A precise method for the analysis of δ18O of dissolved inorganic phosphate in seawater

K. McLaughlin; S. Silva; C. Kendall; Hilary Stuart-Williams; A. Paytan

doi:10.4319/lom.2004.2.202

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A precise method for the analysis of δ18O of dissolved inorganic phosphate in seawater

K. McLaughlin·S. Silva·C. Kendall·Hilary Stuart-Williams·A. Paytan

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Abstract

A method for preparation and analysis of the oxygen isotope composition (δ 18 O) of dissolved inorganic phosphate (DIP) has been developed and preliminary results for water samples from various locations are reported. Phosphate is extracted from seawater samples by coprecipitation with magnesium hydroxide. Phosphate is further purified through a series of precipitations and resin separation and is ultimately converted to silver phosphate. Silver phosphate samples are pyrolitically decomposed to carbon monoxide and analyzed for δ 18 O. Silver phosphate samples weighing 0.7 mg (3.5 µmol oxygen) can be analyzed routinely with an average standard deviation of about 0.3‰. There is no isotope fractionation during extraction and blanks are negligible within analytical error. Reproducibility was determined for both laboratory standards and natural samples by multiple analyses. A comparison between filtered and unfiltered natural seawater samples was also conducted and no appreciable difference was observed for the samples tested. The δ 18 O values of DIP in seawater determined using this method range from 18.6‰ to 22.3‰, suggesting small but detectable natural variability in seawater. For the San Francisco Bay estuary DIP δ 18 O is more variable, ranging from 11.4‰ near the San Joaquin River to 20.1‰ near the Golden Gate Bridge, and was well correlated with salinity, phosphate concentration, and δ 18 O of water.

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Limnology and Oceanography: Methods Article

Source-reported bounding extent: 32.534156° to 42.009247° latitude; -124.409591° to -114.134768° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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BibTeX RIS

K. McLaughlin, S. Silva, C. Kendall, Hilary Stuart-Williams, A. Paytan. 2004-07-03. A precise method for the analysis of δ18O of dissolved inorganic phosphate in seawater. https://doi.org/10.4319/lom.2004.2.202

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