Holocene vegetation and climate history in Baikal Siberia reconstructed from pollen records and its implications for archaeology

Past research has greatly improved our understanding of palaeoenvironmental changes in the Lake Baikal Region, but at the same time has indicated intra-regional variations in this vast study area. Here we present a new AMS-dated late glacial-middle Holocene (ca. 13,500-4000 cal. yr BP) pollen record from Lake Ochaul (54 degrees 14'N, 106 degrees 28'E; altitude 641 m a.s.l.) situated in the less-studied area of Cis-Baikal and compare reconstructed vegetation and climate dynamics with the published environmental history of Trans-Baikal based on the pollen record from Lake Kotokel (52 degrees 47'N, 108 degrees 07'E; altitude 458 m a.s.l.). Although both records show comparable major long-term trends in vegetation, there are considerable differences. Around Ochaul the landscape was relatively open during the Younger Dryas stadial, but forest vegetation started to spread at the late glacial/Holocene transition (ca. 11,650 cal. yr BP), thus ca. 1000 years earlier than around Kotokel. While in both regions taiga forests spread during the early and middle Holocene, the marked increase in Scots pine pollen in the Kotokel record after ca. 6800 cal. yr BP is not seen in that from Ochaul, where birch and coniferous taxa, such as Siberian pine, larch, spruce and fir, dominate, indicating different environmental conditions and driving forces in both study regions. However, the pollen data from Ochaul emphasizes that the Cis-Baikal area also saw a continuous increase in forest cover and in the proportion of conifers over birch trees and shrubs during the early-middle Holocene, which may have contributed to a decrease in the number of large herbivores, the main food resource of the Early Neolithic hunter-gatherer groups. This and rather abrupt reorganization of atmospheric circulation, which affected atmospheric precipitation distribution resulting in thicker and longer-lasting snow cover, may have led to a collapse of Early Neolithic Kitoi populations ca. 6660 cal. yr BP followed by a cultural "hiatus" in the archaeological records during the Middle Neolithic phase (ca. 6660-6060 cal. yr BP). The results stress the importance of sub-regional palaeoenvironmental studies and the need for a representative network of well-dated, high-resolution sediment archives for a better understanding of environmental changes and their potential impacts on the hunter-gatherer populations in the archaeologically-defined micro-regions

Hydrological (in)stability in Southern Siberia during the Younger Dryas and early Holocene

Southern Siberia is currently undergoing rapid warming, inducing changes in vegetation, loss of permafrost, and impacts on the hydrodynamics of lakes and rivers. Lake sediments are key archives of environmental change and contain a record of ecosystem variability, as well as providing proxy indicators of wider environmental and climatic change. Investigating how hydrological systems have responded to past shifts in climate can provide essential context for better understanding future ecosystem changes in Siberia. Oxygen isotope ratios within lacustrine records provide fundamental information on past variability in hydrological systems. Here we present a new oxygen isotope record from diatom silica (ẟ18Odiatom) at Lake Baunt (55°11′15″N, 113°01,45″E), in the southern part of eastern Siberia, and consider how the site has responded to climate changes between the Younger Dryas and Early to Mid Holocene (ca. 12.4 to 6.2 ka cal BP). Excursions in ẟ18Odiatom are influenced by air temperature and the seasonality, quantity, and source of atmospheric precipitation. These variables are a function of the strength of the Siberian High, which controls temperature, the proportion and quantity of winter versus summer precipitation, and the relative dominance of Atlantic versus Pacific air masses. A regional comparison with other Siberian ẟ18Odiatom records, from lakes Baikal and Kotokel, suggests that ẟ18Odiatom variations in southern Siberia reflect increased continentality during the Younger Dryas, delayed Early Holocene warming in the region, and substantial climate instability between ~10.5 to ~8.2 ka cal BP. Unstable conditions during the Early Holocene thermal optimum most likely reflect localised changes from glacial melting. Taking the profiles from three very different lakes together, highlight the influence of site specific factors on the individual records, and how one site is not indicative of the region as a whole. Overall, the study documents how sensitive this important region is to both internal and external forcing

