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: Isotope records are crucial for proxy-model comparison in paleoclimatology because of their advantage of being directly comparable with isotope-enabled paleoclimate model outputs. Oxygen isotopes (δ18O) are commonly measured on carbonates (i.e. ostracods, authigenic carbonates) and biogenic silica (mainly diatoms). Oxygen isotopes in lacustrine carbonates (δ18OCaCO3) have been studied extensively for several decades, yet they are subject to complex species-dependent fractionation processes and not available globally. Lacustrine oxygen isotope records from biogenic silica (δ18OBSi), on the other hand, likely do not display species-dependent fractionation effects (or only very minor) and offer insight even in data-sparse regions devoid of carbonates, such as the Arctic. To date, more than 70 lacustrine δ18OBSi records have been published. These case studies have been complemented with additional efforts addressing climatic and hydrological backgrounds, laboratory techniques and possible species-dependent fractionation as well as deposition and dissolution effects. Here, we present the first comprehensive review and global compilation of lacustrine δ18OBSi records, with explicit regard to their individual lake basin parameters. With this work, we aim at contributing to bridging the gap between modelling and isotope geochemistry approaches regarding terrestrial archives in paleoclimatology. Departing from hitherto prevalent case studies, we assess what we can learn from lacustrine δ18OBSi records globally, considering lake basin characteristics, spatial and temporal coverage as well as hydrological background information. This improves both the usability of δ18OBSi for proxy-model comparison and our understanding of the general constraints for interpreting lacustrine δ18OBSi records.

Description: Central Asia is a large-scale source of dust transport, but it also held a prominent changing hydrological system during the Quaternary. A 223 m long sediment core (GN200) was recovered from the Ejina Basin (synonymously Gaxun Nur Basin) in NW China to reconstruct the main modes of water availability in the area during the Quaternary. The core was drilled from the Heihe alluvial fan, one of the world’s largest alluvial fans, which covers a part of the Gobi Desert. Grain-size distributions supported by endmember modelling analyses, geochemical-mineralogical compositions (based on XRF and XRD measurements), and bioindicator data (ostracods, gastropods, pollen and non-pollen palynomorphs, and n-alkanes with leaf-wax ∂D) are used to infer the main transport processes and related environmental changes during the Pleistocene. Magnetostratigraphy supported by radionuclide dating provides the age model. Grainsize endmembers indicate that lake, playa (sheetflood), fluvial, and aeolian dynamics are the major factors influencing sedimentation in the Ejina Basin. Core GN200 reached the pre-Quaternary quartz- and plagioclase-rich “Red Clay” formation and reworked material derived from it in the core bottom. This part is overlain by silt-dominated sediments between 217 and 110m core depth, which represent a period of lacustrine and playa-lacustrine sedimentation that presumably formed within an endorheic basin. The upper core half between 110 and 0m is composed of mainly silty to sandy sediments derived from the Heihe that have accumulated in a giant sediment fan until modern time. Apart from the transition from a siltier to a sandier environment with frequent switches between sediment types upcore, the clay mineral fraction is indicative of different environments. Mixed-layer clay minerals (chlorite/smectite) are increased in the basal Red Clay and reworked sediments, smectite is indicative of lacustrine-playa deposits, and increased chlorite content is characteristic of the Heihe river deposits. The sediment succession in core GN200 based on the detrital proxy interpretation demonstrates that lake-playa sedimentation in the Ejina Basin has been disrupted likely due to tectonic events in the southern part of the catchment around 1 Ma. At this time Heihe broke through from the Hexi Corridor through the Heli Shan ridge into the northern Ejina Basin. This initiated the alluvial fan progradation into the Ejina Basin. Presently the sediment bulge repels the diminishing lacustrine environment further north. In this sense, the uplift of the hinterland served as a tipping element that triggered landscape transformation in the northern Tibetan foreland (i.e. the Hexi Corridor) and further on in the adjacent northern intracontinental Ejina Basin. The onset of alluvial fan formation coincides with increased sedimentation rates on the Chinese Loess Plateau, suggesting that the Heihe alluvial fan may have served as a prominent upwind sediment source for it.

Description: Relationships between climate, species composition, and species richness are of particular importance for understanding how boreal ecosystems will respond to ongoing climate change. This study aims to reconstruct changes in terrestrial vegetation composition and taxa richness during the glacial Late Pleistocene and the interglacial Holocene in the sparsely studied southeastern Yakutia (Siberia) by using pollen and sedimentary ancient DNA (sedaDNA) records. Pollen and sedaDNA metabarcoding data using the trnL g and h markers were obtained from a sediment core from Lake Bolshoe Toko. Both proxies were used to reconstruct the vegetation composition, while metabarcoding data were also used to investigate changes in plant taxa richness. The combination of pollen and sedaDNA approaches allows a robust estimation of regional and local past terrestrial vegetation composition around Bolshoe Toko during the last ∼35,000 years. Both proxies suggest that during the Late Pleistocene, southeastern Siberia was covered by open steppe-tundra dominated by graminoids and forbs with patches of shrubs, confirming that steppe-tundra extended far south in Siberia. Both proxies show disturbance at the transition between the Late Pleistocene and the Holocene suggesting a period with scarce vegetation, changes in the hydrochemical conditions in the lake, and in sedimentation rates. Both proxies document drastic changes in vegetation composition in the early Holocene with an increased number of trees and shrubs and the appearance of new tree taxa in the lake’s vicinity. The sedaDNA method suggests that the Late Pleistocene steppe-tundra vegetation supported a higher number of terrestrial plant taxa than the forested Holocene. This could be explained, for example, by the “keystone herbivore” hypothesis, which suggests that Late Pleistocene megaherbivores were able to maintain a high plant diversity. This is discussed in the light of the data with the broadly accepted species-area hypothesis as steppe-tundra covered such an extensive area during the Late Pleistocene.

