Abstract

Methane concentration in caves is commonly much lower than the external atmosphere, yet the cave CH4 depletion causal mechanism is contested and dynamic links to external diurnal and seasonal temperature cycles unknown. Here, we report a continuous 3-year record of cave methane and other trace gases in Jenolan Caves, Australia which shows a seasonal cycle of extreme CH4 depletion, from ambient ~1,775 ppb to near zero during summer and to ~800 ppb in winter. Methanotrophic bacteria, some newly-discovered, rapidly consume methane on cave surfaces and in external karst soils with lifetimes in the cave of a few hours. Extreme bacterial selection due to the absence of alternate carbon sources for growth in the cave environment has resulted in an extremely high proportion 2–12% of methanotrophs in the total bacteria present. Unexpected seasonal bias in our cave CH4 depletion record is explained by a three-step process involving methanotrophy in aerobic karst soil above the cave, summer transport of soil-gas into the cave through epikarst, followed by further cave CH4 depletion. Disentangling cause and effect of cave gas variations by tracing sources and sinks has identified seasonal speleothem growth bias, with implied palaeo-climate record bias.

Details

Title
Seasonal total methane depletion in limestone caves
Author
Waring, Chris L 1 ; Hankin, Stuart I 1 ; Griffith, David W T 2 ; Kertesz, Michael A 3 ; Kobylski, Victoria 3 ; Wilson, Neil L 3 ; Coleman, Nicholas V 4 ; Kettlewell, Graham 2 ; Zlot, Robert 5 ; Bosse, Michael 5 ; Bell, Graham 5 

 ANSTO Environmental Research, Lucas Heights, Australia 
 University of Wollongong, Centre for Atmospheric Chemistry, Wollongong, Australia 
 University of Sydney, Sydney Institute of Agriculture, Sydney, Australia 
 University of Sydney, School of Life and Environmental Sciences, Sydney, Australia 
 formerly CSIRO, Technology Court, Pullenvale, Australia 
Pages
1-12
Publication year
2017
Publication date
Aug 2017
Publisher
Nature Publishing Group
e-ISSN
20452322
Source type
Scholarly Journal
Language of publication
English
ProQuest document ID
1957225450
Copyright
© 2017. This work is published under http://creativecommons.org/licenses/by/4.0/ (the “License”). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License.