A climatic link between speleothem formation in south-eastern Spain and Eastern Mediterranean sapropel deposition?

The modern Western Mediterranean climate is characterised by strong seasonality and, especially in south-eastern Spain, by limited rainfall. In contrast, terrestrial and marine archives indicate that the peak of the last interglacial was marked by warmer conditions and potentially more variable climate, partly driven by meltwater outbursts in the North Atlantic. High insolation during interglacials forced a northward displacement of the Intertropical Convergence Zone, increasing rainfall over Northern Africa. Enhanced fluvial input leads to stratification of the Eastern Mediterranean Sea and ultimately to the deposition of sapropels. However, the climatic consequences of these large-scale processes for south-eastern Iberia have not yet been systematically investigated.

Several speleothems from Cueva Victoria, south-eastern Spain, cover the mid-Pleistocene to the Holocene. During the last glacial period, Dansgaard/Oeschger (D/O)-type variability is expressed in the speleothem stable isotope records. Variations in speleothem stable isotope values are interpreted in terms of changes in temperature (δ¹⁸O) and vegetation cover (δ¹³C). In general, warmer temperatures during D/O events are associated with lower δ¹⁸O values due to temperature and moisture source effects. Increased effective precipitation (precipitation-evaporation) is reflected by more negative δ¹³C values, resulting from higher soil microbial activity and denser vegetation cover.

Here, we present a compilation of speleothem records from Cueva Victoria spanning several interglacials and encompassing the timing of multiple sapropel layers in the Eastern Mediterranean. A comparison of speleothem stable isotope signatures during the formation of different sapropels reveals contrasting climatic responses in south-eastern Spain. During glacial phases, speleothem growth coincided with the timing of the sapropel deposition, indicating more humid conditions in south-eastern Spain. In contrast, during the Holocene Climate Optimum and the formation of sapropel 1, elevated δ¹³C values point to a decline in vegetation cover, interpreted as a result of enhanced seasonality. Speleothem formation is almost completely absent during sapropel 5 (≈ 122-128 ka), which may reflect enhanced seasonality with warmer temperatures associated with a reduction in precipitation-evaporation compared to the Holocene.