Precise calibration of equilibrium oxygen isotope fractionations between dissolved phosphate and water from 3 to 37 °C. (1st February 2015)

• Record Type: Journal Article
• Authors: Chang, Sae Jung; Blake, Ruth E.
• Is Part Of: Geochimica et cosmochimica acta. Volume 150(2015:Feb. 01)
• Page Start: 314
• Page End: 329
• Publication Date: 2015-02-01
• Subjects: Geochemistry -- Periodicals; Meteorites -- Periodicals; Géochimie -- Périodiques; Météorites -- Périodiques; Geochemie; Astrochemie; Electronic journals; 551.905
• DOI: 10.1016/j.gca.2014.10.030
• Languages: English
• ISSNs: 0016-7037

Abstract

Abstract: The stable oxygen isotope composition of ortho phosphate (δ 18 OPO4 ) is a widely used (paleo)temperature indicator and more recently, a useful tracer of phosphorus-cycling. In natural aqueous systems (e.g., oceans, rivers, soil/ground water) the largest reactive phosphorus pool is dissolved inorganic phosphate. Here, we present a new experimentally-determined equation for thermodynamic equilibrium O-isotope fractionations between dissolved phosphate and water, catalyzed by the enzyme inorganic pyrophosphatase (PPase) between 3 and 37 °C; 1000 ln α ( PO 4 - H 2 O ) = 14.43 ( ± 0.39 ) 1000 / T ( K ) - 26.54 ( ± 1.33 ) r 2 = 0.99 The new equation is slightly offset by +0.5 to +0.7‰ from recent empirically-determined fractionations based on biogenic apatite, with both based on modern cf-irms TC/EA analysis of Ag3 PO4 . Dissolved phosphate–water fractionations are offset by +0.9 to +2.3‰ from the earlier empirical relation for biogenic phosphate–water fractionation determined using fluorination of BiPO4 . The equation presented here is thus, specific to equilibrium fractions between dissolved phosphate and water and appropriate for use in recent/future oxygen isotope studies of dissolved phosphate using similar cf-irms TC/EA analytical methods.