GLORIA

GEOMAR Library Ocean Research Information Access

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Proceed order?

Export
  • 1
    Keywords: climate change ; Dissertation ; Pleistocene ; environmental change ; Atlantic Ocean ; Africa ; Hochschulschrift ; Paläoklimatologie ; Mittelpleistozän ; Tropenklima ; Atlantischer Ozean Süd ; Zentralafrika
    Type of Medium: Book
    Pages: 187 S , graph. Darst., Kt
    ISBN: 9057440814
    Series Statement: Geologica Ultraiectina 223
    Language: English
    Note: Zsfassung in niederländ. und dt. Sprache , Zugl.: Utrecht, Univ., Diss., 2003
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 2
    Keywords: Hochschulschrift
    Type of Medium: Book
    Pages: 82 Seiten + Appendix
    Language: English
    Note: Kiel, Universität, Diplomarbeit, 1998 (Teil B: Laborarbeit)
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 3
    Publication Date: 2014-06-25
    Description: In this study we reconstruct sea surface temperatures (SSTs) using two lipid-based biomarker proxies (alkenone unsaturation index View the MathML sourceU37K′ and TEX86 index based on glycerol dibiphytanyl glycerol tetraethers) in 36 surface sediment samples from the Indonesian continental margin off west Sumatra and south of Java and the Lesser Sunda Islands. Comparison of measured temperatures (World Ocean Atlas 09) to reconstructed temperatures suggests that SST estimates based on View the MathML sourceU37K′ reflect the SE monsoon SST in the upwelling area south of Java and the Lesser Sunda Islands. Estimates based on TEX86 using the calibration for temperatures 〉20 °C (View the MathML sourceTEX86H) are up to 2 °C lower than View the MathML sourceU37K′-based SSTs. This offset is possibly related to either one or a combination of two factors: (i) the depth habitats of the source organisms and (ii) different seasonal production and/or seasonality of export associated with phytoplankton blooming triggered by primary productivity. In the non-upwelling area off west Sumatra, the alkenone-based SSTs are cooler than measured temperatures during the entire year, likely reflecting the limitations of the View the MathML sourceU37K′ proxy beyond 28 °C, while reconstructed temperatures based on View the MathML sourceTEX86H are consistent with mean annual SST.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 4
    Publication Date: 2014-06-25
    Description: The Miocene expansion of C4 plants (mainly tropical grasses) between 8 and 4 million years (Ma) remains an enigma since regional differences in the timing of the expansion rules out decreased CO2 (pCO2) as a dominant forcing [e.g. Tipple and Pagani, 2007. The early origins of terrestrial C4 photosynthesis. Annu. Rev. Earth Planet. Sci. 35, 435–461]. Other environmental factors, such as low-latitude aridity and seasonality have been proposed to explain the low tree versus grass ratio found in savannahs and tropical grasslands of the world, but conclusive evidence is missing. Here we use pollen and stable carbon (δ13C) and hydrogen (δD) isotope ratios of terrestrial plant wax from a South Atlantic sediment core (ODP Site 1085) to reconstruct Miocene to Pliocene changes of vegetation and rainfall regime of western southern Africa. Our results reveal changes in the relative amount of precipitation and indicate a shift of the main moisture source from the Atlantic to the Indian Ocean during the onset of a major aridification 8 Ma ago. We emphasize the importance of declining precipitation during the expansion of C4 and CAM (mainly succulent) vegetation in South Africa. We suggest that the C4 plant expansion resulted from an increased equator-pole temperature gradient caused by the initiation of strong Atlantic Meridional Overturning Circulation following the shoaling of the Central American Seaway during the Late Miocene.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 5
    Publication Date: 2014-06-27
    Description: The past climate evolution of southwestern Africa is poorly understood and interpretations of past hydrological changes are sometimes The past climate evolution of southwestern Africa is poorly understood and interpretations of past hydrological changes are sometimes contradictory. Here we present a record of leaf-wax δD and δ13C taken from a marine sediment core at 23°S off the coast of Namibia to reconstruct the hydrology and C3 versus C4 vegetation of southwestern Africa over the last 140 000 years (140 ka). We find lower leaf-wax δD and higher δ13C (more C4 grasses), which we interpret to indicate wetter Southern Hemisphere (SH) summer conditions and increased seasonality, during SH insolation maxima relative to minima and during the last glacial period relative to the Holocene and the last interglacial period. Nonetheless, the dominance of C4 grasses throughout the record indicates that the wet season remained brief and that this region has remained semi-arid. Our data suggest that past precipitation increases were derived from the tropics rather than from the winter westerlies. Comparison with a record from the Congo Basin indicates that hydroclimate in southwestern Africa has evolved in antiphase with that of central Africa over the last 140 ka.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Format: application/pdf
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 6
    Publication Date: 2015-02-04
