Seawater carbonate chemistry and shift towards larger diatoms in a natural phytoplankton assemblage under combined high-CO2 and warming conditions

• Main Authors: Sett, Scarlett, Schulz, Kai, Bach, Lennart Thomas, Riebesell, Ulf
• Format: Dataset
• Language: English
• Published: PANGAEA 2023
• Subjects: Alkalinity; total; Aragonite saturation state; Baltic Sea; Bicarbonate ion; Biomass/Abundance/Elemental composition; Calcite saturation state; Calculated using CO2SYS; Calculated using seacarb after Nisumaa et al. (2010); Carbon; inorganic; dissolved; organic; particulate; particulate/Nitrogen; particulate ratio; particulate/Phosphorus; Carbonate ion; Carbonate system computation flag; Carbon dioxide; Cell density; Chlorophyll a; Coast and continental shelf; Community composition and diversity; Coulometric titration; Entire community; Experiment duration; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Laboratory experiment; Mesocosm or benthocosm; Nitrogen; OA-ICC; Ocean Acidification International Coordination Centre; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); Pelagos; Ocean acidification
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.959214; https://doi.org/10.1594/PANGAEA.959214

An indoor mesocosm experiment was carried out to investigate the combined effects of ocean acidification and warming on the species composition and biogeochemical element cycling during a winter/spring bloom with a natural phytoplankton assemblage from the Kiel fjord, Germany. The experimental setup consisted of a “Control” (ambient temperature of ~4.8 °C and ~535 ± 25 μatm pCO2), a “High-CO2” treatment (ambient temperature and initially 1020 ± 45 μatm pCO2) and a “Greenhouse” treatment (~8.5 °C and initially 990 ± 60 μatm pCO2). Nutrient replete conditions prevailed at the beginning of the experiment and light was provided at in situ levels upon reaching pCO2 target levels. A diatom-dominated bloom developed in all treatments with Skeletonema costatum as the dominant species but with an increased abundance and biomass contribution of larger diatom species in the Greenhouse treatment. Conditions in the Greenhouse treatment accelerated bloom development with faster utilization of inorganic nutrients and an earlier peak in phytoplankton biomass compared to the Control and High CO2 but no difference in maximum concentration of particulate organic matter (POM) between treatments. Loss of POM in the Greenhouse treatment, however, was twice as high as in the Control and High CO2 treatment at the end of the experiment, most likely due to an increased proportion of larger diatom species in that treatment. We hypothesize that the combination of warming and acidification can induce shifts in diatom species composition with potential feedbacks on biogeochemical element cycling.