Magnetic minerals in sediments at the Cretaceous/Paleogene boundary (the Gams Section,Eastern Alps)

The paper presents results of detailed magnetomineralogical and microprobe studies of sediments at the Cretaceous/Paleogene (K/T) boundary in two epicontinental sections in the Eastern Alps (Austria), where deposits, including the K/T boundary, outcrop along the Gams River and its tributaries. K/T boundary layers in these sections are similar in the set of such magnetic minerals as iron hydroxides, ferrospinels, hemoilmenite, titanomagnetite, magnetite, hematite, and metallic iron. However, the boundary layer in the Gams-1 section is distinguished by the presence of metallic nickel and its alloy with iron and by the absence of iron sulfides, whereas nickel has not been discovered in the Gams-2 section, which, however, contains iron sulfides of the pyrite type. Therefore, these minerals occur locally. It is suggested that enrichment in iron hydroxides of a common origin can be regarded as a global phenomenon inherent in the K/T boundary and unrelated to an impact event.     

Turbulent measurements in the stable atmospheric boundary layer during SHEBA: ten years after

This paper surveys results of the comprehensive turbulent measurements in the stable boundary layer (SBL) made over the Arctic pack ice during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) in the Beaufort Gyre from October 1997 through September 1998. Turbulent fluxes and mean meteorological data were continuously measured and reported hourly at five levels on a 20-m main SHEBA tower. Eleven months of measurements during SHEBA cover a wide range of stability conditions, from the weakly unstable regime to very stable stratification, and allow studying the SBL in detail. A brief overview of the SBL regimes, the flux-profile relationships, the turbulent Prandtl number, and other parameters obtained during SHEBA is given. The traditional Monin—Obukhov approach, z-less scaling, and gradient-based scaling are evaluated and discussed based on the data from SHEBA.     

The Critical Richardson Number and Limits of Applicability of Local Similarity Theory in the Stable Boundary Layer

Measurements of atmospheric turbulence made over the Arctic pack ice during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) are used to determine the limits of applicability of Monin–Obukhov similarity theory (in the local scaling formulation) in the stable atmospheric boundary layer. Based on the spectral analysis of wind velocity and air temperature fluctuations, it is shown that, when both the gradient Richardson number, Ri, and the flux Richardson number, Rf, exceed a ‘critical value’ of about 0.20–0.25, the inertial subrange associated with the Richardson–Kolmogorov cascade dies out and vertical turbulent fluxes become small. Some small-scale turbulence survives even in this supercritical regime, but this is non-Kolmogorov turbulence, and it decays rapidly with further increasing stability. Similarity theory is based on the turbulent fluxes in the high-frequency part of the spectra that are associated with energy-containing/flux-carrying eddies. Spectral densities in this high-frequency band diminish as the Richardson–Kolmogorov energy cascade weakens; therefore, the applicability of local Monin–Obukhov similarity theory in stable conditions is limited by the inequalities Ri < Ri _cr and Rf < Rf _cr. However, it is found that Rf _cr  =  0.20–0.25 is a primary threshold for applicability. Applying this prerequisite shows that the data follow classical Monin–Obukhov local z-less predictions after the irrelevant cases (turbulence without the Richardson–Kolmogorov cascade) have been filtered out.     

Stable Boundary-Layer Scaling Regimes: The Sheba Data

Turbulent and mean meteorological data collected at five levels on a 20-m tower over the Arctic pack ice during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) are analyzed to examine different regimes of the stable boundary layer (SBL). Eleven months of measurements during SHEBA cover a wide range of stability conditions, from the weakly unstable regime to very stable stratification. Scaling arguments and our analysis show that the SBL can be classified into four major regimes: (i) surface-layer scaling regime (weakly stable case), (ii) transition regime, (iii) turbulent Ekman layer, and (iv) intermittently turbulent Ekman layer (supercritical stable regime). These four regimes may be considered as the basic states of the traditional SBL. Sometimes these regimes, especially the last two, can be markedly perturbed by gravity waves, detached elevated turbulence (‘upside down SBL’), and inertial oscillations. Traditional Monin–Obukhov similarity theory works well in the weakly stable regime. In the transition regime, Businger–Dyer formulations work if scaling variables are re-defined in terms of local fluxes, although stability function estimates expressed in these terms include more scatter compared to the surface-layer scaling. As stability increases, the near-surface turbulence is affected by the turning effects of the Coriolis force (the turbulent Ekman layer). In this regime, the surface layer, where the turbulence is continuous, may be very shallow (< 5 m). Turbulent transfer near the critical Richardson number is characterized by small but still significant heat flux and negligible stress. The supercritical stable regime, where the Richardson number exceeds a critical value, is associated with collapsed turbulence and the strong influence of the earth’s rotation even near the surface. In the limit of very strong stability, the stress is no longer a primary scaling parameter.     

Atmospheric Turbulence Measurements at a Coastal Zone with and without Fog

Boundary-Layer Meteorology - Measurements of atmospheric turbulence at a site in Ferryland (Newfoundland) during the C-FOG (Coastal-Fog) field campaign in September–October 2018 are used to...     

First finding of natural rhenium in the transitional clay layer at the Cretaceous-Paleogene boundary in the Gams section (Eastern Alps,Austria)

As a result of detailed studies by the method of microprobe analysis, a particle of natural rhenium was found for the first time in the transitional clay layer at the Cretaceous-Paleogene boundary in the Gams section (Eastern Alps). It is concluded that the formation of natural rhenium was related to a volcanic aerosol that arose due to the magmatic activity of a mantle plume 65 Myr ago.     

Cosmic dust and micrometeorites in the transitional clay layer at the Cretaceous-Paleogene boundary in the gams section (Eastern Alps): Morphology and chemical composition

Results of investigation of the cosmic matter in the transitional clay layer at the Cretaceous-Paleogene boundary in the Gams section, Eastern Alps, are presented. A great diversity of iron microspherules and particles of different morphologies, pure nickel spherules, awaruite (Fe₃Ni) particles, and diamond crystals are discovered. Iron microspherules are also met in the overlying Paleocene deposits, but their diversity there is not great. The discovered metallic microspherules and particles are described, their chemical compositions are presented, and their origin is discussed.     

The first finding of native platinum in Cretaceous-Paleogene boundary clay,the gams section,Eastern Alps,Austria

For the first time, native platinum was found by microprobe analysis in the course of detailed studies of a transitional clay bed in the Cretaceous-Paleogene boundary, the Gams section, Eastern Alps, Austria. The analysis revealed no impurities. The morphology of platinum grains and its occurrence on the surface of a rounded zircon grain point to platinum syndeposition. It is concluded that native platinum formation was related to the action of volcanic aerosol, resulting from mantle plume activity 65 Ma BP.