Basin morphology and seismic stratigraphy of Lake Kotokel, Baikal region, Russia

The basin of Lake Kotokel, located along the eastern shore of Lake Baikal, Russia, has attracted several scientific projects to investigate the climate, vegetation and lake history throughout the Late Pleistocene and Holocene. However, little was known about its basin structure and sediment architecture. Echo sounding and 3.5 kHz single frequency sub-bottom profiling were used to decipher the basin morphology and seismic stratigraphy to a depth of approximately 50 m. The bathymetric map shows a very shallow lake of 4 m mean water depth and an almost flat lake bottom. A distinct elongated small-sized depression of up to 12 m water depth between the north-western coast and a small island developed along an NW-SE-oriented fault line. A total of 46 km of seismic profiles crossing the lake along 12 transects shows that the bottom sediments consist of three different facies, which accords to previously analyzed core sequences. Several distortions of sediment layers at various sites indicate tectonically induced impact, which resulted in up to 3 m vertical offsets of sediment packages at local sites. The offsets indicate a probably still active fault along the western shoreline of the lake. Soft gyttja of the upper 6 m does not show distortions and may have obscured potential younger tectonic activity. The sediments date to the Late Pleistocene. Small updoming features along the boundary between layers I and II may be assigned to degassing processes or to seismic activity. River channel fills along the north-eastern coast are indicative of a lower lake level prior to 15 ka BP. The sediment stratigraphy indicates that suitable coring sites for paleoclimate studies are only located in the southern part of the basin where almost undisturbed sediments can be expected. © 2012 Elsevier Ltd and INQUA

X-ray fluorescence determination of bromine in lake sediments for paleoclimatic studies

Оценена возможность использования традиционного рентгенофлуоресцентного метода анализа (РФА) с волновой дисперсией (РФА ВД) и РФА с полным внешним отражением (РФА ПВО) для изучения распределения брома по глубине керна на примере донных отложений о. Байкал и о. Хара-Нур. Для проведения РФА ВД излучатели массой 200-300 мг и диаметром 10 мм прессовали в виде таблеток на подложке из борной кислоты; содержания брома рассчитывали способом внутреннего стандарта с коррекцией с использованием фундаментальных параметров. Для РФА ПВО из измельченной пробы массой 20 мг готовили суспензию на основе поверхностно-активного вещества Triton X-100, в которую добавляли внутренний стандарт - раствор Ge. Пределы обнаружения брома равны 1 мг/кг и 0.4 мг/кг для РФА ВД и РФА ПВО соответственно. Показано, что результаты определения брома, полученные с помощью разных вариантов РФА, сопоставимы между собой и могут быть использованы при палеоклиматических реконструкциях. Одним из основных преимуществ предлагаемых методик РФА ВД и РФА ПВО является отсутствие необходимости наличия стандартных образцов донных отложений с аттестованным содержанием брома.One of the signals of changing paleoclimate is the concentration of bromine which is increased in the warm periods and correlated with the content of organic matter in sediments. A conventional wavelength dispersive X-ray fluorescence analysis (WDXRF) and total reflection X-ray fluorescence analysis (TXRF) have been applied to study the bromine distributions in the sediments of Lake Baikal and Lake Khara-Nur. In order to carry out WDXRF, the samples weighing about 200-300 mg with diameter of 10 mm were pressed as tablets on the boric acid base; the bromine concentrations were calculated by the internal standard method with correction using fundamental parameters. For TXRF measurements the powdered sample weighing 20 mg was suspended in the surface-active solution of Triton X-100 and Ge solution was added for the internal standardization. The detection limits of bromine were 1 mg/kg and 0.4 mg/kg for WDXRF and TXRF respectively. It was shown that the results of the bromine determination obtained with different XRF techniques were comparable to each other and can be used for palaeoclimatic reconstruction. One of the main advantages of the offered WDXRF and TXRF techniques is the lack of necessity for the standard reference materials of sediments with certified content of bromine

