Vol 59, No 2 (2019)

Satellite altimeter observation data collected over 22 years are used to analyze the structure and variability of mesoscale fluctuations of ocean currents in the Drake Passage and Scotia Sea. Wavelet analysis of the time series of the absolute dynamic topography of the ocean surface (ADTOS) at a set of points in the study site revealed a high degree of statistical nonstationarity of these time series, which is manifested as short (a few years) intervals of intense ADTOS fluctuations separated by long intervals of weak fluctuations. Analysis of mesoscale ADTOS maps showed that the intervals of strong ocean velocity fluctuations in the vicinity of a specific location are controlled by the alternating cyclonic and anticyclonic formation of eddies and meanders by the jets of the Antarctic Circumpolar Current, intensification of the eddies followed by their decay, and the final confluence with the parent jets. In addition to statistical nonstationarity, considerable spatial variability of the statistical characteristics of mesoscale perturbations of ocean currents was revealed over scales of 150–200 km.

The process of geostrophic adjustment in a rotating layer of shallow water is considered. For initial distributions of the fluid depth in the form of a step and a localized rectangle, this process results in the formation of an isolated jet stream and a system of two counter jet streams, respectively. This paper studies the structural features of these flows, which is related to the nonlinearity of the adjustment process. The main feature for an isolated jet stream is the horizontal asymmetry of its velocity profile. For a system of two opposing flows, a mirror asymmetry is characteristic, which is caused by the sign dependence of the amplitude of the initial depth perturbation. The velocity of flows with a negative sign (depression) always exceeds the velocity with a positive sign (elevation).

The spatial and temporal variability of the transformation of dissolved matter runoff in the Mezen River estuary is studied from data on comprehensive hydrological–hydrochemical research in 2009 and 2015. The conservative behavior of major ions and dissolved forms of Li, Rb, Cs, Sr, B, F, As, Sb, and Mo has been revealed. The additional input of phosphates and silicon to solution (to 93% and 32–38% of their content in river water, respectively) is apparently caused by the transport of these nutrients from pore waters, which are regularly muddled by inflow of bottom sediments and vertical mixing of the water column. The desorption flux of barium and uranium due to long-term interaction of terrigenous material with saline water exceeds their input with continental runoff (180–380% and 90–150%, respectively, of their content in river waters). Up to 50, 43, 29, 32, 44, 50, and 45% of Fe, Pb, Y, La, Ce, Pr, and Nd, respectively, supplied by river runoff as stable organic complexes are removed from solution upon entering sea water due coagulation of colloids. It is concluded that transformation regularities of dissolved matter in the Mezen River estuary are spatially homogeneous and temporally stable. The specifics of migration of dissolved phosphates, silicon, barium, and uranium is caused by the hydrological features of the estuary.

Data on the hydrocarbon composition of bottom sediments from a water area adjacent to an area with massive cottage construction (Kazach’ya Bay, coast of Sevastopol, the Black Sea) are presented. Analysis of bottom sediments performed in the summer 2015 provided values for the pH, Eh, natural humidity, and content of chloroform-extractable compounds, petroleum hydrocarbons, petrochemicals, polyaromatic hydrocarbons, and n-paraffins. Sites with unfavorable and moderately unsatisfactory ecological state were identified. The effect of urban development on the coast on the deterioration of bottom sediments was demonstrated.

The spatial variability of phytoplankton primary production characteristics has been studied along transects between the Shetland Islands and Iceland (transect I) and along 59.5° N (transect II) from June 30 to July 16, 2013. It has been shown that the surface chlorophyll a concentration (Chl₀) varied within more than two orders of magnitude from 0.07 to 6.67 mg/m³ along transect I and from 0.02 to 3.63 mg/m³ along transect II. The water column primary production (PP_int) changed by a factor of 3.8 from 273 to 1040 and by a factor of 5.6 from 68 to 379 mgC/m² per day along transects I and II, respectively. It has been established that the spatial variability of Chl₀ and PPint was consistent with the distribution of the main surface flows and thermohaline fronts. This conclusion was made based on a reliable positive correlation between Chl₀ and the zonal potential temperature gradient (R = 0.43, p < 0.01, N = 65). Phytoplankton assimilation activity along transect II depends on the nutrient concentration. This is confirmed by the reliable positive correlation of the assimilation number with the phosphate concentrations (R = 0.58, p < 0.05, N = 76) and dissolved silicon (R = 0.51, p < 0.05, N = 76).

Ideas about the geomagnetic field’s influence on evolution and biodiversity are controversial. The quantitative distribution of datum levels of oceanic microplankton during the last 2.0 Ma shows a correlation with geomagnetic reversals. A decrease in field intensity increases cosmic irradiation of the Earth’s surface, which can activate mutagenesis leading to the emergence of new species. Moreover, since the correlation of the geomagnetic field intensity with the composition of the atmosphere, temperature, climate, volcanism, and other environmental conditions was revealed, it is possible to assume its influence on evolutionary processes as part of the overall complex of environmental conditions. Geomagnetic polarity superchrons ended with mantle plume formation, which produced trap eruptions and initiated Phanerozoic mass faunal extinctions. The sources of the geomagnetic field and plume formation leading to trap volcanism are at the boundaries of the Earth’s inner spheres, which explains their correlation. And their correlation with impact events as one of the causes of extinction can be explained by a cosmic primary cause that lies beyond the confines of the solar system.

The paper demonstrates the distinct difference between plume volcanism on oceanic and continental plates. A specific characteristic inherent solely to a continental setting is the generation of ultramafic alkali melts of the kimberlite–melilitite–carbonatite series, which has recurred many times in Earth’s history. The main cause of the different types of volcanism in the South Atlantic and Africa was the accumulation of C, H, F, K, Na, and other elements at the base of the subcontinental lithosphere under the influence of the African superplume. Alkali and volatile components to not accumulate on an oceanic plate. The interaction of alkali–carbonate fluids with mantle peridotites under the very thick continental plate led to their metasomatic transformation and the melting of low-silicate CO₂-saturated magmas in hypogene conditions and basalt magmas even more enriched in silica at smaller depths. The melting of hypogene melts of the kimberlite–melilitite–carbonatite family anomalously enriched in REE impurities is controlled by the CO₂ pressure regime. The composition of basalt melts significantly depends on the tectonic formation conditions.

A model of an artificial beach is proposed for protecting a seacoast subjected to erosion under significant storm surge impact. The beach profile properties are based on the Dean equilibrium profile. It is shown that coarser sand yields a greater total beach width, but requires a greater volume of berm material. At the same time, this results in decreased loss of material to longshore sediment transport. The results of applying the model to three sectors of eroded coast in the Kurortny District of St. Petersburg (eastern Gulf of Finland) recommend the use of medium-grained 0.3–0.5 mm sand to construct the artificial beach. In this case, the width of the dry beach section would be about 80–140 m, while the volume of berm material would be (1.3–3.2) × 10² m³ per one meter of coast length depending on the sediment deficit for a given coastal sector. To minimize the relative loss of material, it is suggested to construct a beach no less than 1 km in length; in this case, more than half the initial beach volume would be retained even after 30 years. Modeling of extreme storm impact leads to the conclusion that the designed beach profiles are only slightly deformed and can retain their resources for many years.