    Description: To achieve a better understanding of the hydrologic evolution of the North-West (NW) African monsoon system during the Holocene, in particular during inferred abrupt climate changes at the end of the African Humid Period (AHP), we investigated terrigenous plant lipids deposited in marine sediments offshore NW Africa. Changes in rainfall amount were estimated by compound-specific hydrogen isotope (δD) analyses. The spatial gradient of rainfall isotopic compositions is reflected in marine surface sediments. δD changes in plant waxes covering the last 100 years confirm the observed decrease in rainfall during the late twentieth century Sahel drought, and thus can be used for a quantitative calibration of δD and pre- cipitation. δD changes in sedimentary plant waxes show no abrupt change at the end of the AHP suggesting a gradual precipitation decline. These results are supported by Holocene climate simulations using a coupled atmosphere-land surface model, which includes an explicit modeling of isotopic fractionation within the hydrological cycle.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , NonPeerReviewed
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 7
    Publication Date: 2016-02-01
    Description: Bulk organic parameters and stable and radiocarbon isotope compositions of organic carbon (δ13COC and Δ14COC) as well as various biomarkers (lignin phenols, plant waxes etc.) have been used to investigate the biogeochemical characteristics of organic carbon in the Amazon River system. However, the source, concentration and distribution pattern of lignin on the Amazon shelf and fan has not been assessed so far. In particular, the compound-specific stable carbon isotope compositions (δ13C) of lignin phenols have not been characterized in the Amazon River system. In order to study the distribution of lignin in the lower Amazon basin and its dispersal on the shelf and fan, we used riverbed sediments from the Amazon mainstream and its main tributaries and marine surface sediments on the Amazon shelf and fan. The samples were analyzed for particulate organic carbon content (POC), δ13COC, lignin phenol compositions and compound-specific δ13C of individual lignin phenols. The concentrations of aluminium and silicon (Al/Si) were used as a proxy for grain size[1]. The POC content in the main tributaries ranged from 0.13 to 3.99 wt-% and increased with Al/Si ratio in each tributary. δ13COC varied from -26.1‰ to -29.9‰ VPDB in riverbed sediments. Lignin content (represented by Λ8, sum of eight lignin phenols in OC, expressed as mg/100mg OC) ranged from 0.73 to 6.91 and is positively related with Al/Si ratio in the main tributaries except for the Xingu River, in which Λ8 decreased with Al/Si. Ratios of syringyl to vanillyl (S/V) and cinnamyl to vanillyl (C/V) varied from 0.70 to 1.51 and 0.08 to 0.47, respectively, suggesting that the dominant source of lignin is non-woody angiosperm tissue. The ratios of vanillic acid to vanillin (Ad/Al)v (0.26-0.71) and syringic acid to syringaldehyde (Ad/Al)s (0.15-0.57) indicated relatively fresh, non-degraded lignin. In marine sediments, the δ13COC ranged from -18.6‰ to -26.7‰ and is correlated with the Λ8 value (0.04-2.01). The decreasing Λ8 value along the coast from the Amazon River mouth towards the northwest implies that lignin is distributed by the North Brazil Current. A main plant source of non-woody angiosperm tissue was indicated by the S/V (0.59-1.62) and C/V (0.10-0.43) ratios on the marine samples. The agreement between riverbed and marine sediments suggests that processing of POC during transport from the basin to offshore does not change the plant source information of lignin. Highly degraded lignin on the Amazon fan and the southeast shelf is indicated by (Ad/Al)v (0.49-0.99). δ13C of lignin phenols of 9 marine sediments ranged from -28.6‰ to -33.3‰ and were consistently lower than δ13COC (-19.7‰ to -26.7‰). Depleted δ13C of lignin phenols indicate that the POC produced by the terrestrial biosphere is mainly derived from higher plants using C3 photosynthesis. References Bouchez, J., Galy, V., Hilton, R.G., Gaillardet, J., Moreira-Turcq, P., Pérez, M.A., France-Lanord, C., Maurice, L., 2014. Source, transport and fluxes of Amazon River particulate organic carbon: Insights from river sediment depth-profiles. Geochemica et Cosmochimica Acta 133, 280-298
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 8
    Publication Date: 2015-01-13
    Description: Long chain alkyl diols form a group of lipids occurring widely in marine environments. Recent studies have suggested several palaeoclimatological applications for proxies based on their distributions, but have also revealed uncertainty about their applicability. Here we evaluate the use of long chain 1,14-alkyl diol indices for reconstruction of temperature and upwelling conditions by comparing index values, obtained from a comprehensive set of marine surface sediments, with environmental factors such as sea surface temperature (SST), salinity and nutrient concentration. Previous studies of cultures indicated a strong effect of temperature on the degree of saturation and the chain length distribution of long chain 1,14-alkyl diols in Proboscia spp., quantified as the diol saturation index (DSI) and diol chain length index (DCI), respectively. However, values of these indices for surface sediments showed no relationship with annual mean SST of the overlying water. It remains unknown as to what determines the DSI, although our data suggest that it may be affected by diagenesis, while the relationship between temperature and DCI may be different for different Proboscia species. In addition, contributions from algae other than Proboscia diatoms may affect both indices, although our data provide no direct evidence for additional long chain 1,14-alkyl diol sources. Two other indices using the abundance of 1,14-diols vs. 1,13-diols and C30 1,15- diols have been applied previously as indicators for upwelling intensity at different locations. The geographical distribution of their values supports the use of 1,14 diols vs. 1,13 diols [C28 + C30 1,14-diols]/[(C28 + C30 1,13-diols) + (C28 + C30 1,14-diols)] as a general indicator for high nutrient or upwelling conditions.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 9
