Varieties of fossil resins of South Sakhalin and their molecular composition

Summary The analysis of the organic matter of the Upper Oligocene-Lower Miocene rocks sampled in the outcrops in the central and southern parts of Sakhalin Island was carried out. The Verkhneduiskaya and Sertunaiskaya formations are characterized by a lower oil-generating potential compared to the source rocks of Pilskaya Formation. A comprehensive analysis of pyrolytic, kinetic characteristics and molecular composition were made, and the studied samples were grouped according to types of the initial organic matter and maturity.

The possibility of implementing a medium-term earthquake forecast using the LURR method in the southern part of Sakhalin Island in certain segments of the West Sakhalin and Central Sakhalin faults is considered in light of the medium-term strong earthquake forecast mode (M=5.5 (±0.5)) currently in effect for the central and southern parts of Sakhalin Island (within the latitude range from 47°N to 49.5°N, longitude range from 141.5°E to 143°E) (Protocol No. 2 of the Sakhalin Branch of the Russian Expert Council on Earthquake Prediction dated April 9, 2025). The assessments were carried out within the framework of a two-stage approach to seismic event forecasting, when previously identified medium-term forecast zones using the calculation method are refined using short-term geophysical methods. For the short-term assessment stage, the study used data from electrotelluric potential (vertical component) and subsurface radon volumetric activity measurement sites within the medium-term forecast coverage area. It was shown that in 2025, synchronous increases in electrotelluric potentials were observed at electrotelluric potential measurement sites in the village of Kolkhoznoye (Nevelsky District) and in Yuzhno-Sakhalinsk, which characterizes periods of high seismic activity. Furthermore, anomalies were detected based on subsurface radon volumetric activity measurements at sites in Yuzhno-Sakhalinsk and Firsovo before the earthquake activation in late June 2025 (a double earthquake near Aniva and Bykov). Updated LURR data (July 2025) showed that the only anomalies over the past five years were recorded in mid-2023. Although this study does not identify short-term precursors, it does provide additional data on the persistence of unstable conditions and confirms the relevance of the proposed medium-term forecast based on direct geophysical measurements.

The article is devoted to the adventive flora of the southern part of Sakhalin Island. Nowadays, 274 species of adventive plants, belonging to 192 genera and 57 families, have been identified here. Five families (Amaranthaceae, Cannabaceae, Commelinaceae, Linaceae, and Malvaceae) are represented by invasive species only. The structure of the leading families and genera is analyzed, the participation of adventive species information of plant communities is indicated. Adventive species are classified into life forms, method of entering and degree of naturalization.

The article is dedicated to analyzing the content and distribution of oil hydrocarbons, benz(a)pyrene, and heavy metals in the soils of the southern part of Sakhalin Island. The investigations were conducted in 2003–2010. A dynamical increase in the content of ecotoxicants in soils has been shown. The similar character of the accumulation of oil hydrocarbons, benz(a)pyrene, and heavy metals in the soils has been determined and indicates the possibility of the aerial transmission of pollutants from existing nearby sources.

Radon monitoring in the literature is recognized as a promising method for the prediction of earthquakes. In the last decade, the promise of the radon method for predicting subduction earthquakes has been convincingly demonstrated on Kamchatka. The results obtained on the Kamchatka, give reason to hope for the detection of predictive anomalies in the radon field and for weaker, but not less dangerous, small-focus earthquakes on the Sakhalin Island. The southern part of Sakhalin Island is a region of high seismic hazard. On Sakhalin Island, in a test mode, a network of three radon monitoring stations in the subsoil air is launched using the forced convection method to search for earthquake precursors. Based on the literature data, it is assumed that the effectiveness of radon monitoring near the focal zone of small-focus earthquakes on Sakhalin Island will be significantly higher compared to the conditions of the subduction zone in Kamchatka. Data from the network of radon monitoring stations can be used as an additional parameter to substantiate the conclusions on possible scenarios for the evolution of the seismic process in the south of Sakhalin.

