Summary schematic of karst landscape and speleothem formation. CO 2 from the atmosphere, root-respiration, and decomposition of soil organic matter (SOM) is dissolved into groundwater and speciates into carbonic acid (H 2 CO 3 ) and bicarbonate (HCO 3- ). H 2 CO 3 is responsible for the dissolution of limestone and the incorporation of Ca 2+ , CO 32- and additional HCO 3- into solution. The water subsequently percolates into a cave, which ventilates seasonally, and CO 2 is degassed from solution into low- p CO 2 cave-air driving the precipitation of calcite (CaCO 3 ). 

Contexts in source publication

Context 1

... runoff events into the cave entrance) or as groundwater. This source water then travels through the soil horizon, into the epikarst (a highly weathered/fractured portion of the host-rock), the host-rock, and into caves ( Figure 1). Fairchild et al. (2006) combined these zones into the dissolution region and the precipitation region. ...

Context 2

... CO 2 concentrations, δ 13 C s values, and δ 13 C r values also varied temporally during the period of study. δ 13 C r varied only slightly (< 1‰; Table 2), while δ 13 C s varied seasonally with the highest values measured during the summer (Figure 9, Figure 10).  13 C r values calculated using Davidson's (1995) equation were indistinguishable from values calculated from Keelng plot y-intercepts ( Figure 11). ...

Context 3

... 13 C r varied only slightly (< 1‰; Table 2), while δ 13 C s varied seasonally with the highest values measured during the summer (Figure 9, Figure 10).  13 C r values calculated using Davidson's (1995) equation were indistinguishable from values calculated from Keelng plot y-intercepts ( Figure 11). ...

Context 4

... δ 13 C s values are consistent with two-endmember mixing between atmospheric CO 2 (regional measured average δ 13 C surface = -9.0 ± 0.1‰ and pCO 2 = 397 ppm) and soil-respired CO 2 (where δ 13 C r = δ 13 C s -4.4‰; Figure 11). If the soil CO 2 concentration is above ~4000 ppm, then the atmospheric component would represent less than 10% of soil CO 2 and have a small effect (based on our data ~0.5 to 1‰) on δ 13 C s . ...

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... we contrast the values of juniper δ 13 C s with predicted equilibrium CO 2 δ 13 C values (calculated from directly-sourced δ 13 C DIC ), we find a small difference during the central Texas summer (Figure 9, Figure 10). With the persistence of severe drought conditions through these months soil pCO 2 was significantly lower, likely as a result of decreased plant productivity and significant plant death (Figure 9, Figure 10). ...

Context 6

... we contrast the values of juniper δ 13 C s with predicted equilibrium CO 2 δ 13 C values (calculated from directly-sourced δ 13 C DIC ), we find a small difference during the central Texas summer (Figure 9, Figure 10). With the persistence of severe drought conditions through these months soil pCO 2 was significantly lower, likely as a result of decreased plant productivity and significant plant death (Figure 9, Figure 10). During this low-pCO 2 season, the relative contribution of atmospheric CO 2 , to total soil CO 2 increased and the depth where soil CO 2 only records biologic CO 2 shifted to greater depths in the soil profile (Figure 9, Figure 10). ...

Context 7

... the persistence of severe drought conditions through these months soil pCO 2 was significantly lower, likely as a result of decreased plant productivity and significant plant death (Figure 9, Figure 10). During this low-pCO 2 season, the relative contribution of atmospheric CO 2 , to total soil CO 2 increased and the depth where soil CO 2 only records biologic CO 2 shifted to greater depths in the soil profile (Figure 9, Figure 10). With the return of precipitation and lower surface temperatures subsequent to drought conditions, there was a strong response in the amount of live vegetation present, increased soil pCO 2 , and convergence of δ 13 C s and equilibrium drip water CO 2 values (Figures 8, 10). ...

Context 8

... this low-pCO 2 season, the relative contribution of atmospheric CO 2 , to total soil CO 2 increased and the depth where soil CO 2 only records biologic CO 2 shifted to greater depths in the soil profile (Figure 9, Figure 10). With the return of precipitation and lower surface temperatures subsequent to drought conditions, there was a strong response in the amount of live vegetation present, increased soil pCO 2 , and convergence of δ 13 C s and equilibrium drip water CO 2 values (Figures 8, 10). Given that soil profiles in central Texas are thin (typically 30-45 cm thick), our deepest soil gas well was 34 cm. ...

Context 9

... et al. (1999) documented juniper roots at NB that extended at least 9 m into the subsurface and oak roots as deep as ~25 m. Sampling sites within the cave are located in a chamber approximately 40 m below the surface, which would allow a large distance for vadose groundwater to equilibrate with plant root respired CO 2 (modified by diffusion) before it enters the cave (Figure 14). ...

Context 10

... contrast our work with δ 13 C DIC values of drip water in other caves, we compiled the maximum range of available drip water δ 13 C values from studies in Gibraltar, Italy, Austria, and Florida ( Figure 16 production in the soil horizon and/or epikarst must also be sufficiently high to overwhelm host-rock and PCP inputs. Therefore, in these caves we hypothesize that the primary control on the carbon isotope composition of drip water is respiration from the dominant deeply-rooted vegetation in the region and any subsequent change in δ 13 C DIC must occur via processes within the cave. ...

Context 11

... conditions conducive to CO 2 degassing from drip water, any drip site where T total is maximized should elicit a shift in δ 13 C cc (on the order of ~0.47‰/hour; Figure 15) temporally that would be measurable in a speleothem calcite record. One mechanism to increase T total would be to modify the flow path that drip water follows after entering the cave and prior to falling onto a speleothem. ...

Context 12

... further explore the influence of T total on δ 13 C DIC we evaluated drip rate variability over the same interval of the modern calcite record produced by Feng et al. (in prep.), and found covariation between δ 13 C cc and drip-rate ( Figure 18). We contrasted this observation with drip water data from St. Michaels Cave, Gibraltar (Mattey et al., 2010) and for at least one drip site observed a similar covariation between drip-rate and δ 13 C DIC values, which we would expect to be 'translated' into equal-magnitude variations in δ 13 C cc (Figure 19). ...

Context 13

... further explore the influence of T total on δ 13 C DIC we evaluated drip rate variability over the same interval of the modern calcite record produced by Feng et al. (in prep.), and found covariation between δ 13 C cc and drip-rate ( Figure 18). We contrasted this observation with drip water data from St. Michaels Cave, Gibraltar (Mattey et al., 2010) and for at least one drip site observed a similar covariation between drip-rate and δ 13 C DIC values, which we would expect to be 'translated' into equal-magnitude variations in δ 13 C cc (Figure 19). For the other drip sites in the Mattey et al. (2010) study we saw a trend between drip-rate and the magnitude of carbon isotope variations. ...

Context 14

... highest magnitude changes in δ 13 C cc occurred when pCO 2 and drip-rate were at a minimum (e.g. January 2006 and January 2008) Figure 19. Drip-rate and δ 13 C cc covariation adapted from Mattey et al. (2010) at the Flowstone drip site. ...