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  • 1
    Publication Date: 2014-05-29
    Description: A remarkable sedimentary record that extends from the Miocene to the late Pleistocene/Holocene has been drilled during IODP Expedition 341 (May - July 2013) in the Gulf of Alaska. The recovery and examination of sediments along a transect of five drill sites (U1417 - U1421) from the deep ocean towards the continental slope and offshore the St. Elias Mountains enables the reconstruction of the palaeoceanographic and environmental development in the NE Pacific during a period of significant global cooling and directly addresses the overall research objectives of the IODP programme. The knowledge about palaeo sea surface conditions and their relation to climate changes in the subpolar NE Pacific is relatively scarce and mainly confined to the past 17 ka BP (Barron et al., 2009; Davies et al., 2011; Addison et al., 2012). Biomarker based reconstructions of the sea surface conditions (i.e. sea surface temperature(SST), sea ice coverage, marine primary productivity) that characterised the subpolar NE Pacific during critical time intervals of Plio- and Pleistocene climate change may provide new information on oceanic and atmospheric feedback mechanisms and further enable the identification of teleconnections between the palaeoceanographic evolution in the North Pacific and the North Atlantic. Here we present preliminary biomarker data obtained from sediments from the distal deepwater site U1417 and the proximal site U1419 located at the Gulf of Alaska continental slope. Variability in the distribution and abundance of short- and long-chain n-alkanes, sterols, and C25-highly branched isoprenoids (HBIs) is interpreted to reflect changes in the environmental setting. These data provide insight in marine primary productivity changes(in response to cooling and warming intervals) and the variable input of terrigenous organic matter via meltwater and/or iceberg discharge events. The C25-HBI diene/triene ratio - hitherto used as a sea ice proxy in the Southern Ocean (Etourneau et al., 2013) - is applied to gain information about the variability in polar water/sea ice extent in the study area. Previously, Rowland et al. (2001) documented that not only the degree of unsaturation in C25-HBIs but also the E- to Z-isomerisation in the C25-HBI trienes increases with increasing water temperature. Based on this observation we suggest that the ratio of the Z-isomer to the E-isomer in the trienes might reflect SST changes and could be used as an additional SST proxy. The applicability of this approach, however, needs further evaluation (e.g. through comparisons with alkenone SST data obtained from Expedition 341 sediments).
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 2
    Publication Date: 2007-11-21
    Description: The Budesheimer Bach borehole in the Prum Syncline, Eifel Mountains, Germany encountered upper Frasnian and lowermost Famennian sediments including the Upper Kellwasser Horizon (UKW) and a limestone-dominated sequence ( LKW') which can be correlated with the Lower Kellwasser Horizon in other sections. The palynofacies is characterized by a high abundance of amorphous organic matter (AOM), prasinophytes, miospores and acritarchs indicative of a fully marine, rather distal and oxygen-deficient environment. AOM and a low sterane/hopane ratio suggest that cyanobacteria were important primary producers and that bacterial reworking and oxidation influenced the organic matter composition resulting in reduced total organic carbon (TOC) contents and lower hydrogen index (HI) values. The LKW' and the UKW can be distinguished from the adjacent units by the abundant prasinophytes and some geochemical parameters (e.g. higher HI, lower pristane/phytane ratio, lower aryl isoprenoid ratio) but these differences are not highly significant. However, the sediments between these two horizons show an increased input of bacteria and terrestrial plant material as a result of the regression that follows after the deposition of the Lower Kellwasser Horizon. Aryl isoprenoids originating from diagenetic transformation of the carotenoid isorenieratene, which are markers for anoxygenic photosynthetic green sulphur bacteria, have been detected in all samples but are more abundant in the LKW' and UKW. Hence, photic zone anoxia seems to have been more pronounced during deposition of these horizons, supporting the view that widespread anoxia was an important trigger of the massive end-Frasnian biotic decline.
