Boysen, Krista (2010) Combined effect of increasing carbon dioxide and varying nutrient concentrations on the coccolithophore Emiliania huxleyi. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 58 pp.

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Abstract

The increase in atmospheric carbon dioxide has already caused significantly higher aquatic CO2 concentrations and lower pH values ('ocean acidification') than in pre-industrial times. CO2 entering the ocean alters the seawater carbonate equilibrium, decreasing pH and shifting dissolved inorganic carbon away from carbonate (COC3-2) towards more bicarbonate (HCO2 3) and CO2 (Riebesell et al. 2007). For a 'business-as-usual' emission scenario in the year 2100 (IPCC, IS92a), the CO2 concentration will rise by about a factor of two relative to the present value (380 μatm), and could increase by a factor of three by the middle of the next century10. This will cause seawater pH to further drop by 0.3 and 0.6 pH units, respectively, in addition to the 0.12 pH-unit decrease that has occurred since pre-industrial times (Caldeira & Wickett 2005). Global rising temperatures will also impact surface ocean stratification, which in turn will affect the light regime of the surface waters and nutrient input from deeper layers. Coccolithophores are important primary producers and the most dominant pelagic calcifiers in the ocean. Since primary production and calcification are affected by elevated atmospheric CO2 concentrations and nutrient availability in terms of nitrate and phosphate (Riebesell et al. 2000; Riegman et al. 2000; Zondervan et al. 2002) this study investigated the effect on low and high CO2 concentrations in connection with limited nutrients on physiology of the coccolithophore Emiliania huxleyi. Besides varying carbon dioxide and nutrient concentrations, the focus of this study was set on the stationary phase of growth. The research was conducted as a batch culture experiment in which E. huxleyi was grown under two different pCO2 concentrations (450 and 1600μatm) and three nutrient treatments (redfield-ratio, nitrate limited, phosphate limited). Previous studies on ocean acidification caused by rising CO2 concentrations with E. huxleyi showed that calcification was significantly reduced while photosynthesis increased whereas growth rate remained constant. This study found significant differences, with regard to the results of most other studies. The particulate organic material build up by photosynthesis (POC per cell) decreased under the future pCO2 scenario. The inorganic material by calcification (PIC per cell) increased under the elevated pCO2 concentration with p-limitation. Summed up it could be said that the sensitivity with regard to elevated pCO2 concentrations is significant dependent on the nutrient status of the environment. In stationary phase, the effect of increasing CO2 concentrations varies with the limiting nutrient ratio. With regard to PIC/POC ratio other results are achieved than previous studies showed. Further studies need to be conducted to prove these results.

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