Oxygen fluxes beneath Arctic land-fast ice and pack ice: towards estimates of ice productivity

• Published in: Polar Biology
• Main Authors: Attard, Karl M., Søgaard, Dorte H., Piontek, Judith, Lange, Benjamin A., Katlein, Christian, Sørensen, Heidi L., McGinnis, Daniel F., Rovelli, Lorenzo, Rysgaard, Søren, Wenzhöfer, Frank, Glud, Ronnie N.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer 2018
• Subjects: Arctic; Arctic Ocean; Polar Biology; Sea ice
• Online Access: https://oceanrep.geomar.de/id/eprint/43510/; https://oceanrep.geomar.de/id/eprint/43510/1/Attard2018_Article_OxygenFluxesBeneathArcticLand-.pdf; https://doi.org/10.1007/s00300-018-2350-1

Sea-ice ecosystems are among the most extensive of Earth’s habitats; yet its autotrophic and heterotrophic activities remain poorly constrained. We employed the in situ aquatic eddy-covariance (AEC) O2 flux method and laboratory incubation techniques (H14CO3−, [3H] thymidine and [3H] leucine) to assess productivity in Arctic sea-ice using different methods, in conditions ranging from land-fast ice during winter, to pack ice within the central Arctic Ocean during summer. Laboratory tracer measurements resolved rates of bacterial C demand of 0.003–0.166 mmol C m−2 day−1 and primary productivity rates of 0.008–0.125 mmol C m−2 day−1 for the different ice floes. Pack ice in the central Arctic Ocean was overall net autotrophic (0.002–0.063 mmol C m−2 day−1), whereas winter land-fast ice was net heterotrophic (− 0.155 mmol C m−2 day−1). AEC measurements resolved an uptake of O2 by the bottom-ice environment, from ~ − 2 mmol O2 m−2 day−1 under winter land-fast ice to~ − 6 mmol O2 m−2 day−1 under summer pack ice. Flux of O2-deplete meltwater and changes in water flow velocity masked potential biological-mediated activity. AEC estimates of primary productivity were only possible at one study location. Here, productivity rates of 1.3 ± 0.9 mmol O2 m−2 day−1, much larger than concurrent laboratory tracer estimates (0.03 mmol C m−2 day−1), indicate that ice algal production and its importance within the marine Arctic could be underestimated using traditional approaches. Given careful flux interpretation and with further development, the AEC technique represents a promising new tool for assessing oxygen dynamics and sea-ice productivity in ice-covered regions.