Comparisons between marine productivity and terrestrial input records in the Gulf of California over the last 28 ka

We study the marine and terrestrial contributions in the Gulf of California (GC) to understand the relationship between continental climate and oceanographic variability over the last 28 ka. In Core AII125-8-JPC-20, we examine aeolian and riverine inputs as nutrients for biological productivity. We use biogenic silica (%opal), total organic carbon (%TOC) and calcium carbonate (%CaCO₃) as proxies for primary productivity, and lithic fraction distributions as proxies for terrigenous transport. At the core site, biogenic and lithic components are in phase at millennial-scale in response to regional climate conditions. During the Late Pleistocene, the GC shelf area was above sea level and the western margin showed transient episodes of increased fluvial inputs. Episodic increases in %opal and reduced %TOC suggest upwelling events but ineffective C-export to the sediment. During stadial events (Heinrich 2, Heinrich 1, Younger Dryas), regional declines in %opal, but increases in %CaCO₃ and TOC, suggest efficient C-export by carbonate organisms. During most of the Holocene, dust inputs are higher. Episodic increases in %TOC suggest higher C-accumulation, although this is not controlled by siliceous or calcareous organisms. In the GC, besides upwelling and current advection, nutrient inputs driven by terrestrial climate have an impact on the biological C-pump. © 2020 John Wiley & Sons, Ltd.     

Microscopic evidence of stishovite generated in low‐pressure shock experiments on porous sandstone: Constraints on its genesis

It has been almost exactly half a century since the first synthesis of stishovite in shock experiments on quartz was reported, but its formation conditions during shock is still under debate. Here, we present direct transmission electron microscopic observation of stishovite within material recovered from high‐explosive shock experiments on porous sandstone shocked at 7.5 and 12.5 GPa. Our observations allow for new conclusions on the genesis of stishovite in a close‐to‐nature environment. The formation of stishovite in short‐time shock experiments proves that its crystallization is ultrafast (<1 μs). Crystals were found only embedded in amorphous veins indicating homogeneous nucleation. Crystallization from melt rather than from glass can be concluded from the observation of roundish, defect‐free crystals up to 150 nm in diameter embedded in nondensified glass. The formation of stishovite at 7.5 GPa is in accordance with the phase diagram of silica, if rapid undercooling is present that becomes only possible by the existence of small hot spots in an otherwise cold material, which is supported by transient heat calculation. The absence of coesite at 7.5 GPa suggests kinetic hindrance of its crystallization from melt and, thus, smaller critical cooling rates compared to stishovite where critical cooling rates are estimated to be as large as 10¹¹ K s^?1. While the amorphous veins containing stishovite represent unambiguously hot spots, no associated pressure amplification could be verified within these veins. The rapid liquidus crystallization of stishovite only in hot spots generated in porous material is an alternative formation mechanism to the widely accepted theory of solid–solid transition from quartz to stishovite and might represent the more general mechanism occurring in nature for low shock pressure events.     

Structures along the Orobic thrust, Central Orobic Alps, Italy

A series of regional deformation phases is described for the metamorphic basement and the Permian cover in an area in the central Orobic Alps, northern Italy. In the basement deformation under low-grade amphibolite metamorphic conditions is followed by a second phase during retrograde greenschist conditions. These two phases predate the deposition of the Permian cover and are of probable Variscan age. An extensional basin formed on the eroded basement during the Late Carboniferous, filled with fan conglomerates and sandstones, and rhyolitic volcanic rocks. Well-preserved brittle extensional faults bound these basins. Further extension deformed basement and cover before the onset of Alpine compressional tectonics. Cover and basement were deformed together during two phases of compressional deformation of post-Triassic age, the first giving rise to tectonic inversion of the older extensional faults, the second to new thrust faults, both associated with south-directed nappe emplacement and regional folding. Foliations develop in the cover only during the first phase of deformation as part of the activity on “shortening faults”. Main activity on the Orobic thrust actually postdates the first phase of thrusting and foliation development in the cover.     

