Multi-proxy reconstruction of climate variability during the last 250 ka using precisely dated speleothems from south-eastern Spain.
Mineralogy, Petrology and Geochemistry
Atmospheric Science
Final Report Abstract
Cueva Victoria (CV) speleothems provide, as one of the first records from south-eastern Spain new insights into paleoclimate variability over the past interglacial – glacial cycle. The region is one of the driest in Europe and very sensitive to hydrological changes. From there high temporal resolution paleoclimate archives were not available so far. The lack of terrestrial paleoclimate records emphasizes the importance of precisely dated speleothem records covering an interglacial – glacial cycle. Several precise 230Th/U ages were obtained on CV speleothems as well as stable carbon and oxygen isotope ratios (δ13C and δ18O) and trace element data at high spatial resolution. This project examined climate variability with focus on the last 190 ka, based on stable isotope measurements. However, as displayed in the proposal, preferred speleothem growth occurred also during MIS 7. This is indicated by high 230Th/U age density, but stable isotope measurements for paleoclimate reconstruction are hitherto missing. Although the CV speleothems do not cover the whole 190 ka, they were suitable for paleoclimate reconstructions. On orbital timescale, 230Th/U ages reflect preferential speleothem growth during interglacials, but almost no speleothem growth during glacials. This indicates almost completely dry climate conditions in SE Spain during glacials, which is in agreement with several other paleoclimate records. However, there are some exceptions such as the MIS 6.5, which coincides with humid conditions in the Mediterranean resulting in strong seasonality with sapropel deposition in the Eastern Mediterranean. Apart from that, interglacials display favorable conditions for speleothem growth at CV and thus humid and vegetated conditions in SE Spain. These humid conditions can also be assumed on millennial timescale for warm and humid DO events during MIS 5 to 3. In general, high spatial resolution stable isotope measurements enable to reconstruct changes in vegetation, precipitation and, to a limited extend, in temperature on orbital and millennial timescales. For CV, δ18O values on one hand follow the pattern of latitudinal summer insolation, on the other hand they reflect a combination of SST, amount effect and, to certain extent, the composition of the proximate ocean water as a local source for moisture uptake. Subsequent, fast changes of Northern Hemisphere temperature and hydrological cycle are immediately transferred into speleothem δ18O values, as can be seen by the pattern of DO events with strong shifts in δ18O values. Despite several possibilities of δ13C alteration en route to speleothem precipitation, δ13C values can be reproduced by several flowstone samples from the cave. Concordant with δ18O values, δ13C values are more negative within warm phases as a result of an increase in vegetation. However, during the Holocene, elevated δ13C values indicate less favorable conditions for the vegetation. High summer insolation during the Holocene (9.7 - 7.8 ka) enhances seasonality and, as a result, summer drought is prolonged and extended to the growing season in springtime, which is in agreement to other Mediterranean paleoclimate archives. Thus δ13C in CV are very indicative of vegetation and soil microbiological activity, which is influenced by precipitation and in total a positive annual net precipitation-evapotranspiration balance. Both, δ18O and δ13C values, are suitable to reconstruct paleoclimate conditions in the Western Mediterranean, and react very sensitive to paleoclimatic changes, or even to seasonality. Finally CV speleothems have the potential to fill the missing gap of paleoclimate records between the North Atlantic and the terrestrial central to eastern Mediterranean, and thus grant new insights into one of the driest region of the European Mediterranean on one hand and the understanding of differences over the entire Mediterranean basin, on the other. Whereas Eastern Mediterranean sapropel deposition indicate enhanced seasonality, depending on summer insolation and the position of the Hadley cell, it can lead to prolonged spring and summer drought during interglacials in the Western Mediterranean. Albeit, associated with lower temperatures besides full interglacial conditions, precipitation is significantly increased during sapropel deposition (e.g., S4 and S6) as indicated by very negative stable isotope (δ13C, δ18O) values. To conclude, Cueva Victoria speleothems provide the first robust terrestrial paleoclimate archive from semi-arid SE Spain responding sensitively to changes in paleoclimate, predominantly during warm phases. Changes in δ13C and δ18O with respect to Northern Hemisphere climate changes highlight their potential as proxies for paleoclimate reconstruction in this region.
Publications
- 2019. Palaeoclimate reconstruction of the last 200 ka in south-eastern Spain, based on proxies of speleothems from Cueva Victoria. PhD thesis, Mainz, 162 pp.
Budsky, A.
(See online at https://doi.org/10.25358/openscience-5113) - 2019. Speleothem δ13C record suggests enhanced spring/summer drought in south-eastern Spain between 9.7 and 7.8 ka – A circum-Western Mediterranean anomaly? The Holocene 29 (7), 1113–1133
Budsky, A., Scholz, D., Wassenburg, J.A., Mertz-Kraus, R., Spötl, C., Riechelmann, D.F.C., Gibert, L., Jochum, K.P., Andreae, M.O.
(See online at https://doi.org/10.1177/0959683619838021) - 2019. Western Mediterranean Climate Response to Dansgaard/Oeschger Events: New Insights From Speleothem Records. Geophys. Res. Lett. 46 (15), 9042–9053
Budsky, A., Wassenburg, J.A., Mertz‐Kraus, R., Spötl, C., Jochum, K.P., Gibert, L., Scholz, D.
(See online at https://doi.org/10.1029/2019GL084009)
