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, Piontek, Judith, Lange, Benjamin A., Katlein, Christian, Sørensen, Heidi Louise, McGinnis, Daniel F., Rovelli, Lorenzo, Rysgaard, Søren, Wenzhöfer, Frank, Glud, Ronnie N.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2018
• Subjects: sea-ice; primary production; bacterial production; carbon cycling; Eddy-covariance; Arctic; Arctic Ocean; Polar Biology; Sea ice
• Online Access: https://portal.findresearcher.sdu.dk/da/publications/e0513e76-34fb-451b-939e-9d9810fcdcd8; https://doi.org/10.1007/s00300-018-2350-1; https://findresearcher.sdu.dk/ws/files/143470028/Attard2018_Article_OxygenFluxesBeneathArcticLand_.pdf

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) O 2 flux method and laboratory incubation techniques (H 14 CO 3 −, [ 3 H] thymidine and [ 3 H] 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 O 2 by the bottom-ice environment, from ~ − 2 mmol O 2 m− 2 day− 1 under winter land-fast ice to~ − 6 mmol O 2 m− 2 day− 1 under summer pack ice. Flux of O 2 -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 O 2 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.