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Phosphate defects and apatite inclusions in coral skeletal aragonite revealed by solid-state NMR spectroscopy |
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| Authors: | Harris E Mason Paolo Montagna Laura Kubista Malcolm McCulloch |
| Institution: | a Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100, USA b Istituto di Scienze Marine (ISMAR), Consiglio Nazionale delle Ricerche (CNR), Via P. Gobetti 101, 40122 Bologna, Italy c Lamont-Doherty Earth Observatory Columbia University, 61 Route 9W, Palisades, NY 10964, USA d Woods Hole Oceanographic Institution, 266 Woods Hole Road, MA 02543, USA e School of Earth and Environment, The University of Western Australia (M004), 35 Stirling Highway, Crawley WA 6009, Australia |
| Abstract: | Recent development of paleo-nutrient proxies based on the phosphorus/calcium (P/Ca) ratio in tropical- and deep-water corals (also known as cold-water corals) require an understanding of the processes by which P is incorporated into the coral skeletal aragonite. Here, we apply single- and double-resonance solid-state nuclear magnetic resonance (NMR) spectroscopy to determine the speciation of P in coral aragonite. The results show that the majority of P occurs as phosphate defects in the aragonite structure, but in many samples a significant fraction of the P occurs also in crystalline hydroxylapatite inclusions. Quantification of the amount of hydroxylapatite indicates that its presence is not related simply to external environmental factors and that it can occur at varying abundances in different parts of the same corallite. Since there is currently no model available to describe the relationship between dissolved inorganic phosphate and its incorporation as apatite inclusions into carbonates, careful screening of samples which contain only phosphate in the aragonite structure or selective microsampling could improve proxy development. |
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