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Mollenhauer, Gesine; Eglinton, Timothy Ian; Ohkouchi, Naohiko; Schneider, Ralph R; Müller, Peter J; Grootes, Pieter Meiert; Rullkötter, Jürgen (2003): Alkenone and foraminifera records from sediment samples off Namibia [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.779159, Supplement to: Mollenhauer, G et al. (2003): Asynchronous alkenone and foraminifera records from the Benguela Upwelling System. Geochimica et Cosmochimica Acta, 67(12), 2157-2171, https://doi.org/10.1016/S0016-7037(03)00168-6

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Abstract:
Radiocarbon stratigraphy is an essential tool for high resolution paleoceanographic studies. Age models based on radiocarbon ages of foraminifera are commonly applied to a wide range of geochemical studies, including the investigation of temporal leads and lags. The critical assumption is that temporal coupling between foraminifera and other sediment constituents, including specific molecular organic compounds (biomarkers) of marine phytoplankton, e.g. alkenones, is maintained in the sediments.
To test this critical assumption in the Benguela upwelling area, we have determined radiocarbon ages of total C37-C39 alkenones in 20 samples from two gravity cores and three multicorer cores. The cores were retrieved from the continental shelf and slope off Namibia, and samples were taken from Holocene, deglacial and Last Glacial Maximum core sections. The alkenone radiocarbon ages were compared to those of planktic foraminifera, total organic carbon, fatty acids and fine grained carbonates from the same samples. Interestingly, the ages of alkenones were 1000 to 4500 yr older than those of foraminifera in all samples.
Such age differences may be the result of different processes: Bioturbation associated with grain size effects, lateral advection of (recycled) material and redeposition of sediment on upper continental slopes due to currents or tidal movement are examples for such processes.
Based on the results of this study, the age offsets between foraminifera and alkenones in sediments from the upper continental slope off Namibia most probably do not result from particle-selective bioturbation processes. Resuspension of organic particles in response to tidal movement of bottom waters with velocities up to 25 cm/s recorded near the core sites is the more likely explanation.
Our results imply that age control established using radiocarbon measurements of foraminifera may be inadequate for the interpretation of alkenone-based proxy data. Observed temporal leads and lags between foraminifera based data and data derived from alkenone measurements may therefore be secondary signals, i.e. the result of processes associated with particle settling and biological activity.
Project(s):
Geosciences, University of Bremen (GeoB)
Coverage:
Median Latitude: -23.203591 * Median Longitude: 12.544000 * South-bound Latitude: -24.108000 * West-bound Longitude: 12.358000 * North-bound Latitude: -22.449000 * East-bound Longitude: 12.765000
Date/Time Start: 2000-08-08T00:00:00 * Date/Time End: 2000-08-20T00:00:00
Event(s):
IOW226660-5 (M48/2_359) * Latitude: -24.108000 * Longitude: 12.765000 * Date/Time: 2000-08-08T00:00:00 * Elevation: -1821.0 m * Recovery: 1.58 m * Location: Walvis Bay * Campaign: M48/2 * Basis: Meteor (1986) * Method/Device: Gravity corer (Kiel type) (SL)
IOW226920-2 (M48/2_386) * Latitude: -22.449000 * Longitude: 12.358000 * Date/Time: 2000-08-20T00:00:00 * Elevation: -1683.0 m * Location: Walvis Bay * Campaign: M48/2 * Basis: Meteor (1986) * Method/Device: MultiCorer (MUC)
IOW226920-3 (M48/2_386) * Latitude: -22.450000 * Longitude: 12.360000 * Date/Time: 2000-08-20T00:00:00 * Elevation: -1683.0 m * Location: Walvis Bay/Namibia * Campaign: M48/2 * Basis: Meteor (1986) * Method/Device: Gravity corer (Kiel type) (SL)
License:
Creative Commons Attribution 3.0 Unported (CC-BY-3.0)
Size:
22 datasets

