Phytoplankton processes. Part 2: Rates of primary production and factors controlling algal growth during the Southern Ocean Iron RElease Experiment (SOIREE)

By M. Gall, R. Strzepek, M. T. Maldonado, Philip W. Boyd. 2001

91 citations recorded by the source corpus.

Abstract The Southern Ocean Iron RElease Experiment (SOIREE) fertilised 200 km2 of polar waters (mixed-layer depth, 65 m) south of Australia in February 1999. During the 13-d SOIREE, iron enrichment stimulated primary production, algal growth and biogenic silica production rates. A floristic shift from small to large cells resulted in a greater contribution to community production by diatoms, which contributed >60% to community production towards the end of SOIREE. Column-integrated rates of primary production increased by more than 10-fold, and community production rates (normalised to chlorophyll) had doubled by day 4, but then declined after day 6 to initial rates. Iron enrichment increased the growth rates of the algal community from 0.02 to 0.15 d−1 (based on changes in in-situ chlorophyll concentrations), from 0.02 to 0.2 d−1 (based on algal carbon), and more than doubled initial rates (based on 14C) to 0.2 d−1 during SOIREE. However, these iron-elevated rates were less than the maximum rates (0.69 d−1) predicted for waters at 2.5°C. Community biogenic silica production rates increased by 6-fold, i.e. to a lesser extent than primary production rates, resulting in a 2-fold reduction in the silicic-acid : carbon uptake ratio. Shipboard perturbation experiments indicated that iron, rather than both iron and light, limited algal growth in these waters. However, a significant increase in light attenuation in situ due to algal self-shading, suggested that light limitation of algal growth might become significant after day 13 at this locale. Limitation of algal growth by both iron (and silicic acid and/or zinc) within iron-fertilised waters after day 8 of SOIREE was not evident from the results of a shipboard experiment. A simple mathematical model of particulate organic carbon (POC) potential export during SOIREE predicted large increases in export, due to both elevated production rates and a floristic shift to large cells. However, no significant increase in POC export was observed during SOIREE.

Subfields: Oceanography

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In Oceanography

Citations in the corpus

Iron-mediated changes in phytoplankton photosynthetic competence during SOIREE (2001, background): “2a), mainly due to iron-elevated diatom growth rates (see Gall et al., 2001a).”
Different reactions of Southern Ocean phytoplankton size classes to iron fertilization (2006, background): “Gall et al. (2001b) showed that nano- and microphytoplankton increased their primary production strongly while picophytoplankton primary production did not change much.”
Fe and Zn effects on the Si cycle and diatom community structure in two contrasting high and low-silicate HNLC areas (2005, background): “Fe limitation also controls community structure in these regions, preventing the growth of larger species with high half-saturation constants for Fe uptake (Gall et al., 2001; Sedwick et al., 2000; Timmermans et al., 2001).”
The fate of biogenic iron during a phytoplankton bloom induced by natural fertilisation: Impact of copepod grazing (2008, methodology): “…2) were congruent with those determined independently during the KEOPS cruise and based on a similar approach (Timmermans et al., this issue) and they were in the range of those reported previously for the Southern Ocean (Landry et al., 1995; Froneman and Perissinotto, 1997; Gall et al., 2001).”