyr event as reported by other studies. Our record also shows a distinct climate anomaly around 9.1 kyr, which lasted 70–110 yr and showed a maximum amplitude of 1.0‰, i.e. it had a similar duration and amplitude as the (central) 8.2 kyr event. Compared to the 8.2 kyr event, the 9.1 kyr anomaly shows a more symmetrical structure, but onset and demise still occurred within a few decades only. The different progression of the 8.2 (asymmetrical) and 9.1 kyr anomaly (symmetrical) suggests a fundamental difference in the trigger and/or the response of the climate system. Moreover, both stalagmites show evidence of a climate anomaly around 10.0 kyr, which was of comparable magnitude to the two subsequent events.Using a well constrained modern calibration between air temperature and δ¹⁸O of precipitation for the study area and cave monitoring data (confirming speleothem deposition in Katerloch reflecting cave air temperature), a maximum cooling by ca 3 °C can be inferred at 8.2 and 9.1 kyr, which is similar to other estimates, e.g., from Lake Ammersee north of the Alps. The O isotopic composition of meteoric precipitation, however, is a complex tracer of the hydrological cycle and these temperature estimates do not take into account additional effects such as changes in the source area or synoptic shifts. Apart from that, the relative thickness of the seasonally controlled lamina types in the Katerloch stalagmites remains rather constant across the intervals comprising the isotopic anomalies, i.e. the stalagmite petrography argues against major shifts in seasonality during the early Holocene climate excursions.     

Iron deficiency in pyrrhotite of suevites from the Chesapeake Bay impact crater,USA—A consequence of shock metamorphism?

Abstract– Pyrrhotite from suevite of the 35 Ma Chesapeake Bay impact structure (CBIS) shows a shock metamorphism and we report on several mineralogical and magnetic features. Pyrrhotite shows strong brittle deformation with a high density of stacking faults, twinning parallel to the hexagonal (001) planes and average fault distances in the order of 10 nm. Although the determination of a superstructure was not possible due to the lattice defects, the reflections of the NiAs subcell, which is typical of all pyrrhotite modifications, were clearly detected. This phase is ferrimagnetic with a Curie temperature (T_C) between 350 and 365 °C, and suevite with this phase does not show the 34 K transition. The most peculiar feature is the low metal/sulfur ratio of 0.81, which indicates a distinctly higher vacancy concentration than for 4C pyrrhotite and a composition close to smythite (Fe₉S₁₁). This phase carries a stable natural remanent magnetization and is relatively hard magnetic. Steep inclinations of the natural remanent magnetization vector, however, suggest that this phase has been remagnetized by the drilling process. A possible explanation is the magnetic domain size of faultless areas of about 10 nm in diameter, which is at the lower limit of the single domain size near the threshold, below which superparamagnetic behavior occurs. The low thermal stability of this phase excludes postshock heating above 300 °C for the suevite of the CBIS. Our results imply that the iron‐deficient pyrrhotite is produced by shock metamorphism, although an iron loss due to shock has never been reported before for pyrrhotite.     

Spatial and temporal variability of precipitation in Serbia for the period 1961–2010

Monthly, seasonal and annual sums of precipitation in Serbia were analysed in this paper for the period 1961–2010. Latitude, longitude and altitude of 421 precipitation stations and terrain features in their close environment (slope and aspect of terrain within a radius of 10 km around the station) were used to develop a regression model on which spatial distribution of precipitation was calculated. The spatial distribution of annual, June (maximum values for almost all of the stations) and February (minimum values for almost all of the stations) precipitation is presented. Annual precipitation amounts ranged from 500 to 600 mm to over 1100 mm. June precipitation ranged from 60 to 140 mm and February precipitation from 30 to 100 mm. The validation results expressed as root mean square error (RMSE) for monthly sums ranged from 3.9 mm in October (7.5% of the average precipitation for this month) to 6.2 mm in April (10.4%). For seasonal sums, RMSE ranged from 10.4 mm during autumn (6.1% of the average precipitation for this season) to 20.5 mm during winter (13.4%). On the annual scale, RMSE was 68 mm (9.5% of the average amount of precipitation). We further analysed precipitation trends using Sen’s estimation, while the Mann-Kendall test was used for testing the statistical significance of the trends. For most parts of Serbia, the mean annual precipitation trends fell between −5 and +5 and +5 and +15 mm/decade. June precipitation trends were mainly between −8 and +8 mm/decade. February precipitation trends generally ranged from −3 to +3 mm/decade.

     

On the magnitude and apparent range of variation of the von Karman constant in the atmospheric surface layer

The half-century history of the experimental evaluation of the von Karman constant in the atmospheric surface layer is reviewed, an evidence indicating that this well-known scaling factor,k, is actually a weak variable that decreases with increasing Reynolds number is discussed. A combined average ofk=0.390 with a standard error of ±0.010 is found from two field studies, a result which indicates that there is only one chance in 40 that the true value of the scaling factor in the population from which the experimental sample was drawn could have been as large as the laboratory value of 0.40. Based on experimental and theoretical results given by others, it is suggested thatk varies from a maximum of 0.41 in light winds over open water and smooth land surfaces, to a minimum near 0.37 in stronger winds over forests and cities. This range is shown to imply that a working value ofk=0.39±1% is appropriate for flows over surfaces characterized by 0.7<z ₀<8.7 cm, a roughness subrange which corresponds to a wide variety of terrain types from sparsely vegetated level plains to mixed croplands with occasional hedges and trees.sponsored in part by the Global Change Post Doctoral Program, Office of Health and Environmental Research, U. S. Department of Energy.Work sponsored by the National Science Foundation under Grant No. ATM-9019682.     

