Hellemann, Dana (2012) Effects of warming and ocean acidification on calcification and photosynthesis of Arctic coralline red algae under summer light conditions. (Master thesis), Christian-Albrechts-Universität, Kiel, Germany, 62 pp.

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Abstract

Rising anthropogenic CO2 emissions since the pre-industrial time are warming the atmosphere and lead to an enhanced uptake of heat and CO2 into the ocean, resulting in increasing sea surface temperature (ocean warming (OW)), decreasing ocean pH (ocean acidification (OA)) and decreasing carbonate saturation state. Arctic surface waters are projected to become partly undersaturated with respect to aragonite already within this century. Calcified crustose coralline algae (CCA) are regarded sensitive to dissolution due to their high amount of magnesium carbonate, being more soluble than aragonite. Warming might add to CO2 stress, resulting in potential synergistic effects on calcification in CCA. Knowledge on the calcification process in CCA is limited, however, a linkage to energy generating processes (photosynthesis and respiration) is assumed. To test for single and synergistic effects of OWand OA on calcification and energy generating processes in Arctic CCA, Lithothamnion glaciale was incubated for two months under a cross-factorial design of elevated temperatures (3.5°C, 5.5°C and 7.5°C target values) and elevated pCO2 (390, 560, 840, 1120 μatm target values) (12 treatment combinations, n = 4 + 1 blank). Light conditions simulated Arctic summer (12 μmol photons m-2 s-1). In a side experiment, photosynthetic O2 evolution (O2E) and respiratory O2 consumption (O2C) were measured optode based under control and treatment conditions. Mean calcification rates decreased over the experimental duration and with increasing pCO2, except for the lowest temperature, where calcification was constantly reduced with increasing pCO2. Dissolution occurred first at the end of the experiment and only in the highest temperature treatment. Relative calcification rates at highest temperature increased at low and intermediate pCO2 levels and decreased first at a pCO2 >1000 µatm. These results indicate a negative synergistic effect for high pCO2 and elevated temperature, as well as a positive synergistic effect of intermediate pCO2 and elevated temperature. Results of relative O2E and O2C rates indicate a strong linkage between calcification and energy generating processes. From this study one can conclude, that within this century the Arctic coralline alga L. glaciale might not be negatively affected by elevated temperatures and pCO2 during the Arctic summer season, but rather might profit from those conditions by increasing its calcification rates. Negative effects of elevated temperatures and pCO2 on L. glaciale during the Arctic summer season are first expected for a combination of temperature and pCO2, that is not predicted to occur within this century for the Arctic Ocean.

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