Palaeohydrologic interpretations of Holocene wet episodes recorded in stalagmites from Soreq Cave, Israel: Linking the magnetic and isotopic properties of speleothems

Soil-derived magnetic particles trapped in speleothems can retain valuable information on the physiochemical conditions of the overlying soil and changes in the hydrological system. However, a direct link between magnetic and isotopic properties of speleothems has been only qualitatively established and is known to vary regionally. Here we investigate two Holocene speleothems from Soreq Cave, Israel and provide evidence for strong coupling over centennial to millennial timescales between the inflow of magnetic particles (quantified using the magnetic flux index, IRM_flux), δ¹³C, and rainfall amounts. The two stalagmites formed at separate intervals: one at ~9.5 ky BP capturing the transition from pluvial Eastern Mediterranean conditions associated with Sapropel 1 (S1) and a second at 5.4 ky BP recording mid-Holocene wet-dry cycles.

The late-Holocene speleothem shows an anomalously high δ¹³C episode that is correlated with extremely low IRM_flux, indicating minimal contribution from overlying soils due to either (1) recently denuded soils, or (2) high overland and vadose runoff. By contrast, the mid-Holocene sample shows saw-tooth cycles in both δ¹⁸O and δ¹³C, which are interpreted as rapid climate fluctuations associated with rainfall changes. IRM_flux during this period varies in-phase with the δ¹³C cycles; however, the peaks in IRM_flux values precede those of the isotope values. The apparent lag in isotopic values may be explained by the faster response of the IRM_flux to increased rainfall resulting from the rapid physical translocation of overlying soil particles via groundwater, compared with slower soil organic matter turnover rates, which may vary on timescales of up to thousands of years.

The separate palaeohydrological scenarios resolved from the two speleothems demonstrate how magnetic data can act as a powerful paleo-hydrology proxy, even in weakly-magnetized speleothems growing under semi-arid conditions.