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| Titel |
Environmental change at the southern Cape coast of South Africa as inferred
from a high-resolution Holocene sediment record from Eilandvlei |
| VerfasserIn |
Michael Wündsch, Torsten Haberzettl, Michael E. Meadows, Kelly L. Kirsten, Stephanie Meschner, Peter Frenzel, Jussi Baade, Gerhard Daut, Roland Mäusbacher, Thomas Kasper, Lynne J. Quick, Hayley C. Cawthra, Matthias Zabel |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250133791
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| Publikation (Nr.) |
 EGU/EGU2016-14441.pdf |
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| Zusammenfassung |
| The RAIN project (Regional Archives for Integrated iNvestigations), funded by the German
Federal Ministry of Education and Research (BMBF), focuses on closely integrated
investigations of terrestrial and marine geoarchives from southern Africa in order to assess
environmental changes during the late Quaternary. For this purpose, various marine and
terrestrial sediment records from the three major rainfall zones of South Africa (winter-,
summer- and year-round rainfall zone) were recovered and analysed applying a
wide range of methods (e.g., sedimentology, seismic stratigraphy, geochronology,
organic and inorganic geochemistry, mineralogy, stable isotopes, micropalaeontology,
palynology).
In this contribution, we present results and interpretations obtained from a 30.5 m
sediment core retrieved from the coastal lake Eilandvlei located within the year-round rainfall
zone. Geochemical investigations (Ca, Sr, total inorganic carbon) indicate major changes in
the sediment carbonate contents which were linked to variations in the marine influence
received at the site throughout the covered period. The interpretation of carbonates reflecting
a varying marine influence is corroborated by micropalaeontological analyses (viz. ostracod
and diatom assemblages) which reveal strong similarities with the geochemical data. In order
to establish a reliable radiocarbon (14C) chronology for this record, it is of particular
importance to consider the impact of 14C-depleted (“old”) marine carbon contained in the
measured samples causing reservoir effects. Therefore, two marine molluscan shells collected
alive before AD 1950 (“pre-bomb”) were analysed to determine the regional marine
reservoir offset (ΔR). The obtained ΔR values of 134 ± 38 and 161 ± 38 14C yrs
represent the first data available for the south coast of South Africa. However, the
application of the resulting average ΔR = 148 ± 54 14C yrs for the calibration
of the entire Eilandvlei record underestimates the reservoir effects for the older
deposits. This indicates a temporal variability on the degree of old marine carbon
affecting Eilandvlei during the Holocene, which was possibly caused by changes in the
connectivity between the lake system and the ocean as well as changes in the extent of
upwelling along the coast. To solve this problem, variable past reservoir effects were
determined based on the dating of sample pairs which were assumingly deposited
contemporaneously and are composed of different source material (marine/terrestrial). This
approach provides the most reliable chronology revealing a median basal age of
8880 +145/220 cal BP. Thus, the Eilandvlei core represents an ultra-high-resolution record
of environmental change during the Holocene, which is a unique discovery for entire southern
Africa.
Palaeoenvironmental interpretations of the this record strongly suggest that sedimentation
conditions at Eilandvlei were closely coupled to global sea level changes. Moreover, the
multi-proxy approach provides great potential for palaeoclimatic interpretations of this
record. For example, geochemical proxies reflecting the varying input of terrestrial material
suggest changes in the discharge of inflowing rivers which, in turn, may be linked to
variations in rainfall and hence climate within the year-round rainfall zone of South Africa. |
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