Primary productivity induced by iron and nitrogen in the Tasman Sea - An overview of the PINTS expedition

Publisher:
CSIRO Publishing
Publication Type:
Journal Article
Citation:
Marine and Freshwater Research, 2014, 65 (6), pp. 517 - 537
Issue Date:
2014-01
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The Tasman Sea and the adjacent Sub-Antarctic zone (SAZ) are economically important regions, where the parameters controlling the phytoplankton community composition and carbon fixation are not yet fully resolved. Contrasting nutrient distributions as well as phytoplankton biomass, biodiversity and productivity we observed between the North Tasman Sea and the SAZ. In-situ FV/FM, dissolved and particulate nutrients, iron biological uptake, and nitrogen and carbon fixation were used to determine the factor limiting phytoplankton growth and productivity in the North Tasman Sea and the SAZ. Highly productive cyanobacteria dominated the North Tasman Sea. High atmospheric nitrogen fixation and low nitrate dissolved concentrations indicated that non-diazotroph phytoplankton are nitrogen limited. Deck-board incubations also suggested that, at depth, iron could limit eukaryotes, but not cyanobacteria in that region. In the SAZ, the phytoplankton community was dominated by a bloom of haptophytes. The low productivity in the SAZ was mainly explained by light limitation, but nitrogen, silicic acid as well as iron were all depleted to the extent that they could become co-limiting. This study illustrates the challenge associated with identification of the limiting nutrient as it varied between phytoplankton groups, depths and sites.
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