Open AccessI‐STAL, a model for interpretation of Mg/Ca, Sr/Ca and Ba/Ca variations in speleothems and its forward and inverse application on seasonal to millennial scales
Author(s) -
Stoll Heather M.,
Müller Wolfgang,
Prieto Manolo
Publication year - 2012
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2012gc004183
Subject(s) - speleothem , stalagmite , calcite , geology , trace element , cave , seasonality , precipitation , mineralogy , stable isotope ratio , atmospheric sciences , paleontology , geochemistry , ecology , physics , meteorology , biology , holocene , quantum mechanics
Trace element ratios Mg/Ca, Sr/Ca, and Ba/Ca are readily measured in speleothems and may be closely related to hydrological balance, enhancing paleoclimate information inferred from stable isotope measurements. We develop a model which simulates the variation in dripwater chemistry resulting from variable degree of water‐rock interaction and prior calcite precipitation (PCP), with the latter process depending both on drip interval and drip oversaturation with respect to CaCO 3 . Partition coefficients between speleothem and dripwater are dependent on temperature for Mg and on speleothem growth rate for Sr and Ba, as observed in laboratory experiments. The drip oversaturation state, regulated both by cave pCO 2 and the dilution and soil karst dissolution processes, strongly affects stalagmite trace element concentrations by modulating the extent of PCP and speleothem growth rates. Application of an inverse model confirms that seasonal CO 2 cycles can explain the uncorrelated seasonal cycles in Mg/Ca and Sr/Ca observed in our speleothem records from NW Spain for which high CO 2 coincides with dry season. In absence of seasonal variations in drip interval, cycles in cave pCO 2 can produce seasonal covariation in Sr/Ca, Mg/Ca and Ba/Ca. In long time series (10 4 yr) where seasonal sampling resolution is not obtained in stalagmites, a change from dominance of summer to winter rainfall can shift the season of strongest stalagmite deposition to one of lower mean CO 2 and hence greater PCP and higher Mg/Ca, Sr/Ca and Ba/Ca ratios. Caves best suited to record a dominantly water balance signal, such as mean drip intervals, are those with minimal seasonal variation in cave pCO 2 .