Combined effects of ocean acidification and enhanced irradiances on Arctic phytoplankton assemblages – Why do they not care?

• Main Authors: Hoppe, Clara, Schuback, N, Wolf, Klara, Semeniuk, D, Giesbrecht, K, Maldonado, M T, Varela, D E, Rost, Bjoern, Tortell, P D
• Format: Conference Object
• Language: unknown
• Published: 2016
• Subjects: Arctic; Arctic Ocean; Baffin Bay; Baffin; Davis Strait; Ocean acidification; Phytoplankton; Sea ice; Subarctic
• Online Access: https://epic.awi.de/id/eprint/41613/; https://hdl.handle.net/10013/epic.48488

The Arctic Ocean is one of the regions most prone to on-going ocean acidification (OA) and climate-driven changes, including increased sea surface temperature, sea-ice melt and altered mixing regimes. However, the influence of these changes on Arctic primary productivity, phytoplankton ecology and elemental cycles remains poorly understood. To date, the impact of various environmental stressors on phytoplankton have largely been assessed in isolation, and only limited process-understanding was gained. In order to understand how OA and enhanced irradiances (resulting from sea-ice retreat and increased mixed layer stratification) will alter the species composition, productivity and ecophysiology of Arctic phytoplankton, we conducted two incubation experiments with natural plankton assemblages from Davis Strait (63°N) and Baffin Bay (71°N) during the Arctic-GEOTRACES summer 2015 campaign. Phytoplankton assemblages were exposed to 400 and 1200 µatm pCO2 at both 15% and 35% surface irradiance over two weeks. These incubations were monitored and characterised in terms of phytoplankton growth, nutrient usage, biomass stoichiometry, net primary production (NPP), photophysiology and species composition. Preliminary results indicate that the Subarctic Davis Strait assemblage exhibited light- and CO2-dependent growth rates and NPP, while there were no such differences between treatments in the Arctic Baffin Bay assemblage. The suite of measurements conducted in this study will be exploited to provide a mechanistic understanding of the observed similarities and differences between phytoplankton assemblages. Our results indicate a high level of resilience of Arctic primary producers to climate-dependent environmental change.