Seawater carbonate chemistry and biomarker pigments and phytoplankton community composition in different biogeochemical regions of the Southern Ocean

• Main Authors: Endo, H, Hattori, Hiroshi, Mishima, Tsubasa, Hashida, Gen, Sasaki, H, Nishioka, Jun, Suzuki, Koji
• Format: Dataset
• Language: English
• Published: PANGAEA 2017
• Subjects: 19-Hexanoyloxyfucoxanthin; Alkalinity; total; standard deviation; Antarctic; Aragonite saturation state; Bicarbonate ion; Biomass/Abundance/Elemental composition; Bottles or small containers/Aquaria (<20 L); Calcite saturation state; Calculated using CO2SYS; Calculated using seacarb after Nisumaa et al. (2010); Carbon; inorganic; dissolved; Carbonate ion; Carbonate system computation flag; Carbon dioxide; Cell density; Chlorophyll a; Community composition and diversity; Entire community; Event label; EXP; Experiment; Fucoxanthin; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Initial slope of the photosynthesis-irradiance curve; Inorganic toxins; Laboratory experiment; Light saturated maximum photosynthetic rate; Light saturated maximum photosynthetic rate per Chlorophyll a; Light saturation; Maximum photochemical quantum yield of photosystem II; OA-ICC; Ocean Acidification International Coordination Centre; Open ocean; Partial pressure of carbon dioxide; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); Pelagos; Percentage; pH; Antarc*; Ocean acidification; Polar Biology; Southern Ocean
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.888447; https://doi.org/10.1594/PANGAEA.888447

The ongoing rise in atmospheric CO2 concentration is causing rapid increases in seawater pCO2levels. However, little is known about the potential impacts of elevated CO2 availability on the phytoplankton assemblages in the Southern Ocean's oceanic regions. Therefore, we conducted four incubation experiments using surface seawater collected from the subantarctic zone (SAZ) and the subpolar zone (SPZ) in the Australian sector of the Southern Ocean during the austral summer of 2011-2012. For incubations, FeCl3 solutions were added to reduce iron (Fe) limitation for phytoplankton growth. Ambient and high (~750 µatm) CO2 treatments were then prepared with and without addition of CO2-saturated seawater, respectively. Non-Fe-added (control) treatments were also prepared to assess the effects of Fe enrichment (overall, control, Fe-added, and Fe-and-CO2-added treatments). In the initial samples, the dominant phytoplankton taxa shifted with latitude from haptophytes to diatoms, likely reflecting silicate availability in the water. Under Fe-enriched conditions, increased CO2 level significantly reduced the accumulation of biomarker pigments in haptophytes in the SAZ and AZ, whereas a significant decrease in diatom markers was only detected in the SAZ. The CO2-related changes in phytoplankton community composition were greater in the SAZ, most likely due to the decrease in coccolithophore biomass. Our results suggest that an increase in CO2, if it coincides with Fe enrichment, could differentially affect the phytoplankton community composition in different geographical regions of the Southern Ocean, depending on the locally dominant taxa and environmental conditions.