Methane seepage alters local diagenetic conditions, influencing the coupled biogeochemical cycles of sulfur, carbon, and redox-sensitive elements such as uranium (U) in the sediment. This study investigates the U-isotopic compositions of carbonate-rich sediments and seep carbonates (Site ROV1-5A) in the Haima Cold Seep of the South China Sea and of non-seep marine sediments (sites DS12 and DS388). Terrigenous debris dominates U sources in non-seep marine sediments (S234U, -27%o to +26%o; U/Al, 0.17 mg/kg/wt.%), consistent with upper continental crustal (UCC) signatures. In contrast, seep carbonates (S234U, +105%o to +135%o; U/Al, 4.3 mg/kg/ wt.%) and carbonate-rich sediments (S234U, +38%o to +107%o; U/Al, 1.3 mg/kg/wt.%) exhibit elevated S234U values and U/Al ratios, indicating authigenic U enrichment. Positive correlations between U and carbonate contents suggest that carbonate is the main sedimentary host of authigenic U in methane-seep environments. In comparison to the UCC and non-seep marine sediments (average S238U = -0.27%o), carbonate-rich sediments exhibit 238U enrichment (-0.16%o to +0.01%o) and seep carbonates 238U depletion (-0.45%o to -0.32%o). Seep carbonates, which lack pyrite and exhibit moderately elevated (Mo/U) values (average 1.9), form under anoxic, non-sulfidic conditions. In contrast, carbonate-rich sediments, which are rich in pyrite and exhibit high (Mo/U) values (average 7.6), form under sulfidic conditions. We infer that the alteration of the redox environment resulting from anaerobic oxidation of methane and the abiotic reduction of U(VI) driven by Fe(II) are the primary factors responsible for the observed differences in S238U. Our results indicate that U isotopes are a sensitive proxy for local redox conditions in seep environments. The observed isotopic shifts provide insights into how methane seepage, through processes like AOM and associated redox changes, orchestrates the coupling of multi-elemental cycles and oceanic redox changes.
Estimates for time horizons of permafrost degradation at the Arctic shelf and stability of methane hydrates under antropogenically forced climate changes are obtained. In this, a model for thermophysical processes in the shelf sediments, which is driven by the output of the IAP RAS Earth system model of intermediate complexity for the next 15 kyr. It is obtained that the subsea permafrost at the outer shelf is completely degraded to the late 21st or in the early 22nd century. However, in the regions of the contemporary shallow and intermediate shelve, sediments may be kept perennially frozen for 3 to 8 kyr from the present day, depending on intensity of geothermal heat flux. Anthropogenically-induced warming increases the rate of permafrost degradation several-fold relative to the preindustrial climate. In contrast to the subsea permafrost, methane hydrates stability zone may persist for several centuries after permafrost degradation provided that geothermal heat flux is not larger than 60 mW/m2. If this flux is larger (e.g., 75 mW/m2), methane hydrates become unstable even before the permafrost disappearance.
In the bottoms of river valleys in Evenkia, along with typical thermokarst water bodies, deep funnel-shaped lake basins have become widespread. Their morphology, uncharacteristic of cryogenic formations, and their localization in the vicinity of the epicenter of the famous 1908 Tunguska event (the “Tunguska meteorite”) have sparked debate regarding their origin. This paper presents the results of a morphotectonic analysis of a straight section of the Verkhnyaya Lakura River valley, where a cascade of such lake-like widenings of the river channel is located. The studies showed that the formation of Lake Peyungda and Lake Zapovednoye is primarily driven by tectonic factors, while the unusual morphology of the basins is ensured by additional conditions resulting from the interaction of subsurface erosion processes (suffosion) that developed along zones of tectonic destruction against the background of permafrost degradation with the formation of through taliks beneath the lakes, and subsurface gas-emission at fault nodes. In terms of their formation mechanism, the lakes of the Tunguska Nature Reserve examined here are mature analogs of the gas-emission craters of the Yamal Peninsula.
Detrital zircons from sandstones of the Vasilevsky Ostrov and Lomonosov Formations in the Taitsy-2 reference borehole (central Baltic–Ladoga Monocline, northwestern Russia) were dated by the U–Th–Pb (LA-ICP-MS) method. The results demonstrate that during the Late Vendian–Early Cambrian, the main source areas were the Early Proterozoic rocks of Fennoscandia ( 2.02–1.79 Ga) and Early Riphean crystalline complexes representing relicts of the Gothian, Telemarkian, Danopolonian ( 1.76–1.41 Ga) and Sveconorwegian (Grenvillian) ( 1.36–0.94 Ga) orogenies. In late Kotlin (early Lomonosov) time, the Timanide Orogen (0.67–0.53 Ga) emerged as a new source region. Additionally, the stratigraphic position of the Kotlin Regional Stage is discussed. Its upper part was previously proposed to be reassigned to the Lower Cambrian on the basis of single “young” zircon grains. Such conclusions contradict paleontological data and regional correlation schemes, according to which the analyzed interval is attributed to the terminal deposits of the Upper Vendian. The Vendian–Cambrian boundary is defined by the first appearance of the Rovno–Lontova fossil assemblage in the middle part of the Lower Lomonosov Subformation.
We demonstrate the results of instrumental observations of geophysical fields in the surface layer of the atmosphere during the period of a prolonged and strong magnetic storm from March 20 to March 23, 2026 (Kp = 7), characterized by two well-defined stages of increased magnetic activity. It is shown that the magnetic storm was accompanied by variations in the atmospheric electric field and the amplitude of microbaric oscillations. Based on the results of processing the available data on ionospheric sounding, variations in the critical frequency of F2 ionosphere layer were established caused by a magnetic storm.
