A novel determination of calcite dissolution kinetics in seawater

Subhas, Adam V.; Rollins, Nick; Berelson, William M.; Dong, Sijia; Erez, Jonathan; Adkins, Jess F.

doi:10.1016/j.gca.2015.08.011

Cited by 77 publications

(84 citation statements)

References 64 publications

(127 reference statements)

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“…In addition to measuring dissolution-precipitation reactions in the solid, we measured the appearance of 13 C in seawater dissolved inorganic carbon (DIC) using a Picarro cavity ring-down spectrometer (9). The dissolution of 13 C calcite produces a linear increase of seawater δ 13 C over time.…”

Section: Measuring and Modeling Dissolution-precipitation In The Solumentioning

confidence: 99%

“…The slope of this line is a direct measure of the net dissolution rate (e.g., rates in ref. 9). However, we also observe curvature in plots of δ 13 C versus time (Fig.…”

Section: Measuring and Modeling Dissolution-precipitation In The Solumentioning

confidence: 99%

“…Our results are from closedsystem dissolution experiments that have no headspace and thus isolate this second chemical mechanism of CA on calcite dissolution (ref. 9 …”

Section: Catalysis Via Carbonic Anhydrase and A Link Between Solutionmentioning

confidence: 99%

“…Most of the deep ocean is only mildly undersaturated such that pelagic dissolution is primarily a near-equilibrium phenomenon. However, attempts to quantify the relationship between calcite dissolution rate and Ω are highly variable between different studies, both in functional form and absolute value (4)(5)(6)(7)(8)(9).…”

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Catalysis and chemical mechanisms of calcite dissolution in seawater

Subhas

Adkins

Rollins

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Near-equilibrium calcite dissolution in seawater contributes significantly to the regulation of atmospheric CO 2 on 1,000-y timescales. Despite many studies on far-from-equilibrium dissolution, little is known about the detailed mechanisms responsible for calcite dissolution in seawater. In this paper, we dissolve 13 C-labeled calcites in natural seawater. We show that the timeevolving enrichment of δ 13 C in solution is a direct measure of both dissolution and precipitation reactions across a large range of saturation states. Secondary Ion Mass Spectrometer profiles into the 13 C-labeled solids confirm the presence of precipitated material even in undersaturated conditions. The close balance of precipitation and dissolution near equilibrium can alter the chemical composition of calcite deeper than one monolayer into the crystal. This balance of dissolution-precipitation shifts significantly toward a dissolution-dominated mechanism below about Ω = 0.7. Finally, we show that the enzyme carbonic anhydrase (CA) increases the dissolution rate across all saturation states, and the effect is most pronounced close to equilibrium. This finding suggests that the rate of hydration of CO 2 is a rate-limiting step for calcite dissolution in seawater. We then interpret our dissolution data in a framework that incorporates both solution chemistry and geometric constraints on the calcite solid. Near equilibrium, this framework demonstrates a lowered free energy barrier at the solid-solution interface in the presence of CA. This framework also indicates a significant change in dissolution mechanism at Ω = 0.7, which we interpret as the onset of homogeneous etch pit nucleation.mineral dissolution | isotope geochemistry | oceanography | catalysis T he production and dissolution of calcium carbonate minerals provide a crucial link between the marine carbon and alkalinity cycles. The ocean has absorbed about 25 to 30% of anthropogenic CO2 emissions, dropping mean surface ocean pH since the industrial era (1). As ocean pH decreases, sedimentary carbonate minerals will dissolve to compensate for the loss of buffering capacity, eventually restoring atmospheric pCO2 to about its preindustrial level (2, 3). This reaction will mostly take place in the deep ocean, where the calcite satura-Most of the deep ocean is only mildly undersaturated such that pelagic dissolution is primarily a near-equilibrium phenomenon. However, attempts to quantify the relationship between calcite dissolution rate and Ω are highly variable between different studies, both in functional form and absolute value (4-9).With the exception of very early work by Berner and Morse (7), few studies have attempted to unpack the chemical species responsible for calcite dissolution in seawater. Many studies choose instead to derive empirical relationships between saturation state and dissolution rate (5, 6, 10, 11). In contrast, freshwater and dilute solution dissolution studies have made large advances in identifying key chemical species responsible for observed dissolution...

