Search

The dissolution of settling calcite at the Hawaii Ocean Time-Series Sta. ALOHA in the North Pacific is examined using a calculation of the calcite saturation state based on 5 yr of alkalinity measurements and contemporary understanding of calcite dissolution kinetics. The results are consistent with previously reported field observations of calcite dissolution in the upper 1000 m at Sta. ALOHA. At low settling velocities, uncertainties in the parameterization of the dissolution equation can result in between 20% and 100% dissolution of sinking calcite in the upper 1000 m. The results introduce some doubt with regard to previous claims that field results at ALOHA provide evidence of biologically mediated calcite dissolution.

Isotopic and elemental records of authigenic calcite from lacustrine deposits in the intraforeland basins of Utah were analyzed in an effort to reconstruct the regional paleoclimate, paleohydrology, and paleotopography of the early Cenozoic central North American Cordillera. Isotopic profiles for Paleogene Lakes Uinta, Flagstaff, and Claron show relatively large oxygen isotopic shifts that are diachronous among basins with an ~7[per thousand] decrease in [delta][sup.18][O.sub.calcite] values at ca. 45 Ma in Lake Flagstaff, an ~5[per thousand] decrease in [delta][sup.18][O.sub.calcite] values between ca. 42 and 35 Ma in Lake Claron, and an ~6[per thousand]. decrease in [delta][sup.18][O.sub.calcite] values between ca. 44 and 43 Ma in Lake Uinta. We interpret these negative oxygen isotopic shifts to be the combined result of increased hypsometric mean elevation of basin catchments and related freshening associated with basin infilling. The basins studied also have undergone periods of intense evaporation during periods of hydrologic closure, which, for example, produced an ~7[per thousand] increase in [delta][sup.18][O.sub.calcite] values in Lake Uinta beginning at ca. 51 Ma. Hydrologic closure in the Uinta Basin probably resulted from growth of local topography that diverted previously substantial inflows from low elevation regions within the foreland. This study adds to the growing body of evidence that suggests a pattern of along-strike variations in the timing of topographic development and dissection of the Cordilleran landscape during the early Cenozoic. We favor an interpretation that calls for the middle Eocene rearrangement of regional drainage patterns such that intraforeland basins that once received waters from far-flung foreland river systems became dominated by inflows of low [delta][sup.18]O waters from catchments with higher hypsometric mean elevations that drained the adjacent hinterland and/or basin-bounding uplifts. This drainage reorganization is analogous but subsequent to the large-scale integration of catchments in the northern Cordillera that has been recognized on the basis of isotopic and sedimentological evidence in Montana and Idaho at ca. 50-47 Ma, with rivers flowing southeast into Lake Gosiute at ca. 49 Ma and then for a time reaching Lake Uinta, causing a prominent highstand in that lake at 48.6 Ma. The negative oxygen isotopic shifts presented herein, which occurred between ca. 45 and ca. 35 Ma in the intraforeland basins of Utah, may reflect the north-to-south progression of drainage integration in the Cordillera as magmatism and related topography swept southward through the hinterland and increased the hypsometric mean of catchments that fed subjacent intraforeland basins.

Fast reactions in the medium from which a crystal is growing (e.g., [H.sup.+] + HC[O.sup.-.sub.3] [left and right arrow] [H.sub.2]C[O.sub.3]) occurring near the crystal surface can conflict with the stoichiometry of crystal formula-unit creation (e.g., C[O.sup.2-.sub.3] is readily incorporated in calcite but [H.sup.+] is not). As a result, a thin fast-reaction boundary layer (FRBL) is created within which the fast reactions are out of equilibrium even though they are maintained at equilibrium far from the crystal surface. The FRBL corrects the fluxes of components to and from the surface of the crystal; not taking the FRBL into account leads to violation of mass conservation. This 'paradox' is resolved by showing how the equations of crystal growth can be solved in the fast-reaction limit without violating mass conservation. As this paradox was not understood in the literature, models and geological conclusions drawn should be re-examined. Keywords: Crystal growth, oscillatory crystal zoning, calcite, equilibrium, multiscale analysis

Earthworms of the family Lumbricidae, which includes many common species, produce and secrete up to millimeter-sized calcite granules, and the intricate fine-scale zoning of their constituent crystals is unique for a biomineral. Granule calcite is produced by crystallization of amorphous calcium carbonate (ACC) that initially precipitates within the earthworm calciferous glands, then forms protogranules by accretion on quartz grain cores. Crystallization of ACC is mediated by migrating fluid films and is largely complete within 24 h of ACC production and before granules leave the earthworm. Variations in the density of defects formed as a byproduct of trace element incorporation during calcite crystal growth have generated zoning that can be resolved by cathodoluminescence imaging at ultraviolet to blue wavelengths and using the novel technique of scanning electron microscope charge contrast imaging. Mapping of calcite crystal orientations by electron backscatter diffraction reveals an approximate radial fabric to the granules that reflects crystal growth from internal nucleation sites toward their margins. The survival within granules of ACC inclusions for months after they enter soils indicates that they crystallize only within the earthworm and in the presence of fluids containing biochemical catalysts. The earthworm probably promotes crystallization of ACC in order to prevent remobilization of the calcium carbonate by dissolution. Calcite granules vividly illustrate the role of transient precursors in biomineralization, but the underlying question of why earthworms produce granules in volumes sufficient to have a measurable impact on soil carbon cycling remains to be answered.