Genetic variation at 19 allozyme (including 11 polymorphic) and 10 microsatellite loci was examined in the population samples of odd- and even-broodline pink salmon from the southern part of Sakhalin Island, Southern Kuril Islands, and the northern coast of the Sea of Okhotsk. The estimates of relative interpopulation component of genetic variation over the allozyme loci, per broodline, were on average 0.43% (GST), while over the microsatellite loci it was 0.26% (the theta(ST) coefficient, F-statistics based on the allele frequency variance), and 0.90% (the rho(ST) coefficient, R-statistics based on the allele size variance). The values of interlinear component constituted 2.34, 0.31, and 1.05% of the total variation, respectively. Using the allozyme loci, statistically significant intralinear heterogeneity was demonstrated among the regions, as well as among the populations of Southern Sakhalin Island. Multivariate scaling based on the allozyme data demonstrated regional clustering of the sample groups, representing certain populations during the spawning run or in different years. Most of the microsatellite loci examined were found to be highly polymorphic (mean heterozygosity > 0.880). The estimates of interlinear, interregional, and interpopulation variation over these loci in terms of theta(ST) values were substantially lower than in terms of rho(ST) values. Regional genetic differentiation, mostly expressed at the allozyme loci among the populations from the northern and southern parts of the Sea of Okhotsk (i.e., between the Sakhalin and Kuril populations), was less expressed at the microsatellite loci. The differentiation between these regions observed can be considered as the evidence in favor of a large-scale isolation by distance characterizing Asian pink salmon. It is suggested that in pink salmon, low genetic differentiation at neutral microsatellite loci can be explained by extremely high heterozygosity,of the loci themselves, as well as by the migration gene exchange among the populations (the estimate of the genetic migration coefficient inferred from the "private" allele data constituted 2.6 to 3.4%), specifically, by the ancient migration exchange, which occurred during postglacial colonization and colonization of the range.

Storm surges (the significant sea level rises due to a drop in surface atmospheric pressure and an increase in wind velocity during the passage of deep cyclones over the coastal areas) pose a formidable threat to the coastal settlements of Sakhalin and the South Kuril Islands. As a result of flooding of coastal areas, the impact of storm waves on the shores and coastal facilities is sharply increased. The greatest damage caused by surges on 10.11.1990 and 9.11.1995 which affected the most populated southern part of Sakhalin Island. A long-term sea level series were analyzed, recorded at 9 coastal tide gauges located on the coast of Sakhalin Island and South Kuril Islands. Estimates for the maximum heights of the storm surges and tidal level were obtained separately, as well as for the rare recurrence of the total sea level height with the probability of these individual components superposition. The maximum total height of the sea level was obtained for the Kurilsk station, where the highest storm surge was recorded. The minimum values were obtained for southwestern coast of Sakhalin Island (Kholmsk and Nevelsk stations) were tides are small. Seasonal and inter-annual variations of strong waves were analysed from the data of visual observations.

The local flora of vascular plants of Mayorsky Mountain Massif of Susunay Ridge in the southern part of Sakhalin Island contains 230 species from 171 genera and 71 families. For the first time, 50 species are listed for the massif. The flora of serpentinite outcrops is especially specific. Plant communities on the serpentinites are dominated by species with wide geographical areas (circumpolar, Eurasian, Asian and East Asian), whose share is more than 70% of the total local flora, which is a reflection of the geological past in the process of the alpine flora formation on Sakhalin Island. There are 64 species concentrated on an area of about 0.4 ha (Bistorta pacifica, Leontopodium discolor, Malaxis monophyllos, Rubus pedatus, Thesium refractum, Tofieldia coccinea and others), of which three species (Carex capillaris, Cerastium sugawarae and Pedicularis chamissonis) are found nowhere else on Sakhalin. The nearest localities of isolated populations of subalpine and alpine species on serpentinite outcrops (Carex melanocarpa, Loiseleuria procumbens, Rhododendron parvifolium, Scirpus maximowiczii) are in the northern part of Sakhalin or in the Northern Japan. Mayorskaya Mt. is the locus classicus of Poa sugawarae and Cerastium sugawarae. An annotated checklist of vascular plants is given. The modern flora of Mayorsky Massif is a reflection of paleogeographical history and climate fluctuations.

