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

• Published in: Polar biology Vol. 41; no. 10; pp. 2119 - 2134
• 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: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.10.2018; Springer; Springer Nature B.V
• Subjects: Algae; Biological activity; Biomedical and Life Sciences; Covariance; Dynamics; Earth; Ecology; Ecosystems; Estimates; Fast ice; Flow velocity; Fluxes; Ice; Ice cover; Ice environments; Ice floes; Incubation period; Laboratories; Leucine; Life Sciences; Meltwater; Microbiology; Oceanography; Original Paper; Oxygen; Pack ice; Plant Sciences; Primary production; Productivity; Sea ice; Summer; Thymidine; Tracers; Uptake; Water flow; Winter; Zoology; Arctic Ocean; Arctic region; Eddy-covariance; Bacterial production; Sea-ice; Carbon cycling; Primary production
• ISSN: 0722-4060; 1432-2056
• DOI: 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) 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.