Volume 24, Nº 4 (2024)

This study explores the potential for the penetration of technical waters from the Fukushima nuclear power plant (Fukushima NPP) into the fishing areas of Russia. Using a Lagrangian approach, which examines the advection of a large number of passive markers simulating waters released from the Fukushima NPP, the typical transport pathways to the South Kuril Islands are investigated, and an estimate of the time of such transport is provided. Calculations are conducted using satellite-derived and modelled velocity fields for the test year from August 24, 2022, to August 24, 2023. This study focuses on the advection of Lagrangian markers and highlights the potential for the rapid arrival of them from the Fukushima NPP into the southern Kuril region. This article emphasizes the importance of considering the seasonal variability in Kuroshio meandering and the impact of local mesoscale vortex advection related to the propagation of Lagrangian markers from the Fukushima NPP.

An review of field studies in the Gulf Stream region carried out by the authors in two periods with a break of 25 years is presented to summarize the results. The studies in the early period included hydrographic surveys in the area of a southern meander of the Gulf Stream (1989) and in the area of dividing of a single jet of the current into separate branches: in the Gulf Stream delta (1990). The second, recent, stage includes on-route surveys with SADCP profiler in 2014–2015 while crossing the meandering Gulf Stream at mid-latitudes to study its detailed high-resolution velocity field structure.

Freezing patterns in a porous soil saturated with a saline solution are investigated with regard to osmotic effects, using a model suggested previously by the authors but in a more general formulation. The results include a numerical and an approximate self-similar analytical solution to a nonlinear problem; description of typical freezing behavior in the presence of osmotic pressure. The modeling results agree well with experimental evidence on freezing of saline clay and sand. The model includes three porous domains with ice (I), thermodynamically equilibrated ice+solution (II), and a liquid saline solution (III) in the pores. The modeling is performed for a simplified case of domains II and III that share a mobile phase boundary where the solution freezes up partially, with heat release.

The features of the mineral and chemical composition (major elements) of the Vendian-Cambrian rocks of the Silimkun Formation (V-Є1sl), exposed on the western side of the Upper Kalar graben syncline in the southwest of the Aldan shield, are considered. The studied rocks – sandstones and siltstones, belong to arkoses and subarkoses. According to their chemotype, they correspond normosilites and myosilites. In terms of the alkaline modulus, the studied silites are hyperpotassium and serve as a fairly striking example of the products of Precambrian arid weathering. The standard mineral composition, its variations, the validity of calculations based on petrographic research data, the problems of using climate indices and lithochemical diagrams aimed at reconstructing climatic changes in the geological past are discussed. Chemical Index of Alteration (CIA) index values range from 49, which corresponds to a virtually unchanged rock, to 67. The average is about 58. Minor changes in the index value for this sample are associated primarily with variations in the content of illite cement and muscovite. Robust Weathering index (RW) values range from 37 to 68 (with an average of about 57).

Poleward transports of oceanic and atmospheric heat play an essential role in the Arctic climate system, and their variations in the future will strongly shape the climate of the Arctic. The main aim of this study is to evaluate the performance of the Coupled Model Intercomparison Project phase 6 (CMIP6) models in the historical experiment in simulating the meridional heat fluxes into the Atlantic sector of the Arctic. The secondary objective is to estimate the meridional oceanic and atmospheric heat fluxes up to the end of the 21st century using the best sub-ensembles of the CMIP6 models. According to our results, the CMIP6 models poorly reproduce the interannual variability of the heat fluxes in their historical simulations, and the multi-model ensemble mean values are systematically lower than the mean values derived from the Ocean ReAnalysis System 4 (ORAS4) and European Centre for Medium-Range Weather Forecasts Reanalysis version 5 (ERA5) reanalyses. Climate projections based on the selected CMIP6 models indicate that the future Arctic climate will be characterized by the significantly increased oceanic heat transport at the entrance to the Atlantic sector of the Arctic relative to the period 1958–2014. In contrast, the atmospheric heat and moisture transport will not have dramatic differences in the projected Arctic climate relative to the period 1958–2014. Based on the results obtained, we emphasize that any interpretation of future climate simulations should be done with caution.

Most Peat Hydrological Units (PHU) in South Sumatra, Indonesia, have been threatened by degradation from climate changes, human activities, and environmental factors. This study mapped land cover using Random Forest Classification and identified forest degradation using NDFI (Normalized Difference Forest Index) change analysis in several PHUs of the South Sumatra peatland from 2015 to 2023. We combined Sentinel-1, Sentinel-2, and Landsat-8 data for the land cover classification. Meanwhile, we utilized Landsat-8 to identify forest degradation. Our findings indicate that tree cover significantly decreased in 2015, 2019, and 2023, coinciding with severe drought conditions driven by El Niño events. A significant decrease in forest cover in 2019 was suggested by low tree cover, up to 47.1% of the total area of 1.054 million ha. Therefore, grassland and bare/sparse vegetation had more significant coverage percentages, reaching 22.89% and 11.40%, respectively, in 2019. Deforestation varied but generally decreased from 2015 to 2023, according to the analysis of NDFI changes. Vegetation regrowth increased notably from 2016 to 2020 and remained relatively stable afterward. In addition, forest disturbance decreased from 2015 to 2020 but slightly increased in the last few years. Although two PHUs have encountered more severe degradation, their peatland ecosystems included inside them have distinct characteristics. Specifically, the PHU of Sungai Saleh – Sungai Sugihan encompasses cultivated areas, whereas the PHU of Sungai Sugihan – Sungai Lumpur comprises protected areas. These findings highlight the need for restoration and sustainable land management to prevent further degradation

An approach is proposed for the joint use of the model implemented in the HEC-RAS software and a balance model to describe the transport and transformation of suspended solids in a river delta. In the river estuary region, hydrological areas are distinguished: channel areas, floodplain areas, flooded during high floods and storm surges from the sea, and the delta front areas. For the hydrological areas, a dynamic model of the balance of water and substances transported by water flow is built. Parameterization of the suspended solids sedimentation processes and their resuspension is introduced depending on the speed of water movement and particle size. Three gradations of suspended solids in size are considered: pelitic fraction (clay), alevrit fraction (silt) and fine sand. The emphasis is on assessing the impact of marine storm surges on the transport of suspended solids into the river delta and their deposition. To describe water flows between areas, movement speeds, level dynamics and floodplain flooding processes, a detailed model based on the HEC-RAS software adapted to the conditions of the Don River estuary area is used. Calculations of the transport and accumulation of suspended solids in the Don River estuary area were carried out for two variants of hydrological conditions – with the water surge from the sea and without it. The spatiotemporal variability of the concentration and granulometric composition of suspended sediment depending on hydrological conditions is considered. It is shown that in the absence of surge phenomena and low water flow rates, suspended solids are mainly deposited in the avandelta outside the sea edge of the delta, and during the surge period they saturate the water and, at the stage of rising its level, enter the delta, partially settling in the branches and in the floodplain areas. At the same time, at the stage of the water level decline, they are carried out of the channel segments beyond the sea edge of the delta, and mostly remain in the floodplain areas. For low-water conditions with the observed frequency of surge events and in the absence of floods, the Don estuary area retains on average 20% of suspended solids entering with the Don River runoff.