| Summary: | The increase in atmospheric CO2 concentrations caused by anthropogenic activities could lead to aragonite (polymorph of calcium carbonate) sub-saturation in parts of the Arctic surface ocean by 2020 if emissions follow business as usual scenarios. Most pronounced effects are expected to take place during winter-time. Sub-saturated water was shown to negatively impact a variety of marine calcifying organisms. The polar calcifying pteropod Limacina helicina can contribute up to 20% of the Arctic zooplankton biomass at times and has a key function in the Arctic epipelagic food web. The temperate-boreal sibling species L. retroversa is frequently introduced to Arctic regions with Atlantic water masses. Both species contribute significantly to vertical carbon flux. In September/October 2009 and in January/February 2010 incubation experiments were carried out in Ny Ålesund/Svalbard at three temperatures (3, 5 and 8°C) and four pCO2 levels (180, 400, 750 and 1150 ppm) with durations of 29 and 9 days, respectively. In the 2009 experiment we used a novel approach of a 13C stable isotope incubation for measuring pteropod calcification rates. First results show that 13C concentrations varied in the total particulate carbon (TPC) of the organism but stayed constant in the particulate organic carbon (POC). From mass-balance calculations the variation in the TP13C concentrations result from 13C concentration changes of the particulate inorganic carbon (PIC) and/or changing PIC/POC ratios. The first is most likely affected by different calcification rates whereas the second could be additionally affected by changing respiration rates in response to the applied treatments. Our results show trends of 13C enrichment in organisms with increasing temperature and with decreasing pCO2 levels, suggesting a positive temperature and a negative CO2 effect on pteropod calcification rates. To investigate species-specific differences, in winter 2010 (January/February) temperature and CO2 perturbation experiments were carried out with ...
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