Description: This dataset is part of a dataset collection. Please read the documentation in Kiel fjord carbonate chemistry data between 2015 (February) and 2016 (January) doi:10.1594/PANGAEA.876551 for details on sampling, measurement and data processing.

Description: Anthropogenic carbon dioxide (CO2) emissions are reducing the pH in the world's oceans. The plankton community is a key component driving biogeochemical fluxes, and the effect of increased CO2 on plankton is critical for understanding the ramifications of ocean acidification on global carbon fluxes. We determined the plankton community composition and measured primary production, respiration rates and carbon export (defined here as carbon sinking out of a shallow, coastal area) during an ocean acidification experiment. Mesocosms (~ 55 m3) were set up in the Baltic Sea with a gradient of CO2 levels initially ranging from ambient (~ 240 µatm), used as control, to high CO2 (up to ~ 1330 µatm). The phytoplankton community was dominated by dinoflagellates, diatoms, cyanobacteria and chlorophytes, and the zooplankton community by protozoans, heterotrophic dinoflagellates and cladocerans. The plankton community composition was relatively homogenous between treatments. Community respiration rates were lower at high CO2 levels. The carbon-normalized respiration was approximately 40 % lower in the high CO2 environment compared with the controls during the latter phase of the experiment. We did not, however, detect any effect of increased CO2 on primary production. This could be due to measurement uncertainty, as the measured total particular carbon (TPC) and combined results presented in this special issue suggest that the reduced respiration rate translated into higher net carbon fixation. The percent carbon derived from microscopy counts (both phyto- and zooplankton), of the measured total particular carbon (TPC) decreased from ~ 26 % at t0 to ~ 8 % at t31, probably driven by a shift towards smaller plankton (〈 4 µm) not enumerated by microscopy. Our results suggest that reduced respiration lead to increased net carbon fixation at high CO2. However, the increased primary production did not translate into increased carbon export, and did consequently not work as a negative feedback mechanism for increasing atmospheric CO2 concentration.

Description: Microzooplankton (microZP, protists) and mesozooplankton (mesoZP, metazoans) abundances and biomass as well as presence of domoic acid (DA, phycotoxin) during the mesocosm experiment in the Canary Islands in autumn 2019. Depth-integrated (0-2.5m) water samples were taken over the course of 33 days, in 2-day intervals for microZP and mesoZP and 4-day intervals for DA. MicroZP was assessed by Utermöhl light microscopy and its biomass estimated using biovolume to carbon conversion factors from the literature. MesoZP samples were split into three size fractions (55-200, 200-500 and 〉500 µm), preserved with 70% ethanol and assessed under a stereo microscope. For biomass, mesoZP were measured in an element analyser. MesoZP data is provided for copepods only (dominant group) and all metazoan zooplankton combined (mainly copepods and appendicularians). For DA, particulate matter was filtered (〉0.7µm) and analysed via liquid chromatography and tandem mass spectrometry. The upwelling treatment started on day 6. Methodological details in Goldenberg et al. (doi:10.3389/fmars.2022.1015188) and Goldenberg et al. (under review).