Stalagmite carbon isotopes and dead carbon proportion (DCP) in a near-closed-system situation: An interplay between sulphuric and carbonic acid dissolution

Bajo, Petra; Borsato, Andrea; Drysdale, Russell N.; Hua, Quan; Frisia, Silvia; Zanchetta, Giovanni; Hellström, John; Woodhead, Jon

doi:10.1016/j.gca.2017.04.038

Cited by 58 publications

(55 citation statements)

References 80 publications

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“…Elevated Mg in the fracture water is closely related to the occurrence of particular carbonate host rocks such as ankerite, Mg‐rich limestone or (Fe‐) dolomite at Erzberg. The fact that prior aragonite or calcite precipitation increased the aqueous Mg/Ca ratios is also supported by the consistently high erzbergite δ 13 C values (preferential outgassing of isotopically light 12 CO 2 and enrichment of δ 13 C DIC ; Bajo et al ., ). Prior aragonite precipitation would further explain the lower Sr and Ba concentrations in waters of the southern Erzberg section (Table ), i.e.…”

Section: Discussionmentioning

confidence: 97%

“…Similarly, (prior) aragonite precipitation would also diminish the overall uranium concentration in aqueous solution based on the respective fractionation behaviour (Wassenburg et al ., ) and might be the explanation for low to very low U contents measured in some erzbergite samples (Table ). Most of these hydrogeochemical mechanisms proposed are known to depend on water infiltration, flow routes and discharge, such that aqueous Mg/Ca increases related to prior CaCO 3 precipitation are typically favoured during overall dry environmental/aquifer conditions (Huang & Fairchild, ; Riechelmann et al ., ; Bajo et al ., ). The low discharge of modern water encountered in fractures at Erzberg supports this conclusion.…”

Section: Discussionmentioning

confidence: 97%

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Aragonite–calcite veins of the ‘Erzberg’ iron ore deposit (Austria): Environmental implications from young fractures

et al. 2018

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The well‐known Erzberg site represents the largest siderite (FeCO3) deposit in the world. It consists of various carbonates accounting for the formation of prominent CaCO3 (dominantly aragonite) precipitates filling vertical fractures of different width (centimetres to decimetres) and length (tens of metres). These commonly laminated precipitates are known as ‘erzbergite’. This study focuses on the growth dynamics and environmental dependencies of these vein fillings. Samples recovered on‐site and from mineral collections were analyzed, and these analyses were further complemented by modern water analyses from different Erzberg sections. Isotopic signatures support meteoric water infiltration and sulphide oxidation as the principal hydrogeochemical mechanism of (Ca, Mg and Fe) carbonate host rock dissolution, mobilization and vein mineralization. Clumped isotope measurements revealed cool formation temperatures of ca 0 to 10°C for the aragonite, i.e. reflecting the elevated altitude Alpine setting, but unexpectedly low for aragonite nucleation. The 238U–234U–230Th dating yielded ages from 285·1 ± 3·9 to 1·03 ± 0·04 kyr bp and all samples collected on‐site formed after the Last Glacial Maximum. The observed CaCO3 polymorphism is primarily controlled by the high aqueous Mg/Ca ratios resulting from dissolution of Mg‐rich host rocks, with Mg/Ca further evolving during prior CaCO3 precipitation and CO2 outgassing in the fissured aquifer. Aragonite represents the ‘normal’ mode of erzbergite formation and most of the calcite is of diagenetic (replacing aragonite) origin. The characteristic lamination (millimetre‐scale) is an original growth feature and mostly associated with the deposition of stained (Fe‐rich) detrital particle layers. Broader zonations (centimetre‐scale) are commonly of diagenetic origin. Petrographic observations and radiometric dating support an irregular nature for most of the layering. Open fractures resulting from fault tectonics or gravitational mass movements provide water flow routes and fresh chemical reaction surfaces of the host rock carbonates and accessory sulphides. If these prerequisites are considered, including the hydrogeochemical mechanism, modern water compositions, young U‐Th ages and calculated precipitation rates, it seems unlikely that the fractures had stayed open over extended time intervals. Therefore, it is most likely that they are geologically young.

