| Summary: | Arctic Observing Network (AON) Annual Observations of the Biological and Physical Marine Environment in the Chukchi and near-shore Beaufort Seas near Barrow, AK. Carin Ashjian, Woods Hole Oceanographic Institution Robert Campbell, University of Rhode Island Stephen Okkonen, University of Alaska Fairbanks NISKIN BOTTLE DATA This data set contains the nutrient concentrations (phosphate (PO4), nitric oxide (NO2+NO3), silicic acid (SiO4), nitrite (NO2), and ammonium (NH4)), total chlorophyll a concentration, the concentration of coccoid cyanobacteria, photosynthetic eukaryotes, and diatoms, and the abundances of protists (dinoflagellates and ciliates) as both cells/ml and as µg C/L as well as sample depth, position (latitude and longitude, date, station number, and temperature, salinity, and fluorescence for water samples collected using Niskin bottles during August and September 2010. More information regarding sample collection and the associated conductivity temperature depth (CTD) casts numbers can be found in the event log for this cruise. Niskin bottles were deployed either just above the CTD (40 m) or by hand on a line over the side (0 m and 10 m samples) and tripped by messenger. Water was sampled immediately upon recovery of the Niskins. For chlorophyll a analysis, 100 ml of seawater was filtered onto GF-F glass fiber filters in triplicate for each bottle. Two hundred ml subsamples for determination of microzooplankton biomass and abundance were preserved with 5 percent final concentration acid Lugol solution for inverted microscopy. For flow cytometry samples, 3 ml aliquots were pipetted into 4 ml cryovials and preserved with 0.2 percent final concentration of freshly made paraformaldehyde. The samples were gently mixed and let sit in the dark at room temperature for 10 minutes before quick-freezing and storage -80 degrees Celsius until flow cytometric analysis was performed. Analyses of nutrient, chlorophyll a, and flow cytometry samples followed methods described in Ashjian et al. (2010) that are reproduced below. Analysis of microzooplankton abundance followed methods described in Sherr et al. (in review) that are reproduced below. Nutrient and chlorophyll a samples were frozen in a -20 degrees Celsius freezer immediately after collection and transferred to a -80 degrees Celsius freezer within 6-8 hours. Water for the abundance of < 5 µm photosynthetic picoplankton by flow cytometry was drawn into 60 ml, brown bottles and kept cold for ~6-8 hours before being subsampled and frozen at -80 degrees Celsius. Chlorophyll a concentrations were analyzed within 2 months. The filters were extracted in 6 ml of 90% acetone in 13 x 100 mm glass culture tubes at -20 oC for 18 to 24 hours. At the end of the extraction period, the filter was carefully removed from each tube, and the chlorophyll a concentration determined using a calibrated Turner Designs fluorometer. A solid chlorophyll a standard was used to check for fluorometer drift at the beginning of each reading of chlorophyll a samples. Extracted chlorophyll values were used to ground-truth the chlorophyll fluorescence sensors on the Acrobat and the CTD. (Ashjian et al., 2010) Nutrient analyses were performed using a hybrid Technicon AutoAnalyzer IITM and Alpkem RFA300TM system following protocols modified from Gordon et al. (1995). Standard curves with four different concentrations were run daily at the beginning and end of each run. Fresh standards were made prior to each run by diluting a primary standard with low-nutrient surface seawater. Triplicate deionized water blanks were analyzed at the beginning and end of each run to correct for any baseline shifts. In this protocol, the coefficients of variation for duplicates at low nutrient concentrations are typically < 1% (Fleischbein et al., 1999) while at high nutrient concentrations coefficients of variation are 23 % for nitrate and silicate (Corwith andWheeler, 2002). (Ashjian et al., 2010). Nutrient analyses were conducted by Joe Jennings at Oregon State University. In the laboratory, samples for the abundance of < 5 µm photosynthetic microbes were thawed and kept on ice in a dark container until subsamples of 500 µl were enumerated on a BectonDickinson FACSCaliber flow cytometer with a 488-nm laser (Sherr et al. 2005). Populations of coccoid cyanobacteria and of photosynthetic eukaryotes were distinguished by differences in side light scatter (SSC) and by fluorescence in orange (cyanobacteria) and in red (eukaryotic phytoplankton) wavelengths. (Ashjian et al., 2010). Microzooplankton were enumerated from the Lugol-preserved samples. From 15 to 50 ml were settled for a minimum of 24 hours and then the whole slide inspected by inverted light microscopy. A Nikon inverted microscope mated to a computer digitizing system via a drawing tube was used to identify and measure microzooplankton cells and to convert linear dimensions to cell volumes using equations appropriate for individual cell shapes (Roff and Hopcroft, 1986). All ciliate and dinoflagellate cells in each sample were counted and sized. From 60 to 400 protist cells were counted and sized in each sample inspected. Cell biomass for dinoflagellates was estimated using an algorithm of Menden-Deuer and Lessard (2000) and for ciliates was estimated using the 0.19 pgC µm-3 value of Putt and Stoecker (1989). Ratios of heterotrophic dinoflagellate biomass, and of > 40 µm sized microzooplankton biomass, as a fraction of total microzooplankton biomass were also calculated. Microzooplankton were enumerated by Celia Ross, under the direction of Evelyn and Barry Sherr, at Oregon State University. Fluorescence values from the fluorometer on the CTD were ground-truthed using the extracted chlorophyll a data; the chlorophyll fluorescence values reported here for each bottle are derived from those corrected values from the CTD fluorometer. Ashjian, C.J., Braund, S.R., Campbell, R.G., George, J.C., Kruse, J. Maslowski, W., Moore, S.E., Nicolson, C.R., Okkonen, S.R., Sherr, B.F., Sherr, E.B., Spitz, Y. 2010. Climate variability, oceanography, bowhead whale distribution, and Iñupiat subsistence whaling near Barrow, AK. Arctic 63: 179-194. Menden-Deuer, S., Lessard, E., 2000. Carbon to volume relationships for dinoflagellates, diatoms, and other protist plankton. Limnology and Oceanography 45, 569579 Putt M., Stoecker D.K. 1989. An experimentally determined carbon: volume ratio for marine oligotrichous ciliates from estuarine and coastal waters. Limnology and Oceanography 34: 10971103. Roff J.C., Hopcroft R.R. 1986. High precision microcomputer based measuring system for ecological research. Canadian Journal of Fisheries and Aquatic Sciences 43: 20442048. Sherr, EB, Sherr, BF, Ross, C. Microzooplankton grazing impact in the Bering Sea during spring sea ice conditions. In review, Deep-Sea Research II.
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