ALBERT

Description: A high-resolution pollen record from Lake Teletskoye documents the climate-related vegetation history of the northern Altai Mountain region during the last millennium. Siberian pine taiga with Scots pine, fir, spruce, and birch dominated the vegetation between ca. AD 1050 and 1100. The climate was similar to modern. In the beginning of the 12th century, birch and shrub alder increased. Lowered pollen concentrations and simultaneous peaks in herbs (especially Artemisia and Poaceae), ferns, and charcoal fragments point to colder and more arid climate conditions than before, with frequent fire events. Around AD 1200, regional climate became warmer and more humid than present, as revealed by an increase of Siberian pine and decreases of dry herb taxa and charcoal contents. Climatic conditions were rather stable until ca. AD 1410. An increase of Artemisia pollen may reflect slightly drier climate conditions between AD 1410 and 1560. Increases in Alnus, Betula, Artemisia, and Chenopodiaceae pollen and in charcoal particle contents may reflect further deterioration of climate conditions between AD 1560 and 1810, consistent with the Little Ice Age. After AD 1850 the vegetation gradually approached the modern one, in conjunction with ongoing climate warming.

Description: A unique 800-yr-long record of annual temperatures and precipitation over the south of western Siberia has been reconstructed from the bottom sediments of Teletskoye Lake, Altai Mountains using an X-ray fluorescence scanner (XRF) providing 0.1-mm resolution timeseries of elemental composition and X-ray density (XRD). Br content appears to be broadly correlative with mean annual temperature variations because of changes in catchment vegetation productivity. Sr/Rb ratio reflects the proportion of the unweathered terrestrial fraction. XRD appears to reflect water yield regime and sediment flux. Sedimentation is rather continuous because annual clastic supply and deposited mass are the same. The artificial neural networks method was applied to convert annual sedimentary time-series of XRD, Br content, and Sr/Rb ratio to annual records of temperature and precipitation using a transfer function. Comparison of these reconstructed Siberian records with the annual record of air temperature for the Northern Hemisphere shows similar trends in climatic variability over the past 800 yr. Estimated harmonic oscillations of temperature and precipitation values for both historical and reconstructed periods reveal subdecadal cyclicity.

Description: Lake high-stand sediments are found in three onshore terraces at Lake Donggi Cona, northeastern Tibetan Plateau, and reveal characteristics of hydrological changes on lake shorelines triggered by climate change, geomorphological processes, and neo-tectonic movements. The terraces consist of fluvial–alluvial to littoral-lacustrine facies. End-member modeling of grain-size distributions allowed quantification of sediment transport processes and relative lake levels during times of deposition. Radiocarbon dating revealed higher than modern lake levels during the early and mid Holocene. Lake levels follow the trend of Asian monsoon dynamics, and are modified by local non-climatic drivers. Site-specific impacts explain fluctuations during the initial lake-level rise ~ 11 cal ka BP. Maximum lake extension reached ~ 9.2 cal ka BP, at ~ 16.5 m above present lake level (a.p.l.l.). Littoral and lacustrine sediment deposition paused during a phase of fluvial activity and post-depositional cryoturbations at ~ 8.5 cal ka BP, when the lake level fell to ~ 8 m a.p.l.l. After a second maximum at ~ 7.5 cal ka BP, lake level declined slightly at ~ 6.8 cal ka BP, probably due to a non-climatic pulse that caused lake opening. The level remained high until a transition towards drier conditions ~ 4.7 cal ka BP. Though discontinuous, high-stand sediments provide a unique, high-resolution archive.

Description: Aquatic macrophytes from a lacustrine environment are highly prone to a reservoir effect, resulting in an overestimation of age. This is often caused by the incorporation of dissolved carbon (CO2 and HCO3–) through photosynthesis from lake waters that have a different 14C activity than the atmosphere. The atmosphere-water disparity is often produced by a mixing of carbon between the water body and its terrestrial surroundings, a process highly prone to temporal variations. Thus, only a comprehensive understanding of the 14C budget over time enables a reliable chronology of lacustrine records. We studied lacustrine sediments from Lake Heihai on the northern Tibetan Plateau with a recent reservoir effect of 6465 ± 75 14C yr as estimated from accelerator mass spectrometry (AMS) dating of three living aquatic plants. Age inversions in a well-laminated composite core from the lake suggest that the reservoir effect markedly changed over the depositional period. In the lower part of the core, an excellent correlation was observed between the allochthonous input of dolomite and the inverse 14C ages, indicating the incorporation of dissolved 14C-dead carbon from a limestone catchment in the plant material. For the upper part of the core, sediment recycling of Holocene high-stand deposits may have further contributed to the reservoir effect. These findings give rise to a reliable process- and provenance-based chronology within a confidence interval supported by 137Cs measurements and magnetostratigraphic investigations. Our results highlight the need to identify the interactions of lakes with their surroundings to estimate reservoir-corrected ages in lacustrine settings.