Basin morphology and seismic stratigraphy of Lake Kotokel, Baikal region, Russia

The basin of Lake Kotokel, located along the eastern shore of Lake Baikal, Russia, has attracted several scientific projects to investigate the climate, vegetation and lake history throughout the Late Pleistocene and Holocene. However, little was known about its basin structure and sediment architecture. Echo sounding and 3.5 kHz single frequency sub-bottom profiling were used to decipher the basin morphology and seismic stratigraphy to a depth of approximately 50 m. The bathymetric map shows a very shallow lake of 4 m mean water depth and an almost flat lake bottom. A distinct elongated small-sized depression of up to 12 m water depth between the north-western coast and a small island developed along an NW-SE-oriented fault line. A total of 46 km of seismic profiles crossing the lake along 12 transects shows that the bottom sediments consist of three different facies, which accords to previously analyzed core sequences. Several distortions of sediment layers at various sites indicate tectonically induced impact, which resulted in up to 3 m vertical offsets of sediment packages at local sites. The offsets indicate a probably still active fault along the western shoreline of the lake. Soft gyttja of the upper 6 m does not show distortions and may have obscured potential younger tectonic activity. The sediments date to the Late Pleistocene. Small updoming features along the boundary between layers I and II may be assigned to degassing processes or to seismic activity. River channel fills along the north-eastern coast are indicative of a lower lake level prior to 15 ka BP. The sediment stratigraphy indicates that suitable coring sites for paleoclimate studies are only located in the southern part of the basin where almost undisturbed sediments can be expected. © 2012 Elsevier Ltd and INQUA

РЕНТГЕНОФЛУОРЕСЦЕНТНОЕ ОПРЕДЕЛЕНИЕ БРОМА В ДОННЫХ ОТЛОЖЕНИЯХ ОЗЕР ДЛЯ ПАЛЕОКЛИМАТИЧЕСКИХ ИССЛЕДОВАНИЙ

One of the signals of changing paleoclimate is the concentration of bromine which is increased in the warm periods and correlated with the content of organic matter in sediments. A conventional wavelength dispersive X-ray fluorescence analysis (WDXRF) and total reflection X-ray fluorescence analysis (TXRF) have been applied to study the bromine distributions in the sediments ofLakeBaikal andLakeKhara-Nur. In order to carry out WDXRF, the samples weighing about 200-300 mg with diameter of10 mm were pressed as tablets on the boric acid base; the bromine concentrations were calculated by the internal standard method with correction using fundamental parameters. For TXRF measurements the powdered sample weighing 20 mg was suspended in the surface-active solution of Triton X-100 and Ge solution was added for the internal standardization. The detection limits of bromine were 1 mg/kg and 0.4 mg/kg for WDXRF and TXRF respectively. It was shown that the results of the bromine determination obtained with different XRF techniques were comparable to each other and can be used for palaeoclimatic reconstruction. One of the main advantages of the offered WDXRF and TXRF techniques is the lack of necessity for the standard reference materials of sediments with certified content of bromine.Keywords: X-ray fluorescence analysis, XRF, TXRF, SRXRF, sediments, bromine, paleoclimate(Russian) DOI: http://dx.doi.org/10.15826/analitika.2015.19.4.008G.V. Pashkova1*, E.V. Ivanov2,T.S. Aisueva2, А.А. Shchetnikov1, Yu.N. Markova2, A.L. Finkelshtein2 1Institute of the Earth’s Crust, Siberian Branch of Russian Academy of Sciences, Irkutsk,  Russian Federation2Vinogradov Institute of Geochemistry, Siberian Branch of Russian Academy of Sciences, Irkutsk, Russian FederationОценена возможность использования традиционного рентгенофлуоресцентного метода анализа (РФА) с волновой дисперсией (РФА ВД) и РФА с полным внешним отражением (РФА ПВО) для изучения распределения брома по глубине керна на примере донных отложений о. Байкал и о. Хара-Нур. Для проведения РФА ВД излучатели массой 200-300 мг и диаметром10 мм прессовали в виде таблеток на подложке из борной кислоты; содержания брома рассчитывали способом внутреннего стандарта с коррекцией с использованием фундаментальных параметров. Для РФА ПВО из измельченной пробы массой 20 мг готовили суспензию на основе поверхностно-активного вещества Triton X-100, в которую добавляли внутренний стандарт – раствор Ge. Пределы обнаружения брома равны 1 мг/кг и 0.4 мг/кг для РФА ВД и РФА ПВО соответственно. Показано, что результаты определения брома, полученные с помощью разных вариантов РФА, сопоставимы между собой и могут быть использованы при палеоклиматических реконструкциях. Одним из основных преимуществ предлагаемых методик РФА ВД и РФА ПВО является отсутствие необходимости наличия стандартных образцов донных отложений с аттестованным содержанием брома.Ключевые слова: рентгенофлуоресцентный анализ, РФА, РФА ПВО, РФА СИ, донные отложения, бром, палеоклимат.DOI: http://dx.doi.org/10.15826/analitika.2015.19.4.00