    Publication Date: 2016-10-09
    Description: Polar regions are strongly affected by global climate change since warming is projected to be strongest in high latitudes. Understanding temperature changes is crucial to unravel the impact of climate change there. Rising sea surface temperatures (SST) modify oceanographic conditions of the polar and subpolar seas. In the northern hemisphere, increasing mean annual air temperatures (MAAT) lead to thawing of permafrost soils which may initiate release of vast amounts of fossil carbon to the environment. In order to study changes in SST, MAAT and the intensity of carbon export from East Siberia to the adjacent NW Pacific and Bering Sea over the last deglaciation we analyzed terrigenous and marine biomarkers (n-alkanes, branched GDGT & isoprenoid GDGTs) from two sediment cores recovered at the continental margin off Kamchatka peninsula (NW Pacific), and from the western Bering Sea. We test the applicability of TEX86 as a tool for SST-reconstructions over the last deglaciation and thereby produce a TEX86 based SST-record in the Bering Sea. The results are compared to Uk’37 and Mg/Ca based SST. The TEX86 record is interpreted to reflect summer subsurface temperatures. We further investigate the CBT/MBT indices calculated from the branched GDGTs as well as δD of n-alkanes as tools for the reconstruction of MAAT. MAAT based on CBT/MBT shows a pattern similar to Greenland ice core temperature records with cooling events during the Heinrich Event 1 (HE1) and the Younger Dryas (YD). The results for the late Holocene match the modern MAAT of Kamchatka peninsula. However, from the Last Glacial Maximum to the onset of the Bølling/Allerød interstadial (B/A) CBT/MBT produces unrealistic temperatures that are as high as during Holocene. Possibly the record shows summer temperatures during LGM and the early deglaciation and reflects the annual mean at the beginning of the B/A. When interpreting these findings one has to keep in mind that concentrations of branched GDGT are very low (BIT lower than 0.1). Thus it is questionable whether CBT/MBT can be used as temperature proxy since the signal may be affected by in-situ production. In contrast to the CBT/MBT our δD records have hardly no similarity with Greenland ice core data. The B/A does not differ from LGM conditions but there is a slight decrease during YD. While the record of the Bering Sea shows an abrupt increase of 40 ‰ during the early Holocene the NW-Pacific shows a gradual increase of the same magnitude over the whole Holocene period. During the HE1 both records show a sharp increase reaching the Holocene level. This indicates interglacial-like temperatures which is unrealistic for stadial conditions. Coeval changes in the CPI and n-C23/n-C27 indicate that δD is overprinted by a change in the carbon source. Potential explanations include redeposition of material mobilized during deglacial sea-level rise, or release of fossil carbon from permafrost. Terrigenous biomarkers were quantified and used to study the history of carbon export. Accumulation rates of n-alkanes and branched GDGT increase during the YD and are strikingly high during the Preboreal indicating enhanced carbon mobilization. Decomposing permafrost soils in East Siberia and on the Kamchatka peninsula is a likely carbon source.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 10
    Publication Date: 2016-12-01
    Description: When using biomarkers such as n-alkanes as tools for paleo-environmental reconstructions, it is imperative to determine their specific sources for each setting. Towards that goal, we analysed a set of various potential organic matter (OM) sources such as aquatic and terrestrial plants, dust, and soils from Laguna Potrok Aike (LPA) and surrounding areas in Southern Patagonia. We determined chain length distributions and hydrogen (δD) and carbon (δ13C) isotopic compositions of n-alkanes of different OM sources in order to quantify their relative contributions to lake sediments. Our results reveal that mid-chain n-alkane, n-C23, is predominantly produced by submerged aquatic plants, whereas long-chain n-alkanes (n-C29 to n-C31) are derived from various terrestrial sources. We estimated their relative contributions to the sediment using two approaches, i.e. based on the n-alkane distributions and their δD and δ13C values. Both approaches result in similar estimates of aquatic and terrestrial contributions for mid- and long-chain n-alkanes to the sediment. 62-73% of the mid-chain n-C23 alkanes originate from aquatic sources while 66-77% of the long-chain n-alkanes originate from dust and 14-30% from terrestrial plants. Our study shows that mid-chain n-alkanes such as n-C23 alkane in LPA are derived mainly from aquatic macrophytes and thus have the potential to record changes in lake-water isotopic composition. In contrast, the n-C29 alkane reflects the isotopic signal of various terrestrial sources from Southern Patagonia.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Format: application/pdf
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...