The cryptotephra record of the Marine Isotope Stage 12 to 10 interval (460–335 ka) at Tenaghi Philippon, Greece: Exploring chronological markers for the Middle Pleistocene of the Mediterranean region

Precise chronologies that allow direct correlation of paleoclimate archives are a prerequisite for deciphering the spatiotemporal characteristics of short-term climate variability. Such chronologies can be established through the analysis of tephra layers that are preserved in the respective sedimentary archives. Here we explore the yet untapped tephrochronological potential of the Eastern Mediterranean region for the Middle Pleistocene, specifically for the interval spanning Marine Isotope Stages (MIS) 12–10 (460–335 ka). High-resolution cryptotephra analysis was carried out on peat cores spanning the MIS 12–10 interval that have been recovered from the iconic climate archive of Tenaghi Philippon, NE Greece. Eighteen primary cryptotephras were identified, and major- and trace-element analyses of single glass shards from all cryptotephras were performed in order to correlate them with their eruptive sources. The results suggest origins from both Italian and Aegean Arc volcanoes. Specifically, one cryptotephra layer could be firmly correlated with the Cape Therma 1 eruption from Santorini, which makes it the first distal tephra finding for this eruptive event. While eight further cryptotephras could be tentatively correlated with their volcanic or even eruptive sources, the provenance of another nine cryptotephras as yet remains unknown. The relatively large number of cryptotephras that could not be assigned to specific volcanic sources and eruptive events reflects the still considerable knowledge gap regarding the geochronology and geochemistry of proximal tephra deposits from the Middle Pleistocene of the Central and Eastern Mediterranean regions. Due to the lack of well-dated Middle Pleistocene eruptions, we provide age estimates for all cryptotephra layers identified in the MIS 12–10 interval at Tenaghi Philippon based on high-resolution pollen data from the same cores. While eight of the identified cryptotephras were deposited within MIS 12 (~438–427 ka), one cryptotephra was deposited at the onset of MIS 11 (~419 ka), five cryptotephras during the younger part of MIS 11 (~391–367 ka), and four cryptotephras during MIS 10 (~359–336 ka). The high number of cryptotephras from multiple sources as recorded in the MIS 12–10 interval at Tenaghi Philippon highlights the key role of this archive for linking tephrostratigraphic lattices for the Middle Pleistocene of the Central and Eastern Mediterranean regions

Late Quaternary vegetation and lake system dynamics in north-eastern Siberia: Implications for seasonal climate variability

© 2015 Elsevier LtdAlthough the climate development over the Holocene in the Northern Hemisphere is well known, palaeolimnological climate reconstructions reveal spatiotemporal variability in northern Eurasia. Here we present a multi-proxy study from north-eastern Siberia combining sediment geochemistry, and diatom and pollen data from lake-sediment cores covering the last 38,000 cal. years. Our results show major changes in pyrite content and fragilarioid diatom species distributions, indicating prolonged seasonal lake-ice cover between ∼13,500 and ∼8900 cal. years BP and possibly during the 8200 cal. years BP cold event. A pollen-based climate reconstruction generated a mean July temperature of 17.8 °C during the Holocene Thermal Maximum (HTM) between ∼8900 and ∼4500 cal. years BP. Naviculoid diatoms appear in the late Holocene indicating a shortening of the seasonal ice cover that continues today. Our results reveal a strong correlation between the applied terrestrial and aquatic indicators and natural seasonal climate dynamics in the Holocene. Planktonic diatoms show a strong response to changes in the lake ecosystem due to recent climate warming in the Anthropocene. We assess other palaeolimnological studies to infer the spatiotemporal pattern of the HTM and affirm that the timing of its onset, a difference of up to 3000 years from north to south, can be well explained by climatic teleconnections. The westerlies brought cold air to this part of Siberia until the Laurentide ice-sheet vanished 7000 years ago. The apparent delayed ending of the HTM in the central Siberian record can be ascribed to the exceedance of ecological thresholds trailing behind increases in winter temperatures and decreases in contrast in insolation between seasons during the mid to late Holocene as well as lacking differentiation between summer and winter trends in paleolimnological reconstructions

Late Quaternary vegetation and lake system dynamics in north-eastern Siberia: Implications for seasonal climate variability