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Section: Measuring and Modeling Dissolution-precipitation In The Solumentioning

confidence: 99%

“…The slope of this line is a direct measure of the net dissolution rate (e.g., rates in ref. 9). However, we also observe curvature in plots of δ 13 C versus time (Fig.…”

Section: Measuring and Modeling Dissolution-precipitation In The Solumentioning

confidence: 99%

“…Our results are from closedsystem dissolution experiments that have no headspace and thus isolate this second chemical mechanism of CA on calcite dissolution (ref. 9 …”

Section: Catalysis Via Carbonic Anhydrase and A Link Between Solutionmentioning

confidence: 99%

mentioning

confidence: 99%

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Catalysis and chemical mechanisms of calcite dissolution in seawater

Subhas

Adkins

Rollins

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…Percent CaCO 3 and δ 13 C were measured on a separate aliquot using a modified Picarro CRDS‐Liaison system (Dong et al, ; Subhas et al, ). Between 0.8 and 3 mg of sediment sample was weighed into 12 ml Labco Exetainer vials with screw‐top septum caps.…”

Section: Methodsmentioning

confidence: 99%

Selective Preservation of Coccolith Calcite in Ontong‐Java Plateau Sediments

Subhas¹,

McCorkle

Quizon

et al. 2019

Paleoceanog and Paleoclimatol

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Dissolution of calcite in deep ocean sediments, which is required to balance global marine CaCO 3 production and burial fluxes, is still a poorly understood process. In order to assess the mechanisms of dissolution in sediments, we analyzed four multicore tops taken along a depth transect on the Ontong-Java Plateau. These cores were taken directly on the equator, and span water column calcite saturation states from ∼0.93 to ∼0.74, allowing us to assess the effect of dissolution on carbonate sediment composition. The top 2 cm of each multicore was sectioned and sieved to separate coccolith from foraminiferal calcite, and the %CaCO 3 , 13 C, Δ 14 C, and Mg/Ca were evaluated. The mass ratio of coccoliths to foraminifera increases by a factor of 3 as a function of water depth, reflecting the preferential dissolution of foraminifera. Carbon isotope ( 13 C and Δ 14 C) data suggest that most dissolution takes place at the sediment-water interface and primarily affects foraminifera. Mg/Ca analyses indicate that the Mg content of the entire foraminiferal assemblage decreases as a function of dissolution. In contrast, coccolith dissolution takes place within the sediments, rather than at the interface. Together these two processes cause coccoliths to be up to 1,000 radiocarbon years younger than foraminifera from the same depth horizon. Despite this within-sediment coccolith dissolution flux, sediments below the calcite saturation horizon remain enriched in coccolith calcite. Combined with global seafloor hypsometry and calcium carbonate content, this enrichment suggests that globally, coccoliths may outweigh foraminifera in deep ocean sediments by a factor of 1.8.

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Calibration of the B/Ca proxy in the planktic foraminifer Orbulina universa to Paleocene seawater conditions

et al. 2017

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The B/Ca ratio of planktic foraminiferal calcite, a proxy for the surface ocean carbonate system, displays large negative excursions during the Paleocene‐Eocene Thermal Maximum (PETM, 55.9 Ma), consistent with rapid ocean acidification at that time. However, the B/Ca excursion measured at the PETM exceeds a magnitude that modern pH calibrations can explain. Numerous other controls on the proxy have been suggested, including foraminiferal growth rate and the total concentration of dissolved inorganic carbon (DIC). Here we present new calibrations for B/Ca versus the combined effects of pH and DIC in the symbiont‐bearing planktic foraminifer Orbulina universa, grown in culture solutions with simulated Paleocene seawater elemental composition (high [Ca], low [Mg], and low total boron concentration ([B]T). We also investigate the isolated effects of low seawater [B]T, high [Ca], reduced symbiont photosynthetic activity, and average shell growth rate on O. universa B/Ca in order to further understand the proxy systematics and to determine other possible influences on the PETM records. We find that average shell growth rate does not appear to determine B/Ca in high calcite saturation experiments. In addition, our “Paleocene” calibration shows higher sensitivity than the modern calibration at low [B(OH)4−]/DIC. Given a large DIC pulse at the PETM, this amplification of the B/Ca response can more fully explain the PETM B/Ca excursion. However, further calibrations with other foraminifer species are needed to determine the range of foraminifer species‐specific proxy sensitivities under these conditions for quantitative reconstruction of large carbon cycle perturbations.

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A novel determination of calcite dissolution kinetics in seawater

Cited by 77 publications

References 64 publications

Catalysis and chemical mechanisms of calcite dissolution in seawater

Catalysis and chemical mechanisms of calcite dissolution in seawater

Selective Preservation of Coccolith Calcite in Ontong‐Java Plateau Sediments

Calibration of the B/Ca proxy in the planktic foraminifer Orbulina universa to Paleocene seawater conditions

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