Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 7 3 2010 10.5194/bg-7-1017-2010 http://www.biogeosciences.net/7/1017/2010/ http://www.biogeosciences.net/7/1017/2010/bg-7-1017-2010.html http://www.biogeosciences.net/7/1017/2010/bg-7-1017-2010.pdf 1017 1029 2010-03-17 Effect of CO₂ on the properties and sinking velocity of aggregates of the coccolithophore <I>Emiliania huxleyi</I> A. Biermann abiermann@ifm-geomar.de A. Engel Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany present address: IFM-GEOMAR, Leibniz Institute of Marine Sciences, Düsternbrooker Weg 20, 24105 Kiel, Germany Coccolithophores play an important role in organic matter export due to their production of the mineral calcite that can act as ballast. Recent studies indicated that calcification in coccolithophores may be affected by changes in seawater carbonate chemistry. We investigated the influence of CO₂ on the aggregation and sinking behaviour of the coccolithophore <I>Emiliania huxleyi</I> (PML B92/11) during a laboratory experiment. The coccolithophores were grown under low (~180 &mu;atm), medium (~380 &mu;atm), and high (~750 &mu;atm) CO₂ conditions. Aggregation of the cells was promoted using roller tables. Size and settling velocity of aggregates were determined during the incubation using video image analysis. Our results indicate that aggregate properties are sensitive to changes in the degree of ballasting, as evoked by ocean acidification. Average sinking velocity was highest for low CO₂ aggregates (~1292 m d^&minus;1) that also had the highest particulate inorganic to particulate organic carbon (PIC/POC) ratio. Lowest PIC/POC ratios and lowest sinking velocity (~366 m d^&minus;1) at comparable sizes were observed for aggregates of the high CO₂ treatment. 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