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 97%

Aragonite–calcite veins of the ‘Erzberg’ iron ore deposit (Austria): Environmental implications from young fractures

et al. 2018

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“…Radiocarbon ( 14 C hereafter) dating has fundamentally changed our knowledge of the timing of events and rates of change in archeological and climate proxy records ever since it was pioneered in the late 1940s (Arnold and Libby, 1949). To provide more accurate data for 14 C calibration beyond the tree-ring record, speleothems gained importance as a source of information on atmospheric 14 C. Stalagmite records from tropical and temperate climate zones overlapping the (floating) tree-ring data (Beck et al, 2001;Hoffmann et al, 2010;Southon et al, 2012) have been included in the most recent comprehensive 14 C intercalibration data set IntCal13 (Reimer et al, 2013). Radiocarbon calibration based on speleothems relies on the assumption of a low and constant dead carbon fraction (DCF) in the stalagmite, even though one of the included calibration records showed DCF variation by almost a factor of 2 during the YD (Beck et al, 2001;Hoffmann et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

“…To provide more accurate data for 14 C calibration beyond the tree-ring record, speleothems gained importance as a source of information on atmospheric 14 C. Stalagmite records from tropical and temperate climate zones overlapping the (floating) tree-ring data (Beck et al, 2001;Hoffmann et al, 2010;Southon et al, 2012) have been included in the most recent comprehensive 14 C intercalibration data set IntCal13 (Reimer et al, 2013). Radiocarbon calibration based on speleothems relies on the assumption of a low and constant dead carbon fraction (DCF) in the stalagmite, even though one of the included calibration records showed DCF variation by almost a factor of 2 during the YD (Beck et al, 2001;Hoffmann et al, 2010). A unique speleothem calibration record was recently published by Cheng et al (2018), who presented a continuous atmospheric 14 CO 2 reconstruction from stalagmites with a very low (< 6 %) and constant DCF.…”

Section: Introductionmentioning

confidence: 99%

“…Several studies attributed this relation to changes in open-vs. closed-system conditions of limestone dissolution, which controls the contribution of very old host rock carbonate to drip water dissolved inorganic carbon (DIC) (Griffiths et al, 2012;Noronha et al, 2014). In a recent study, DCF values exceeding 50 % in a Holocene stalagmite from Corchia Cave, Italy, have been reported (Bajo et al, 2017). Such high DCF values are above the theoretical limit for closed-system carbonate dissolution systems and were attributed to enhanced host rock dissolution by sulfuric acid.…”

Section: Introductionmentioning

confidence: 99%

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Climate-induced speleothem radiocarbon variability on Socotra Island from the Last Glacial Maximum to the Younger Dryas

et al. 2020

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In this study, the dead carbon fraction (DCF) variations in stalagmite M1-5 from Socotra Island in the western Arabian Sea were investigated through a new set of highprecision U-series and radiocarbon ( 14 C) dates. The data reveal an extreme case of very high and also climate-dependent DCF. For M1-5, an average DCF of 56.2 ± 3.4 % is observed between 27 and 18 kyr BP. Such high DCF values indicate a high influence of aged soil organic matter (SOM) and nearly completely closed-system carbonate dissolution conditions. Towards the end of the last glacial period, decreasing Mg/Ca ratios suggest an increase in precipitation which caused a marked change in the soil carbon cycling as indicated by sharply decreasing DCF. This is in contrast to the relation of soil infiltration and DCF as seen in stalagmites from temperate zones.

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Karst Hydrogeology, Geomorphology and Caves

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Stalagmite carbon isotopes and dead carbon proportion (DCP) in a near-closed-system situation: An interplay between sulphuric and carbonic acid dissolution

Cited by 58 publications

References 80 publications

Aragonite–calcite veins of the ‘Erzberg’ iron ore deposit (Austria): Environmental implications from young fractures

Aragonite–calcite veins of the ‘Erzberg’ iron ore deposit (Austria): Environmental implications from young fractures

Climate-induced speleothem radiocarbon variability on Socotra Island from the Last Glacial Maximum to the Younger Dryas

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