Seasonal Variations in Modern Speleothem Calcite Growth in Central Texas, U.S.A.

Abstract

Variations in growth rates of speleothem calcite have been hypothesized to reflect changes in a range of paleoenvironmental variables, including atmospheric temperature and precipitation, drip-water composition, and the rate of soil CO 2 delivery to the subsurface. To test these hypotheses, we quantified growth rates of modern speleothem calcite on artificial substrates and monitored concurrent environmental conditions in three caves across the Edwards Plateau in central Texas. Within each of two caves, different drip sites exhibit similar annual cycles in calcite growth rates, even though there are large differences between the mean growth rates at the sites. The growth-rate cycles inversely correlate to seasonal changes in regional air temperature outside the caves, with near-zero growth rates during the warmest summer months, and peak growth rates in fall through spring. Drip sites from caves 130 km apart exhibit similar temporal patterns in calcite growth rate, indicating a controlling mechanism on at least this distance. The seasonal variations in calcite growth rate can be accounted for by a primary control by regional temperature effects on ventilation of cave-air CO 2 concentrations and/or drip-water CO 2 contents. In contrast, site-to-site differences in the magnitude of calcite growth rates within an individual cave appear to be controlled principally by differences in drip rate. A secondary control by drip rate on the growth rate temporal variations is suggested by interannual variations. No calcite growth was observed in the third cave, which has relatively high values of and small seasonal changes in cave-air CO 2. These results indicate that growth-rate variations in ancient speleothems may serve as a paleoenvironmental proxy with seasonal resolution. By applying this approach of monitoring the modern system, speleothem growth rate and geochemical proxies for paleoenvironmental change may be evaluated and calibrated.

Reconstructing modern stalagmite growth from cave monitoring, local meteorology, and experimental measurements of dripwater films

“…(ii) High vertical extension rates are conducive to generating highresolution geochemical proxy datasets from stalagmites, yet to-date few studies have characterised stalagmite growth on intra-annual to decadal timescales and its implications for geochemical climate signal capture. (iii) Seasonal growth rate fluctuations potentially bias net proxy signals towards the season favourable to deposition (Baldini et al, 2008;Banner et al, 2007;Fairchild et al, 2006;Frisia et al, 2000;Mattey et al, 2008;Spötl et al, 2005). (iv) Growth rate variability may be related to climate signal modification by other processes, such as biomass change above the cave (e.g., Baldini et al, 2005) and surface and epikarst hydrology Bradley et al, 2010;Darling, 2004).…”

“…Recent research has characterised their spatio-temporal variability at certain sites (Banner et al, 2007;) and, in particular, highlighted the importance of cave atmosphere pCO 2 dynamics for speleothem palaeoclimatology (Baldini et al, 2008;Fairchild et al, 2006). Although interpreting climatic variability from stalagmite morphology alone is challenging (Dreybrodt, 1988), understanding the physical controls on stalagmite growth, such as drop volume and dripwater film thickness, is necessary for proper linkage of local climate variability, cave environment systematics, and stalagmite growth behaviour.…”

High-resolution stalagmite δ 13C record of soil processes from southwestern China during the early MIS 3

“…Therefore, the Wulu δ 13 C record most likely reflects the biogenic CO 2 production related to soil processes, although the confirmation of this interpretation via cave monitoring is currently restricted by deficit of active calcite deposition. Changes in the CO 2 degassing rate may also contribute to changes in the calcite δ 13 C [25], however, larger variations were only observed at the edge of stalagmites [13,26], sub-sampling along the central growth axis of stalagmite may effectively avoid this influence [27]. Even that the stochastic changes of CO 2 degassing contribute to the calcite δ 13 C, it can not result in the periodic variability observed in our record.…”

Seasonal cave air ventilation controlling variation in cave air PCO2 and drip water geochemistry at Inazumi Cave, Oita, northeastern Kyushu, Japan

“…Spötl et al (2005) conducted pioneering work in the Obir Cave, Austria, and reported seasonal variation in the cave air P CO 2 as the main variable affecting CO 2 degassing and CaCO 3 precipitation from the drip water. Subsequent studies have revealed similar trends (e.g., Banner et al, 2007;Mattey et al, 2010;Boch et al, 2011;Wang et al, 2016), and the variation in P CO 2 has increasingly gained attention as an important variable controlling drip water kinetics.…”

“…As the cave air P CO 2 decreases, however, HCO 3 -and Ca 2+ gradually highlight the decreasing trend and the sequential differences. This might be caused by the incursion of outside air that lowers the air P CO 2 and promotes CO 2 degassing and CaCO 3 precipitation from the drip-water (Spötl et al, 2005;Banner et al, 2007;Boch et al, 2011). The pronounced differences of the WBD from SS3U are measured when the cave air P CO 2 was < 1,500 ppm, indicating that seepage water instantaneously outgasses CO 2 once it encounters low air P CO 2 , implying that the WBD contains a more accurate chemical signature within the carbonate rock matrix above the cave than the dripping water.…”