Description: Surface mineralogical compositions and their association to modern processes are well known from the east Atlantic and south-west Indian sectors of the Southern Ocean, but data from the interface of these areas - the Prydz Bay–Kerguelen region - is still missing. The objective of our study was to provide mineralogical data of reference samples from this region and to relate these mineralogical assemblages to hinterland geology, weathering, transport and depositional processes. Clay mineral assemblages were analysed by means of X-ray diffraction technique. Heavy mineral assemblages were determined by counting of gravity-separated grains under a polarizing microscope. Results show that by use of clay mineral assemblages four mineralogical provinces can be subdivided: i) continental shelf, ii) continental slope, iii) deep sea, iv) Kerguelen Plateau. Heavy mineral assemblages in the fine sand fraction are relatively uniform except for samples taken from the East Antarctic shelf. Our findings show that mineralogical studies on sediment cores from the study area have the potential to provide insights into past shifts in ice-supported transport and activity and provenance of different water masses (e.g. Antarctic slope current and deep western boundary current) in the Prydz Bay–Kerguelen region.

Description: The clay mineralogical composition of a 552 cm long sediment core from Lake Terrasovoje in Amery Oasis, East Antarctica, was analysed and compared with that in surface sediments from other locations in the vicinity. The lower part of the sediment core is formed by sub- and proglacial sediments with a dominance of smectite and illite, and lower amounts of kaolinite and chlorite. The upper part of the core is deposited after 12 500 cal yr bp and mainly composed of illite and kaolinite, with low amounts of smectite and chlorite, such as found in samples from rock outcrops and covering sediments throughout Amery Oasis. The clay composition in the lower section of core Lz1005 suggest that the basin of Lake Terrasovoje was filled by a 150–200 m thickened Nemesis Glacier prior to 12 500 cal yr bp rather than by local ice caps.

Description: Situated in the Yana-Highlands, the Batagai profile is one of the few inland permafrost outcrops in Yakutia and, for the time being, the biggest and most active thermoerosional cirque worldwide. With Yerkhoyansk recorded as place of the pole of cold, the Yana Highlands represent the region with the most severe climatic continentality in the northern hemisphere. In contrast to the numerous sequences in today’s coastal lowlands, the Batagai sequence was always unaffected by maritime climate influence during its formation and thus better indicates the macro-climate evolution in NE-Siberia. As result of intense thermal degradation, the outcrop formed within 30 years only and cut deep into ice-rich permafrost deposits. The 60 m deep outcrop is now about 850 m in diameter, but erosion rates as high as 15 m/year are changing the dimensions continuously. The Batagai profile thus represents a unique window into the past (and future) of ice-rich permafrost deposits in Yakutia. Field based observations have shown that the permafrost sequence consists of 4 distinct units: below a thin Holocene surface cover, a 30 meter thick Ice Complex with characteristic thick ice wedges has formed. At the base of the Ice Complex, there is an up to 2 m thick layer of plant material including large woody remains. Subjacent to this organic layer of supposedly Eemian origin, there is a horizontally stratified unit composed of silty-sand and without thick syngenetic ice wedges presumably deposited during the Middle Pleistocene. At the very base of the sequence, there appears to emerge another unit including syngenetic ice wedges. This unit was not accessible for sampling. The accessible upper about 45 meter of the sequence were sampled from top to bottom in one meter steps using, due to the difficult accessibility of the permafrost wall, thermokarst mounds in the less steep part of the outcrop. The samples were taken for sedimentological analyses and especially for plant macrofossil and other palaeoecological studies. Whereas sediments give insight into the genesis of the sequence, fossil plant macroremains provide information on local vegetation patterns and habitats at the time of deposition; while palynological analyses reflect the regional vegetation and climate history. First palaeobotanical results will be represented in Session 13: Palaeoenvironments in permafrost affected areas. The sedimentological analyses revealed that, despite clearly delimitable bedding units visible at the outcrop, there is no distinct litho-stratigraphical differentiation recognizable in the grain size distribution or other sedimentological parameters. Accordingly, the sequence is characterized by a grain size signature typical for Ice Complex deposits. In comparison to other Yakutian ice-rich permafrost sequences, e.g. in the coastal lowlands, the Batagai profile is however distinguished by a higher fraction of fine sand over the whole recorded sequence. This might be due to increased aeolian deposition from local sources, e.g. from barren ridges in the highlands uncovered by vegetation. The assumption that aeolian deposition played a substantial role in the formation of the sequence is also suggested by impressive dunes in the immediate vicinity of the profile at the boundary of Batagai city.