Comparison of Large-Eddy Simulation Data with Spatially Averaged Measurements Obtained by Acoustic Tomography – Presuppositions and First Results

An attempt is made to compare results oflarge-eddy simulation (LES) in a convective boundarylayer using the model PALM with experimental data obtained from acoustic travel time tomography.This method provides two-dimensional data arrays, which are considered as more suitable forLES-validation than classical local orline-integrated measurements, because the tomographic data are area- or volume-averaged.For a quantitative comparison with experimental data in general, some prerequisites have to be considered: First of all, the initial and boundary conditions of the LES model have to be provided correctly by the experiment. Considering measurement errors, a sensitivity study was performed to investigate the influence of inaccurate initial and boundary conditions on the simulation results.This showed that for determining some boundary conditions, such as the surface temperature and the roughness length, high measurement accuracies are necessary, which are difficult to reach or which at least require considerable extra measurement efforts.The initial and boundary conditions provided by the Lindenberg experiment in 1999 turned out to be of insufficient accuracy to allow quantitative comparisons.However, a qualitative comparison was performed instead to investigate if the acoustic tomography method is a proper method for comparisons with LES models in general.It showed a good qualitative agreement with some quantitative differences. These differences can partly be explained by the sensitivity of the LES to initial and boundary conditions and by the limitations of the acoustic tomography.     

Origins and accumulation of organic matter in expanded Albian to Santonian black shale sequences on the Demerara Rise, South American margin

Ocean Drilling Program Leg 207 recovered thick sequences of Albian to Santonian organic-carbon-rich claystones at five drill-sites on the Demerara Rise in the western equatorial Atlantic Ocean. Dark-colored, finely laminated, Cenomanian–Santonian black shale sequences contain between 2% and 15% organic carbon and encompass Oceanic Anoxic Events 2 and 3. High Rock-Eval hydrogen indices signify that the bulk of the organic matter in these sequences is marine in origin. However, δ¹³C_org values lie mostly between −30‰ and −27‰, and TOC/TN ratios range from 15 to 42, which both mimic the source signatures of modern C₃ land plants. The contradictions in organic matter source indicators provide important implications about the depositional conditions leading to the black shale accumulations. The low δ¹³C_org values, which are actually common in mid-Cretaceous marine organic matter, are consequences of the greenhouse climate prevailing at that time and an associated accelerated hydrologic cycle. The elevated C/N ratios, which are also typical of black shales, indicate depressed organic matter degradation associated with low-oxygen conditions in the water column that favored preservation of carbon-rich forms of marine organic matter over nitrogen-rich components. Underlying the laminated Cenomanian–Santonian sequences are homogeneous, dark-colored, lower to middle Albian siltstones that contain between 0.2% and 9% organic carbon. The organic matter in these rocks is mostly marine in origin, but it occasionally includes large proportions of land-derived material.     

Towards an accurate real-time locator of infrasonic sources

Infrasonic signals propagate from an atmospheric source via media with stochastic and fast space-varying conditions. Hence, their travel time, the amplitude at sensor recordings and even manifestation in the so-called “shadow zones” are random. Therefore, the traditional least-squares technique for locating infrasonic sources is often not effective, and the problem for the best solution must be formulated in probabilistic terms. Recently, a series of papers has been published about Bayesian Infrasonic Source Localization (BISL) method based on the computation of the posterior probability density function (PPDF) of the source location, as a convolution of a priori probability distribution function (APDF) of the propagation model parameters with likelihood function (LF) of observations. The present study is devoted to the further development of BISL for higher accuracy and stability of the source location results and decreasing of computational load. We critically analyse previous algorithms and propose several new ones. First of all, we describe the general PPDF formulation and demonstrate that this relatively slow algorithm might be among the most accurate algorithms, provided the adequate APDF and LF are used. Then, we suggest using summation instead of integration in a general PPDF calculation for increased robustness, but this leads us to the 3D space-time optimization problem. Two different forms of APDF approximation are considered and applied for the PPDF calculation in our study. One of them is previously suggested, but not yet properly used is the so-called “celerity-range histograms” (CRHs). Another is the outcome from previous findings of linear mean travel time for the four first infrasonic phases in the overlapping consecutive distance ranges. This stochastic model is extended here to the regional distance of 1000 km, and the APDF introduced is the probabilistic form of the junction between this travel time model and range-dependent probability distributions of the phase arrival time picks. To illustrate the improvements in both computation time and location accuracy achieved, we compare location results for the new algorithms, previously published BISL-type algorithms and the least-squares location technique. This comparison is provided via a case study of different typical spatial data distributions and statistical experiment using the database of 36 ground-truth explosions from the Utah Test and Training Range (UTTR) recorded during the US summer season at USArray transportable seismic stations when they were near the site between 2006 and 2008.     