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  • 3
    Publication Date: 2014-04-17
    Description: Organic geochemical proxy data from surface sediment samples and a sediment core from Lake Donggi Cona were used to infer environmental changes on the northeastern Tibetan Plateau spanning the last 18.4 kyr. Long-chain n-alkanes dominate the aliphatic hydrocarbon fraction of the sediment extract from most surface sediment samples and the sediment core. Unsaturated mid-chain n-alkanes (nC23:1 and nC25:1) have high abundances in some samples, especially in core samples from the late glacial and early Holocene. TOC contents, organic biomarker and non-pollen-palynomorph concentrations and results from organic petrologic analysis on selected samples suggest three major episodes in the history of Lake Donggi Cona. Before ca. 12.6 cal ka BP samples contain low amounts of organic matter due to cold and arid conditions during the late glacial. After 12.6 cal ka BP, relatively high contents of TOC and concentrations of Botryococcus fossils, as well as enhanced concentrations of mid-chain n-alkanes and n-alkenes suggest a higher primary and macrophyte productivity than at present. This is supported by high contents of palynomorphs derived from higher plants and algae and was possibly triggered by a decrease of salinity and amelioration of climate during the early Holocene. Since 6.8 cal ka BP Lake Donggi Cona has been an oligotrophic freshwater lake. Proxy data suggest that variations in insolation drive ecological changes in the lake, with increased aquatic productivity during the early Holocene summer insolation maximum. Short-term drops of TOC contents or biomarker concentrations (at 9.9 cal ka BP, after 8.0 and between 3.5 and 1.7 cal ka BP) can possibly be related to relatively cool and dry episodes reported from other sites on the north-eastern Tibetan Plateau, which are hypothesized to occur in phase with Northern Hemisphere cooling events.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 4
    Publication Date: 2019-07-17
    Description: Since the Tibetan Plateau has an essential influence on atmospheric circulations, it is important for our understanding of the dynamics of global changes and therefore interesting for paleoecological research (Lehmkuhl and Owen, 2005). Sedimentary organic matter is an excellent recorder of environmental conditions. Different n-alkane patterns have been assigned to different sources of organic matter. δ13C of aquatic macrophytes is usually in the range of C3 plants, however limited CO2 availability due to high pH or alkalinity or due to high respiration at dense plant stands, can lead to HCO3- assimilation and hence to a shift towards more positive δ13C values (Allen and Spence, 1981). To test correlations between environmental and sedimentary organic matter parameters, recent sediments of 50 Tibetan lakes (1500 5300 m a.s.l) were analysed for amounts of n-alkanes, bulk organic δ13C and compound-specific δ13C values of n-alkanes. Furthermore, bulk δ13C of the dominant aquatic macrophyte species Potamogeton pectinatus (L) was measured. The sediments can be separated into three groups by hierarchical cluster analysis according to their n-alkane patterns. Some samples show a remarkable terrestrial influence of long-and mid-chain n-alkanes with a strong odd-over-even predominance (type I) while others are dominated primarily by mid-chain n-alkanes derived from aquatic macrophytes with no odd-over even predominance (type II). Type III sediments are similar to type II, but contain also a strong terrestrial component (high relative amounts of C29, C31 and C33 n-alkanes). Short-chain n-alkanes of algal origin are scarce in most of the lake sediments (Figure 1). δ13C values of Potamogeton bulk biomass and of bulk organic matter range from -6.0 to -21.4 and -18.4 to -28.1, respectively. δ13C values of long-chain n-alkanes (C29-C31) show relatively little variations between -29 and -34. However, in some samples a shift towards more positive values, up to -21, is visible in mid-chain n-alkanes. Generally, odd-numbered n-alkanes are more enriched in 13C than even-numbered ones (Figure 1). In our lake sample set, pHs of the lake waters are varying from 7.1 to 10.5. Comparing bulk δ13C values of sediments and plants with pHs, a trend to more positive values at high pHs is visible. The correlation between δ13C of Potamogeton biomass and of mid-chain n-alkanes (C20-C26) is weak in all samples, but rather good in type II sediments (R2: 0.35 - 0.72). There is also a good correlation between bulk δ13C values of sediments and plant organic matter (R2 = 0.71). We conclude that limited CO2 availability at high pHs can be one explanation for a positive shift of δ13C values of mid-chain n-alkanes in macrophyte dominated lakes, a fact which can be applied for the interpretation of δ13C values of n-alkanes in sediment cores.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 5
