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Marine Ecology Progress Series

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MEPS 483:47-66 (2013)  -  DOI:

Inorganic C utilization and C isotope fractionation by pelagic and sea ice algal assemblages along the Antarctic continental shelf

Philippe D. Tortell1,2,*, Mathew M. Mills3, Christopher D. Payne1, Maria T. Maldonado1, Melissa Chierici4,6, Agneta Fransson5,7, Anne-Carlijn Alderkamp3, Kevin R. Arrigo3

1Department of Earth, Ocean and Atmospheric Sciences, and 2Department of Botany, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
3Department of Environmental Earth Systems Sciences, Stanford University, Stanford, California 94305, USA
4Department of Chemistry and Molecular Biology, University of Gothenburg, Göteborg 412 96, Sweden
5Department of Earth Sciences, University of Gothenburg, Box 460, 405 30 Göteborg, Sweden
6Present address: Institute of Marine Research, Postboks 6404, Tromsø 9294, Norway
7Present address: Norwegian Polar Institute, Fram Centre, Tromsø 9296, Norway

ABSTRACT: Physiological characteristics of inorganic C uptake were examined in Southern Ocean ice algae and phytoplankton assemblages. Ice algal and phytoplankton assemblages were largely dominated by diatoms and Phaeocystis antarctica, and showed a high capacity for HCO3- utilization, with direct HCO3- transport accounting for ~60% of total inorganic C uptake. Extracellular carbonic anhydrase (eCA) was detectable in all samples, but with significantly lower activity in sea ice algae. Neither HCO3- transport nor eCA activity was related to the in situ partial pressure of CO2 (pCO2) or taxonomic composition of samples. The half-saturation constant (KS) for inorganic C ranged from ~100 to 5000 µM, and showed significantly more variability among sea ice algae than phytoplankton assemblages. For the phytoplankton assemblages, there were significant positive correlations between in situ pCO2 and KS (higher C substrate affinity in low pCO2 waters), and also between KS and maximum C uptake rates (Vmax). In contrast, KS and Vmax in sea-ice algal assemblages were not correlated to each other, or to any other measured variables. The C isotope composition of particulate organic carbon(δ13C-POC) in the phytoplankton assemblages showed modest variability (range -30 to -24.6‰) and was significantly correlated to the ratio of inferred growth rates (derived from Vmax) and in situ CO2 concentrations, but not to any measured C uptake parameters. δ13C-POC in sea ice algal samples (range -25.7 to -12.9‰) was significantly heavier than in the phytoplankton assemblages, and not correlated to any other variables. Our results provide evidence for the widespread occurrence of carbon-concentrating mechanisms in Southern Ocean sea ice algae and phytoplankton assemblages.

KEY WORDS: Phytoplankton · Sea ice algae · Inorganic carbon uptake · HCO3- · Carbonic anhydrase

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Cite this article as: Tortell PD, Mills MM, Payne CD, Maldonado MT and others (2013) Inorganic C utilization and C isotope fractionation by pelagic and sea ice algal assemblages along the Antarctic continental shelf. Mar Ecol Prog Ser 483:47-66.

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