Carbon stock assessment of mangrove ecosystems in Batticaloa Lagoon,Sri Lanka,with different degrees of human disturbances

This article presents a carbon stock assessment to illustrate the organic carbon distribution and storage within mangrove ecosystems in Sri Lanka. The living tree biomass and soil carbon pools were investigated in three sites with varying degree of human disturbance in Batticaloa Lagoon. Soil carbon content was derived by the Walkley Black method from soil samples and mangrove trees were measured for calculations in general allometric equations. The mangroves that were extremely converted into a shrimp farm in Kokkaddicholai recorded a carbon (C) stock of 100.9 kg m‐2. Dominated by the poisonous Excoecaria agallocha stands, the regenerating mangroves in Manmunai Bridge Island hosted the largest C stock measuring 786.4 kg C m‐2. The Kannankudah site—dominated by Avicennia marina, Lumnitzera racemosa and Excoecaria agallocha stands, recorded a C stock of 593.1 kg C m‐2. Cuts and stumps indicated wood harvesting for local livelihoods. The soil C content pool contributed most significantly to the total C stock, with the top 30 cm containing the largest C concentration in all soil profiles. The soil carbon content was highest (5.1 per cent) in Kannankudah, second highest (3.6 per cent) in the disturbed but regenerating forest at Manmunai Bridge Island, and the lowest (0.3 per cent) at the converted site of Kokkaddicholai.     

Meridional Motions and Reynolds Stress Determined by Using Kanzelhöhe Drawings and White Light Solar Images from 1964 to 2016

Sunspot position data obtained from Kanzelhöhe Observatory for Solar and Environmental Research (KSO) sunspot drawings and white light images in the period 1964 to 2016 were used to calculate the rotational and meridional velocities of the solar plasma. Velocities were calculated from daily shifts of sunspot groups and an iterative process of calculation of the differential rotation profiles was used to discard outliers. We found a differential rotation profile and meridional motions in agreement with previous studies using sunspots as tracers and conclude that the quality of the KSO data is appropriate for analysis of solar velocity patterns. By analyzing the correlation and covariance of meridional velocities and rotation rate residuals we found that the angular momentum is transported towards the solar equator. The magnitude and latitudinal dependence of the horizontal component of the Reynolds stress tensor calculated is sufficient to maintain the observed solar differential rotation profile. Therefore, our results confirm that the Reynolds stress is the dominant mechanism responsible for transport of angular momentum towards the solar equator.     

Advancing development projects through mega-events: the 2010 football World Cup and bus rapid transit in South Africa

In 2010, the focus of the sporting world was on South Africa, the first African country to host a Football World Cup, and the largest mega-event ever held on the continent. Mega-events like the World Cup have become instruments for governments seeking material improvements to highways and telecommunications as well as the more elusive nation-building and sanguine legacies. Whereas the literature typically concentrates on stadia and sports-related infrastructure, this paper focuses on bus rapid transit (BRT) as an “indirect legacy” to understand the way in which cities exploit the financial and political capital made available to advance projects long delayed behind more pressing endeavors. The compressed time horizons, unlocked financing and focused planning can be a “mixed blessing” however by limiting the scope of the project to the event. The paper concludes that in South Africa advancing development through the World Cup reinforced state authority and legitimacy.     

Thermal Properties of a Supraglacial Debris Layer with Respect to Lithology and Grain Size

This paper focuses on the impacts of debris cover on ice melt with regards to lithology and grain size. Ten test plots were established with different debris grain sizes and debris thicknesses consisting of different natural material. For each plot, values of thermal conductivity were determined. The observations revealed a clear dependence of the sub‐debris ice melt on the layer thickness, grain size, porosity and moisture content. For the sand fraction the moisture content played a dominant role. These test fields were water saturated most of the time, resulting in an increased thermal conductivity. Highly porous volcanic material protected the ice much more effectively from melting than similar layer thicknesses of the local mica schist. However, the analysis of thermal diffusivities demonstrated that the vertical moisture distribution of the debris cover must be taken into consideration, with the diffusivity values being significantly lower in deeper layers.