Abstract
Abstract. We present and compare the dynamics (i.e., changes in standing stocks, saturation levels and concentrations) of O2, Ar and N2 in landfast sea ice, collected in Barrow (Alaska), from February through June 2009. The comparison suggests that the dynamic of O2 in sea ice strongly depends on physical processes (gas incorporation and subsequent transport). Since Ar and N2 are only sensitive to the physical processes in the present study, we then discuss the use of O2 / Ar and O2 / N2 to correct for the physical contribution to O2 supersaturations, and to determine the net community production (NCP). We conclude that O2 / Ar suits better than O2 / N2, due to the relative abundance of O2, N2 and Ar, and the lower biases when gas bubble formation and gas diffusion are maximized. We further estimate NCP in the impermeable layers during ice growth, which ranged from −6.6 to 3.6 μmol O2 L−1 d−1, and the concentrations of O2 due to biological activity in the permeable layers during ice decay (3.8 to 122 μmol O2 L−1). We finally highlight the key issues to solve for more accurate NCP estimates in the future.
Highlights
Sea ice is a composite material with a matrix of pure ice and inclusions of brine (Weeks, 2010)
The net community production (NCP), i.e., the net carbon fixation due to photosynthesis and respiration of the microorganisms in sea ice is a crucial measurement in polar ecological studies, because it is generally the sole source of fixed carbon for the higher trophic-level species in ice-covered oceans (Arrigo et al, 2010; Brierley and Thomas, 2002; Michel et al, 1996)
The temporal variation of the three gas standing stocks were similar, but differed from that of the ice thickness: while sea ice continuously thickened from BRW2 (82 cm) to BRW10 (142 cm), the gas standing stocks increased from BRW2 to BRW8 but decreased at BRW10
Summary
Sea ice is a composite material with a matrix of pure ice and inclusions of brine (Weeks, 2010). A traditional standard technique is to measure the accumulation of algal biomass and its temporal change via the measurements of chlorophyll a (chl a) or particulate organic carbon (POC) Another traditional standard technique is to measure the maximum photosynthetic rate and photosynthetic efficiency in a laboratory, and to deduce the changes of biomass based on the concentration of chl a and the light intensity from the field, assuming that the photosynthetic parameters obtained in laboratory still hold for field measurements. Both standard techniques have one major limitation: they require the extraction and the melting of sea ice, which inevitably alters the growth environment of the microorganisms (e.g., sudden change of brine salinity due to bulk ice melting)
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