Application of a novel method for phosphorus determinations in the oligotrophic North Pacific Ocean

Thomson-Bulldis, Angie, David Karl

Limnol. Oceanogr., 43(7), 1998, 1565-1577 | DOI: 10.4319/lo.1998.43.7.1565

ABSTRACT: Phosphorus (P) is an essential macronutrient and is present in seawater as both dissolved inorganic (primarily orthophosphate, Pi) and organic compounds. Current analytical techniques measure soluble reactive phosphorus (SRP) as a surrogate for Pi and soluble nonreactive phosphorus as a surrogate for dissolved organic phosphorus (DOP). A new method provides a measure of Pi concentrations directly and eliminates interference from other reactive P compounds. The same method can also be used to make direct measurements of non-Pi phosphorus (NPiP) concentrations (i.e., [total dissolved P] - [Pi]) with greater precision and accuracy limits than current methods provide. With this new method, Pi concentrations in North Pacific surface waters were found to be lower, by up to 50% or more, than SRP concentrations measured with standard autoanalyzer techniques. Mean (±SD) N-PiP concentrations in the deep (> 1,000 m) North Pacific were determined to be 16.2 ± 12.5 nM. These results have significant implications for turnover and residence times of dissolved P pools and for utilization of DOP in the deep sea. This new method for Pi and N-PiP measurements has numerous potential applications in marine and freshwater research.

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