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  • 1
    Publication Date: 2017-01-20
    Description: During expedition 202 aboard the RV Sonne in 2009, 39 seafloor surface sediment sites were sampled over a wide sector of the North Pacific and adjoining Bering Sea. The data served to infer land–ocean linkages of terrigenous sediment supply in terms of major sources and modes of sediment transport within an over-regional context. This is based on an integrated approach dealing with grain-size analysis, bulk mineralogy and clay mineralogy in combination with statistical data evaluation (end-member modelling of grainsize data, fuzzy cluster analysis of mineralogical data). The findings on clay mineralogy served to update those of earlier work extracted from the literature. Today, two processes of terrigenous sediment supply prevail in the study area: fardistance aeolian sediment supply to the pelagic North Pacific, and hemipelagic sediment dispersal from nearby land sources via ocean currents along the continental margins and island arcs. Aeolian particles show the finest grain sizes (clay and fine silt), whereas hemipelagic sediments have high abundances of coarse silt. Exposed sites on seamounts and the continental slope are partly swept by strong currents, leading to residual enrichment of fine sand. Four sediment sources canbe distinguished on the basis of distinct index minerals revealed by statistical data analysis: dust plumes from central Asia (quartz, illite), altered materials from the volcanic regions of Kamchatka and the Aleutian Arc (smectite), detritus from the Alaskan Cordillera (chlorite, hornblende), and fluvial detritus from far-eastern Siberia and the Alaska mainland (quartz, feldspar, illite). These findings confirm those of former studies but considerably expand the geographic range of this suite of proxies as far south as 39°N in the open North Pacific. The present integrated methodological approach proved useful in identifying the major modern processes of terrigenous sediment supply to the study region. This aspect deserves attention in the selection of sediment core sites for future palaeoenvironmental reconstructions related to aeolian and glacial dynamics, as well as the recognition of palaeoocean circulation patterns in general.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
    Publication Date: 2019-08-23
    Description: A multi-proxy study including sedimentological, mineralogical, biogeochemical and micropaleontological methods was conducted on sediment core PS69/849-2 retrieved from Burton Basin, MacRobertson Shelf, East Antarctica. The goal of this study was to depict the deglacial and Holocene environmental history of the MacRobertson Land–Prydz Bay region. A special focus was put on the timing of ice-sheet retreat and the variability of bottom-water formation due to sea ice formation through the Holocene. Results from site PS69/849-2 provide the first paleo-environmental record of Holocene variations in bottom-water production probably associated to the Cape Darnley polynya, which is the second largest polynya in the Antarctic. Methods included end-member modeling of laser-derived high-resolution grain size data to reconstruct the depositional regimes and bottom-water activity. The provenance of current-derived and ice-transported material was reconstructed using clay-mineral and heavy-mineral analysis. Conclusions on biogenic production were drawn by determination of biogenic opal and total organic carbon. It was found that the ice shelf front started to retreat from the site around 12.8 ka BP. This coincides with results from other records in Prydz Bay and suggests warming during the early Holocene optimum next to global sea level rise as the main trigger. Ice-rafted debris was then supplied to the site until 5.5 cal. ka BP, when Holocene global sea level rise stabilized and glacial isostatic rebound on MacRobertson Land commenced. Throughout the Holocene, three episodes of enhanced bottom-water activity probably due to elevated brine rejection in Cape Darnley polynya occured between 11.5 and 9 cal. ka BP, 5.6 and 4.5 cal. ka BP and since 1.5 cal. ka BP. These periods are related to shifts from warmer to cooler conditions at the end of Holocene warm periods, in particular the early Holocene optimum, the mid-Holocene warm period and at the beginning of the neoglacial. In contrast, between 7.7 and 6.7 cal. ka BP, brine rejection shut down, maybe owed to warm conditions and pronounced open-water intervals.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
    Publication Date: 2017-10-20
    Description: In the arid environment, due to the scarcity of a continuous terrestrial archive, lacustrine sequences are often employed as a paleoenvironmental repository. However, numerous spatial and temporal heterogeneities exist concerning previously studied sites in arid central Asia. Furthermore, surveys using a XRF core scanning technique on lacustrine sequences retrieved in hyperarid desert settings are largely rare. Hence, two parallel sediment cores (ONW I; ONW II) were retrieved from Orog Nuur, in the Gobi Desert of Mongolia. Continuous, high-resolution elemental abundances at a 1-cm scanning step size were examined in core ONW II using XRF core scanning. To constrain the data quality, elements with high error margins relative to measured peak areas and those elements/proxies below the significance level during the multivariate statistics are excluded for environmental/ provenance implications. Based on multivariate statistical evaluation, the bulk-geochemistry of the core sediments are governed by (1) grain-size composition, (2) authigenic productivity (Ca, Cl, CaCO3) in an alkaline environment, (3) allochthonous organic material (TOC and C/Natomic), and (4) terrigenous input via fluvial inflows, as well as quasi-constant aeolian input through the late Quaternary (Al, Si, K, Ti, and Fe). Disparate source lithotypes, as well as authigenic productivity of the lake system existed before and after Termination I. The Holocene was dominated by a distinct high productivity alkaline environment with more felsic and alkaline input relative to the late Pleistocene. This might be attributed to an increased hydrodynamic strength of riverine inflow and/or intensified erosion and weathering of felsic source rocks in the upper catchment of the Orog Nuur. Therefore, in order to gain a better understanding of the bulk-geochemistry of lake sediments, the coupled provenance and environmental signatures, as well as land surface processes in the catchment need to be systematically discerned. Thus, the XRF core scanning data obtained in this study would have practical and complimentary merit for other lacustrine studies focused on the desert realm across the globe.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
    Publication Date: 2019-07-16
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
    Publication Date: 2017-06-13
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
    Publication Date: 2019-07-16
    Description: Fossil diatom assemblages in a sediment core from a small lake in Central Kamchatka (Russia) were used to reconstruct palaeoenvironmental conditions of the late Holocene. The waterbody may be a kettle lake that formed on a moraine of the Two-Yurts Lake Valley, located on the eastern slope of the Central Kamchatka Mountain Chain. At present, it is a seepage lake with no surficial outflow. Fossil diatom assemblages show an almost constant ratio between planktonic and periphytic forms throughout the record. Downcore variations in the relative abundances of diatom species enabled division of the core into four diatom assemblage zones, mainly related to changes in abundances of Aulacoseira subarctica, Stephanodiscus minutulus, and Discostella pseudostelligera and several benthic species. Associated variations in the composition and content of organic matter are consistent with the diatom stratigraphy. The oldest recovered sediments date to about 3220 BC. They lie below a sedimentation hiatus and likely include reworked deposits from nearby Two-Yurts Lake. The initial lake stage between 870 and 400 BC was characterized by acidic shallow-water conditions. Between 400 BC and AD 1400, lacustrine conditions were established, with highest contributions from planktonic diatoms. The interval between AD 1400 and 1900 might reflect summer cooling during the Little Ice Age, indicated by diatoms that prefer strong turbulence, nutrient recycling and cooler summer conditions. The timing of palaeolimnological changes generally fits the pattern of neoglacial cooling during the late Holocene on Kamchatka and in the neighbouring Sea of Okhotsk, mainly driven by the prevailing modes of regional atmospheric circulation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 7
    Publication Date: 2022-07-04
    Description: Thermokarst lakes in the Siberian Arctic contain sediment archives that can be used for paleoenvironmental inference. Until now, however, there has been no study from the inner Lena River Delta with a focus on diatoms. The objective of this study was to investigate how the diatom community in a thermokarst lake responded to past limnogeological changes and what specific factors drove variations in the diatom assemblage. We analysed fossil diatom species, organic content, grain-size distribution and elemental composition in a sediment core retrieved in 2009 from a shallow thermokarst lake in the Arga Complex, western Lena River Delta. The core contains a 3,000-year record of sediment accumulation. Shifts in the predominantly benthic and epiphytic diatom species composition parallel changes in sediment characteristics. Paleoenvironmental and limnogeological development, inferred from multiple biological and sedimentological variables, are discussed in the context of four diatom zones, and indicate a strong relation between changes in the diatom assemblage and thermokarst processes. We conclude that limnogeological and thermokarst processes such as lake drainage, rather than direct climate forcing, were the main factors that altered the aquatic ecosystem by influencing, for example, habitat availability, hydrochemistry, and water level.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 8
    Publication Date: 2022-08-12
    Description: This article presents a review of the current data on the level of paleolimnological knowledge about lakes in the Russian part of the northern Eurasia. The results of investigation of the northwestern European part of Russia as the best paleolimnologically studied sector of the Russian north is presented in detail. The conditions of lacustrine sedimentation at the boundary between the Late Pleistocene and Holocene and the role of different external factors in formation of their chemical composition, including active volcanic activity and possible large meteorite impacts, are also discussed. The results of major paleoclimatic and paleoecological reconstructions in northern Siberia are presented. Particular attention is given to the databases of abiotic and biotic parameters of lake ecosystems as an important basis for quantitative reconstructions of climatic and ecological changes in the Late Pleistocene and Holocene.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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