Control of the phytoplankton response during the SAGE experiment: A synthesis

• Published in: Deep Sea Research Part II: Topical Studies in Oceanography
• Main Authors: Peloquin, J., Hall, Julie A, Safi, Karl A, Ellwood, Michael, Law, Cliff S, Thompson, Karen, Kuparinen, J., Harvey, Michael, Pickmere, Stuart
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Pergamon-Elsevier Ltd
• Subjects: Keywords: Microzooplanktons; SAGE; Silicic acids; SOLAS; Sub-Antarctic Pacific; Algae control; Biomass; Chlorophyll; Ecology; Growth rate; Organic carbon; Phytoplankton; Experiments; air-sea interaction; algal bloom; coastal zone; community st Growth rate; Iron addition experiment; Light limitation; Microzooplankton grazing; Silicic acid; Antarctic; Pacific; New Zealand; Antarc*
• Online Access: http://hdl.handle.net/1885/68546; https://doi.org/10.1016/j.dsr2.2010.10.019; https://openresearch-repository.anu.edu.au/bitstream/1885/68546/5/01_Peloquin_Control_of_the_phytoplankton_2011.pdf.jpg

The SOLAS Air-Sea Gas Exchange (SAGE) experiment was conducted in Sub-Antarctic waters off the east coast of the South Island of New Zealand in the late summer of 2004. This mesoscale iron enrichment experiment was unique in that chlorophyll a (chl a) and primary productivity were only 2× OUT stations values toward the end of the experiment and this enhancement was due to increased activity of non-diatomaceous species. In addition, this enhancement in activity appeared to occur without a significant build up of particulate organic carbon. Picoeukaryotes (<2 γm) were the only members of the phytoplankton assemblage that showed a statistically significant increase, a doubling in biomass. To better understand the controls of phytoplankton growth and biomass, we present results from a series of on-deck perturbation experiments conducted during SAGE. Results suggest that the pico-dominated phytoplankton assemblage was only weakly inhibited by iron. Diatoms with high growth rates comprised a small (<1%) fraction of the phytoplankton assemblage, were likely iron limited, and potentially further limited by silicic acid and therefore did not significantly contribute to bloom dynamics. On deck experiments and comparison of SAGE with other iron addition experiments suggested that neither light availability nor deep mixed layers limited phytoplankton growth. Although no substantial increase in grazing rate or specific phytoplankton growth rate was detected, microzooplankton biomass doubled over SAGE as a result of an increase in cell size. The importance of microzooplankton grazing was highlighted by the fact that they were capable of consuming 15-49% of the total phytoplankton production per day. Removal was highest on eukaryotic picophytoplankton production with a mean value of 72% (29-143%). Patch dilution played an important role during SAGE; the mean patch net algal growth:dilution rate, 1.13 (0.4-2.2) was the lowest reported for a mesoscale iron enrichment experiment. Phytoplankton biomass, estimated by ...