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 Th/U dating of the travertine, to estimate the C contents of the total dissolved inorganic carbon in the ancient thermal water at the time of precipitation of the travertine (C). With the known values of C 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 C contents (C) in the ancient thermal water were estimated. The findings in this study are that (1) both C and δС have decreased in young waters compared to the ancient waters; (2) although atmospheric C activity (C) has also decreased in the same time, the decrease in C is faster than the decrease in C. Under certain assumptions, one could link changes in C and δC to climate change. Decrease in δС of soil CO and decrease in C was caused predominantly by warmer and wetter climate, decomposition of fossil organic matter, and decrease in C. There could be also increased dissolution of solid carbonate and increased carbon exchange between DIC and soil CO, caused by thawing permafrost.