HR: 0800h
AN: B31D-0617    [Abstracts]
TI: Phosphorus Speciation in Skeletal Aragonite of Deep Sea Corals
AU: * Mason, H E
EM: hmason@ic.sunysb.edu
AF: Department of Geosciences, 255 Earth and Space Sciences Stony Brook University, Stony Brook, NY 11794-2100, United States
AU: Montagna, P
EM: p.montagna@icram.org
AF: ICRAM, Via di Casalotti 300, Rome, 00166, Italy
AU: Phillips, B L
EM: brian.phillips@sunysb.edu
AF: Department of Geosciences, 255 Earth and Space Sciences Stony Brook University, Stony Brook, NY 11794-2100, United States
AB: Phosphorus plays an important role in the world oceans as a limiting nutrient and can serve as an indicator of productivity. This link to bioactivity also relates P concentration to changes in atmospheric CO₂ through biotic sequestration. The P concentration of ocean water is also connected to changes in deep sea ocean circulation that are also vehicles for global climate change. A paleoproxy for oceanic P concentration recently has been developed based on the P content in skeletal aragonite of deep-sea corals. The P-content of the septa record the ambient ocean P concentration at the time the time of deposition, which can be measured at high spatial resolution by methods such as ICP-MS. Although the correlation of P content of coral aragonite and ambient seawater suggests that phosphate is incorporated into the aragonite structure during crystal growth, the P speciation in the skeletal aragonite is unknown. We have studied P speciation in deep-sea coral aragonite collected from various localities using P-31 single pulse (SP) and cross polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopic techniques. Spectra of all samples contain a broad peak (>6 ppm full width at half maximum; FWHM) at a chemical shift of 3.0 to 3.5 ppm which is tentatively assigned to phosphate defects in the aragonite structure. Variable contact time CP/MAS NMR spectra indicates that the broad peak at 3.0 to 3.5 ppm is enhanced at short CP contact times, suggesting that H bearing species are important for accommodating phosphate in the aragonite structure. A subset of the samples gives spectra containing an additional, narrow peak (~ 1.5 ppm FWHM) at a chemical shift of 2.6 ppm. The spectral characteristics of this narrow peak, including both chemical shift and CP dynamics, are similar those of hydroxyl-containing apatite phases. On this basis and the small width of the peak it is assigned to crystalline apatite inclusions. These inclusions account for up to 34% of the phosphorus. No simple relationship of apatite content is apparent with P-content or between septa and thecal wall. These results suggest that most of the P in coral aragonite is incorporated as a defect in the crystal structure, but that some apatite may form as a surface precipitate that is incorporated during crystal growth.
DE: 0419 Biomineralization
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 0489 Trace element cycling (4875)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting