Benthic Phosphorus Dynamics in the Gulf of Finland, Baltic Sea

Benthic fluxes of soluble reactive phosphorus (SRP) and dissolved inorganic carbon (DIC) were measured in situ using autonomous landers in the Gulf of Finland in the Baltic Sea, on four expeditions between 2002 and 2005. These measurements together with model estimates of bottom water oxygen conditions were used to compute the magnitude of the yearly integrated benthic SRP flux (also called internal phosphorus load). The yearly integrated benthic SRP flux was found to be almost 10 times larger than the external (river and land sources) phosphorus load. The average SRP flux was 1.25?±?0.56?mmol?m^?2?d^?1 on anoxic bottoms, and ?0.01?±?0.08?mmol?m^?2?d^?1 on oxic bottoms. The bottom water oxygen conditions determined whether the SRP flux was in a high or low regime, and degradation of organic matter (as estimated from benthic DIC fluxes) correlated positively with SRP fluxes on anoxic bottoms. From this correlation, we estimated a potential increase in phosphorus flux of 0.69?±?0.26?mmol?m^?2?d^?1 from presently oxic bottoms, if they would turn anoxic. An almost full annual data set of in situ bottom water oxygen measurements showed high variability of oxygen concentration. Because of this, an estimate of the time which the sediments were exposed to oxygenated overlying bottom water was computed using a coupled thermohydrodynamic ocean?Csea and ecosystem model. Total phosphorus burial rates were calculated from vertical profiles of total phosphorus in sediment and sediment accumulation rates. Recycling and burial efficiencies for phosphorus of 97 and 3%, respectively, were estimated for anoxic accumulation bottoms from a benthic mass balance, which was based on the measured effluxes and burial rates.     

Seismicity in the far Arctic areas: Severnaya Zemlya and the Taimyr Peninsula

Journal of Seismology - A permanent seismic station was for the first time installed on Severnaya Zemlya in the Russian Arctic. This made it possible to record low-magnitude earthquakes occurring...     

A major change in magma sources in late Mesozoic active margin of the circum-Sea of Japan domain: Geochemical constraints from late Paleozoic to Paleogene mafic dykes in the Sergeevka belt,southern Primorye,Russia

More than 30 mafic dykes crop out in the Sergeevka belt in the coastal South Primorye, Far East Russia, of which geologic settings have been unclear for years. This study conducted major- and trace elements characterization, Sr–Nd isotope analyses, and Ar–Ar amphibole and U–Pb zircon datings for these rocks in order to identify their origin. The results demonstrated that all dykes are characterized by high Ba/Yb and low Nb/Y, Zr/Y, and Th/Yb ratios, which suggest their origin from arc melts derived from thin wedge mantle and shallow-dipping slab. These dykes are clearly separated into two distinct age/geochemistry suites; that is, the Paleogene and Early Cretaceous one with dolerites/basalts and adakitic rocks, and the Permian–Triassic one with high-Mg and high-Al gabbro-dolerite varieties. Their geochemistry suggests that the older suite was sourced from a primitive depleted MORB mantle (DMM)-type mantle, whereas the younger suite from an enriched mantle II (EM2)-type mantle domain. The transition in source type from DMM to EM2 occurred during the Jurassic-earliest Cretaceous time, probably by a strong influence of a mantle plume onto the long-continuing subduction-related magmatism. The plume influence reached the maximum when the unique meimechite-picrite complex formed in the region.     

