Andrey Yatsuk

The existing management strategies of macrophyte beach wrack are not always environmentally sound. In this study, we tried to assess the impact of the presence or absence of macrophyte beach wrack on the CO₂ flux and the possibility of creating an environmentally sound recycling of macrophyte beach wrack based on their removal from the beach and processing into biochar. The study was conducted on the coast of the Sea of Japan in the bay of Kievka. The Picarro G4301 portable laser gas analyzer was used to measure CO₂ fluxes in areas with and without macrophyte beach wrack. The CO₂ flux was 23 times higher at plots with macrophyte beach wrack, compared with plots without macrophyte beach wrack. In the plots after manual removal of the macrophyte beach wrack, on average, there was a 1.6-fold decrease in flow values compared to the plots with the macrophyte beach wrack. Considering the frequency of emissions in the study area, which is associated with frequent cyclones and storms, it is possible to organize the systematic cleaning of macrophyte beach wrack for the production of biochar. Creating projects based on the conversion of macrophyte beach wrack into biochar can have both environmental and economic benefits. The environmental benefits include the reduction of CO₂ flux at plots after manual removal of macrophyte beach wrack; the long-term storage of carbon from macrophyte beach wrack biomass in the form of biochar; and the reduction of CO₂ flux from soils (carbon sequestration) with the correct technology of introducing biochar into the soil. However, for a more accurate assessment, monitoring seasonal measurements and economic calculations of the entire technological chain of production, risks, and footprint are necessary.

This work presents new data on the composition and concentrations of hydrocarbon gases in the upper horizons of bottom sediments of Avacha Bay and the adjacent zone of the Pacific Ocean. The established concentrations of methane and the sums of its homologues are highly variable, from 0.0003 to 120.9385 and from 0.00005 to 0.00753 cm³/kg. Gas anomalies are formed in the sediments of the shallow shelf (Avacha Bay, Russkaya Bay, Vilyuchinskaya Bay and Listvennichnaya Bay) and in the outer shelf and the continental slope at sea depths of 14–800 m and sampling depths of 3–50 cm. The data on the isotopic composition of carbon δ¹³C–CH₄ from –78.1 to –33.4‰ and δ¹³C–CO₂ from –19.8 to –11.1‰ indicate the formation of natural gases of various polygenetic (mixed) origin in the bottom sediments of the region and, with a high probability, their significant influx from the underlying sediments.

The results of the generalization and scientific analysis of gas-geochemical studies of hydrocarbon gases in the bottom sediments of the eastern sector of the Laptev and the East Siberian Seas are presented. In the course of studies, methane and the sum of its homologs were found in the sediments of the region in the concentrations of 0.0010–12.1502 and 0.000002–0.03626 cm³/kg. In general, the distribution of hydrocarbon gases in the bottom sediments is characterized by significant variability and the formation of local, linear and areal hydrocarbon anomalies. This fact is explained by the presence of underlying gas-saturated indigenous sources, tectonic conditions, seismic activity, geostructural position, sediment occurrence depth, and the influence of other geological factors. Based on the generalization and analysis of the authors’ data, a map of the distribution of hydrocarbon gases in the bottom sediments of the central part of the East Arctic shelf was compiled for the first time.

The paper presents for the first time the results of gas geochemical studies in the bottom-water-atmosphere system of coastal-marine ecosystems of Kievka Bay and the adjacent shelf. Regional estimates of methane and carbon dioxide content in bottom sediments, the water column and the near-water atmosphere were obtained. The maximum methane content up to 447 nmol/l was established in the bottom sediments of the central part of the bay, the place of accumulation of organic saturated fine-grained silt sediments, and the minimum in the open part of the sea. Methane concentrations in water varied from 2.6 to 17.5 nmol/l, with maxima in the surface horizons of the central part of the Kievka Bay water area. CO2 concentrations in the near-water layer of the atmosphere varied in the range from 422.10 to 477.37 ppm, averaging 426.56 ppm. The concentration of CH4 varied from 2.029 to 2.070 ppm, averaging 2.032 ppm. The methane flux at the water-atmosphere boundary varied from 0.01 to 18.10 mol/km2 day, averaging 2.7 mol/km2 day. The increased concentrations and fluxes of methane in the surface horizons of the shallow waters of Kievka Bay and the decreased salinity values indicate the influence of the river runoff of the Kievka River, as well as the potential influence of shelf bottom sediments. In general, the studies revealed methane emissions into the atmosphere of varying intensity (from weak to high), which characterizes Kievka Bay as a low-intensity source of methane entering the atmosphere during the autumn transition period of the year.

Information is provided on the results of gas geochemical and hydrometeorological studies of Amur and Ussuri bays, Sea of Japan, on cruises 84 and 85 of the R/V Professor Gagarinskiy in December 2022. For the first time for the winter period, synchronous measurements of greenhouse gases and atomic mercury were carried out in the surface marine boundary layer of Peter the Great Gulf, and new information was obtained on the seasonal characteristics of gas geochemical fields in the water column and bottom sediments.

