Phytocenosis biodiversity at various water levels in mesotrophic Lake Arakhley, Lake Baikal basin, Russia

Small lakes have lower water levels during dry years as was the case in 2000–2020. We sought to show the biodiversity of plant communities at various water levels in Lake Arakhley. Changes in moisture content are reflected in the cyclical variations of the water level in the lake, which decreased approximately 2 m in 2017–2018. These variations affect the biological diversity of the aquatic ecosystems. We present the latest data on the state of the plant communities in this mesotrophic lake located in the drainage basin of Lake Baikal. Lake Arakhley is a freshwater lake with low mineral content and a sodium hydrocarbonate chemical composition. Changes in the nutrient concentration were related to precipitation; inflow volume and organic matter were autochtonous at low water levels. The most diverse groups of phytoplankton found in the lake were Bacillariophyta, Chlorophyta, and Chrysophyta. High biodiversity values indicate the complexity and richness of the lake’s phytoplankton community. A prevalence of Lindavia comta was observed when water levels were low and Asterionella formosa dominated in high-water years. The maximum growth depth of lacustrine vegetation decreased from 11.0 m to 4.0 m from 1967 to 2018. Decreasing water levels were accompanied by a reduction in the littoral zone, altering the communities of aquatic plants. The hydrophyte communities were monodominant in the dry years and were represented by Ceratophyllum demersum. The vegetation cover of the lake was more diverse in high-water years and variations in the lake’s water content altered the composition of biogenic substances. These changes were reflected in the lake’s phytocenosis

Late Pleistocene–Holocene environmental and cultural changes in Primorye, southern Russian Far East: A review

This article presents an analytical review of the available palaeoenvironmental and archaeological records from the southern part (ca. 42°18′–45°30′N) of Primorye spanning the last ca. 21,000 years. The outlined climate and environmental history of the coastal and continental zones of southern Primorye, based mainly on vegetation reconstructions derived from the study of fossil pollen from sedimentary deposits from various archives, is compared with the archaeological cultural sequence of the region. This shows synchronicity between several phases of climate change and cultural transition, migration and changes in population numbers and/or subsistence strategies. The pronounced warming trend during the Early Holocene (Preboreal and Boreal stages) is associated with increasing numbers of long-term camp sites of the Late Palaeolithic hunter-gatherers and a growing importance of aquatic food resources. The Holocene maximum temperature and moisture conditions during the Atlantic stage were paralleled by the emergence and flourishing of the Neolithic Rudnaya, Vetka and Boisman cultures (ca. 7.7–5.5 14C ka BP/8.5–6.2 cal ka BP). The latter was a specialised maritime forager culture distributed along the Sea of Japan coast, which likely reflects climate conditions and sea water temperatures that promoted a broad spectrum of marine food resources. Towards the end of the Atlantic stage, sea levels decreased and transformed the coastal landscape of southern Primorye, which probably contributed to the decline of the Boisman culture. At the same time, the climate started to become cooler, which is likely related to the eastward migration of Zaisanovskaya culture groups from more continental (cooler) regions to milder southern Primorye. Continuous cooling during the Subboreal was accompanied by further immigrations of Zaisanovskaya people and an increase in millet cultivation, which probably occurred in the region between ca. 4.6–4.1 14C ka BP/5.3–4.6 cal ka BP. With the emergence of the Palaeometal Epoch cultures (ca. 3.6 14C ka BP/4.0 cal ka BP), food production diversified (growing number of cultivated crops, animal husbandry) and intensified, which probably decreased the people's dependence on climatic conditions unfavourable for food procurement. However, the maximum flourishing (ca. 2.8–2.6 14C ka BP/2.9–2.6 cal ka BP) of the Palaeometal Epoch Yankovskaya culture, represented by a maximum number of documented settlement sites in Primorye's prehistoric sequence, was likely related to a coeval short phase of climate amelioration with higher air and sea water temperatures and an increased sea level, which promoted agriculture and a higher productivity of coastal waters

Palynological Research of Bohai Abrikosovsky Settlement (Primorsky Krai)

