PARTIAL CHARACTERIZATION OF THE DISSOLVED ORGANIC PHOSPHORUS POOL IN THE OLIGOTROPHIC NORTH PACIFIC-OCEAN

The combined application of two independent methods for phosphorus (P) determination in seawater, continuous-flow UV photodecomposition and magnesium-induced coprecipitation (MAGIC), was used to provide a parti al characterization of the dissolved P pools at Sta. ALOHA (22 degrees 45'N, 158 degrees W) in the oligotrophic subtropical North Pacific Oc ean. Comprehensive laboratory analyses of the UV light-induced photode composition of a variety of specific organic P compounds dissolved in seawater confirmed that submicromolar concentrations of monophosphate compounds could be analytically separated from nucleotide di-and triph osphates based upon a previously described temperature-controlled low- pressure, mercury vapor UV irradiation treatment. When combined with a recently described high-precision P-detection system, the total disso lved phosphorus (TDP) in seawater could be reproducibly subdivided int o three chemically distinct pools: soluble reactive phosphorus (SRP; p resumably dominated by orthophosphate), UV-labile phosphorus (PUV-L; c ontaining primarily monophosphate esters), and W-stable phosphorus (PU V-S; containing primarily nucleotide di- and triphosphates, nucleic ac ids, and other compounds that are resistant to the UV treatment). Fiel d application of these procedures to samples collected at Sta. ALOHA d uring the period September 1991 to March 1992 (HOT-30 to HOT-35) revea led the presence of all three operationally defined pools. In the uppe r portion of the water column (0-100 m) the TDP pool (29.26 +/- 2.32 m mol P m(-2)) contained, on average, 23% SRP, 26% PUV-S, and 51% PUV-L. With increasing depth, the concentration of PUV-L decreased while tha t of the PUV-S pool increased; the PUV-L:PUV-S ratios decreased from v alues of 2-5 in the upper water column to less than or equal to 1.0 at 200 m.