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Abstract We present new stable oxygen and carbon isotope composite records (δ18O, δ13C) of speleothems from Sandkraal Cave 1 (SK1) on the South African south coast for the time interval between 104 and 18 ka (with a hiatus between 48 and 41 ka). Statistical comparisons using kernel-based correlation analyses and semblance analyses based on continuous wavelet transforms inform the relationships of the new speleothem records to other proxies and their changes through time. Between 105 and ~70 ka, changes of speleothem δ18O values at SK1 are likely related to rainfall seasonality. Variations of δ13C values are associated with changes of vegetation density, prior carbonate precipitation (PCP), CO2degassing in the cave, and possibly variations of the abundance of C3and C4grasses in the vegetation. The relationships of δ18O with other proxies shift between ~70 and 48 ka (Marine Isotope Stages 4–3) so that both stable isotope records now reflect CO2degassing, evaporation, and PCP. Similar relationships also continue after the hiatus for the deposition phase between 42 and 18 ka. Our findings support modeling results suggesting drier conditions in the study area when the Southern Hemisphere westerlies are shifted north and the paleo–Agulhas Plain is exposed.
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Climatic stability recorded in speleothems may contribute to higher biodiversity in the Cape Floristic Region
Abstract AimThe geography and genesis of diversity remain an enduring topic in ecology and evolution. Mediterranean Climate Ecosystems (MCEs), with their high plant diversities in winter rainfall climates, pose a challenge to popular hypotheses evoking high water availability and temperature as necessary for the evolution of high diversity. We test the hypothesis of environmental stability as a driver for the evolution of regional‐scale floristic diversity using speleothem oxygen (δ18O) and carbon (δ13C) isotopic values as proxies for past climatic variability in the Cape Floristic Region (CFR) and other MCEs. Locationsouth‐western Africa, California, Mediterranean Basin. TaxonPlantae. MethodsWe present new speleothem δ18O and δ13C records from a cave near Robertson in the western CFR. Stable isotope samples included in the analyses cover the time intervals between 240 and 670 ka BP with hiatuses at 630–500 ka and 360–310 ka. The dispersion of these stable isotope records is used as a measure for climatic variability. We compare our new analyses to speleothem records that cover full glacial and interglacial conditions in other MCEs (California and the Mediterranean Basin) as well as in eastern regions of the CFR. All sites used in this comparison have lower vascular plant biodiversity than the western CFR. ResultsAnalyses of the dispersion of the δ18O and δ13C datasets suggest that the highly diverse western CFR experienced climatic stability across several glacial–interglacial cycles, compared with the less diverse regions within and outside of the CFR. Main ConclusionThis result provides support for the hypothesis that lower extinction rates associated with Pleistocene biome stability may explain the higher diversity in the CFR relative to other MCEs.
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- PAR ID:
- 10420770
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Biogeography
- Volume:
- 50
- Issue:
- 6
- ISSN:
- 0305-0270
- Page Range / eLocation ID:
- p. 1077-1089
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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