LIMNOLOGY AND OCEANOGRAPHY, 43, 1565-1577

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

Angie Thomson-Bulldis and David Karl

SOEST, University of Hawaii, Honolulu, HI 96822

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 (N-PiP) 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.