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

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Wenzhöfer,  Frank
HGF MPG Joint Research Group for Deep Sea Ecology & Technology, Max Planck Institute for Marine Microbiology, Max Planck Society;

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Citation

Attard, K. M., Sogaard, D. H., Piontek, J., Lange, B. A., Katlein, C., Sorensen, H. L., et al. (2018). Oxygen fluxes beneath Arctic land-fast ice and pack ice: towards estimates of ice productivity. POLAR BIOLOGY, 41(10), 2119-2134. doi:10.1007/s00300-018-2350-1.


Cite as: http://hdl.handle.net/21.11116/0000-0003-B874-B
Abstract
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 ((HCO3-)-C-14, [H-3] thymidine and [H-3] 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 0.003-0.166mmolCm(-2)day(-1) and primary productivity rates of 0.008-0.125mmolCm(-2)day(-1) for the different ice floes. Pack ice in the central Arctic Ocean was overall net autotrophic (0.002-0.063mmolCm(-2)day(-1)), whereas winter land-fast ice was net heterotrophic (-0.155mmol C m(-2) day(-1)). AEC measurements resolved an uptake of O-2 by the bottom-ice environment, from similar to-2mmolO(2)m(-2) day(-1) under winter land-fast ice to similar to-6mmolO(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 +/- 0.9mmolO(2)m(-2)day(-1), much larger than concurrent laboratory tracer estimates (0.03mmolCm(-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.