NATURAL ACTIVITIES OF P-32 AND P-33 AND THE P-33 P-32 RATIO IN SUSPENDED PARTICULATE MATTER AND PLANKTON IN THE SARGASSO SEA/

A procedure is presented to determine the turnover time of P in the pe lagic food web at the Bermuda Atlantic Time-series Study (BATS) statio n in the Sargasso Sea (31 degrees 50'N, 64 degrees 10'W). This method is based on observations made in suspended particulate matter and net- plankton of cosmic ray produced P-32 (half-life, 14.3 days) and P-33 ( half-life, 25.3 days). Measurements were made of the specific activiti es of P-32 (i.e. P-32/P) and P-33 (i.e. P-33/P) and the P-33/P-32 acti vity ratio in particulate matter collections by low-level P counting. The specific activities of P-32 were higher by one-to-two orders of ma gnitude compared to earlier studies in more eutrophic sites. This larg e difference is mainly due to the extremely low concentrations of stab le P off Bermuda, which in addition made possible the determination of the activity of the weak beta emitter P-33. Our study, over a 1 year period, shows an increase in the P-33/P-32 ratio in higher trophic lev els relative to our previously reported ratios in the rain, reflecting P turnover time in plankton on timescales of days to weeks. Model P t urnover times in zooplankton of 60-80 days, a zooplankton grazing flux of 90 mg C m(-2) day(-1) and an upper limit fecal material Aux of 27 mg C m(-2) day(-1) were determined. These results show promise for the use of cosmogenic P-32 and P-33 in rainwater and marine plankton for the study of zooplantkon dynamics in the upper ocean. Copyright (C) 19 96 Elsevier Science Ltd