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 6
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
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  • 8
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
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  • 9
    Publication Date: 2019-07-17
    Description: d13C values of aquatic macrophytes are usually in the range of C3 plants, however limited CO2 availability due to high pH or alkalinity or due to high respiration at dense plant stands, can lead to HCO3- assimilation and hence to a shift towards more positive d13C values. Epicuticular leaf waxes of plants contain n-alkanes and different n-alkane patterns have been assigned to different sources of organic matter. Long- and mid-chain n-alkanes (C23 -C31) with a strong odd-over-even predominance are usually interpreted to be of terrestrial origin while mid-chain n-alkanes (C20 -C26) with no or weak odd-over-even predominance were assigned to aquatic macrophytes.Recent sediments of 50 Tibetan lakes were analysed for amounts of n-alkanes, bulk organic d13C and compound-specific d13C values of n-alkanes. Furthermore, bulk d13C of the dominant aquatic macrophyte species Potamogeton pectinatus (L) was measured. Sediments could be separated into three groups by hierarchical cluster analysis according to their n-alkane patterns. Some samples show a remarkable terrestrial influence (type I) while others were obviously dominated primarily by aquatic macrophytes (type II). Type III sediments are similar to type II, but contain also a strong terrestrial component (high relative amounts of C29, C31 and C33 n-alkanes). Short-chain n-alkanes of algal origin are scarce in most of the lake sediments.d13C values of Potamogeton bulk biomass and of bulk organic matter range from -6.0 to -21.4 and -18.4 to -28.1, respectively. d13C values of long-chain n-alkanes show relatively little variations between -29 and -34. However, in some samples a shift towards more positive values, up to -21, is visible in mid-chain n-alkanes. Generally, odd-numbered n-alkanes are more enriched in 13C than even-numbered ones. In our sample set, pHs of the lake waters are varying from 7.1 to 10.5. Comparing bulk d13C values of sediments and plants with pHs, a trend to more positive values at high pHs is visible. The correlation between d13C of Potamogeton biomass and of mid-chain n-alkanes is weak in all samples, but rather good in type II sediments (R2: 0.35 - 0.72). There is also a good correlation between bulk d13C values of sediments and plant organic matter (R2 = 0.71). We conclude, that limited carbon availability at high pHs can be one explanation for a positive shift of d13C values of mid-chain n-alkanes in macrophyte dominated lakes.
    Repository Name: EPIC Alfred Wegener Institut
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  • 10
    Publication Date: 2015-01-13
    Description: In the context of global change, the Southern African region has to address great challenges in terms of its natural resources, in particular to cope with the impact of climate and land use change on the water balance, the soil fertility and the quantity of land suitable for common requirements. In the BMBF-funded project GeoArchives researchers from the German Research Centre for Geosciences, the Technical University of Munich and Senckenberg am Meer jointly exploit diverse Southern African archives of landscape development and climate change. The examination of these terrestrial and marine archives will provide deep insights into the climatic evolution and environmental conditions in Southern Africa during the Holocene. The highly interdisciplinary approach integrates geomorphology, soil science, sedimentology, inorganic and organic geochemistry, geomicrobiology and remote sensing. By assessing the possible impact of future climate change and land-use change on specific sensitive environments in Southern Africa we will provide future-oriented earth system management strategies with a geoscience rationale.
    Keywords: ddc:550
    Language: German
    Type: http://purl.org/escidoc/metadata/ves/publication-types/article
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