Some features of seasonal variations in the methane content in the atmosphere over northern Eurasia

The climatic trends and basic features of seasonal variations in and anomalies of the concentration of methane in the atmospheric surface layer are considered on the basis of the current notion of the processes that form the global field of methane in the Earth’s atmosphere. Measurement data on the surface concentration of methane, which were obtained in Moscow and at a number of observation stations in Europe and Siberia in the fall-winter period of the first decade of the 21st century, have been analyzed. It is shown that, in the anomalously warm winter months of 2006/2007, the concentration of methane in the atmosphere over Moscow was higher than in the previous and following years. The excess concentration of methane amounted to 10% in March 2007, which is higher than the mean range of seasonal variations in the monthly mean concentration of surface methane. A comparison between the data obtained in Moscow and the data obtained at three stations of the NOAA global monitoring network and at three Russian Hydrometeorological Research Center stations shows the high spatial variability of the methane concentration in the atmosphere over northern Eurasia. The complex and multifactor processes that determine the content of methane in the atmospheric surface layer result in noticeable spatial and interannual deviations from the mean seasonal cycle of its concentration, which can manifest themselves on both regional and global scales. It is possible that the resumed increase in the content of methane in the Earth’s atmosphere recorded in 2007 (after its relative stabilization in the early 2000s) at the global monitoring network was also caused, to some extent, by the anomalously warm winter of 2006–2007 in northern Europe and western Siberia.     

Comparative analysis of oceanic corrections to gravity calculated from the PREM and IASP91 models

The effect of oceanic loading Δg in the vertical component of gravity is assessed in two different models of the Earth, namely, the PREM model and the European model IASP91. For this purpose, we considered the Molodensky boundary problem which describes the deformations of the gravitating elastic compressible sphere. We derived the equation that links the boundary conditions on the surface and at the bottom of the mantle, and calculated the load Love numbers for the studied models. By the example of the territory of Western Europe, it is shown that the value of the correction, Δg, noticeably depends on the applied seismic models of the upper mantle and the lithosphere.     

On determination of low oxygen concentrations with Winkler technique

The accuracy and detection limit of the oxygen technique is an actual problem in studying the processes that occur in the redox zone. The formal accuracy of the Winkler technique is 1 μM (0.02 mL L⁻¹) and its detection limit is about 3.0 μM (0.06 mL L⁻¹). These values are significantly higher than the similar characteristics (in molar concentrations) for such parameters as the hydrogen sulphide, nitrates, manganese, and others. In this work, we describe some recommendations for increasing the accuracy of the Winkler technique. The results of the application of these recommendations for the suboxic zone of the Black Sea are presented. During the 100th cruise of the R/V Professor Shtokman, argon-filled balloons were attached to the upper valves of Niskin bottles during the sampling, which allowed protecting the samples from contamination with atmospheric oxygen. The titration was performed with an automatic Metrohm Titrino burette with potentiometric end point detection. That allowed us to significantly increase the accuracy and decrease the detection limit compared with the visual techniques. The oxidized forms of metals present in the sea water (Mn(IV), Mn(III); Fe(III)) were measured, which allowed us to correct the Winkler technique calculations for the oxidizers. The studies performed during the 100th cruise of the R/V Professor Shtokman confirmed the absence of a layer of the coexistence of oxygen and hydrogen sulphide.     

Comparison of the model oceanic gravimetrical effect with the observations

The model calculations of the oceanic gravimetrical effect are compared with some recent observations. The theoretical estimates of the amplitudes and phases calculated by the ATLANTIDA3.0 program, which was developed by the authors, quite well agree with the empirical data obtained in different regions of the world. In particular, it is established that in almost 80% cases our model provides a better fit of the observations than the results calculated by the LOAD89 program of the ETERNA3.3 package developed by Wenzel.     

