Study of isotopes of carbon,thorium, and uranium in travertine and thermal spring samples: implications for effects of changes in geochemical environment and processes

Data on modern radiocarbon activity in the old travertine formations of the Pymvashor hydrothermal system were used, in combination with ²³⁰Th/U dating of the travertine, to estimate the ¹⁴C contents of the total dissolved inorganic carbon in the ancient thermal water at the time of precipitation of the travertine (¹⁴C_calc). With the known values of ¹⁴C_calc and average age of the thermal water, and under the assumption that the residence time of the water in aquifer was constant over the last 13.9?±?1.5 ka, the initial ¹⁴C contents (¹⁴C₀) in the ancient thermal water were estimated. The findings in this study are that (1) both ¹⁴C₀ and δ¹³С have decreased in young waters compared to the ancient waters; (2) although atmospheric ¹⁴C activity (¹⁴C_atm) has also decreased in the same time, the decrease in ¹⁴C₀ is faster than the decrease in ¹⁴C_atm. Under certain assumptions, one could link changes in ¹⁴C₀ and δ¹³C to climate change. Decrease in δ¹³С of soil CO₂ and decrease in ¹⁴C₀ was caused predominantly by warmer and wetter climate, decomposition of fossil organic matter, and decrease in ¹⁴C_atm. There could be also increased dissolution of solid carbonate and increased carbon exchange between DIC and soil CO₂, caused by thawing permafrost.