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

Phosphorus (P) is an essential macronutrient and is present in seawater as both dissolved inorganic (primarily orthophosphate, P i ) and organic compounds. Current analytical techniques measure soluble reactive phosphorus (SRP) as a surrogate for P i and soluble nonreactive phosphorus as a surrogate for dissolved organic phosphorus (DOP). A new method provides a measure of P i 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 (NP i P) concentrations (i.e., [total dissolved P] — [P i ]) with greater precision and accuracy limits than current methods provide. With this new method, P i 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‐P i P 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 P i and N‐P i P measurements has numerous potential applications in marine and freshwater research.