DEEP-SEA RESEARCH II: SPECIAL VOLUME

Natural activities of ³²P and ³³P and the ³³P/³²P ratio in suspended particulate matter and plankton in the Sargasso Sea

Nathalie A. D. Waser^1,3, Michael P. Bacon¹ and Anthony F. Michaels²

¹Woods Hole Oceanographyic Institution, Woods Hole, MA 02543-1543, U.S.A.

²Bermuda Biological Station for Research, Ferry Reach GE01, Bermuda

³Present Address:
Department of Oceanography, University of British Columbia, Vancouver, B.C., V6T 1Z4, Canada

(Received 17 November 1994; in revised form 2 June 1995; accepted 17 August 1995)

A procedure is presented to determine the turnover time of P in the pelagic food web at the Bermuda Atlantic Time-series Study (BATS) station in the Sargasso Sea (31 50'N, 64 10'W). This method is based on observations made in suspended particulate matter and net-plankton of cosmic ray produced ³²P (half-life, 14.3 days) and ³³p (half-life, 25.3 days). Measurements were made of the specific activities of ³²P (i.e. ³²P/P) and ³³P (i.e. ³³P/P) and the ³³P/³²P activity ratio in particulate matter collections by low-level Beta counting. The specific activities of ³²P were higher by one-to-two orders of magnitude compared to earlier studies in more eutrophic sites. This large difference is mainly due to the extremely low concentrations of stable P off Bermuda, which in addition made possible the determination of the activity of the weak Beta emitter ³³P. Our study, over a 1 year period, shows an increase in the ³³P/³²P ratio in higher trophic levels relative to our previously reported ratios in the rain, reflecting P turnover time in plankton on timescales of days to weeks. Model P turnover 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 flux of 27 mg C m^-2 day^-1 were determined. These results show promise for the use of cosmogenic ³²P and ³³P in rainwater and marine plankton for the study of zooplantkon dynamics in the upper ocean.