ALBERT

Description: Sediment cores from the Northwind Ridge north of the Arctic Chukchi-Alaskan margin were analyzed for a suite of stratigraphic and provenance proxies. Based on the correlation to previously studied regional records, cores under study present sedimentary environments of Marine Isotope Stages (MIS) 1e11 (~0.4 Ma) on millennial time scales. Contrasting glacial-interglacial conditions and provenance were characterized by means of clay-mineral and geochemical (elemental and isotopic) proxies along with grain size. Interglacial environments are interpreted as sea-ice dominated, with pre-Holocene sediment transported mostly from the East Siberian to Chukchi-Alaskan margin. In comparison with the recent conditions, this pattern suggests a stronger Transpolar Drift expanding into the Canada Basin at the expense of the Beaufort Gyre, or stronger along-shelf currents. Glacial intervals prior to MIS4 have a predominantly North American signature with carbonaceous or terrigenous source rocks. Carbonaceous inputs marked by Ca peaks are tracked to the western Canadian Arctic Archipelago eroded by the Laurentide Ice Sheet (LIS). Terrigenous sources (Zr peaks) are likely related to areas impacted by the Innuitian Ice Sheet and/or the LIS Mackenzie ice stream. MIS 4 and 2 intervals have a different composition with the Siberian/Chukchi rather than North American provenance. A stronger winnowing indicated by grain size in the glacial intervals suggests a stronger mid-depth circulation. Study results provide new boundary conditions for modeling paleocirculation and glaciations in the western Arctic Ocean.

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.

Description: We present a methodological approach for the characterization of spatial variations of environmental and transport conditions based on geochemical data. We analyzed the geochemical characteristics of terrestrial sediments on an alluvial fan and adjacent areas in the eastern part of the Donggi Cona catchment. The geochemical characteristics of the sediment samples were measured using X-ray fluorescence spectroscopy. A factor model based on nine elements (Sr, Rb, Zn, Fe, Mn, V, Ti, Ca and K) gave the best results using factor analysis. Our results show that factor analysis of geochemical data can explain spatial variations in the catchment, even within a relatively small area with more or less constant climatological conditions. The four most important factors of our model explain 68.4% of the total variance within the dataset. The four factors represent a carbonate, weathering and two redox condition signals, respectively. The spatial distribution of factor loadings points to regions with specific environmental conditions. These regions show a certain carbonate input or production (factor 1), specific weathering rates (factor 2) or specific redox conditions (factors 3 and 4). The factor loadings of the first and second factor are used to reclassify the data into four groups, being dune, loess, lake and fluvial gravel sediments. This reclassification confirmsor improves the prior field classification in 70% of all cases. For 23% of the samples, the model gave a different interpretation. The factor loadings in these cases represent the origin of the material rather than its present sediment type, thereby giving valuable information about sediment provenance. Since the third and fourth factor seem more dependent on location, they do not differentiate between different sediment types. Multivariate statistics of the geochemistry of terrestrial sediments (i) allows the subdivision of samples into different sediment types, (ii) indicates dominant regions for weathering, carbonate production and manganese washout and (iii) gives suggestions about the provenance of the sediments. This is the first detailed study of geochemical parameters on the Tibetan Plateau not focusing on lake cores, resulting in a spatial characterization of the local geochemistry. This gives insight in the sediment transport connections between the catchment and the lake, illustrating the value of terrestrial sediments as additional indicator of environmental variations.