The article presents the results of measuring CO2 fluxes on the beach in areas with and without marine macrophytes and at the water-atmosphere boundary in Kievka Bay. Such studies were conducted for Kievka Bay for the first time. A chamber dynamic method and a laser gas analyzer were used to measure CO2 fluxes at all plots. Higher values of CO2 fluxes were noted on the beach in areas with dry beach macrophytes compared to wet beach macrophytes. Areas with macrophytes had 23 times higher values of CO2 fluxes compared to areas without beach macrophytes. To identify patterns and intensity of CO2 gas exchange between the sea and the atmosphere, long-term monitoring measurements are necessary, since there are many variable factors. When measuring gas exchange between the sea and the atmosphere, sharp short-term increases or decreases in CO2 concentration were noted on the graphs of concentration versus measurement time. This was not associated with technical failures of the gas analyzer or features of the floating chamber. This introduces difficulties in interpreting the data, since the linearity of the graph is lost and the error in the flow value increases.

The paper presents brief results of gas-geochemical and hydrometeorological studies of the outer water area of Peter the Great Bay (Sea of Japan), obtained as a result of a marine expedition study on the R/V Professor Gagarinskiy (cruise 83) in October–November 2022. Areal atmochemical measurements of climatically active gases (CH₄, CO₂, H₂O vapor) and Hg(0) in the near layer of the atmosphere of the outer water area of Peter the Great Bay were performed for the first time. Gas geochemical fields in bottom sediments and water column are detailed. The current position of gas flares within the outer shelf of Posyet Bay is determined. Long-term stations for marine daily monitoring were carried out.

The article describes a hard- and software controlled complex for gas-strain monitoring, consisting of stationary laser strainmeters and a laser nanobarograph, a stationary gas analyzer, and a weather station installed at Shultz Cape in the Sea of Japan; and a mobile shipboard complex, consisting of a gas analyzer and a weather station installed in a scientific research vessel. In the course of trial methodological measurements on these systems, general patterns were identified in the dynamics of greenhouse gases and deformation of the Earth’s crust in the range of diurnal and semi-diurnal tides, and also in the range of ultra-low frequencies, caused by atmospheric wave processes and, possibly, individual tones of the Earth’s eigen oscillations.

Gases from bottom sediments of the Laptev–Siberian Sea zone contain methane (up to 8.3047 cm³/kg) and its homologues (up to pentane including) totaling 0.0259 cm³/kg. The established values of the carbon isotope composition of methane (δ¹³С), the molecular weight of the hydrocarbon fraction, the weight concentrations of С₁–С₅ hydrocarbons and their ratios, the “wetness” and “transformation” coefficients of the hydrocarbons fraction indicate the presence of various syngenetic and epigenetic gases in different source rocks: bottom sediments, peatlands, coal, gas, and gas hydrate? deposits, solid bitumen, igneous rocks, and inferred oil and gas reservoirs. It has been established that the vertical and lateral distribution of hydrocarbon gases in sediments depends on the influence of a complex of geological factors: fold and fault tectonics, magmatism and seismic activity in the region, coal, oil and gas potential and bitumen content, organic saturation and lithological composition, hydrogeological, geocryological, and other conditions for accumulation of gases or their degassing.

—In bottom sediments of the New Siberian sedimentary basin and adjacent geostructures of the East Siberian Sea, we identified СН₄, as well as its limit and unsaturated homologues (up to and including C₅H₁₂), CO₂, CO, H₂, He, H₂S, O₂, N₂, and Ar. Isotope-gas-geochemical parameters δ¹³С СО₂, СН₄ and С₂Н₆, of the molecular mass of hydrocarbon fraction and genetic coefficients indicate the presence of both syngenetic and epigenetic gases of various gas sources in sediments, including recent sediments, peatlands, coal-bearing and gas-bearing formations, solid bitumen, igneous formations, accumulations of gas hydrates and prognostic condensate-gas, condensate, oil-and-gas and gas-and-oil reservoirs. Concentrations of CO₂ and CO reach 29.25 and 0.06 cm³/kg, CH₄ and the sum of its homologues – 5.93 and 0.031, Н₂ and He – 0.78 and 0.318, H₂S – 0.092 cm³/kg; this indicates that gas-geochemical anomalies, exceeding the anomaly criteria by 6–124 times, form in bottom sediments. The formation and distribution of abnormal concentrations of natural gases depend on the complex influence of gas-controlling factors – geological structure, fold and fault tectonics, magmatism, coal-oil-gas content, bituminous content, organic saturation, lithological composition, water-physical and reservoir properties of sediments, hydrogeological, geocryological and other conditions for accumulation of natural gases or their degassing.