| Summary: | Funded by: NSF Office of Polar Programs (#1023346 and #1023140) Principal Investigators: Dr. Andy Juhl (Lamont-Doherty Earth Observatory) andyjuhl@ldeo.columbia.edu 61 Route 9W Palisades NY 10964 Tel: 845-365-8837 Dr. Susanne Neuer (Arizona State University) susanne.neuer@asu.edu PO Box 874501 Tempe, AZ 85287-4501 Tel: 480-727-7254 Contributors: Dr. Craig Aumack Kyle Kinzler Cora McHugh Brittany Held Megan Wolverton Amy Hansen Mark Wiener Physical/chemical and biological measurements of properties of sea ice and under-ice water collected near Barrow, AK in spring 2011 and 2012 The data file summarizes field observations of ice properties and constituents. All field observations of ice properties, snow, ice algae and under ice water in this study were conducted on landfast, first-year sea ice located within 10 km of Point Barrow, Alaska (71.38°, 156.48°) on the near-shore Beaufort and Chukchi Sea shelf (< 3 km from shore). Samples were collected May - early June 2011-2012 at a water depth of approximately 6-8 m. The stations selected were free of rubble and pressure ridges, decreasing the chance of contaminating debris from the shore and/or re-suspended sediment. During 2011, field work was conducted from May 3 to May 26. Stations were selected and sampled from a range of overlying snow depths (0 - 42 cm). The snow depth at each station was measured with a meter stick and snow depth was consistent (± 2 cm) within a radius of approximately 2 m. In 2012, four stations were sampled from May 15 to June 4 every 3 – 7 days. Stations were selected according to the initial snow depths. Station 1 started with 5 cm, Station 2 with 1.5 cm, Station 3 with 21 cm, and Station 4 with 30 cm. Before collecting ice cores, snow was cleared in an area of approximately 1 m2 and cores were drilled using a hand powered portable drill attached to a 14-cm diameter ice corer (Kovacs, Roseburg, OR). After cores were removed from the ice, the bottom 10-cm section was sectioned off using a Bonesaw (G3, North Vancouver, BC) driven by an electric hand drill and immediately placed into polyethylene bags for transport in an insulated cooler to protect core sections from light and temperature changes. Two replicate cores were taken at each station (within 10 cm) for microscopy as well as bulk nutrients, which required separate processing techniques. All cores were taken to the Barrow Arctic Research Center (BARC) laboratory in Barrow, AK for processing. Ice cores were extracted, measured for ice thickness, then three sections were cut out for further processing: the ice bottom layer (0-10 cm from the ice-water interface), a section representing the lower ice layers (10-20 cm from the ice-water interface), and a section representing the upper ice layers (50-60 cm from the ice surface). In most cases, multiple replicate ice cores were collected from each sample location because different analyses required different sample processing. Replicate cores were usually separated by 10-20 cm. Using holes made by the coring, water samples were collected from approximately 2 m below the ice bottom using a peristaltic pump, by carefully lowering a weighted tube through the ice, making sure not to collect suspended ice or benthic sediment. Further processing occurred in the nearby Barrow Arctic Research Consortium (BARC) laboratory. At the BARC lab, ice cores to be used for measurements of bulk salinity, dissolved organic carbon (DOC), and nutrients were slowly melted at approximately 4˚C with no dilution. Nutrient and DOC samples were filtered (GF/F), then subsamples were frozen at -20˚C until analyzed (DOC samples were first acidified with HCl). Ice cores to be used for measurements of particulate organic carbon and nitrogen (POC/PON), particulate carbohydrates (pCHO), extracted chlorophylls (Chl) and microscopy, were diluted 2:1 with filtered seawater obtained in the vicinity of the sampling site. The water was filtered in the laboratory using Sterivex™ capsules (pore size of 0.2 µm, Pall Corp. Port Washington, NY) and added to the ice samples to prevent osmotic shock to organisms during melting (Gradinger et al. 1991, Juhl et al. 2011). The ice cores were melted in a dark walk-in incubator