ИСТИНА

Детальная реконструкция развития бореальной трансгрессии на европейском севере России в контексте изменений климата, уровня моря и влияния атлантических вод

The ongoing climatic changes that are most pronounced in the Arctic and Subarctic in terms of ice cover reduction, glacier melting, increased river runoff, sea level rise, permafrost melting and replacement of plant communities, determine the growing interest in reconstructing climatic and paleoenvironmental changes during previous ( pre-technogenic) interglacial and deglacial epochs. The most interesting are the penultimate glacial termination II at the end of marine isotope stage (MIS) 6 and the MIS 5e interglacial, which corresponds to the beginning of the Mikulinian interglacial in European Russia and the Eemian interglacial in western Europe. In terms of orbital parameters it was close to the modern Holocene interglacial, and deposits of this age are well preserved in the oceans and, in some places, also on land (Kukla et al., 2002). At the same time, there are significant differences between these interglacials, the nature of which is not fully understood. In particular, this concerns the pattern of oceanic circulation in the Nordic seas and adjacent Arctic regions during the period of rapid sea-level rise during melting of vast ice shelves at the end of MIS 6 and at the beginning of MIS 5e, when these regions were connected not only through the Barents Sea and Fram Strait, but also across the North-Baltic-White Sea corridor (Donner, 1995; Funder et al., 2002). On the one hand, the rapid northward movement of thermophilic vegetation in a maritime climate (Zagwijn, 1996) indicates climate warming, and the appearance of thermophilic marine species among fossil macro- and microfauna in the White Sea and Karelia since the onset of the interglacial about 130 ka is interpreted as an evidence of increasing the influence of Atlantic waters (Ikonen, Ekman, 2001; Funder et al., 2002; Grøsfjeld et al., 2006). On the other hand, paleoceanographic data from coeval sediments of the Nordic seas and Fram Strait indicate colder surface water temperatures compared to the Holocene and a significant weakening of the Atlantic water inflow due to the large volume of glacial melt water that persisted up to the middle / final stages of the Eemian (Bauch et al., 1999, 2000; Bauch, 2013; Rasmussen et al., 2003; Zhuravleva et al., 2017). The current project is aimed at studying regional paleoenvironmental variability and the possible inflow of transformed Atlantic waters to northern European Russia during the Boreal (Mikulinian, Eemian) transgression, corresponding to the deglaciation Moscovian (Saalian) glaciation (MIS 6) and the beginning of the penultimate Mikulinian (Eemian) interglacial (MIS 5e). Research objects are marine sediment beds of the Boreal transgression, as well as, in part, the underlying / overlying moraine, lacustrine-glacial and alluvial sediments from two regions: the northeastern coast of the White Sea (Bych'e section on the Peza river) and Karelia (borehole in Petrozavodsk). These deposits were previously studied with a low resolution (see the review by Ikonen and Ekman, 2001; Grøsfjeld et al., 2006; Devyatova, 1982); interestingly, findings of thermophilic planktonic foraminifers were reported for the borehole from Petrozavodsk. As a result of joint Russian-German field work in 2005-2006, obtained a new borehole in Petrozavodsk and described and carried out high-resolution sampling in a new Bych'e section located 5 km downstream from the previously explored outcrop (Grøsfjeld et al., 2006). In July 2021, as part of the GIN RAS expedition, additional sampling for OSL dating and XRF scanning of sediments will be carried out in the new Bych'e section. The main focus and novelty of our research lies in the multiproxy and high-resolution study of sediment sections to obtain a detailed record of paleoevents, their age constraints for regional and distant correlations. Samples from the 4.5-m sequence of marine sediments in Bych'e section, which directly overlies Moscovian till, were taken at 5 cm interval (currently, they have been analyzed at 20 cm interval). The borehole sediments will be sampled continuously. It is planned that marine sediment sequence will be studied at 10 cm interval. Altogether, this will provide the necessary high-resolution research approach. A complex of analytical methods and quantitative approaches will be used. Lithological analysis (wt% of the > 63 μmfraction, abundance of lithic fragments in the > 500 μm fraction representing ice- and iceberg-rafted debris) will make it possible to reconstruct changes in paleodepths resulting from an interplay of global eustatic sea-level rise and local isostaic rebound pattern, as well as the past sea-ice cover extent. Spore-and-pollen analysis is the basis for stratigraphic subdivision of the sections and correlation with sediment sequences from neighboring regions (Kola Peninsula, Karelian Isthmus, southern Baltic Sea coast, etc.). The application of the numerical method of biome reconstructions based on the interpretation of fossil spore-pollen spectra (Prentice et al., 1996; Tarasov et al., 1998) (this approach will be applied for the first time to pollen records from marine sediments of the northern European Russia) will increase the reliability of palynological reconstructions. Fossil foraminifers, ostracods, and aquatic palynomorphs will make it possible to reconstruct various parameters of the aquatic environment - paleodepths, water column stratification, freshwater impact and river runoff intensity, sea-ice cover character and extgent, bioproductivity, presence of transformed Atlantic waters, etc. Special attention will be paid to Atlantic water index species, the published taxonomic lists and their ecological interpretations will be critically analyzed, taking into account the data available to the project executors on the distribution of these species in the modern sediments of Eurasian Arctic seas (Stepanova et al., 2003, 2007; Ovsepyan, 2016, unpublished data). Records of oxygen and carbon isotopic composition of foraminiferal tests will make it possible to reconstruct water mass properties (freshwater influence, degree of stratification, Atlantic water inflow), sea-ice cover characteristics and bioproductivity. Absolute ages will be obtained by OSL and U / Th dating. Along with spore-and-pollen analysis, this will allow for a more reliable chronostratigraphic assignment of the studied layers. Variations in the chemical composition of sediments, determined by XRF scanning, will make it possible to reconstruct depositional environments and correlate the studied sections. During the implementation of the project, detailed and chronostratigraphically constrained records of the past environmental changes in two key areas of the Boreal (Mikulinian, Eemian) transgression will be obtained - in the northeastern White Sea that has been affected by Atlantic water inflow from the Barents Sea and Fram Strait, and in Karelia on the Onega lake coast, that has been located next to the “paleo-watershed” of the basin connecting the North, Baltic and White seas. This will allow us 1) to obtain high-resolution regional records of paleoenvironmental variability related to climate changes and relative sea-level history; 2) to clarify the duration of the White Sea-Baltic Sea connection; 3) to compare the obtained results with published data on coeval marine sediments on land (Kola Peninsula, Karelian Isthmus, southern coast of the Baltic Sea, etc.) and sediment cores from the Nordic seas in order to access the influence of Atlantic water inflow in the northern European Russia.

