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 230 Th/U dating of the travertine, to estimate the 14 C contents of the total dissolved inorganic carbon in the ancient thermal water at the time of precipitation of the travertine (14 Ccalc ). With the known values of 14 Ccalc 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 14 C contents (14 C0 ) in the ancient thermal water were estimated. The findings in this study are that (1) both 14 C0 and δ13 С have decreased in young waters compared to the ancient waters; (2) although atmospheric 14 C activity (14 Catm ) has also decreased in the same time, the decrease in 14 C0 is faster than the decrease in 14 Catm . Under certain assumptions, one could link changes in 14 C0 and δ13 C to climate change. Decrease in δ13 С of soil CO2 and decrease in 14 C0 was caused predominantly by warmer and wetter climate, decomposition of fossil organic matter, and decrease in 14 Catm . There could be also increased dissolution of solid carbonate and increased carbon exchange between DIC and soil CO2 , caused by thawing permafrost.