Description: Wir leben in einer Zeit des Klimawandels, der sich unter anderem im Schwund polarer Eismassen zeigt. Dieses Phänomen ist in der Erdgeschichte nicht außergewöhnlich. Außergewöhnlich ist allerdings die momentane Ursache dafür, das menschliche Klimaexperiment. Ein Blick in die Vergangenheit zeigt, dass das Antlitz der Erde nicht nur vom Kommen und Gehen von Ozeanen und Gebirgen sowie vagabundierenden Kontinenten diktiert wurde, sondern auch stets vom natürlichen Klimawandel geprägt war. Aus der Vergangenheit können wir lernen, welche Umweltbedingungen uns künftig unter den prognostizierten künftigen Szenarien des Klimawandels erwarten könnten. Lagen Teile Afrikas vor 300 Millionen Jahren unter Gletschern begraben, so lebten vor 150 Millionen Jahren die Dinosaurier in einer uns fremdartigen Welt mit eisfreien Polen und weit verbreitet unter tropisch bis subtropischen Bedingungen. Heute erleben wir eine Welt mit ewigem Eis in der Antarktis und schwankenden Eisausbreitungen in der Arktis, Nordamerika und Europa. So ist die norddeutsche Landschaft ein Erbe der letzten Eiszeit vor 20.000 Jahren, als skandinavische Eisschilde bis nach Schleswig-Holstein und Brandenburg reichten und die Nordseeküste nördlich von England lag. Das heutige Nordseebecken wurde von Tundra eingenommen, so wie wir sie heute aus Ostsibirien kennen. Die heutige Arktis mit grönländischem Eis, sibirischem Dauerfrost und Meereis am Nordpol stellt einen Rest dieser eiszeitlichen Welt dar. Die Frage ist, wie lange noch? Inzwischen hat der Umweltwandel auch die Antarktis erreicht. Der Vortrag beleuchtet die geowissenschaftliche Vorgehensweise zu diesem Erkenntnisgewinn. Das Spektrum der Forschungsansätze reicht von der traditionellen Feldgeologie in abgelegen Regionen bis hin zu modernen Forschungsschiffeinsätzen und der Heimarbeit im Labor und am Rechner.

Description: The Beenchime-Salaatinsky Crater (BSC) is located west of the Olenyok River in Northern Yakutia, ~ 260 km south-west of Tiksi and the Lena Delta. The age and origin (volcanic versus meteoritic) of this crater is poorly understood. The key scientific interest in re-visiting the BSC is the reappraisal of the Quaternary sedimentation dynamics for a better understanding of the sediment history and thickness in the basin. This aides for an assessment, if the site is prospective for a deeper drilling of a Quaternary (or Cenozoic) sediment archive. Soil pits and auger cores from slopes and lowland terrain in the basin were sampled and studied to infer sediment ages and transport dynamics. This also included a thermokarst lake placed in the centre of the basin. Studied properties include grain-size distribution, organic carbon and nitrogen contents (TOC and TN), heavy mineral compositions, δ13C of organic carbon, 14C ages from sediment, δ18O and δD from ground ice and waters, and lake bathymetry from GPR profiling, in addition. We conclude that the crater floor in the BSC is underlain by fluvial/alluvial sediments from the MIS 3 period. Thermokarst lake formation took place during the Holocene Thermal Maximum between 7600 and 6100 cal yr BP. The lake has been shrinking hereafter. Fluvial/alluvial sedimentation along the drainage pattern was active again between 5700 to 1500 cal yr BP, and it was flanked by the accumulation of peaty and organic-rich sediments and the formation of ice-wedge polygons.

Description: Lake sediments constitute important terrestrial archives of past climate and environments. While different kinds of proxy data can be obtained from these sediments, oxygen isotopes (δ18O) are of particular interest in paleoclimatology. They record changes of climate and hydrology in a quantitative way. Commonly, δ18O is measured on carbonates (i.e. ostracods) and biogenic silica (mainly diatoms). While oxygen isotopes in lacustrine carbonates (δ18OCaCO3) have been studied extensively for several decades, they are subject to complex species-dependent fractionation processes and not available globally. Lacustrine oxygen isotope records from biogenic silica (δ18OBSi), on the other hand, likely do not display species-dependent fractionation effects (or only very minor) and offer insight even in data-sparse regions devoid of carbonates, such as the Arctic. More than 40 lacustrine δ18OBSi records from mid- and high-latitude regions of the northern hemisphere have been published to date. Interpreting case studies of δ18OBSi, however, is challenging due to a complex interplay of climatic and hydrological factors. Therefore, these individual case studies have been complemented with additional efforts addressing climatic and hydrological backgrounds, laboratory techniques, possible species-dependent fractionation as well as deposition and dissolution effects. Here, we combine records from sites across northern Eurasia and North America to a circum-arctic stack in order to infer common underlying trends throughout the Holocene. With this work, we aim at providing new insight on the variability of Holocene hydroclimate as well as on the interplay between lacustrine archives and the δ18O-proxy. This improves both the usability of δ18OBSi for proxy-model comparison and our understanding of the general constraints for interpreting lacustrine δ18OBSi records