1. Подробная характеристика разреза морских осадков бореальной трансгрессии в разрезе Бычье – графики распределения по разрезу литологических и геохимических характеристик, численности и таксономического состава микрофоссилий, изотопного состава кислорода и углерода раковин фораминифер, описание палинозон на основе спорово-пыльцевой диаграммы, численные биомные реконструкции и расчеты пыльцевых индексов тепло- и влагообеспеченности. Определение возраста осадков методами ОСЛ и 230Th/U датирования. Сопряженный анализ и синтез всех полученных данных по изменениям параметров палеосреды, стратиграфическое подразделение осадков разреза и детальная реконструкция региональных палеособытий; 2. Сравнение полученных результатов изучения разреза Бычье с опубликованными данными по соседним регионам, межрегиональные корреляции; 3. Две подготовленные к печати статьи в изданиях, индексируемых в базах данных «Сеть науки» (Web of Science Core Collection) или «Скопус» (Scopus).

Талденкова Е.Е., Руденко О.В. и Овсепян Я.С. имеют большой опыт сотрудничества в исследованиях послеледниковой и голоценовой истории евразийских арктических морей, а также неоплейстоценовой истории Арктического бассейна в рамках российско-германских научных проектов (Climate Change in the Arctic; Laptev Sea System; Changing Arctic Transpolar System (CATS), CATS Synthesis: The Changing Arctic Transpolar System) и 4-х проектов РФФИ под руководством Талденковой Е.Е. (№ 08-05-0084а ; №11-05-01091а «Морская континентальная окраина Российской Арктики: плейстоцен-голоценовая история и современное состояние», №15-05-08497 «Плейстоценовая и голоценовая история развития природной среды подводных хребтов Менделеева и Ломоносова и прилегающей континентальной окраины Евразии»). Эти исследования отличает высокая детальность и комплексность подхода, повышающие достоверность палеогеографических реконструкций. Большая часть участников проекта - известные в России и за рубежом аналитики-исследователи со значительным опытом натурных наблюдений и экспедиций в высокоширотные районы Арктики. На их счету более 20 совместных докладов на российских и международных научных форумах, конгрессах ИНКВА. У участников более 30 совместных публикаций, в том числе в международных рецензируемых научных журналах из категории Q1. Обоснованием достижимости решения поставленных задач являются пилотные исследования образцов из разреза Бычье, подтвердившие высокую репрезентативность и полноту разреза и возможность обеспечить качественные аналитические данные для реконструкций и региональных корреляций. В связи со строительством дороги к селу Бычье транспортная доступность разреза улучшилась, и в июле 2021 г. в рамках экспедиции ГИН РАН Я.С. Овсепян отобрал дополнительные образцы на ОСЛ-датирование и XRF сканирование осадков. У коллектива есть доступ к необходимому оборудованию для успешного проведения аналитических работ (МГУ, ГИН РАН, ОГУ, ААНИИ, ИО РАН).