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Knowledge of calcite dissolution kinetics in seawater is a critical component of our understanding of the changing global carbon budget. Towards this goal, we provide the first measurements of the temperature dependence of calcite dissolution kinetics in seawater. We measured the dissolution rates of 13 C-labeled calcite in seawater at 5, 12, 21, and 37°C across the full range of saturation states (0 < Ω = < 1). We show that the dissolution rate is non-linearly dependent on Ω and that the degree of non-linearity both increases with temperature, and changes abruptly at "critical" saturation states (Ωcrit). The traditional exponential rate law most often utilized in the oceanographic community, R=k(1-Ω) n , requires different fits to k and n depending upon the degree of undersaturation. Though we

The marine calcium carbonate (CaCO 3 ) cycle is integral to the global carbon cycle. The production of biogenic CaCO 3 tends to raise atmospheric CO 2 due to consumption of surface ocean alkalinity, while the ballasting of organic matter and export into the deep ocean provided by this material tends to lower CO

This study provides laboratory data of calcite dissolution rate as a function of seawater undersaturation state (1-) under variable pressure. 13 C-labeled calcite was dissolved in unlabeled seawater and the evolving  13 C composition of the fluid was monitored over time to evaluate the dissolution rate. Results show that dissolution rates are enhanced by a factor of 2-4 at 700 dbar compared to dissolution at the same under ambient pressure (10 dbar). This dissolution rate enhancement under pressure applies over an range of 0.65 to 1 between 10 dbar and 700 dbar. Above 700 dbar (up to 2500 dbar), dissolution rates become independent of pressure. The observed enhancement is well beyond the uncertainty associated with the thermodynamic properties of calcite under pressure (partial molar volume ΔV), and thus should be interpreted as a kinetic pressure effect on calcite dissolution. Dissolution at ambient pressure and higher pressures yield non-linear dissolution kinetics, the pressure effect does not significantly change the reaction order n in Rate = k(1-) n , which is shown to vary from 3.10.3 to 3.80.5 from 10 dbar to 700 dbar over = 0.65 to 0.9. Furthermore, two different dissolution mechanisms are indicated by a discontinuity in the rate-undersaturation relationship, and seen at both ambient and higher pressures. The discontinuity, = 0.870.05 and 0.900.03 at 10 dbar and 1050 dbar respectively, are similar within error. The reaction order, n, at >0.9 is 0.470.27 and 0.460.15 at 10 dbar and 700 dbar respectively. This is considered to be the threshold between step retreat dissolution and defect-assisted dissolution. The kinetic enhancement of dissolution rate at higher pressures is related to a decrease in the interfacial

Boron carbide (B4C) powder was synthesized by heating a gel precursor with pyrolysis and carbothermal processes.

The enzyme carbonic anhydrase (CA) is crucial to many physiological processes involving CO2, from photosynthesis and respiration, to calcification and CaCO3 dissolution. We present new measurements of CA activity along a North Pacific transect, on samples from in situ pumps, sediment traps, discreet plankton samples from the ship's underway seawater line, plankton tows, and surface sediment samples from multicores. CA activity is highest in the surface ocean and decreases with depth, both in suspended and sinking particles. Subpolar gyre surface particles exhibit 10× higher CA activity per liter of seawater compared to subtropical gyre surface particles. Activity persists to 4700 m in the subpolar gyre, but only to 1000 m in the subtropics. All sinking CA activity normalized to particulate organic carbon (POC) follows a single relationship (CA/POC = 1.9 ± 0.2 × 10−7 mol mol−1). This relationship is consistent with CA/POC values in subpolar plankton tow material, suspended particles, and core top sediments. We hypothesize that most subpolar CA activity is associated with rapidly sinking diatom blooms, consistent with a large mat of diatomaceous material identified on the seafloor. Compared to the basin‐wide sinking CA/POC relationship, a lower subtropical CA/POC suggests that the inventory of subtropical biomass is different in composition from exported material. Pteropods also demonstrate substantial CA activity. Scaled to the volume within pteropod shells, first‐order CO2 hydration rate constants are elevated ≥ 1000× above background. This kinetic enhancement is large enough to catalyze carbonate dissolution within microenvironments, providing observational evidence for CA‐catalyzed, respiration‐driven CaCO3 dissolution in the shallow North Pacific.