Ocean alkalinity enhancement (OAE), has been put forward as a potential technique to reduce atmospheric CO2 levels. OAE accelerates the natural rock weathering process by adding alkaline minerals directly into seawater. However, sudden alterations in seawater pH and alkalinity might shift the plankton community structure. Unfortunately, the impacts of OAE on marine ecosystems, especially zooplankton, are mostly unexplored. The present study assessed the direct (physiological stress) and indirect (changes in phytoplankton dynamics) effects of increased alkalinity and pH on the zooplankton community. Natural plankton communities were studied during two large-scale mesocosm experiments under simulated OAE conditions in a Norwegian fjord and at Helgoland roads in the North Sea. In the fjord, an alkalinity gradient from delta 0 to 600 µEql-1 was tested and a comparative analysis was conducted between calcium and silica mineral-based OAE set-ups. In contrast, only calcium-based mineral was used in Helgoland Road with a higher range of alkalinity levels, ranging from delta 0 to 1500 µEql-1 . We assessed the zooplankton community composition in both studies. The results were corroborated with laboratory experiments, using cosmopolitan copepod species Acartia tonsa¸ where no direct effects of increased alkalinity were observed, suggesting their relative resiliency toward altered OAE. Overall, our study emphasized the importance of a multitrophic study of marine communities to understand the potential ecological consequences of emerging techniques such as OAE.

Primary Presenter: Amrita Bhaumik, Alfred Wegener Institute, Helmoholtz Center for Polar and Marine Research (amrita.bhaumik@awi.de)

Authors:

Amrita Bhaumik, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Biologische Anstalt Helgoland, Kurpromenade, 27483, Helgoland, Germany  (amrita.bhaumik@awi.de)

Synne Spjelkavik, Centre for Gelatinous Plankton Ecology and Evolution, DTU Aqua - Technical University of Denmark, 2800 Kgs. Lyngby, Denmark  ()

Cédric L. Meunier, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Biologische Anstalt Helgoland, Kurpromenade, 27483, Helgoland, Germany  ()

Ulf Riebesell, Biological Oceanography, GEOMAR Helmholtz Centre for Ocean Research Kiel, 24148, Kiel, Germany  ()

Cornelia Jaspers, Centre for Gelatinous Plankton Ecology and Evolution, DTU Aqua - Technical University of Denmark, 2800 Kgs. Lyngby, Denmark  ()

Maarten Boersma, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Biologische Anstalt Helgoland, Kurpromenade, 27483, Helgoland, Germany  ()