IRON ADDITION EXPERIMENTS IN THE ANTARCTIC: A REANALYSIS

In an accompanying paper, Martin et al. [this issue] interpret the results of four iron enrichment experiments using Antarctic seawater to indicate iron limitation of phytoplankton growth and nitrate uptake and suggest that Fe additions may contribute to reducing atmospheric CO2 and the greenhouse problem. We have published a review [Dugdale and Wilkerson, 1989] of nitrogen uptake measurements using N-15 in Antarctic waters and here reanalyze the nitrate depletion data of Martin et al. [this issue], reported as absolute uptake rates (rho with units of concentration per unit time), in the context of previous investigations by converting the data to nitrogen-specific uptake rates (V, in reciprocal time units). We conclude that Fe addition to the enclosed water does not affect the algal growth terms due to nitrate uptake per se, but apparently influences loss terms enabling phytoplankton biomass to accumulate in the experimental bottles.