Evaluation of Urban Local-Scale Aerodynamic Parameters: Implications for the Vertical Profile of Wind Speed and for Source Areas

Nine methods to determine local-scale aerodynamic roughness length \((z_{0})\) and zero-plane displacement \((z_{d})\) are compared at three sites (within 60 m of each other) in London, UK. Methods include three anemometric (single-level high frequency observations), six morphometric (surface geometry) and one reference-based approach (look-up tables). A footprint model is used with the morphometric methods in an iterative procedure. The results are insensitive to the initial \(z_{d}\) and \(z_{0}\) estimates. Across the three sites, \(z_{d}\) varies between 5 and 45 m depending upon the method used. Morphometric methods that incorporate roughness-element height variability agree better with anemometric methods, indicating \(z_{d}\) is consistently greater than the local mean building height. Depending upon method and wind direction, \(z_{0}\) varies between 0.1 and 5 m with morphometric \(z_{0}\) consistently being 2–3 m larger than the anemometric \(z_{0}\). No morphometric method consistently resembles the anemometric methods. Wind-speed profiles observed with Doppler lidar provide additional data with which to assess the methods. Locally determined roughness parameters are used to extrapolate wind-speed profiles to a height roughly 200 m above the canopy. Wind-speed profiles extrapolated based on morphometric methods that account for roughness-element height variability are most similar to observations. The extent of the modelled source area for measurements varies by up to a factor of three, depending upon the morphometric method used to determine \(z_{d}\) and \(z_{0}\).     

Sediment budgeting of short-term backfilling processes: The erosional collapse of a Carolingian canal construction

Sediment budgeting concepts serve as quantification tools to decipher the erosion and accumulation processes within a catchment and help to understand these relocation processes through time. While sediment budgets are widely used in geomorphological catchment-based studies, such quantification approaches are rarely applied in geoarchaeological studies. The case of Charlemagne's summit canal (also known as Fossa Carolina) and its erosional collapse provides an example for which we can use this geomorphological concept and understand the abandonment of the Carolingian construction site. The Fossa Carolina is one of the largest hydro-engineering projects in Medieval Europe. It is situated in Southern Franconia (48.9876°N, 10.9267°E; Bavaria, southern Germany) between the Altmühl and Swabian Rezat rivers. It should have bridged the Central European watershed and connected the Rhine–Main and Danube river systems. According to our dendrochronological analyses and historical sources, the excavation and construction of the Carolingian canal took place in AD 792 and 793. Contemporary written sources describe an intense backfill of excavated sediment in autumn AD 793. This short-term erosion event has been proposed as the principal reason for the collapse and abandonment of the hydro-engineering project. We use subsurface data (drillings, archaeological excavations, and direct-push sensing) and geospatial data (a LiDAR digital terrain model (DTM), a pre-modern DTM, and a 3D model of the Fossa Carolina] for the identification and sediment budgeting of the backfills. Dendrochronological findings and radiocarbon ages of macro remains within the backfills give clear evidence for the erosional collapse of the canal project during or directly after the construction period. Moreover, our quantification approach allows the detection of the major sedimentary collapse zone. The exceedance of the manpower tipping point may have caused the abandonment of the entire construction site. The spatial distribution of the dendrochronological results indicates a north–south direction of the early medieval construction progress. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

Physical laboratory analyses of intergravel flow through brown trout redds (Salmo trutta fario) in response to coarse sand infiltration

In the spawning environment of salmonids, the quality of the intergravel flow is an essential abiotic requirement for the survival success of incubated embryos. As one of the most frequently investigated anthropogenic environmental impacts, the enhanced mobilization of fine sediments (<1 mm) and their entry into riverine ecosystems is considered as a major cause for the degradation of a variety of biological processes and habitats, including the spawning habitats of salmonids. In catchments draining crystalline bedrock, however, like the Bohemian Massif in the northern part of Austria, the excessive loading of river channels with coarse sand and fine gravel sediments (D = 1–10 mm) and less cohesive than fines is common as a consequence of altered catchment land use. Here, far less understanding exists of the mechanism and the possible implications of coarse sand infiltration on the functioning of the intergravel flow in salmonid redds. To investigate the intergravel flow hydraulics in response to coarse sand infiltration (D₅₀ = 2 mm) in brown trout spawning redds (Salmo trutta fario ) under controlled conditions, a laboratory flume experiment with three infiltration scenarios was conducted: (1) no infiltration; (2) segmental infiltration; and (3) full section infiltration. A more than two times drop in the average intergravel flow velocity was documented from scenario 1 (5.85 cms^?1) to scenario 2 (2.53 cms^?1) and another clear reduction was seen from scenario 2 (2.53 cms^?1) to scenario 3 (1.61 cms^?1). Moreover, in scenario 3, a clear reduction of the intergravel flow distance traveled was observed. Based on the findings we conclude that future considerations regarding the sustainable catchment management of salmonid fisheries should include programs to reduce not only the excessive entry of fines, but, in the relevant catchments, also the entry of excessive coarse sand into the riverine ecosystem. Copyright © 2016 John Wiley & Sons, Ltd.