Quantitative estimation of Prior Calcite Precipitation in speleothems using Ca isotopes (δ44/42Ca): Application to precisely dated European multi-proxy records between MIS 11 and the Holocene
Several past interglacials are believed to be warmer and/or wetter than the Holocene and might act as an analogue for future climate change (e.g., Marine Isotope Stage (MIS) 5 and 11). In addition, the last glacial period, including MIS 3, was characterised by rapid climate oscillations, i.e., the Dansgaard-Oeschger (D/O) events, which showed a rapid warming within a few decades in Greenland. Therefore, the precise reconstruction of past climate variability is a crucial task for future climate predictions. Speleothems are well-established palaeoclimate archives and allow the construction of long and continuous climate proxy records, especially during interglacials, where sufficient liquid water is available. Thus, the majority of published European speleothem records stem from the Holocene, whereas the number of records from previous interglacials is considerably lower. The strength of speleothems as palaeoclimate archive relies on the application and understanding of geochemical proxies, such as carbon and oxygen stable isotopes and trace elements. The latter (e.g., Mg and Sr) are often used to reconstruct prior calcite precipitation (PCP), a process where Ca-carbonate is precipitated in air pockets within the host rock prior to entering the cave. The understanding of this process can ultimately help to reconstruct aridity and rainfall. However, even multi-proxy approaches usually only allow qualitative reconstructions. Non-traditional stable Ca isotopes (δ44/42Ca) provide the unique opportunity to quantify PCP using speleothems based on modern observations of the host rock, drip water and recently precipitated calcite.
Here we propose to generate Ca isotope records of speleothem samples from five different caves, located in Germany (Hüttenbläserschachthöhle, Bunker Cave, Dechenhöhle, Bleßberg Cave) and Spain (Cueva Victoria). The speleothems cover several interglacials between MIS 11 (ca. 424 – 374 ka) and the Holocene and allow the comparison of interglacial conditions between different caves, covering the same time interval. In addition, the Cueva Victoria speleothem record covers all interglacials between MIS 11 and the Holocene and provides the exceptional opportunity to compare interglacials within the same cave. Furthermore, the D/O events during MIS 3 allow us to estimate changes in PCP within short time scales. We will use multi-proxy approaches including non-traditional stable Ca isotopes, 230Th/U-dating, stable carbon and oxygen isotopes, trace elements and Sr isotopes to obtain a robust and precisely dated palaeoclimate reconstruction. The modern Ca isotope data will allow us to quantitatively estimate PCP undern modern-day conditions, using data from the natural cave systems, as well as from a cave analogue experimental setup. The comparison with meteorological precipitation data can ultimately allow to even reconstruct (semi-)quantitative rainfall amounts for all interglacials covering the past ca. 400 ka.