Influence of changing carbonate chemistry on morphology and weight of coccoliths formed by Emiliania huxleyi

[摘要] The coccolithophore Emiliania huxleyi is a marine phytoplankton species capable of formingsmall calcium carbonate scales (coccoliths) which cover the organic part ofthe cell. Calcification rates of E. huxleyi are known to be sensitive to changes inseawater carbonate chemistry. It has, however, not yet been clearlydetermined how these changes are reflected in size and weight of individualcoccoliths and which specific parameter(s) of the carbonate system drivemorphological modifications. Here, we compare data on coccolith size,weight, and malformation from a set of five experiments with a largediversity of carbonate chemistry conditions. This diversity allowsdistinguishing the influence of individual carbonate chemistry parameterssuch as carbon dioxide (CO₂), bicarbonate (HCO₃⁻), carbonateion (CO₃²⁻), and protons (H⁺) on the measured parameters.Measurements of fine-scale morphological structures reveal an increase ofcoccolith malformation with decreasing pH suggesting that H⁺ is themajor factor causing malformations. Coccolith distal shield area varies fromabout 5 to 11 μm². Changes in size seem to be mainly induced byvarying [HCO₃⁻] and [H⁺] although influence of[CO₃²⁻] cannot be entirely ruled out. Changes in coccolith weightwere proportional to changes in size. Increasing CaCO₃ production ratesare reflected in an increase in coccolith weight and an increase of thenumber of coccoliths formed per unit time. The combined investigation ofmorphological features and coccolith production rates presented in thisstudy may help to interpret data derived from sediment cores, wherecoccolith morphology is used to reconstruct calcification rates in the watercolumn.

[学科分类] 地球化学与岩石