Intense decadal-scale wet episodes recorded by magnetic minerals in Soreq cave (Israel) Holocene stalagmites
Abstract
Recently it has been shown that magnetic minerals in speleothems can hold unique records of both paleomagnetic field variations and paleoclimate changes. Here we demonstrate the application of rock- and paleomagnetism on Holocene stalagmites from Soreq cave, Israel. Soreq is situated approximately 40 km from the Eastern Mediterranean Sea at an elevation of 400m above sea level. Extensive geochemical research on Soreq speleothems has shown that variations in oxygen (δ18O) and carbon (δ13C) isotopic values correspond with changes in the amount of rainfall, and calibration studies using modern measurements over the last two decades have enabled geochemists to create isotope-based paleo-precipitation proxies for stalagmites from Soreq. To explore the coupling between δ18O, δ13C and mineral magnetism of Soreq speleothems, we examined stalagmites with decadal-resolution isotopic time-series and compared their rock-magnetic data to the isotopic profiles. Because these stalagmites contain exceedingly little magnetite, the most useful parameter was isothermal remanent magnetization (IRM) flux. We find that during most of the investigated time intervals, the IRM flux varies subtly between 0.5 and 2 Am2kg-1yr-1, which corresponds to isotopic precipitation rate estimates between 300 and 700 mm/yr. However, certain intervals with extremely low δ18O (<12.5 ‰) and δ13C (<6 ‰) values are interpreted to represent increased rainfall episodes and exhibit dramatic and anomalous increases in IRM flux, up to 6 Am2kg-1yr-1. The elevated IRM flux for these multi-decadal intervals indicates that something temporarily changed about the delivery of magnetic minerals into the cave; perhaps associated with the seasonality or intensity of rainfall, or by changes in the groundwater plumbing system above a drip point. Such episodes could not be identified using isotopic data alone, and demonstrate that the magnetism of speleothems can be a powerful proxy to complement other characterization methods.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMGP22A..07S
- Keywords:
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- 0419 Biomineralization;
- BIOGEOSCIENCES;
- 1512 Environmental magnetism;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1522 Paleomagnetic secular variation;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1540 Rock and mineral magnetism;
- GEOMAGNETISM AND PALEOMAGNETISM