Primary production estimate of sea ice algae Author: R.Gradinger Cruise: SBI spring 2002 Grant Number: NSF 0125464 Dr. Rolf Gradinger Associate Professor School of Fisheries and Ocean Sciences University of Alaska Fairbanks 245 O'Neil Building PO Box 757220 Fairbanks, AK 99775-7220 U.S.A. phone: 907 474 7407 fax: 907 474 7204 e-mail: rgradinger@ims.uaf.edu homepage: http://www.sfos.uaf.edu/directory/faculty/gradinger/ sea ice research: http://www.sfos.uaf.edu/research/seaicebiota/ Description of methodology Uptake rates of isotopically labeled precursors (13C: NaH13CO3; Cambridge Isotope Lab. Inc.) were used to determine the ice algal and phytoplankton carbon assimilation under simulated in situ conditions in a refrigerated incubator (-1 ¼C, PAR=14 __ m-2 s-1). At each site, 500 ml of brine (collected in sack holes representing ice algal populations) and surface water (5 m depth) were incubated for 4 to 6 hours with 13C tracer additions of 4 to 6% of the natural concentrations in duplicate treatments. We report the average of these treatments because the variability between the production estimates of the two samples was <15% of the average in all samples. At the end of the incubations, samples were filtered onto pre-combusted Whatman GF/F filters, rinsed with filtered sea water and immediately frozen for mass spectrometric analysis in Fairbanks. Primary production rates were calculated following the equations provided in Legendre and Gosselin (1996). The carbon specific production values of the brine samples were multiplied with the sea ice bottom POC values to estimate the primary production of the ice algae in the bottom 10cm of the ice floes which contained the highest POC concentrations at all stations. Data have been published in Gradinger (2008). Ref: Gradinger, R. (2008): Sea ice algae: major contributors to primary production and algal biomass in the Chukchi and Beaufort Sea during May/June 2002. Deep Sea Res in press Legendre, L., Gosselin, M., 1996. Estimation of N or C uptake rates by phytoplankton using 15N or 13C: revisiting the usual computation formulae. J. Plankton Res. 19, 263-271