Typhoon rainfall impact on drip water δ¹⁸O in Xianyun cave, Southeast China

Abstract

Precisely dated high-resolution speleothems may record past typhoon events, however, the state of the art cave monitoring is a prerequisite to identify suitable stalagmites for the reconstruction of such events. With this motivation, we examined the isotopic composition (δ 18 O and d-excess values) of rainfall, outside river, cave drip water, and an underground river in the Xianyun cave system, located in southeastern China. Monthly to bimonthly monitoring of environmental and isotopic conditions was conducted for 1 year, from December 2018 to December 2019, including a typhoon event (August 24, 2019 to August 26, 2019), called Bailu. The δ 18 O of rainfall samples over the cave and outside river water ranged from −9.7‰ to −1.9‰ and −8.2‰ to −6.3‰, respectively, while the δ 18 O of Typhoon Bailu rainfall and instantaneous outside river water ranged from −19.6‰ to −6.3‰ and −10.4‰ to −7.7‰, respectively. Typhoon Bailu-induced rainfall showed distinctly negative δ 18 O values as compared to those of the monthly and bimonthly rainfall, exhibiting a three-stage inverted U-shaped variation characteristic. Four drip water monitoring sites inside the cave revealed low variations during the studied period with average values of −7.8‰, −8.0‰, −8.0‰, and −8.1‰. However, during the typhoon, the drip water δ 18 O values exhibited similar characteristic as outside rainfall but with just 0.2‰ negative deviation owing to precipitation amount and drip water source reservoir. The integration of rainfall amount with drip water source reservoir determines the degree to which a typhoon isotopic signature gets diluted during epikarst infiltration. This study provides the first instrumental evidence of typhoon signal in karst system in southeastern China. Our results imply that the δ 18 O of drip water in Xianyun cave can instantaneously respond to typhoon rainfall. However, the 0.2‰ shift in drip water δ 18 O is difficult to be recorded by speleothems. We suggest multiyear monitoring to ascertain fully if the stalagmites could be used as paleotyphoon proxy.

Variations of stable isotope in Typhoon Lupit (2021) rainfall and its response to upstream convective processes

“…Typhoon Lupit rainfall isotopes were not correlated with rainfall amount throughout the sampling period or during each stage. These results are consistent with the previous studies demonstrating that the amount effect can only be detected in monthly and annual precipitation, and not in daily or event precipitation (He et al, 2018;Jackisch et al, 2022;Kurita et al, 2009;Xu et al, 2019;Yang et al, 2021).…”

“…Rainwater samples from Typhoon Lupit were collected on open ground in front of the Stable Isotope Laboratory, School of Geographical Sciences, Fujian Normal University, Fuzhou, where a subtropical monsoon climate typically dominates. Approximately one to two typhoons impact or make landfall annually from June to September in Fuzhou (Xu et al, 2019; Yang et al, 2021). Rainfall caused by typhoons usually accounts for 50%–80% of the monthly precipitation and 6%–17% of the annual precipitation (Xu et al, 2019).…”

“…Several studies have attempted to elucidate how typhoons affect rainfall δ 18 O, but the mechanism causing these changes and whether they can contribute to the δ 18 O variations observed over such a short time scale in the case of a cyclone is still unclear (e.g. Gedzelman et al, 2003; Jackisch et al, 2022; Lawrence et al, 1998; Lawrence & Gedzelman, 1996; Sánchez‐Murillo et al, 2019; Xu et al, 2019; Yang et al, 2021). Typhoons produce rainwater with extremely depleted stable isotope values compared with other tropical or subtropical storms.…”