Том 24, № 6 (2024)
Статьи
LATE MIDDLE TO LATE ORDOVICIAN PHOSPHATE ACCUMULATION OF THE MOYERO RIVER SECTION (SIBERIA): A RECORD OF UPWELLING AND GLOBAL COOLING
Аннотация
The phosphate-bearing rocks (phosphate rocks and phosphorites) were studied over a 45-meter interval of the Moyero river section, covering the upper part of the Darriwilian and the lower part of the Sandbian stages of the Ordovician. These rocks were investigated by field observations and laboratory methods, including optic and scanning electron microscopy, X-ray diffraction analyses. The accumulation of phosphatic matter is manifested in carbonates, sandstones, and aleurolites in the form of grains (ooids and peloids), intraclasts, phosphatic and phosphatized shells. In argillites, it is represented by cryptocrystalline matter. Phosphate matter consists of fluorapatite. The peaks of phosphate accumulation are associated with the formation of layers of physically reworked granular phosphorites (condensation horizons) directly above the depositional sequence boundaries. The formation of the studied phosphate-bearing rocks during the Darriwilian-Sandbian transition was influenced by a combination of global (Great Ordovician Biodiversification Event (GOBE), reduction in sea surface temperature, atmospheric CO2, high sea level, flooding of craton margins) and regional (equatorial position of Siberia, arid climate, facies) factors. Global conditions led to the enrichment of seawater with phosphorus and the effect of upwelling. Regional conditions determined the characteristics of phosphate formation. Studied phosphate-bearing rocks can be considered as a record of upwelling on the Siberian craton during the Middle-Late Ordovician transition and one of the manifestations of long-term global cooling started early in the Middle Ordovician.
Russian Journal of Earth Sciences. 2024;24(6):ES6001
ES6001
АЛГОРИТМЫ АВТОМАТИЧЕСКОГО ДЕТЕКТИРОВАНИЯ И ЛОКАЦИИ ИНФРАЗВУКОВЫХ СОБЫТИЙ В СИСТЕМЕ PSDL
Аннотация
В работе представлено описание автоматизированной системы и реализованных в ней алгоритмов для обнаружения, ассоциации и локации низкочастотных акустических событий по данным инфразвуковых групп. Описан алгоритм обнаружения инфразвуковых сигналов методом расчета функции взаимной корреляции между записями отдельных датчиков группы. Реализованный алгоритм оптимизирован для работы с группами, состоящими из большого количества сенсоров, что позволяет минимизировать вычислительную нагрузку на систему мониторинга в режиме, близком к реальному времени. Описана процедура распознавания длительных сигналов с возможно меняющимся во времени положением источника, таких как движущийся транспорт или снежные лавины. Также в работе приводится описание алгоритмов ассоциации инфразвуковых сигналов, зарегистрированных разными группами, а также локации источника сигнала по данным нескольких инфразвуковых групп. Система способна анализировать одновременно данные сейсмического и инфразвукового мониторинга и обнаруживать пары сигналов двух видов, ассоциируемых с общим источником. Алгоритм такой ассоциации также приведен в работе. Описанная система автоматического обнаружения и локации инфразвуковых сигналов может быть применена для мониторинга опасных природных и техногенных процессов и явлений в режиме, близком к реальному времени.
