20-EPN-030: Identification of Metabolic Activity in Millennial Old Cave Ice
Visit by Aurel Persoiu of the Emil Racovita Institute of Speleology (Romania) to TA2 Facility 17 – Stable/Clumped Isotopes Laboratory (Hungary).
Dates of visit: 15-29 November 2023
Report Summary: Scarisoara Ice Cave (Apuseni Mts., Romania) hosts a more than 10,000 years old ice block. Previous studies have shown that the ice hosts a varied microbial and fungal ecosystem, with more than 50% of taxa being culturable (i.e., alive). The main question of this project was whether the oxygen gas was consumed in the ice by the metabolic activity of microbes (and/or fungi), so we aimed to determine the Ar/O2 ratio in the gas extracted from the ice.
Two duplicate ice samples were analysed. One of them was deposited during the warm Medieval Warm Period, roughly between AD 800 and 1200 (labelled MWP), while the other accumulated during the subsequent cold Little Ice Age, between AD 1200 and 1850 (labelled as LIA). The Ar/Kr and Ar/Xe ratios indicate the ice was deposited as ponding water was slowly freezing. No entrapped air bubbles were present in the ice. This data fits to modern observations, since the top of the ice are covered by liquid water during summertime, which subsequently freezes in winter. As Ar/O2 ratios show oxygen depletion cannot be detected in the ice. The δ13C of CO2 in the air equilibrated water samples compares to dissolved atmospheric CO2, while δ13C in the ice samples represents depleted CO2 from the root zone of vegetation growing above the cave. δ18O of O2 is similar to that of atmospheric oxygen. As a conclusion, we cannot confirm that oxygen depletion occurs on the ice due to microbial consumption; however, the results are not conclusive and a subsequent sampling campaign to collect more samples is scheduled for 18-25 February 2023.
