Yuval Burstyn: Soreq Cave, Israel
Channel: Institute for Rock Magnetism
Date: 2021-06-04

12th Institute for Rock Magnetism Conference

Session 3: Speleothem Magnetism 

Conveners: Josh Feinberg (IRM, University of Minnesota) and Ricardo Trindade (University of São Paulo)

Tite: Holocene palaeohydrological variations in the Eastern Mediterranean inferred from magnetic and isotopic properties of speleothems from Soreq Cave, Israel

Authors: Yuval Burstyn (1), Ron Shaar (1), Jonathan Keinan (1), Yael Ebert (1), Avner Ayalon (2), Miryam Bar-Matthews (2), and Joshua M. Feinberg (3)

Institutions:
(1) The Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
(2) Geological Survey of Israel, 32 Yesha'ayahu Leibowitz Street, Jerusalem, 9692100, Israel
(3) Institute for Rock Magnetism, University of Minnesota, Minneapolis, MN 55455, USA

Abstract:
Soil-derived magnetic particles trapped in speleothems retain valuable information on the physicochemical conditions of overlying soil and changes in bedrock hydrology. This study demonstrates the feasibility of speleothem magnetism as a powerful paleo-hydrology proxy, even in weakly-magnetized speleothems growing in semi-arid conditions.

The link between magnetic and isotopic proxies of speleothems has been only partly established. Here we demonstrate strong coupling between the inflow of magnetic particles (quantified using the magnetic flux index IRMflux) and stable isotope proxies in two Holocene speleothems from Soreq Cave (Israel). The stalagmites formed between ~9.7 and ~5.4 ky BP, with an overlap between ~7.0 and ~6.4 ky BP, capturing the pluvial Eastern Mediterranean conditions associated with Sapropel 1 (S1), which are followed by the transition to mid-Holocene wet-dry cycles. Extremely low IRMflux during S1, indicating a minimal contribution of magnetic particles from overlying soils, is associated with anomalously high δ13C values approaching bedrock composition. Low IRMflux can be explained by reduced soil contribution to karst water (erosion or formation “shut down”) or increased runoff transported into the cave via fissures (change in hydrological routing). By contrast, IRMflux during the mid-Holocene covaries with the saw-tooth cyclicity of δ13C and δ18O, which is interpreted as rapid climate fluctuations associated with rainfall changes. The peaks in the IRMflux during this period seem to precede those of the isotope values. The apparent lag can be explained by the faster response of IRMflux to increased rainfall resulting from rapid physical translocation of overlying soil particles via groundwater, compared with slower soil organic matter turnover rates.


The Soreq Cave as a case study demonstrates two opposite responses of the magnetic flux parameter to precipitation rates. While the wet early-Holocene is characterized with a negative correlation to rainfall, most likely due to soil degradation, the mid-Holocene follows a positive correlation.