Russian Journal of Earth Sciences. 2024;24(6):ES6002
ES6002
OPTIMAL INTERPOLATION METHOD FOR GENERATING A DIGITAL BATHYMETRIC MODEL FOR SHALLOW WATERS: A CASE STUDY OVER MAURITIUS COAST
Аннотация
Bathymetry unveils the underwater topography of oceans, seas, rivers, and lakes. It is a fundamental data resource for various applications, like physical oceanography, marine geology, geophysics, and marine resources. The techniques to compute the seafloor depths are ship-borne echo sensors, empirical models of satellite-derived bathymetry, and aerial-space-borne laser altimetry. The digital bathymetric surfaces are generally generated from a distributed seafloor depths. Once these depth points are collected, the next step to generate a continuous surface is to select and implement interpolation. Numerous interpolation methods have advantages and disadvantages that can hamper the accuracy of the surface, which generally depends on the shape of the extent, distribution, and point density. To date, there is no recommended interpolation method when the study extent is circular with well-distributed points – the core objective of this research is oriented towards this. An attempt was made to generate a digital bathymetric surface for the Mauritius coast with ∼ 1.2 million depth points accrued from the NASA ICESat-2 geolocated photons and sounding depths from the marine charts. These points were used as input to interpolation methods like Inverse Distance Weighted, Natural Neighbour, and various forms of Ordinary Kriging. Our findings show that all the methods have generated visually similar surfaces, but the Inverse Distance Weighted interpolation has given the output with less quantified uncertainty
Russian Journal of Earth Sciences. 2024;24(6):ES6003
ES6003
DISTRIBUTION OF DISSOLVED OXYGEN AND NUTRIENTS IN ABYSSAL WATERS FLOWING INTO THE BRAZIL BASIN, SOUTHWEST ATLANTIC
Аннотация
The Vema Channel is a deep narrow passage in the South Atlantic and a main path for bottom water which flows northward from the Argentine Basin to the Brazil Basin and after all into the North Atlantic. The thermohaline structure and dynamics in it have been studied for many years. In this study we report our new data on dissolved oxygen and nutrients measurements performed in 2022 at the exit of the Vema Channel. This is the first time that such measurements have been made with high spatial resolution. Data from standard oceanographic sections located near the study area are also analyzed. A significant dependence in the distribution of dissolved oxygen and nutrients on the hydrological structure is shown. Local dissolved oxygen minimum indicates the lower boundary of Circumpolar waters. It was also revealed insignificant temporal variability of nutrients concentration.
Russian Journal of Earth Sciences. 2024;24(6):ES6004
ES6004
KINEMATIC CHARACTERISTICS OF ICEBERG D28 DRIFT USING SATELLITE DATA SENTINEL-1A/B SAR
Аннотация
The goal of the article is to track down the giant tabular iceberg D28 trajectory from its calving in September 2019 from Amery Ice Shelf until reaching the western part of the Weddell Sea in March 2023 and to present characteristics of the iceberg state and movement, derived from satellite radar data. The Maximally Stable Extremal Regions (MSER) method, which used as an imagery recognition technique for time-dependent visual conditions, has been applied to automatically identify iceberg’s positions. On the basis of the Sentinel-1A/B SAR data during 1,275 days, timeseries of D28 location, spatial orientation, mass, area, moment of inertia, linear and angular velocity, kinetic and rotational energy, grounding location are presented. D28 dynamics display strongly pronounced regionality, generalized into the three distinct sections of its drift along the Antarctic coast. These sections are in good agreement with existent concepts in the oceanographic literature, concerning the system of Antarctic Slope Current / Antarctic Slope Front.
Russian Journal of Earth Sciences. 2024;24(6):ES6005
ES6005
WHAT SHOULD WE KNOW TO PREDICT GEOMAGNETICALLY INDUCED CURRENTS IN POWER TRANSMISSION LINES?
Аннотация
This review considers several issues of space weather studies that are directly related to the problem of geomagnetically induced current (GIC) excitation in the power line transmission systems. Expectations to reduce the damage to technological systems from space weather were related with elaboration of models capable of real-time predictions of electromagnetic disturbances at the Earth's surface. However, the examination of the feasibility of the MHD simulation to predict the level of geomagnetic field variability, and consequently GICs, during the May 27–28, 2017 storm showed that the modeling reasonably well reproduced the global magnetospheric parameters, but the predicted magnetic field variability dB/dt has turned out to be more than order of magnitude less than that observed. The reason is the inability of current global MHD models to adequately predict the fine structure of the storm/substorm – Pi3 disturbances, and consequently GICs that they drive. Moreover, impulsive disturbances such as Pi3 pulsations demand a special tool for their analysis. Data processing technique for a 2D network of magnetic stations has to be elaborated to automatically recognize eddy current structures in the ionosphere and estimate their characteristics. The proposed technique applied to Pi3 pulsations on March 17, 2013 revealed that each vortex caused a disturbance of the vertical magnetic component Z and GIC burst up to ∼ 100A. The efficiency of GIC generation by different types of magnetic storms must be examined. For that it is necessary to compare GIC responses to storms caused by coronal mass ejection and by corotating interaction region, and to estimate the normalized GIC-effectiveness of each storm. The excitation rate of GIC during storms may be associated with the occurrence of mesoscale current vortices.
Russian Journal of Earth Sciences. 2024;24(6):ES6006
ES6006