EFFECT OF IRON ON PRODUCTIVITY AND SIZE DISTRIBUTION OF ANTARCTIC PHYTOPLANKTON

In shipboard experiments, addition of Fe to samples from Antarctic shelf waters or from deep waters close to the shelf break did not have any detectable effect on phytoplankton populations. Fe addition to pelagic waters, however, increased Chl a concentrations by a factor of 4-7 times during 1-2 weeks of incubation and also resulted in a shift from a nanoplankton-dominated population to one dominated by microplankton. If these shipboard experimental results are extrapolated to in situ results following enrichment of Antarctic pelagic waters with Fe, there may be some mitigation of the greenhouse effect caused by elevated CO2 concentrations in the atmosphere. Not only would the rate of primary production increase, but also the percentage of primary production that is exported to deep water might be increased because of Fe favoring the growth of microplankton.