© 2015 Elsevier Ltd. Although the climate development over the Holocene in the Northern Hemisphere is well known, palaeolimnological climate reconstructions reveal spatiotemporal variability in northern Eurasia. Here we present a multi-proxy study from north-eastern Siberia combining sediment geochemistry, and diatom and pollen data from lake-sediment cores covering the last 38,000cal. years. Our results show major changes in pyrite content and fragilarioid diatom species distributions, indicating prolonged seasonal lake-ice cover between ~13,500 and ~8900cal. years BP and possibly during the 8200cal. years BP cold event. A pollen-based climate reconstruction generated a mean July temperature of 17.8°C during the Holocene Thermal Maximum (HTM) between ~8900 and ~4500cal. years BP. Naviculoid diatoms appear in the late Holocene indicating a shortening of the seasonal ice cover that continues today. Our results reveal a strong correlation between the applied terrestrial and aquatic indicators and natural seasonal climate dynamics in the Holocene. Planktonic diatoms show a strong response to changes in the lake ecosystem due to recent climate warming in the Anthropocene.We assess other palaeolimnological studies to infer the spatiotemporal pattern of the HTM and affirm that the timing of its onset, a difference of up to 3000 years from north to south, can be well explained by climatic teleconnections. The westerlies brought cold air to this part of Siberia until the Laurentide ice-sheet vanished 7000 years ago. The apparent delayed ending of the HTM in the central Siberian record can be ascribed to the exceedance of ecological thresholds trailing behind increases in winter temperatures and decreases in contrast in insolation between seasons during the mid to late Holocene as well as lacking differentiation between summer and winter trends in paleolimnological reconstructions

Ранний диагенез донных осадков пресноводных озер острова Вайгач

The paper presents results of studying the diagenetic transformation of bottom sediments from two freshwater lakes — Talatinskoe and Tundrovoe — in the Vaigach Island. The study of biogeochemical processes in the conditions of present-day climate instability is especially important for Arctic water ecosystems, since their environmental sustainability is extremely low, and the effects of global warming are most significant. According to available climate forecasts, the Vaigach Island is located in the zone of maximum changes in natural complexes. The lake-river systems of the island are unique island geosystems, but to date they are poorly understood.Our aim was to carry out comprehensive research on the biogeochemical processes of the sulfur cycle as the geochemical aspect of the bacterial sulfate reduction process, which involves the conjugation of the cycles of carbon, sulfur and iron, participating in redox processes that play an important role in sedimentation and early diagenesis. In order to achieve this goal, a multi-method (hydrochemical, geochemical, etc.) approach was developed using standard generally approved laboratory practices adapted to the study goals.Based on the pollen data, it was found that the formation of the bottom sediments of Lake Talatinskoe occurred in the current climatic conditions of the tundra. The data on the distribution of grain size fractions allow us to conclude that the sediment sequences of both lakes undergo regular destruction and mixing during seasonal freezing-thawing. This was reflected in the random distribution of all the parameters studied and in the impossibility of determining the sedimentation rate. The data obtained on the quantitative characteristics of sulfate reduction parameters (reduced compounds, forms of reactive iron, the amount of organic matter and its qualitative composition), their distribution and transformation indicate a low intensity of redox processes in precipitation. The most likely reason for this is the high degree of humification of the terrigenous organic matter and the low temperatures of the microorganisms’ habitat.Приведены результаты комплексных исследований процессов диагенетического преобразования донных осадков пресноводных озер о. Вайгач - Талатинское и Тундровое. Установлено (по данным спорово-пыльцевого анализа), что формирование донных отложений оз. Талатинское происходило в современных климатических условиях тундры. Показано, что отсутствие закономерностей в распределении всех изучаемых параметров и невозможность определения скорости осадконакопления, обусловлены перемешиванием отложений обоих озер в ходе сезонного замерзания-оттаивания. Данные о количественных характеристиках параметров сульфатредукции (соединений восстановленной серы, форм реакционноспособного железа, органического вещества), их распределении и трансформации свидетельствуют о низкой интенсивности редокс-процессов в осадках вследствие малой доступности органического вещества для микроорганизмов и суровости среды их обитания

Invariance of visual perception

Perception and thinking is based largely on the ability of the brain to find in the world invariant features. The purpose of the study – to determine the ranges invariant perception, for various transformations of images of objects (angular size – magnitude, turn corners-projections), under which quantitative characteristics of their perceptions remained unchanged. The recognition psychophysical threshold measuring of incomplete line drawing images (Gollin-test) with different sizes and rotations was provided. The experimental data of invariance perception to the image size transformation and rotating of images are presented. We demonstrate that there is a wide range of angular sizes (from 1.0 up to 50 degrees of visual angle) across which the threshold of recognition of incomplete images does not depend on object size. However, there was found to be a narrow range of small sizes of stimulus (0.19–1, 0 degrees of visual angle) at which there was found to be a dependence of performance on object size. The thresholds of recognition of 3-D objects when viewed as incomplete 2-D images were measured at psychophysical experiments varying perspective of 3-D objects during testing. The memory template of the test objects description has "invariance" properties from 15 up to an angle of 60 degrees. The algorithm for template formation of 3-D objects in the human visual system need to be modeled, taking account of the invariance mechanism. The model of invariant perception, combining well-known model log-polar model and wavelet transform as the primary stage of filtration, and then match filtering and decision-making