Куйтунская долина - экзогеодинамический полигон для отработки междисциплинарной методики исследования седиментационных обстановок формирования покровного лессовидного комплекса в позднем плейстоцене Забайкалья

An interdisciplinary research in the Late Quaternary loess-like cover deposits in the valley of the Kuytunka River (Western Transbaikalia) was aimed at reconstructing the conditions and dynamics of regional sedimentation. Particular attention is paid to assessing the information capacity of the methods involved therein: lithofacies analysis, grain-size analysis, and petromagnetic and lithochemical analyses. It is shown that the results of each method independently provide additional information on the processes of sedimentation, are not duplicated, and make it possible to obtain a full characterization of the factors and features of sedimentogenesis. It was found that the valley sedimentation was of cyclic character: warm (soil formation) periods changed to the periods of cooling-(accumulation of sandy-loamy strata); all processes occurred predominantly in semi-arid climate with slight fluctuations in humidity. The mode of the normal formation of a blanket of sedimentary material manifests itself in the structure and properties of deposits exposed on the southern slope of the valley (Kuytun-1 section). Intensive slope processes, and reworking and remixing of sediments on the gentle valley north-exposure slope by catastrophic flows (slope mudflows) and cryogenesis are reflected in the structure and properties of the deposits exposed in the Kuytun-2 section. There are shown the advantages of an integrated approach for detailing the structure of the sections, explaining the genesis of sediments, determining the most probable source areas for the sediment and modes of sediment transport, and reconstructing sedimentary environments.Междисциплинарное изучение позднечетвертичных покровных лессовидных отложений в долине р. Куйтунка (Западное Забайкалье) выполнено с целью реконструкции обстановок и динамики регионального осадконакопления. Особое внимание в работе уделено оценке информативности используемых при исследованиях таких образований методами литолого-фациального, гранулометрического, петромагнитного и литохимического анализа. Показано, что результаты каждого метода дают независимую, дополнительную информацию о процессах осадконакопления, не дублируют друг друга и позволяют получить полноценную характеристику условий и особенностей седиментогенеза. Установлено, что осадконакопление в долине носило циклический характер: периоды потеплений (почвообразования) сменялись периодами похолоданий (накопления супесчано-суглинистых толщ), все процессы происходили в преимущественно семиаридном климате с небольшими колебаниями влажности. Режим «нормального» образования покровного осадочного чехла при участии делювиальных процессов зафиксирован в строении и свойствах отложений, вскрытых на склоне южной экспозиции долины (разрез Куйтун-1). Интенсивные склоновые процессы, переработка, перемешивание отложений пологого склона долины северной экспозиции катастрофическими потоками (склоновые сели) и криогенезом отражены в строении и свойствах облессованных отложений, вскрытых разрезом Куйтун-2. Показаны преимущества комплексного подхода для детализации строения разрезов, уточнения генезиса осадков, определения наиболее вероятных источников сноса и способов транспортировки осадочного материала, реконструкций обстановок осадконакопления

