Overview 363 3.6.2. Indirect Evidence of the Influences of Organic Matter on Calcium Carbonate 363 3.6.3. Direct Evidence for Organic Matter Adsorption on Calcium Carbonate 365 4. Oceanic Sources of Marine Carbonates 366 4.1. Overview 366 4.2. Primary Carbonate Sources for Deep Sea Sediments 366 4.3. Shallow Water Biogenic Carbonate Sources 367 4.3.1. General Considerations 367 4.3.2. Sources of Fine-Grained Carbonate Sediments 367 4.3.3. Sources of Carbonate Sands 368 4.3.4. Carbonate Cements 370 4.3.5. Dolomite Formation 371 4.3.6. Carbonate Minerals Formed in Siliciclastic Sediments 371 5. Dissolution of Calcium Carbonate 372 5.1. Dissolution of Carbonate Minerals in the Pelagic Environment 372 5.1.1. General Considerations 372 5.1.2. Dissolution in the Water Column 372 5.1.3. Dissolution on the Deep Sea Floor 372 5.2. Dissolution of Carbonate Minerals in Carbonate-Rich Shallow Water Sediments 373 6. Response of Carbonate-Rich Sediments to the Acidification of the Ocean Due to Rising Atmospheric pCO 2 374 6.1. General Principles and Considerations 374 6.2. The Major Ocean Basins 374 6.3. Shallow Water Carbonate-Rich Sediments 375 7. Summary and Thoughts on Possible Future Research Directions 375 7.1. Summary 375 7.2. Thoughts on Possible Future Research Directions 377 8. Acknowledgements 378 9. References 378

A formulation based on defect-generated dissolution stepwaves of the variation of dissolution rate with the degree of undersaturation is validated by near-atomic-scale observations of surfaces, Monte Carlo simulations, and experimental bulk dissolution rates. The dissolution stepwaves emanating from etch pits provide a train of steps similar to those of a spiral but with different behavior. Their role in accounting for the bulk dissolution rate of crystals provides a conceptual framework for mineral dissolution far from equilibrium. Furthermore, the law extends research to conditions closer to equilibrium and predicts a nonlinear decrease in the rate of dissolution as equilibrium is approached, which has implications for understanding artificial and natural processes involving solid-fluid reactions.

Here we present that graphene oxide (GO) can act as a terminal electron acceptor for heterotrophic, metal-reducing, and environmental bacteria. The conductance and physical characteristics of bacterially converted graphene (BCG) are comparable to other forms of chemically converted graphene (CCG). Electron transfer to GO is mediated by cytochromes MtrA, MtrB, and MtrC/OmcA, while mutants lacking CymA, another cytochrome associated with extracellular electron transfer, retain the ability to reduce GO. Our results demonstrate that biodegradation of GO can occur under ambient conditions and at rapid time scales. The capacity of microbes to degrade GO, restoring it to the naturally occurring ubiquitous graphite mineral form, presents a positive prospect for its bioremediation. This capability also provides an opportunity for further investigation into the application of environmental bacteria in the area of green nanochemistries.

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Plasmon resonance is expected to occur in metallic and doped semiconducting carbon nanotubes in the terahertz frequency range, but its convincing identification has so far been elusive. The origin of the terahertz conductivity peak commonly observed for carbon nanotube ensembles remains controversial. Here we present results of optical, terahertz, and DC transport measurements on highly enriched metallic and semiconducting nanotube films. A broad and strong terahertz conductivity peak appears in both types of films, whose behaviors are consistent with the plasmon resonance explanation, firmly ruling out other alternative explanations such as absorption due to curvature-induced gaps.

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