Description: The potential impact of rising carbon dioxide (CO2) on carbon transfer from phytoplankton to bacteria was investigated during the 2005 PeECE III mesocosm study in Bergen, Norway. Sets of mesocosms, in which a phytoplankton bloom was induced by nutrient addition, were incubated under 1x (~350 µatm), 2x (~700 µatm), and 3x present day CO2 (~1050 µatm) initial seawater and sustained atmospheric CO2 levels for 3 weeks. 13C labelled bicarbonate was added to all mesocosms to follow the transfer of carbon from dissolved inorganic carbon (DIC) into phytoplankton and subsequently heterotrophic bacteria, and settling particles. Isotope ratios of polar-lipid-derived fatty acids (PLFA) were used to infer the biomass and production of phytoplankton and bacteria. Phytoplankton PLFA were enriched within one day after label addition, whilst it took another 3 days before bacteria showed substantial enrichment. Group-specific primary production measurements revealed that coccolithophores showed higher primary production than green algae and diatoms. Elevated CO2 had a significant positive effect on post-bloom biomass of green algae, diatoms, and bacteria. A simple model based on measured isotope ratios of phytoplankton and bacteria revealed that CO2 had no significant effect on the carbon transfer efficiency from phytoplankton to bacteria during the bloom. There was no indication of CO2 effects on enhanced settling based on isotope mixing models during the phytoplankton bloom, but this could not be determined in the post-bloom phase. Our results suggest that CO2effects are most pronounced in the post-bloom phase, under nutrient limitation.

Description: Ocean acidification and carbonation, driven by anthropogenic emissions of carbon dioxide (CO2), have been shown to affect a variety of marine organisms and are likely to change ecosystem functioning. High latitudes, especially the Arctic, will be the first to encounter profound changes in carbonate chemistry speciation at a large scale, namely the under-saturation of surface waters with respect to aragonite, a calcium carbonate polymorph produced by several organisms in this region. During a CO2 perturbation study in 2010, in the framework of the EU-funded project EPOCA, the temporal dynamics of a plankton bloom was followed in nine mesocosms, manipulated for CO2 levels ranging initially from about 185 to 1420 matm. Dissolved inorganic nutrients were added halfway through the experiment. Autotrophic biomass, as identified by chlorophyll a standing stocks (Chl a), peaked three times in all mesocosms. However, while absolute Chl a concentrations were similar in all mesocosms during the first phase of the experiment, higher autotrophic biomass was measured at high in comparison to low CO2 during the second phase, right after dissolved inorganic nutrient addition. This trend then reversed in the third phase. There were several statistically significant CO2 effects on a variety of parameters measured in certain phases, such as nutrient utilization, standing stocks of particulate organic matter, and phytoplankton species composition. Interestingly, CO2 effects developed slowly but steadily, becoming more and more statistically significant with time. The observed CO2 related shifts in nutrient flow into different phytoplankton groups (mainly diatoms, dinoflagellates, prasinophytes and haptophytes) could have consequences for future organic matter flow to higher trophic levels and export production, with consequences for ecosystem productivity and atmospheric CO2.

Description: This data is part of the BMBF project CUSCO (Coastal Upwelling Systems in a Changing Ocean). Here we report the dissolved inorganic carbon concentration and total alkalinity during a 35-day experiment, where we enclosed natural plankton communities in in-situ mesocosms off Peru. The experiment investigated the interactive effects of light and upwelling on the Humboldt upwelling ecosystem by mimicking a gradient of upwelling intensities (0%, 15%, 30%, 45% and 60%) under summer-time high light and winter-time low light. Integrated seawater samples from a depth between 0 and 10m were collected using a 5L Integrating Water sampler (IWS; Hydro-Bios, Kiel). Dissolved inorganic carbon (DIC) and total alkalinity (TA) samples were obtained by 0.2µm gentle pressure filtration, poisoned with saturated 7.5 % mercury chloride (HgCl2) solution and frozen at -20°C until measurement. Samples for Total Alkalinity (TA) were measured by means of potentiometric titration with 0.05 M HCl using an automated titration device (862 Metrohm Compact Titrosampler). All DIC samples taken until day 17 were measured using an Automated Infra-Red Inorganic Carbon Analyzer (AIRICA) with a LICOR detector (LI-7000 CO2/H20 Analyzer, MARIANDA, Kiel). Certified reference material (Dickson standard for oceanic CO2 Measurements - CRM Batch 142 with salinity = 33.389 and DIC = 2038,07 µmol/kg) was measured and used to correct measured sample values. Additional DIC samples were measured using gas chromatography-mass spectrometry (GC-MS) to determine the 13C signal. The data of the GC-MS was adjusted to the AIRICA data using a linear transformation. Missing days were filled using an average of the day before and after.

Description: Global warming (and the consequent increase in sea surface temperature) is expected to modify rates of gross primary production (GPP), respiration (R), and net calcium carbonate (CaCO3) dissolution in permeable coral reef carbonate sediments. Previous simulations of seawater warming on coral reef sediments found a decline in the GPP/R ratio and an associated increase in CaCO3 dissolution but were only conducted over a short timescale (〈 24 h). To date, no studies have examined the prolonged (〉 24 h) effect of seawater warming on coral reef CaCO3 sediment metabolism and dissolution, which may allow the benthic community to acclimatise. This study used 600-L flume aquaria to examine the effect of seawater warming on GPP, R, and CaCO3 dissolution in the permeable coral reef CaCO3 sediments of Mo'orea, French Polynesia over a period of 15 d. On average, when exposed to warmed seawater (+ 2.8 ºC), R in the CaCO3 sediments was enhanced (+ 58 %) to a greater extent than GPP (+19 %), resulting in a decline in GPP/R (- 23 %) and an associated increase in net CaCO3 dissolution (+ 126 %). The magnitude of these warming-mediated metabolic changes increased each day until reaching a plateau after about 8 days, indicating that 24-h experiments may be underestimating the effect of warming over longer timescales. Interestingly, the increase in dissolution relative to control treatments was more striking during the day (+ 163 %) than at night (+ 89 %), suggesting that warming acted to both enhance geochemical dissolution and reduce biogenic calcification or inorganic precipitation. Together, these data indicate that, over the timescale observed here, photosynthesis and associated inorganic and biogenic CaCO3 precipitation do not exhibit the ability to counterbalance the warming-mediated increase in sediment heterotrophy and CaCO3 dissolution.