ALBERT

Description: To date no study exists that directly addresses changes in dynamics of heterotrophic bacteria in surface waters in relation to partial pressure of CO2 (pCO2). Therefore, we studied the effect of changes in pCO2 on bacterial abundance and activities by using mesocosms with different pCO2 levels (~190, ~370, and ~700 ppmV, representing past, present-day, and future atmospheric pCO2, respectively). Abundance of total bacteria did not differ with increasing pCO2 throughout the whole study period, whereas bacterial protein production (BPP) was highest at highest pCO2. This effect was even more pronounced for cell-specific production rates, especially those of attached bacteria, which were up to 25 times higher than those of free bacteria. During the breakdown of the bloom, however, the abundance of both free and attached bacteria was significantly increased with pCO2. Differences in bacterial growth rate (µ) were smaller than those of BPP, but both µ and BPP of attached bacteria were elevated under high pCO2. Averages of total protease as well as α- and α -glucosidase activities were highest at elevated pCO2 levels, but a statistically significant dependence on pCO2 was only evident for protease activity. There is a measurable but indirect effect of changes in pCO2 on bacterial activities that are mainly linked to phytoplankton and presumably particle dynamics

Description: We investigated the carbon acquisition of three marine microalgae, Skeletonema costatum, Phaeocystis globosa, and Emiliania huxleyi in response to different light regimes. Rates of photosynthetic O2 evolution and CO2 and HCO3- uptake were measured by membrane inlet mass spectrometry in cells acclimated to cycles of 16 : 8 light : dark (LD; h : h) and 12 : 12 LD and were compared with those obtained under continuous light. In addition, cellular leakage was estimated for different photoperiods and ambient CO2 concentrations during growth. Maximum rates of photosynthesis more or less doubled under LD cycles compared with continuous light. In S. costatum and E. huxleyi, a remarkably higher contribution of HCO3- to the overall carbon uptake was observed under LD cycles. In contrast, P. globosa did not change its CO2 :HCO3- uptake ratio in response to daylength. Half saturation concentrations (K1/2) for O2 evolution and inorganic carbon (Ci) uptake were also influenced by the photoperiod. Under LD cycles K1/2 values for photosynthesis in S. costatum and P. globosa were similar or higher compared with continuous light, whereas they were much lower in E. huxleyi. With the exception of CO2 uptake in E. huxleyi and P. globosa, affinities for Ci decreased under the LD cycles. Cellular leakage was highest for E. huxleyi and lowest for S. costatum and generally decreased with increasing CO2 concentration. Although this study confirms species specific differences in the CO2-concentrating mechanisms (CCMs), the effect of daylength on CO2 and HCO3- uptake has hitherto not been described. We put forward the idea that variations in light condition influence the cellular carbon demand, thereby imposing a stronger control on CCM regulation than the naturally occurring changes in CO2 supply.

Description: In recent studies the Sr/Ca ratio of coccolithophore calcite was used as a proxy for past coccolithophore growth and calcification rates. Since Sr and Ca concentrations in seawater have not remained constant through time, interpretation of Sr/Ca data from the coccolith-dominated sedimentary record requires knowledge about the incorporation of seawater Sr into coccolith calcite during coccolithogenesis. Here we show that Sr/Ca of Emiliania huxleyi coccoliths is linearly related to seawater Sr/Ca, meaning that the Sr exchange coefficient does not change with changing seawater Sr/Ca. The exchange coefficient for Sr in this study, 0.39, is close to values presented in the literature and is high compared with values obtained by inorganic precipitation experiments. This suggests a strong effect of cell physiology on biogenic calcite precipitation in coccolithophores. We present a conceptual model, based on the transmembrane transport of Sr and Ca, which explains the offset.

Description: We studied the direct effects of CO2 Engel et al. in the seawater was modified by an aeration system. The triplicate mesocosm treatments represented low (190 parts per million by volume (ppmV) CO2 organisms in a mesocosm experiment. In nine outdoor enclosures (11 m3 present (410 ppmV CO2 and high (710 ppmV CO2 pCO2 and related changes in seawater carbonate chemistry on marine planktonic each), the partial pressure of CO2 (pCO2 conditions. After initial fertilization with nitrate and phosphate a bloom dominated by the coccolithophorid Emiliania huxleyi occurred simultaneously in all of the nine mesocosms; it was monitored over a 19-day period. The three CO2 treatments assimilated nitrate and phosphate similarly. The concentration of particulate constituents was highly variable among the replicate mesocosms, disguising direct CO2 within each treatment, however, indicated that the net specific growth rate of E. huxleyi, the rate of calcification per cell, and the elemental stoichiometry of uptake and production processes were sensitive to changes in pCO2 This broad influence of CO2 -related effects. Normalization of production rates . on the E. huxleyi bloom suggests that changes in CO2 physiology with likely effects on the marine biogeochemistry.