Different response of trace elements in the drip-water of Kaiyuan Cave on Shandong Peninsula (coastal North China) to hydroclimatic changes from 2012 to 2014

Abstract

Water-rock interaction (WRI) and prior calcite precipitation (PCP) are often employed to interpret the variation in the trace elements present in speleothems and are assumed to be strengthened under drier climates. However, this interpretation is sometimes not consistent with speleothem records in monsoonal China (Zhou et al., 2011; Ban et al., 2018). In this study, a three-year monitoring program was carried out from 2012 to 2014 at Kaiyuan Cave on Shandong Peninsula, coastal North China to investigate how the element geochemistry of drip-water responds to changes in hydroclimate. It was found that trace elements and their ratios to Ca (X/Ca ratio) responded differently to hydroclimatic change at Kaiyuan Cave during the period from 2012 to 2014. Sr and Ba, which are controlled by incongruent dissolution of the host-rock and are sensitive to residence time, show a long-term increasing trend from 2012 to 2014, while Mg and U illustrate a long-term decreasing trend possibly due to reduced dissolution of the host-rock and less input from the soil layer. All the X/Ca ratios are affected by WRI, but the soil layer may have played a role to some extent on the Sr/Ca, Ba/Ca and U/Ca ratios. These findings indicate that trace elements (and X/Ca ratios) of karstic drip-water and speleothems do not respond in the same direction to hydroclimate change as is often suggested in previous publications. Caution is advised when these geochemical proxies are applied to interpret changes in precipitation and/or summer monsoon intensity in China.