An attempt is made to explore the reactivity of the reactive bifunctional surface intermediate as a function of the abundance of adsorbed water. The mechanism of the interfacial chemistry of CaC[O.sub.3] in the presence of important atmospheric trace gases that corrode or chemically react with CaC[O.sub.3] such as C[O.sub.2], S[O.sub.2], and atmospheric acidity such as HN[O.sub.3] and HCl.

Electronic structure calculations performed at the density functional theory level were employed to study the surface termination of the {1014} calcite surface in contact with a gaseous phase containing water and carbon dioxide. The results revealed that a nonstoichiometric termination could occur in atmospheric conditions at high relativity, hence suggesting that nonstoichiometic surfaces play a major role in the chemistry of calcite surfaces.

A Knudsen cell reactor is used for examining the heterogeneous uptake of gaseous nitric acid on dolomite (CaMg(CO3)2) and calcite (CaCO3) particles under dry conditions at 296 k. The value of the initial heterogeneous uptake coefficient for CaMg(CO3)2 was (7+4) X 10(super -4) and the value for CaCO3 is (2+0.4) X 10(super -3).

The free energy profiles of water and three metal ions (magnesium, calcium and strontium) adsorbing on the (1014) calcite surface in aqueous solution is calculated with the help of molecular dynamics with parametrized equations to describe the interatomic forces. The model is able to reproduce the interactions between water and metal ions regardless of whether they are mineral surface or in bulk water.

Atomistic simulation methods are used to model the interaction of water with the {1014} calcite surface and the energetics for the removal of carbonate groups in the presence of water. The calculations suggest that carbonate groups at some step edges and low-index surfaces will dissociate water to form OH groups on the surface and release carbon dioxide, but that this reaction does not take place on the undefective {1014} surface.

Dynamical simulations are applied to understand the nucleation pathway of amorphous calcium carbonate involved in the nucleation and growth of calcium carbonate mineral that represents one of the most significant biominerals. Amorphous calcium carbonate nanoparticles are observed to exploit size-dependent water content to render itself more stable than the favored bulk phase, calcite, below a critical diameter of close to 4 nm.

A computational method was created and tested to design peptide-calcite protein-biomineralization systems. The study results could have significant implications for the potential role of the basic residues in sequence-order specificity for peptide-mineral interactions.

A combination of the X-ray absorption near-edge structure spectroscopy and X-ray photoelectron emission microscopy studies is employed to explain the significance of the presence of different macromolecules. The occlusion of the different asprich peptides from calcite and other permanently disorder biomineral crystals is also analyzed.

The application of the various mixtures and assemblies of proteins and polysaccharides in the formation of aragonite complexes is determined. The use of the nacre protein fragment templates for the purpose is also analyzed.

The differences in calcite c-axis orientations in the tooth of the purple sea urchin (Strongylocentrotus purpuratus) are shown by using high-resolution X-ray photoelectron emission spectromicroscopy and microbeam X-ray diffraction. The studies have shown that co-orientation of the nanoparticles in the polycrystalline matrix has occurred via solid-state secondary nucleation, propagating out from fibers and plates into the amorphous precursor nanoparticles.

A novel research on AP7, a member of the intrinsically disordered protein class (IDP) and also an extracellular aragonite-associated protein, and the new aspects of AP7 mineralization activity is presented. The ability of the partially disordered C-RING protein to perform inorganic phase stabilization and aggregate formation has provided insight into the protein-mediated nacre formation process.

The solid-state magic angle spinning NMR was employed to understand the structure and composition of biogenic calcite formed by Emiliania huxleyi, a unicellular alga with sculptured calcite cell coverings known as coccoliths. The results obtained provide insight into the incorporation of P/N moieties as structural defects within E. huxleyi biogenic calcite and on the state of the adjacent crystalline carbonates.

Calcite cleavage surface reconstructs in humid air through pit formation and film growth is investigated through the time-sequenced contact-force micrographs. It is suggested that the islands contain loosely bound water that are hydrated calcium carbonate phase stabilized by the calcite surface.

Succinic acid (SUC) was used to react with calcite to better understand the aspartic (ASP)-calcite interfacial reaction. The results show that the amine group on ASP must be an active participant in surface binding and ASP differs from SUC only in the possession of the [alpha]-N[H.sub.2] group.

Ethylenediamine tetraacetate (EDTA)-mediated calcite dissolution occurs through a different process than water-promoted dissolution. Observations in EDTA solutions demonstrate, that, after penetration through a critical pit depth barrier, step velocity increases linearly with pit depth for EDTA-promoted dissolution, whereas step velocity in simple water solutions is independent of pit depth.

The surface chemistry of calcite, the most common and stable phase of calcium carbonate, is studied by using infrared spectroscopy. The results reveal that carbonic acid might be an important, albeit short-lived, intermediate in the surface chemistry of calcium carbonate.