For the first time palynological research was carried out on the Abrikosovsky settlement, located in the Krounovka river valley. This site is dated back to the epoch of the Bohai state (698–926). It was determined that during its existence there were transformations of surrounding landscape associated with climatic and anthropogenic causes. Several stages of the settlement development have been defined. Pollen of cultivated, edible wild plants and industrial crops were found in the cultural layer sediments. The inhabitants of the settlement could use stalks of nettle or hemp for the production of textiles. Reed could be one of the building materials (fascine making), its phytoliths were found in the cultural layer. It was determined that one of the natural disasters was recurring strong freshets and floods in the second half of the summer

Pyrochlore-Group Minerals in the Granite-Hosted Katugin Rare-Metal Deposit, Transbaikalia, Russia

Pyrochlore group minerals are the main raw phases in granitic rocks of the Katugin complex-ore deposit that stores Nb, Ta, Y, REE, U, Th, Zr, and cryolite. There are three main types: Primary magmatic, early postmagmatic (secondary-I), and late hydrothermal (secondary-II) pyrochlores. The primary magmatic phase is fluornatropyrochlore, which has high concentrations of Na2O (to 10.5 wt.%), F (to 5.4 wt.%), and REE2O3 (to 17.3 wt.%) but also low CaO (0.6–4.3 wt.%), UO2 (to 2.6 wt.%), ThO2 (to 1.8 wt.%), and PbO (to 1.4 wt.%). Pyrochlore of this type is very rare in nature and is limited to a few occurrences: Rare-metal deposits of Nechalacho in syenite and nepheline syenite (Canada) and Mariupol in nepheline syenite (Ukraine). It may have crystallized synchronously with or slightly later than melanocratic minerals (aegirine, biotite, and arfvedsonite) at the late magmatic stage when Fe from the melt became bound, which hindered the crystallization of columbite. Secondary-I pyrochlore follows cracks or replaces primary pyrochlore in grain rims and is compositionally similar to the early phase, except for lower Na2O concentrations (2.8 wt.%), relatively low F (4 wt.%), and less complete A- and Y-sites occupancy. Secondary-II pyrochlore is a product of late hydrothermal alteration, which postdated the formation of the Katugin deposit. It differs in large ranges of elements and contains minor K, Ba, Pb, Fe, and significant Si concentrations but also low Na and F. Its composition mostly falls within the field of hydro- and keno-pyrochlore

A new modern analogue reference dataset and its application to the 430-kyr pollen record from Lake Biwa

This study presents a newly compiled dataset of modern pollen and climate data from 798 sites across Japan and the Russian Far East. This comprehensive reference dataset combined with the modern analogue technique (MAT) provides a powerful tool for pollen-based reconstruction of the Quaternary Northwest Pacific climate. Pollen-derived reconstruction of the modern climate at the reference pollen-sampling sites matches well with the estimated modern climate values (R2 values vary between 0.79 and 0.95, and RMSEP values vary between 5.8 and 9.7% of the modern climatic range for all nine tested variables). The successful testing of the method encourages its application to the fossil pollen records. We used a coarse-resolution pollen record from Lake Biwa to reconstruct glacial-interglacial climate dynamics in central Japan since ~438 kyr and compared it to the earlier reconstruction based on a less representative reference dataset. The current and earlier results consistently demonstrate that the coldest glacial intervals experienced pronounced cooling in winter and moderate cooling in summer, supporting the growth of cool mixed forest (COMX) where warm mixed forest (WAMX) predominates today. During the last glacial, maximum (~24 kyr BP) mean temperatures of the coldest (MTCO) and warmest (MTWA) month were about -13 °C (RMSEP = 2.34 °C) and 21 °C (RMSEP = 1.66 °C) respectively, and annual precipitation (PANN) was about 800 mm (RMSEP = 158.06 mm). During the thermal optimums of the interglacial intervals, the temperatures of the coldest and warmest month were above 0 °C and 25 °C respectively, leading to the reconstruction of WAMX and temperate conifer forest (TECO). Although both these vegetation types grow in the southern part of Japan today, WAMX requires warmer space. The presence of WAMX during marine isotope stages (MIS) 11 and 1, and its absence during MIS 9 and MIS 5 contradict the marine isotope and Antarctic ice records, suggesting that the latter two interglacials were the warmest of the last 800 kyr. The apparent contradiction allows at least three different explanations including low temporal resolution of the pollen record; different trends in CO2 concentrations during 'short' and 'long' interglacials; and regional climate variability and non-linear response of different regions to the global forcing. More definitive conclusions will be possible on the basis of forthcoming high-resolution pollen records from central Japan