ТЕОРЕТИЧЕСКИЕ ОСНОВЫ СТРУКТУРНОЙ ГЕОМОРФОЛОГИИ (К 110-ЛЕТИЮ Н.А. ФЛОРЕНСОВА)

Nikolai Aleksandrovich Florensov is a Russian scientist who is famous for his contribution to the theoretical foundations of structural geomorphology.He formulated the law of the circulation of material in the Earth's crust, which is manifested by a periodically arisinglithodynamicflow, in the development cycle of which two main phases are distinguished as ascending and descending geodynamics. In our opinion, there is also the third phase, stabilization.This process is reflected in the morphological types of mountains. Considering the conditions of intracontinental orogeny, N.A.Florensovdistinguished two main types: constructive and destructive.Developing this concept, he solved a number of theoretical and philosophical problems concerning the inextricable relationship between the relief and the structure of the geological substratum, its geodynamics and, as a consequence, proposed to consider their relationship as changes in geomorphological formations in time and space. The scientific creativity of NA. Florensov, as a whole, is comparable in importance with that of other most prominent geomorphologists of the late 19th and 20th centuries, including V.M. Davis, W. Penk, S.S. Shults, I.P. Gerasimov, and L. King. Н.А. Флоренсов являлся одним из основоположников развития теоретических основ структурной геоморфологии. Им был открыт закон круговорота вещества земной коры в виде периодически возникающего литодинамического потока, в цикле развития которого наблюдаются две главные фазы – восходящей и нисходящей геодинамики. Авторы статьи выделяют еще и третью фазу – стабилизации. Внешним отображением этого процесса являются морфологические типы гор. В условиях внутриконтинентального орогенеза Н.А. Флоренсов выделял два основных типа: конструктивный и деструктивный. Разрабатывая данную концепцию, Николай Александрович решил ряд теоретико-философских задач о неразрывной связи рельефа со структурой геологического субстрата, его геодинамикой и, как следствие этого, предложил рассматривать их связь как смену геоморфологических формаций во времени и пространстве. Оценивая значение научного творчества Н.А. Флоренсова в целом, авторы статьи считают, что оно соизмеримо с таковым других великих геоморфологов конца XIX–XX вв., таких как В.М. Дэвис, В. Пенк, С.С. Шульц, И.П. Герасимов и Л. Кинг.

Hydrological (in)stability in Southern Siberia during the Younger Dryas and early Holocene

Southern Siberia is currently undergoing rapid warming, inducing changes in vegetation, loss of permafrost, and impacts on the hydrodynamics of lakes and rivers. Lake sediments are key archives of environmental change and contain a record of ecosystem variability, as well as providing proxy indicators of wider environmental and climatic change. Investigating how hydrological systems have responded to past shifts in climate can provide essential context for better understanding future ecosystem changes in Siberia. Oxygen isotope ratios within lacustrine records provide fundamental information on past variability in hydrological systems. Here we present a new oxygen isotope record from diatom silica (ẟ18Odiatom) at Lake Baunt (55°11′15″N, 113°01,45″E), in the southern part of eastern Siberia, and consider how the site has responded to climate changes between the Younger Dryas and Early to Mid Holocene (ca. 12.4 to 6.2 ka cal BP). Excursions in ẟ18Odiatom are influenced by air temperature and the seasonality, quantity, and source of atmospheric precipitation. These variables are a function of the strength of the Siberian High, which controls temperature, the proportion and quantity of winter versus summer precipitation, and the relative dominance of Atlantic versus Pacific air masses. A regional comparison with other Siberian ẟ18Odiatom records, from lakes Baikal and Kotokel, suggests that ẟ18Odiatom variations in southern Siberia reflect increased continentality during the Younger Dryas, delayed Early Holocene warming in the region, and substantial climate instability between ~10.5 to ~8.2 ka cal BP. Unstable conditions during the Early Holocene thermal optimum most likely reflect localised changes from glacial melting. Taking the profiles from three very different lakes together, highlight the influence of site specific factors on the individual records, and how one site is not indicative of the region as a whole. Overall, the study documents how sensitive this important region is to both internal and external forcing