Plankton respiration rate is a major component of global CO2 production and is forecasted to increase rapidly in the Arctic with warming. Yet, existing assessments in the Arctic evaluated plankton respiration in the dark. Evidence that plankton respiration may be stimulated in the light is particularly relevant for the high Arctic where plankton communities experience continuous daylight in spring and summer. Here we demonstrate that plankton community respiration evaluated under the continuous daylight conditions present in situ, tends to be higher than that evaluated in the dark. The ratio between community respiration measured in the light (Rlight) and in the dark (Rdark) increased as the 2/3 power of Rlight so that the Rlight:Rdark ratio increased from an average value of 1.37 at the median Rlight measured here (3.62 µmol O2 L-1 d-1) to an average value of 17.56 at the highest Rlight measured here (15.8 µmol O2 L-1 d-1). The role of respiratory processes as a source of CO2 in the Arctic has, therefore, been underestimated and is far more important than previously believed, particularly in the late spring, with 24 h photoperiods, when community respiration rates are highest.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This study is a contribution to projects ARCTICMET and ATOS, funded by the Spanish Ministry of Economy and Competitiveness (CTM2011-15792-E and POL2006-00550/CTM, respectively), the ATP project funded by the FP-7 of the EU (CTM2009-07781-E), and the CarbonBridge project (no. 226415) funded by the Norwegian Research Council. Work in Young Sound was funded by the Greenland Ecosystem Monitoring (GEM) program. We thank the crew of R/V Helmer Hanssen and Young Sound participants for support, and Arsenio Granados for the measurement of δ18O-H2O of spiked samples. We gratefully acknowledge the contributions from the Arctic Research Centre, Aarhus University. This work is a contribution to the Arctic Science Partnership (ASP) asp-net.org. M.S.-M. was supported by a La Caixa PhD fellowship. E.M. was supported by a JAE Pre-doc fellowship from the Spanish National Research Council (CSIC) and the BBVA Foundation, and a visiting student fellowship from King Abdullah University of Science and Technology (KAUST).