Cosmogenic ³²P and ³³P in the atmosphere and aligotrophic ocean and applications to the study of phosphorus cycling

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution November 1992

Cosmogeruc P-32 (14.28 days) and P-33 (25.3 days) are powerful tracers of upperocean P cycling, when coupled with time-series of the atmospheric sources. A methodwas developed to determine the low-level beta activities in rainwater and plankton. Thewet deposition rates of P-32 and P-33 were determined during 12 months at a marine site, atBermuda, coinciding with measurements of the activities and activity ratioP-33/P-32 insuspended particles and plankton tows at BATS station. The in situ production rates ofradiophosphorus in the upper ocean were estimated by measuring the activities induced inCl, K and S targets by cosmic rays. Knowledge of all the sources of radiophosphorus tothe Sargasso Sea allowed the cycling of P-32 andP-33 in suspended particles and macrozooplanktonto be studied. The study was based on the determination of the activity ratioP-33/P-32 in different particulate pools. The activity ratio was higher in particle collectionsdominated by higher levels in the food web. The increase in the ratio in plankton relativeto rain allowed the determination of the turnover times of P in plankton and in situ grazingrates.

Funding for this research was provided by NSF (grants OCE-8800957. OCE-8817836 and OCE-902284), DOE (grant DE-FG02-88ER60681), Woods HoleOceanographic Institution, Ocean Venture Funding of Woods Hole OceanographicInstitution and Scurlock Funds of Mr Arch Scurlock to MIT/WHOI Joint Program.