Karstification below dam sites: a model of increasing leakage from reservoirs

Unnaturally steep hydraulic gradients below foundations or across abutments of dams may cause solutional widening of fractures in karstifiable rocks of carbonates or gypsum. This could cause increasing leakage which may endanger the performance of the construction. To investigate this problem recent models on natural karstification have been applied. We have performed numerical simulations of leakage below a model dam with a grouting curtain reaching down to 100 m below its impermeable foundation of 100 m width. Water is impounded to a depth of 100 m. The dam is located on a terrane of fractured rock dissected by two perpendicular sets of fractures with spacing of 5 m, and with a log-normal distribution of their initial aperture widths of about 0.02 cm. In the first state of karstification these fractures widen slowly, until a pathway of widened fractures below the grouting has reached the downstream side with exit widths of about 1 mm. This causes a dramatic increase of leakage, and turbulent flow sets in. After this breakthrough at time T, in the second state of karstification, dissolution rates become even along these fractures and cause widening of about 0.1 cm year^-1 for limestone, and at least of 1 cm year^-1 for gypsum. This leads to an increase in leakage to excessive rates within 25 years for limestone, but only 5 years for gypsum. We have performed a sensitivity analysis of breakthrough time T for the various parameters which determine the problem. The result shows breakthrough times in the order of several tens of years for both limestone and gypsum. We have also modelled leakage to caves or karst channels 200 m below the bottom of the reservoir, which could induce the formation of sinkholes. The model can be extended to more realistic settings. In conclusion, our results support the prediction that increasing leakage at dam sites can be caused by recent karstification which is activated after filling the reservoir, possibly leading to serious problems within its lifetime.     

Icebergs in the Southern Ocean and Factors Defining Their Distribution

Using the data of ~58 000 ship observations of Antarctic icebergs in 1947–2014, the map of average summertime concentration of icebergs (namely, of their number within a circle with the radius of 15 nautical miles) in the Southern Ocean was constructed. The main features of the iceberg distribution are revealed, and their possible reasons are investigated. It is shown that in the open ocean sea currents play a key role in the iceberg distribution. Wind effects are pronounced when ocean currents are weak or absent. According to the authors’ estimates, wind plays a decisive role only in the formation of one wide quasimeridional tongue of high iceberg concentration in the Weddell Sea. It is difficult to assess the impact of Antarctic glaciers’ productivity on the iceberg distribution, because currents, wind, and breaking and jamming of icebergs in shallow water areas cause their rapid redistribution. The clear physical explanation of the main features of iceberg concentration distribution on the constructed map indicates that it provides a rather real pattern.     

A compact form for the analytic description of temperature dependence of saturation vapor pressure over plane surfaces of water and ice

A possibility is studied of extending the range of action of the simple three-parameter formula (ITS-90 scale) proposed in the previous work of the author [2] for the dependence of saturation vapor pressure E on temperature T within the range of 250 to 490 K. The results demonstrated that the dependence ln[E(T)/E(T _bas)] = (T - T _bas)[A - B(T - T _bas) + C(T - T _bas)²]/T with four sets of coefficients A, B, and C obtained using one base temperature Tbas equal to the temperature of triple point of water T _t = 273.16 K and two additional base values T _bas2 = 473.16 K and T _bas3 = 623.16 K makes it possible to approximate rather accurately the initial experimental and computed data in the temperature range from the point of homogeneous freezing of 235 K to the critical temperature of 647 K for liquid water and from 193 K to T _t for ice. A procedure used for obtaining the inverse function T(E) by solving the third-degree algebraic equation is validated. A hypothesis is proposed for the physical substantiation of additional base points in the form of “a noticeable appearance of dimers at the point T _bas2 and their 100% concentration at the temperature T _bas3.”     

Nonlinear low frequency cut-off of the spectrum of the lower hybrid magnetospheric plasma turbulence

By solving the nonlinear equation of the magnetized plasma in the weak turbulence limit the level of the spectral energy density of the lower hybrid oscillations expanding in the plasma of the Earth's polar magnetosphere, is found. As an approximation the instability which initiates turbulence is considered in a plasma with two interpenetrating beams of nonrelativistic electrons with velocities along the geomagnetic field. The saturation of the instability is due to induced scattering of the oscillations by electrons and ions of the plasma.The spectral distribution of the lower hybrid turbulence has a maximum near the low frequency boundary.