Impacts of frontal stability and topography on cross-shelf exchange in the Northern Gulf of Mexico

The shelfbreak wintertime thermal front in the Northeastern Gulf of Mexico often exhibits meandering, eddy formation and warm-water intrusion. A high level of frontal variability plays an essential role in exchange processes across the shelf. This study examines the impacts of local frontal instability and bottom topography on turbulent heat exchange across the front using the results of two numerical models. Analysis of a series of numerical experiments reveals that the flow is baroclinically unstable. Predicted frontal instability contributes significantly to cross-frontal exchange and accounts for about 35% of the total eddy heat flux. Onshore eddy heat flux has the highest intensity at the frontal position. In addition, eddy activity and heat flux are sensitive to variation of bottom topography. For topographic features and frontal characteristics that are typical of the area, bottom steepness enhances the flux and is nearly proportional to the cross-frontal heat exchange. The study attempts to explain physical mechanisms that drive frontal circulation in the area and to quantify heat transport across the shelf. Estimated heat fluxes can provide important information for climate and ecosystem modeling of the Mississippi Bight.     

On the transformation of the chemical composition of the Volga River discharge waters at the Caspian shallows

The Volga River discharge consists of the waters transferred by fast currents through channels and the waters which are passing through the shallow areas of the delta overgrown by cane. Using the hydrochemical data, it is possible to track distribution of the waters modified by “biofilters” of macrophytes in the delta shallows starting from the external edge of the delta. The main distinctive features of these waters are the high content of dissolved oxygen, the abnormally high values of the pH, and the low content of dissolved inorganic carbon (both total and as CO₂). These waters extend in the shape of 1 to 3-km-wide strips at a distance of 20–40 km from the outer border of the delta. The analysis of the data obtained during the expeditions run by the Institute of Oceanology of the Russian Academy of Sciences in 2003–2009, along with archived and published data, show that such “modified” waters occur almost constantly along the outer edge of the Volga River delta.     

Anticyclogenesis of surface pressure field in winter season,blocking, and variability of the Earth angular velocity

Analyzed are the anomalies of monthly mean values of surface pressure over Eurasia in winter seasons of 1901–2010. It is noted that the centers of large monthly positive pressure anomalies (16–24 hPa) are usually located within the 60°–70°N latitude zone. The Siberian high is well developed but the pressure anomalies in its center amount to 3–8 hPa only. The large monthly pressure anomalies at the isobaric surface of 500 hPa in the first natural synoptic area are mainly accompanied by the E-type of circulation (according to G.Ya. Vangengeim). The number of days with the western (W) type of circulation is extremely small and is practically absent when the anomalies in the center exceed 20 hPa (blocking process). The time periods of increase (decrease) in the annual number of days with W-circulation are well agreed with the periods of the Earth rotation acceleration (deceleration). The positive pressure anomalies were four or five times more frequent in the periods of the Earth angular velocity decrease: in 1933–1972 and after 2004.     

Comparison of two methods for calculating tidal loads

The spherical harmonic expansion up to order n = 1440 of the oceanic tidal heights is derived for the waves of the CSR3.0 model. On the basis of the load Love numbers for the PREM model, the oceanic load effect in gravity is calculated. It is shown that the results provided by the spherical expansion technique and the method utilizing the Green’s function satisfactorily agree even at the order of the expansion n = 720. The obtained model predictions are compared to the oceanic load effect measured by the Global Geodynamics Project (GGP) network of superconducting gravimeters.     

The Results of Integrated Modeling of the Oceanic Gravimetric Effect

The implications of a broad range of factors for the intensity of the oceanic gravimetric effect has been estimated. These factors include dissipation, mass correction, the selection of the oceanic tidal model and Earth’s density model, and discarding the near-zone approximation, as well as allowance for the ellipticity of the Earth and the relative, Coriolis, and inertial accelerations. It has been shown that, with the presentday requirements to computational accuracy, the joint effect of these factors, rather than the separate contributions of each individual factor are of primary importance. The load Love numbers are calculated up to degree n = 50000.