Combined effect of sea surface warming and ocean acidification on coccolithophores at cold seas

Sea surface warming and ocean acidification are known to be the greatest phenomenon affecting the growth and physiology of marine organisms, in particular on calcifiers. Coccolithophores represent an important group of calcifying unicellular algae and play an important role in the global carbon. In this study, the effect of increased pCO2 (186, 384 and 784 ppmV CO2 corresponding to glacial, present and future CO2 conditions respectively) and sea surface warming especially at cold seas (4, 6 and 8°C) at the exponential growth phase of Emiliania huxleyi was examined using a semi continuous batch culture experiments. It has been showed that the growth rate was proportional to the increasing temperature and inversely proportional to the pCO2 increase. The effect of temperature on organic production was highly significant as the Coccosphere size, POC (particulate organic carbon) per cell and PIC (particulate inorganic carbon) per cell was decreased with the increase in temperature. POC per cell increased and PIC per cell decreased with increase in pCO2 resulted in lower PIC: POC ratios at future CO2 concentrations which indicate reduction in export of organic carbon as lower PIC/POC ratio will reduce the ballast effect on the sinking cells at the future pCO2 conditions. The difference in PIC: POC ratios were higher at higher temperatures. C: N ratios were much higher than the Redfield ratios of 6.625 at higher temperatures indicating more carbon sequestration per nitrate input where as no significant impact of pCO2 observed on C: N ratios. Scanning electron micrographs also showed reduction in coccosphere size with increase in temperature and coccolith malformation at the present and future pCO2 conditions. In general, the results show that sea surface warming will favor the E huxleyi cells at nutrient replete conditions to increase growth rate but ocean acidification will have adverse effect on PIC/POC ratios of coccolithophorid cells and the proportion of impact on PIC/POC ration would increase with sea surface warming at cold seas.

Anjaneya Reddy, M. (2011). Combined effect of sea surface warming and ocean acidification on coccolithophores at cold seas. MSc Thesis. Alfred Wegener Institute for Polar and Marine Research: Bremen. 35 pp. More information.

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