High-resolution modelling of a large-scale river plume

Evolution of a large-scale river plume is studied numerically using the Massachusetts Institute of Technology general circulation model. The model parameters were set close to those observed in the area of the Columbia River mouth. The fine-resolution grid along with the non-hydrostatic dispersion included in the model allowed for the reproduction of detailed inner plume structure, as well as a system of internal waves radiated from the plume’s boundary. It was found that not only first-mode but also second- and third-mode internal waves are radiated from the plume at the latest stages of its relaxation when the velocity of the front propagation drops below an appropriate wave phase speed of internal baroclinic mode. The model output shows that the amplitude of these high-mode waves is of the same order as the leading first-mode waves, which in combination with the specific vertical structure (location of the maximum structure function beyond the pycnocline layer) creates favourable conditions for the generation of shear instabilities. High-resolution model output also reveals evidence of a fine internal structure of the plume characterized by the presence of secondary fronts inside the plume and secondary internal wave systems propagated radially from the lift-off area to the outer boundary. These structures intensify the mixing processes within the propagating plume with predominance of the entrainment mechanism developing on the lower boundary between the plume’s body and underlying waters. The scheme of horizontal circulation in the plume was reproduced by the methodology of Lagrange drifters released near the mouth at different depths.

     

Palaeotemperature curve for the Late Cretaceous of the northwestern circum-Pacific

In the northwestern circum-Pacific, two main trends in Late Cretaceous temperatures can be recognized. (1) In general, a recurrent warming trend is thought to have begun in the Turonian–Campanian, reaching temperature maxima in the early Late Santonian and early Late Campanian, and temperature minima in the earliest Santonian and perhaps early Campanian. (2) During the Maastrichtian, temperatures dropped sharply, with only a slight warming in the early Late Maastrichtian. The existence of a thermal maximum at the Coniacian–Santonian transition has previously been expected, but is not confirmed by new isotopic results.     

Arsenic mobility in two mine tailings drainage systems and its removal from solution by natural geochemical barriers

Sulfide-mineral-bearing mill wastes are sources of high concentrations of acid, soluble metals, and As. These are serious problems for ore mining areas such as the Kemerovo and Cheljabinsk regions in Russia. This study evaluated the distribution of the mill wastes, the mobility of As from the wastes, and the potential of natural materials to attenuate As dispersion in the broader environment. Arsenic contents in wastes of the Belovo Zn-processing (Kemerovo) and the Karabash Cu-smelting plants (Cheljabinsk) are 2–3 orders of magnitude higher than the content of continental crust. Main mineral forms of As in these wastes are arsenopyrite (FeAsS) and scorodite (FeAsO₄·2H₂O). High dissolved As concentrations are found in water draining the wastes and in rivers adjacent to the mill sites. The water concentrations commonly exceed drinking water standards. High As concentrations in bottom sediments of the affected rivers extend a 100 m downstream of the waste drainage input. These sediments are also a source of river water contamination. Experiments were conducted to evaluate the ability of natural water to mobilize As from the wastes. The Belovo tailings released 86% of their contained As to the infiltrating water, whereas the less reactive Karabash tailings released only 22% of total As. The experimental leachates were used as influent to columns that tested the ability of limestone and natural clay to reduce the concentration of dissolved As and associated metals. Some dissolved As was precipitated with Fe, Pb and Sb initially in the limestone column. The decrease in dissolved As is consistent with the accumulation of As in yellow ferriferous sediments in the Belovo settling pond. In the pond and wetland sediments, As mobility is also decreased by the formation of sulfides and arsenides. Cubanite (CuFe₂S₃), klaprothite (Cu₃BiS₃)_, rammelsbergite (NiAs₂), maucherite (Ni₁₁As₈), semseyite (Cu₉Sb₈S₂₁), and skutterudite (CoAs₃) were found in the chemically reducing lower sediments of the Belovo settling pond.     

Foliar Applied Nickel on Buckwheat (Fagopyrum esculentum) Induced Phenolic Compounds as Potential Antioxidants

In this study, Fagopyrum esculentum (common buckwheat) sprayed with nickel (Ni) (0, 0.5, 1.0, 3.0, and 5.0 mM) for different duration has been investigated for Ni accumulation, malondialdehyde (MDA), total phenolics, and phenolic acids. Ni accumulation significantly increased in dose‐dependent manner. Plants exposed for 72 h, showed visible damages as chlorosis and irreversible necrosis. The MDA and total phenolic contents increased at 24 h of Ni treatments. HPLC data revealed that phenolic acids are in good correlation with concentration and durations of treatments. After 24 and 48 h the contents of chlorogenic, p‐hydroxybenzoic, hesperetic, p‐anisic, and caffeic acids increased in Ni treated leaves. On the other hand, p‐hydroxybenzoic, hesperetic, p‐anisic, p‐coumaric, caffeic acids contents decreased after 72 h of Ni exposure. Vanillic and cinnamic acid followed same pattern and increased significantly at 3.0 and 5.0 mM after 48 h of Ni exposure. It may suggest that buckwheat can be possible hyperaccumulators of Ni, because of high Ni accumulation in tissues through foliar treatment. Furthermore, the analyzed phenolic acids have potential role as antioxidants, which provide tolerance to buckwheat against Ni treatment.     

Chemical and phase heterogeneity of Ti-Fe-Mn-silica microspherules in crushed ore samples

A Fe-Ti-Mn-silicate microspherule from the heavy mineral fraction of crushed geological samples from an underground mine (Kellyam gold deposit, Yakutia) was examined by transmission electron microscopy. The 400-μm microspherule has a complex chemical composition and contains the following elements (in order of decreasing content): O, Ti, Si, Mn, Fe, Al, Mg, Ca, and K. The material of the micro-spherule shows a polyphase structure and chemical heterogeneity with separation into amorphous oxide-silicate (SiO₂) and crystalline metallic (α-Ti + FeTi) constituents. The spherical shape and the character of internal heterogeneity suggest that the microspherule was formed owing to the rapid solidification of a melt droplet. The nanoscale heterogeneity of the microspherule is a consequence of a two-stage process. (1) Liquid immiscibility in the initial melt droplet before its solidification resulted in the incomplete spatial separation of Si + Al and Ti + Fe + Mn and appearance of SiO₂ globules with admixtures of Al, Ca, K, Mg, Ti, Fe, and Mn approximately 100 nm in size. (2) Chemical heterogeneity developed subsequently both within the globules and within the matrix at the stage of melt solidification or after the solidification. The second-stage chemical heterogeneity was manifested in (a) the separation of heavy minor element oxides (Ti, Fe, and Mn) from the light elements Si, Al, K, Ca, and Mg(?) within the globules and (b) the separation of the matrix material into crystalline metallic (α-Ti + FeTi) and amorphous oxide-silicate [SiO₂-MgO-Mn₃O₄(?)-Fe₂O₃(?)-TiO₂(?)] parts. The obtained results do not rule out the possibility of formation of such microspherules during drilling operations.