Does iron fertilization lead to rapid carbon export in the Southern Ocean?

Abstract

The Southern Ocean has the potential to influence climate due to its large inventory of excess macronutrients such as nitrate and phosphate. It has been hypothesized that if the supply of the micronutrient iron increased, it would lead to enhanced uptake of atmospheric CO2 and hence the sequestration of carbon via sinking particles [Martin, 1990]. While much has been learned about iron limitation and low phytoplankton biomass in high‐nutrient, low‐chlorophyll regions [Martin, 1991; Coale et al., 1996], less is known about the effect of Fe on particle export. Here we present results from the first detailed study of particle export during a mesoscale iron fertilization experiment (the Southern Ocean Iron Release Experiment (SOIREE)). Measurements of the natural tracer thorium‐234 indicate negligible particle export within 14 days after the initial infusion of iron. We attribute this lack of response to colder water temperatures that promote slower cell metabolism in phytoplankton and hence slower secondary responses of herbivores and particle aggregation.