G05_P06

Multi-Pool Monitoring of Organic and Inorganic Carbon at Milandre Cave, Switzerland – Implications for Future Paleoecosystem Proxies.

Rowan S¹,  Luetscher M², Szidat S¹, Laemmel T¹, Kost O³, Lechleitner F¹

¹University Of Bern, Bern, Switzerland, ²Swiss Institute for Speleology and Karst Studies, La Chaux-de-Fonds, Switzerland, ³ETH Zurich, Zurich, Switzerland

The organic matter (OM) fraction of speleothems, typically comprising 0.01-0.3% of the total carbon (Blyth et al., 2016), has the potential to offer information about past ecosystems. The provenances of speleothem OM are not well understood, though are speculated to be dominated by contributions from overlying vegetation and soil. Other potential sources include microbial activity within the karst system, cave fauna, and fossil carbon sourced from the carbonate (Blyth et al., 2016). The isotopic characterisation (𝛿¹³C and ¹⁴C) of stalagmite OM may give information about past ecological and climatic state of the surrounding region (Blyth et al., 2016).

Here we present the first results of a monitoring study of the organic and inorganic carbon fluxes in Milandre cave (Switzerland), whereby the main carbon source reservoirs will be monitored for two years. Our preliminary data includes 1) atmospheric, cave, soil, and well CO² 𝛿¹³C and ¹⁴C, and 2) cave drip water dissolved inorganic carbon (DIC) 𝛿¹³C, collected before significant degassing could take place. The cave gas samples are more depleted in ¹⁴C than soil and well gas samples. This suggests either an additional fossil reservoir of CO² contributing to the cave air or substantial influence from degassing of carbonate-derived CO₂ from drips in the cave. The DIC 𝛿¹³C is isotopically light, implying that the cave is an open system with a substantial contribution of biologically respired CO₂ feeding carbonate growth. This information will be used to constrain the source of speleothem OC and its suitability as a proxy.