Description: Sediments of a thermokarst system on the north-eastern Tibetan Plateau were studied to infer changes in the lacustrine depositional environment related to climatic changes since the early Holocene. The thermokarst pond with a length of 360 m is situated in a 14.5 × 6 km tectonically unaffected intermontane basin, which is underlain by discontinuous permafrost. A lake sediment core and bankside lacustrine onshore deposits were analysed. Additionally, fossil lake sediments were investigated, which document a former lake-level high stand. The sediments are mainly composed of marls with variable amounts of silt carbonate micrite, and organic matter. On the basis of sedimentological (grain size data), geochemical (XRF), mineralogical (XRD) and micropaleontological data (ostracods and chironomide assemblages) a reconstruction of a paleolake environment was achieved. Lacustrine sediments with endogenic carbonate precipitation suggest a lacustrine environment since at least 19.0 cal ka BP. However, because of relocation and reworking processes in the lake, the sediments did not provide distinct information about the ultimate formation of the lake. The high amount of endogenic carbonate suggests prolonged still-water conditions at about 9.3 cal ka BP. Ostracod shells and chironomid head capsules in fossil lake sediments indicate at least one former lake-level high stand, which were developed between the early and middle Holocene. From the late Holocene the area was possibly characterized by a lake-level decline, documented by a hiatus between lacustrine sediments and a reworked loess or loess-like horizon. After the lake-level decline and the following warming period, the area was affected by thermally-induced subsidence and a re-flooding of the basin because of thawing permafrost.

Description: A 380 cm long sediment core from Lake Temje (central Yakutia, Eastern Siberia) was studied to infer Holocene palaeoenvironmental change in the extreme periglacial setting of eastern Siberia during the last 10,000 years. Data on sediment composition were used to characterize changes in the depositional environment during the ontogenetic development of the Lake Temje. The analysis of fossil chironomid remains and statistical treatment of chironomid data by the application of a newly developed regional Russian transfer functions provided inferences of mean July air temperatures (TJuly) and water depths (WD). Reconstructed WDs show minor changes throughout the core and range between 80 and 120 cm. All the fluctuations in reconstructed water depth lie within the mean error of prediction of the inference model (RMSEP = 0.35) so it is not possible to draw conclusions from the reconstructions. A qualitative and quantitative reconstruction of Holocene climate in central Yakutia recognized three stages of palaeoenvironmental changes. The early Holocene between 10 and 8 ka BP was characterized by colder-than-today and moist summer conditions. Cryotextures in the lake sediments document full freezing of the lake water during the winter time. A general warming trend started around 8.0 ka BP in concert with enhanced biological productivity. Reconstructed mean TJuly were equal or up to 1.5 °C higher than today between 6.0 ka and 5.0 ka BP. During the entire late Holocene after 4.8 ka BP, reconstructed mean TJuly remained below modern value. Limnological conditions did not change significantly. The inference of a mid-Holocene climate optimum supports scenarios of Holocene climatic changes in the subpolar part of eastern Siberia and indicates climate teleconnections to the North Atlantic realm.

Description: Aeolian sediments on the Tibetan Plateau are an important archive of palaeoclimatic information. This study presents a detailed analysis of sediments from the Donggi Cona catchment on the north-eastern part of the Tibetan Plateau. Long- and short-distance sediment transport leads to a complex pattern of aeolian sediment deposition that depends on climatic changes as well as on the availability of sediments. Based on the largest dataset of OSL datings (51) from a single catchment on the Tibetan Plateau so far, different periods of increased sediment transport have been reconstructed. Increased aeolian deposition in this high elevation environment started in the early Holocene with the accumulation of sands from around 10.5 to 7 ka. Loess sediments have been preserved from a period from 10.5 to 7.5 ka. Both archives are related to the strengthening of the Asian summer monsoons characterized by wetter and warmer climate. This change in climate supported the trapping of aeolian sediments. Under full monsoon conditions from around 9 ka onwards fluvial processes resulted in erosion of the aeolian archives and the formation of colluvial sediments until 6 ka. A dry and cooler climate resulted in the reactivation of dune sands from 3 ka to present, possibly in combination with stronger human influence. Aeolian sediments on the Tibetan Plateau therefore indicate two different climatic modes. During the early Holocene wetter conditions were favourable to retain aeolian sediments. The reactivation of sediment in the late Holocene due to small-scale disturbances in the vegetation cover, points to a cooler and drier climate.

