Responses to ocean acidification in plankton communities were studied during a CO2-enrichment experiment in the Arctic Ocean, accomplished from June to July 2010 in Kongsfjorden, Svalbard (78°56, 2' ...N, 11°53, 6' E). Enclosed in 9 mesocosms (volume: 43.9–47.6 m3), plankton was exposed to CO2 concentrations, ranging from glacial to projected mid-next-century levels. Fertilization with inorganic nutrients at day 13 of the experiment supported the accumulation of phytoplankton biomass, as indicated by two periods of high Chl a concentration.This study tested for CO2 sensitivities in primary production (PP) of particulate organic carbon (PPPOC) and of dissolved organic carbon (PPDOC). Therefore, 14C-bottle incubations (24 h) of mesocosm samples were performed at 1 m depth receiving about 60% of incoming radiation. PP for all mesocosms averaged 8.06 ± 3.64 μmol C l−1 d−1 and was slightly higher than in the outside fjord system. Comparison between mesocosms revealed significantly higher PPPOC at elevated compared to low pCO2 after nutrient addition. PPDOC was significantly higher in CO2 enriched mesocosms before as well as after nutrient addition, suggesting that CO2 had a direct influence on DOC production. DOC concentrations inside the mesocosms increased before nutrient addition and more in high CO2 mesocosms. After addition of nutrients, however, further DOC accumulation was negligible and not significantly different between treatments, indicating rapid utilization of freshly produced DOC. Bacterial biomass production (BP) was coupled to PP in all treatments, indicating that 3.5 ± 1.9% of PP, or 21.6 ± 12.5% of PPDOC provided sufficient carbon for synthesis of bacterial biomass. The response of 14C-based PP rates to CO2 enrichment was at odds with O2-based net community production (NCP) rates that were also determined during this study, albeit at lower light level. We conclude that the enhanced release of labile DOC during autotrophic production at high CO2 exceedingly stimulated activities of heterotrophic microorganisms. As a consequence, increased PP induced less NCP, as suggested earlier for carbon limited microbial systems in the Arctic.
In two experiments we studied the effects of behavioral models on routine deviation decisions in observers. Participants repeatedly chose among four card-deck lotteries together with a human model ...(confederate, Exp. 1) or a non-human model (computer, Exp. 2) that made correct decisions in the majority of the trials. In a learning phase, participants acquired a choice routine (preferring one deck over others). In a subsequent test phase, participants had to adapt to changes in the payoff structure that required them to deviate from their routine. We found a strong tendency to maintain the routine despite negative feedback (routine effect). In a social situation (Exp.1), models decrease routine effects more intensely than in non social situations (Exp.2). The process of adaptation follows a belief updating process. Results indicate that the model effect is not due to an increase of the sample of relevant information nor to application of a simply copy heuristic. Rather, deviation models may provide a cue for change that fosters reevaluation of the situation in the observer.
In two experiments we studied the effects of behavioral models on routine deviation decisions in observers. Participants repeatedly chose among four card-deck lotteries together with a human model ...(confederate, Exp. 1) or a non-human model (computer, Exp. 2) that made correct decisions in the majority of the trials. In a learning phase, participants acquired a choice routine (preferring one deck over others). In a subsequent test phase, participants had to adapt to changes in the payoff structure that required them to deviate from their routine. We found a strong tendency to maintain the routine despite negative feedback (routine effect). In a social situation (Exp.1), models decrease routine effects more intensely than in non social situations (Exp.2). The process of adaptation follows a belief updating process. Results indicate that the model effect is not due to an increase of the sample of relevant information nor to application of a simply copy heuristic. Rather, deviation models may provide a cue for change that fosters reevaluation of the situation in the observer.
