Cosmogenic ³²P and ³³P used as tracers to study phosphorus recycling in the upper ocean

Abstract

The elements C, N and P are mostly biologically recycled in the upper ocean. Consequently, nutrient cycling and food web dynamics are central problems in marine biology and chemistry. The natural stable isotopes ¹³C and ¹⁵N and the radioisotopes ³H, ¹⁴C and ³²P have been used to estimate rates of in situ photosynthesis, nucleic acid synthesis^1,2 and new production^3–8, but previously there was no practical way of studying the gross character of nutrient cycles in their natural environment. We have now developed a method based on two naturally occurring radioisotopes, ³²P (half-life, 14.3 days) and ³³P (half-life, 25.3 days) to study phosphorus recycling in the upper ocean. We have studied their concentrations in the dissolved inorganic phosphorus, dissolved organic phosphorus and participate organic phosphorus from waters within and below the mixed layer. These isotopes permit study of P cycling on the timescales compatible with those involved in biogeochemical pro-cesses and in trophic interactions within the food web.