Description: We investigated chironomid assemblages of a well-dated sediment core from a small seepage lake situated at the eastern slope of the Central Kamchatka Mountain Chain, Far East Russia. The chironomid fauna of the investigated Sigrid Lake is dominated by littoral taxa that are sensitive to fluctuations of the water level. Two groups of taxa interchangeably dominate the record responding to the changes in the lake environment during the past 2800 years. The first group of littoral phytophilic taxa includes Psectrocladius sordidellus-type, Corynoneura arctica-type and Dicrotendipes nervosus-type. The abundances of the taxa from this group have the strongest influence on the variations of PCA 1, and these taxa mostly correspond to low water levels, moderate temperatures and slightly acidified conditions. The second group of taxa includes Microtendipes pedellus-type, Tanytarsus lugens-type, and Tanytarsus pallidicornistype. The variations in the abundances of these taxa, and especially of M. pedellus-type, are in accordance with PCA 2 and correspond to the higher water level in the lake, more oligotrophic and neutral pH conditions. Water depths (WD) were reconstructed, using a modern chironomid-based temperature and water depth calibration data set (training set) and inference model from East Siberia (Nazarova et al., 2011). Mean July air temperatures (T July) were inferred using a chironomid-based temperature inference model based on a modern calibration data set for the Far East (Nazarova et al., 2015). The application of transfer functions resulted in reconstructed T July fluctuations of approximately 3 �C over the last 2800 years. Low temperatures (11.0e12.0 �C) were reconstructed for the periods between ca 1700 and 1500 cal yr BP (corresponding to the Kofun cold stage) and between ca 1200 and 150 cal yr BP (partly corresponding to the Little Ice Age [LIA]).Warm periods (modern T July or higher) were reconstructed for the periods between ca 2700 and 1800 cal yr BP, 1500 and 1300 cal yr BP and after 150 cal yr BP. WD reconstruction revealed that the lake level was lower than its present level at the beginning of the record between ca 2600 and 2300 cal yr BP and ca 550 cal yr BP. Between ca 2300 and 700 cal yr BP as well as between 450 and 150 cal yr BP, the lake level was higher than it is today, most probably reflecting more humid conditions.

Description: 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 38,000 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.

Description: Profundal lake sediment cores are often interpreted in line with diverse and detailed sedimentological processes to infer paleoenvironmental conditions. The effects of frozen lake surfaces on terrigenous sediment deposition and how climate changes on the Tibetan Plateau are reflected in these lakes, however, is seldom discussed. A lake sediment core from Hala Lake (590 km2), northeastern Tibetan Plateau spanning the time interval from the Last Glacial Maximum to the present was investigated using high-resolution grain-size composition of lacustrine deposits. Seismic analysis along a north–south profile across the lake was used to infer the sedimentary setting within the lake basin. Periods of freezing and melting processes on the lake surface were identified by MODIS (MOD10A1) satellite data. End-member modeling of the grain size distribution allowed the discrimination between lacustrine, eolian and fluvial sediments. The dominant clay sedimentation (slack water type) during the global Last Glacial Maximum (LGM) reflects ice interceptions in long cold periods, in contrast to abundant eolian input during abrupt cold events. Therefore, fluvial and slack water sedimentation processes can indicate changes in the local paleoclimate during periods of the lake being frozen, when eolian input was minor. Inferred warm (i.e., ∼22.7 and 19.5 cal. ka BP) and cold (i.e., ∼11–9 and 3–1.5 cal. ka BP) spells have significant environmental impacts, not only in the regional realm, but they are also coherent with global-scale climate events. The eolian input generally follows the trend of the mid-latitude westerly wind dynamics in winter, contributing medium-sized sand to the lake center, deposited within the ice cover during icing and melting phases. Enhanced input was dominant during the Younger Dryas, Heinrich Event 1 and at around 8.2 ka, equivalent to the well-known events of the North Atlantic realm.