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Datasets listed in this publication series

  1. Mollenhauer, G (2002): Foraminifera conventional radiocarbon age data of sediment core IOW226660-5. https://doi.org/10.1594/PANGAEA.80960
  2. Mollenhauer, G (2002): Alkenone conventional radiocarbon age data of sediment core IOW226660-5. https://doi.org/10.1594/PANGAEA.80961
  3. Mollenhauer, G (2002): Bulk organic carbon conventional radiocarbon age data of sediment core IOW226660-5 (Table 3). https://doi.org/10.1594/PANGAEA.80962
  4. Mollenhauer, G (2002): Bulk organic carbon conventional radiocarbon age data of sediment core IOW226660-5 (Table 4). https://doi.org/10.1594/PANGAEA.80963
  5. Mollenhauer, G (2002): Fatty acid conventional radiocarbon age data of sediment core IOW226660-5. https://doi.org/10.1594/PANGAEA.80964
  6. Mollenhauer, G; Müller, PJ (2003): Carbon and nitrogen data of sediment core IOW226660-5. https://doi.org/10.1594/PANGAEA.132786
  7. Mollenhauer, G; Müller, PJ (2003): TOC and C37-alkenones of sediment core IOW226660-5. https://doi.org/10.1594/PANGAEA.132785
  8. Mollenhauer, G; Müller, PJ (2003): Density and water content of sediment core IOW226660-5. https://doi.org/10.1594/PANGAEA.132787
  9. Mollenhauer, G; Müller, PJ (2002): TOC, CaCO3 and C/N ratio of sediment core IOW226660-5. https://doi.org/10.1594/PANGAEA.80970
  10. Mollenhauer, G; Müller, PJ (2002): UK37 and alkenone sea surface temperatures of sediment core IOW226660-5. https://doi.org/10.1594/PANGAEA.80968
  11. Mollenhauer, G (2002): Conventional radiocarbon age data of sediment core IOW226920-2. https://doi.org/10.1594/PANGAEA.80982
  12. Mollenhauer, G (2002): Foraminifera conventional radiocarbon age data of sediment core IOW226920-3. https://doi.org/10.1594/PANGAEA.80976
  13. Mollenhauer, G (2002): Alkenone conventional radiocarbon age data of sediment core IOW226920-3. https://doi.org/10.1594/PANGAEA.80977
  14. Mollenhauer, G (2002): Bulk organic carbon conventional radiocarbon age data of sediment core IOW226920-3. https://doi.org/10.1594/PANGAEA.80978
  15. Mollenhauer, G (2002): Bulk organic carbon conventional radiocarbon age data of sediment core IOW226920-3. https://doi.org/10.1594/PANGAEA.80979
  16. Mollenhauer, G (2002): Fatty acid conventional radiocarbon age data of sediment core IOW226920-3. https://doi.org/10.1594/PANGAEA.80980
  17. Mollenhauer, G (2002): Fine fraction carbonate conventional radiocarbon age data of sediment core IOW226920-3. https://doi.org/10.1594/PANGAEA.80981
  18. Mollenhauer, G; Müller, PJ (2003): Carbon and nitrogen data of sediment core IOW226920-3. https://doi.org/10.1594/PANGAEA.132791
  19. Mollenhauer, G; Müller, PJ (2003): TOC and C37-alkenones of sediment core IOW226920-3. https://doi.org/10.1594/PANGAEA.132790
  20. Mollenhauer, G; Müller, PJ (2003): Density and water content of sediment core IOW226920-3. https://doi.org/10.1594/PANGAEA.132792
  21. Mollenhauer, G; Müller, PJ (2002): TOC, CaCO3 and C/N ratio of sediment core IOW226920-3. https://doi.org/10.1594/PANGAEA.80972
  22. Mollenhauer, G; Müller, PJ (2002): UK37 and alkenone sea surface temperatures of sediment core IOW226920-3. https://doi.org/10.1594/PANGAEA.80806