Controls of primary production in two phytoplankton blooms in the Antarctic Circumpolar Current

The Antarctic Circumpolar Current has a high potential for primary production and carbon sequestration through the biological pump. In the current study, two large-scale blooms observed in 2012 during a cruise with R.V. Polarstern were investigated with respect to phytoplankton standing stocks, primary productivity and nutrient budgets. While net primary productivity was similar in both blooms, chlorophyll a –specific photosynthesis was more efficient in the bloom closer to the island of South Georgia (39 °W, 50 °S) compared to the open ocean bloom further east (12 °W, 51 °S). We did not find evidence for light being the driver of bloom dynamics as chlorophyll standing stocks up to 165 mg m-2 developed despite mixed layers as deep as 90 m. Since the two bloom regions differ in their distance to shelf areas, potential sources of iron vary. Nutrient (nitrate, phosphate, silicate) deficits were similar in both areas despite different bloom ages, but their ratios indicated more pronounced iron limitation at 12 °W compared to 39 °W. While primarily the supply of iron and not the availability of light seemed to control onset and duration of the blooms, higher grazing pressure could have exerted a stronger control toward the declining phase of the blooms

Controls of primary production in two phytoplankton blooms in the Antarctic Circumpolar Current

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Controls of primary production in two phytoplankton blooms in the Antarctic Circumpolar Current

11 páginas, 6 figuras, 2 tablas.-- C.J.M. Hoppe ... et al.-- Proyecto Carbochange.-- This is an open access article under the CCBY-NC-ND licenseThe Antarctic Circumpolar Current has a high potential for primary production and carbon sequestration through the biological pump. In the current study, two large-scale blooms observed in 2012 during a cruise with R.V. Polarstern were investigated with respect to phytoplankton standing stocks, primary productivity and nutrient budgets. While net primary productivity was similar in both blooms, chlorophyll a –specific photosynthesis was more efficient in the bloom closer to the island of South Georgia (39 °W, 50 °S) compared to the open ocean bloom further east (12 °W, 51 °S). We did not find evidence for light being the driver of bloom dynamics as chlorophyll standing stocks up to 165 mg m−2 developed despite mixed layers as deep as 90 m. Since the two bloom regions differ in their distance to shelf areas, potential sources of iron vary. Nutrient (nitrate, phosphate, silicate) deficits were similar in both areas despite different bloom ages, but their ratios indicated more pronounced iron limitation at 12 °W compared to 39 °W. While primarily the supply of iron and not the availability of light seemed to control onset and duration of the blooms, higher grazing pressure could have exerted a stronger control toward the declining phase of the bloomsC.J.M.H. and B.R. were funded by the European Research Council (ERC) under the European Community׳s Seventh Framework Programme (FP7/2007-2013), ERC Grant agreement no. 205150. S.T. was funded by the German Science Foundation (DFG), project TR 899/2 and the Helmholtz Impulse Fond (HGF Young Investigator Group EcoTrace). Funding to M.S. was supplied by CAPES, Brazil (Grant BEX 3483/09-6), and to A.B. by the Helmholtz Innovation Fund Phytooptics. This work was funded by the MINECO of Spain (Grant CGL2010-11846-E) and the Government of the Balearic Islands (Grant AAEE083/09). J.S.E. was supported by the JAE-Doc program of the CSIC. M.H. was supported through EU FP7 project CARBOCHANGE, which received funding from the European Community׳s Seventh Framework Programme under Grant agreement no. 264879. This work was furthermore supported by the DFG in the framework of the priority programme "Antarctic Research with comparative investigations in Arctic ice areas" by a Grant HO 4680/1Peer reviewe