The seismotectonic position of the strong earthquake that occurred in the southern part of Sakhalin Island on September 13, 2020, is considered. The maximum shaking intensity was reported in the town of Uglegorsk. The ground shaking with Community Internet Intensity CII = 5.5 caused damage to the buildings with low seismic capacity. Significant ground shaking in the study area had already taken place in the case of the Mw 6.8 Uglegorsk earthquake in 2000. It has been suggested that the recent earthquake was triggered by the 2000 Uglegorsk earthquake (Mw 6.8). Currently, Sakhalin oblast is considered as a pilot region for the implementation of a novel federal program for the relocation of people from dilapidated housing. In this respect, the proposed method of assessment of the seismic potential of fault zones in the areas where construction is planned, taking into account the postseismic effects, is of very high importance.

Amber.

Based on a critical analysis of literature data for the past 200 years and the results of our own multiyear studies, an annotated list of marine, brackish-water, and anadromous (migratory) fish found in Aniva Bay (southern part of the Sea of Okhotsk, southern part of Sakhalin Island) is given: 274 species (against 164 previously mentioned) in three classes, 22 orders, 67 families, 161 genera. For a number of species, information is provided on collection specimens that confirm their presence within the studied water area. For each species, Latin and English names, taxonomic remarks, information on conservation status, ecology, abundance and commercial importance are given. The first part provides brief information about the history of the study and geographical and climatic-oceanographic characteristics of the bay as well as the first 137 species of the annotated list, represented by 83 genera, 35 families, and 19 orders.

This paper studies the phylogeography of Alnus alnobetula s. l. in the Asian part of the Russian range with the use of chloroplast DNA (cpDNA) sequences (intergenic spacers trnH-psbA, trnS-trnG, and psaA-trnS). Nine haplotypes were identified as a result of a combination of polymorphism of all sites in 241 plants in 20 populations of A. alnobetula. High interpopulation differentiation (GST = 0.914, NST = 0.928) and a significant phylogeographic structure (NST > GST, p < 0.05) were found. Reconstruction of genealogical relationships of green alder haplotypes revealed five highly divergent genetic lineages: one geographically widespread throughout Siberia and the Urals and several allopatric lines in the Far East of Russia, namely, the Chukotka Peninsula and the mouth of the Yana River, Magadan oblast, Primorye and the central part of Sakhalin Island, and the southern part of Sakhalin Island. Our data confirm that in the past the range of this species in the Far East was fragmented in several refugia that were isolated for a long time in various ice-free regions. This could have contributed to a high level of intraspecific polymorphism of green alder as a result of the divergence of endemic haplotypes, with almost non-overlapping distribution. However, the level of their molecular divergence does not correspond to the level of morphological differences.

Structure and Productivity of Vegetation of Coastal Marshes in the Southern Part of Sakhalin Island (Salmon Bay Carboniferous Polygon)

A catalogue of aftershocks of the 2007 Nevelsk earthquake (M w = 6.2) was prepared on the basis of the data from the local network of digital seismic stations established on the southern part of Sakhalin Island. The parameters of the aftershock hypocenters were determined using the method of the seismic wave travel time inversion. The errors in the determination of the coordinates of the seismic events were analyzed. The particularities of the spatiotemporal distribution of the aftershocks in the source zone of the earthquake were established. It was shown that a strong aftershock was a subsource earthquake with its own source zone. This explains the disagreement between the energetic characteristics and the size of the aftershock zone of the Nevelsk earthquake.

Ichthyological studies of spawners of salmonids in the south of Sakhalin Island were studied. Cases of furunculosis disease were revealed. The agent of the disease Aeromonas salmonicida was isolated. Its morphological, physiological-biochemical, and antagonistic properties were studied, and the virulence of the isolated strains was determined. For supporting the species status of the studied strains of A. salmonicida, a molecular-genetic analysis was performed.