Abstract
Abstract This study demonstrates the feasibility of speleothem magnetism as a paleo-hydrology proxy in speleothems growing in semi-arid conditions. Soil-derived magnetic particles in speleothems retain valuable information on the physicochemical conditions of the overlying soil, and changes in bedrock hydrology. Yet, the link between magnetic and isotopic proxies of speleothems has been only partly established. We reveal strong coupling between the inflow of magnetic particles (quantified using the magnetic flux index, IRMflux) and δ13C in two Holocene speleothems from Soreq Cave (Israel). The stalagmite record spans from ca. 9.7 to ca. 5.4 ka, capturing the warm-humid conditions associated with the early Holocene and the transition to mid-Holocene wet-dry cycles. Extremely low IRMflux during the early Holocene, indicating minimal contribution from the overlying soil, is accompanied by anomalously high δ13C (approaching bedrock values) hypothesized to be caused by high rainfall and soil erosion. By contrast, IRMflux during the mid-Holocene covaries with the saw-tooth cyclicity of δ13C and δ18O, interpreted as rapid fluctuations in rainfall amount. The peaks in IRMflux precede the negative (wet) δ13C peaks by ~60–120 yr. The apparent lag is explained as a rapid physical translocation of overlying soil particles via groundwater (high IRMflux) as a response to increasing rainfall, compared with slower soil organic matter turnover rates (10–102 yr).
Highlights
Speleothem paleoenvironmental proxy records focus on stable oxygen and carbon isotope time series (δ18O and δ13C, respectively) (e.g., Fairchild and Baker, 2012; Bar-Matthews et al, 2019)
Data from mid-latitude stalagmites suggest that more magnetic particles are delivered into a cave as rainfall increases (e.g., Bourne et al, 2015; Zhu et al, 2017), while the opposite relationship is observed in tropical caves, where magnetic particles are delivered primarily during dry periods (Jaqueto et al, 2016; Fu et al, 2021)
Our study examines the coupling between magnetic parameters and δ13C values over centennial to millennial timescales in two Holocene stalagmites from Soreq Cave, Israel (31°45′21′′N, 35°01′20′′E)
Summary
Speleothem paleoenvironmental proxy records focus on stable oxygen and carbon isotope time series (δ18O and δ13C, respectively) (e.g., Fairchild and Baker, 2012; Bar-Matthews et al, 2019). Coupling these data with other climate proxies increases the accuracy and precision of paleoclimate interpretations (Fairchild and Baker, 2012). The composite isotope record from Soreq secondary calcite speleothems spans ∼180 ka and is the quintessential proxy time series for the eastern Mediterranean (Bar-Matthews et al, 2019, and references therein; Section S1 in the Supplemental Material). Soreq data bracket the timing of the terrestrial occurrence of sapropel S1 (AlmogiLabin et al, 2009) and reveal mid-Holocene wet-dry cycles simultaneous with cultural transitions in the Levant (Bar-Matthews and Ayalon, 2011)
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