or refrigerator at 4˚C for approximately 48-72 hours. Samples for POC/PON, pCHO and Chl were filtered onto GF/F filters, and frozen until analyzed. Melted sea ice samples were fixed with acid Lugol’s solution (2.5% final concentration) in 20-ml scintillation vials. The samples were kept at room temperature in darkness until they were transported to Arizona State University (ASU) for analysis. Samples for microscopy were fixed with Lugol’s solution (for counts of diatom genera). Values in the data files already account for the dilution steps and subsample volumes. All available data for an ice core segment are given within each row of the data table. Microscopy was only conducted on the ice bottom segments (0-10 cm from the ice bottom). See Aumack et al. (2014) and Kinzler (2014) for more information. Nutrient analysis All nutrient analyses were conducted at The University of Maryland Center for Environmental Science Nutrient Analytical Services Laboratory. Specific information regarding the instruments, method and and detection limits can be found at www.nasl.cbl.umces.edu. Determination of Total Dissolved Nitrate An exact amount of sample is placed into a test tube where Potassium Persulfate Digestion Reagent is added based on the initial sample volume. Under initially alkaline conditions and heat, nitrate is the sole nitrogen product. The now digested samples are buffered, then mixed and passed through a granulated copper-cadmium column to reduce nitrate to nitrite. The nitrite, both originally present and reduced from nitrate, is determined by diazotizing with sulfanilamide and coupling with N-1-napthylethylenediamine dihydrochloride to form a colored solution suitable for photometric measurement. Determination of Total Dissolved Ammonium Filtered samples are mixed with sodium tartrate and sodium citrate. The coupled samples reacted with alkaline phenol and hypochlorite, catalyzed by sodium nitroprusside, yielding an intense blue color suitable for photometric measurement. Determination of Orthophosphate Filtered samples are mixed with a sulfuric acid-antimony-molybdate solution, and subsequently with an ascorbic acid solution, yielding an intense blue color suitable for photometric measurement. Determination of Silicate Filtered samples are mixed with ascorbic acid, reducing the silicomolybdate to “molybdenum blue” yielding an intense blue color suitable for photometric measurement. Oxalic acid is then added to minimize interference from phosphates. Determination of Total Organic Carbon and Inorganic Carbon The Shimazu TOC-L uses a high temperature combustion method to analyze aqueous samples for total carbon, total organic carbon, and inorganic carbon. For organic carbon samples are filtered through a 0.7 μm GF/F and are then acidified and sprayed with ultra-pure carrier grade air to drive off inorganic carbon. High temperature combustion (680°C) on a catalyst bed of platinum coated alumina balls breaks down all carbon compounds into carbon dioxide. The CO2 is carried by ultra-pure air to a non-dispersive infrared detector where total CO2 is measured. For inorganic carbon, an aliquot of sample is injected into a receptacle of 25% v/v phosphoric acid where the carbonates within the samples are reduced to CO2. This carbon dioxide is than carried by ultra-pure air to a non-dispersive infrared detector where CO2 is measured. Carbonate alkalinity is then calculated after the concentration of inorganic carbon is determined. Determination of Total Carbohydrates (pCHO) Filtered samples are mixed with sulfuric acid and a 5% phenol reagent (Dubois et al. 1956). The concentrated sulfuric acid breaks down any polysaccharides, oligosaccharides, and disaccharides to monosaccharides, which react with the phenol yielding an intense yellow-gold color suitable for photometric m easurement. Chlorophyll Analysis The chlorophyll concentration in the ice was determined by filtering the melted ice cores onto precombusted (6 h at 450° C) Whatmann GF/F filters until the filter began to turn green (volumes filtered ranged from 100 to 1000 mL). Filters were kept frozen (-20°C) until chlorophyll was extracted using 90% acetone for 24 h. A fluorometer (Turner Designs TD-700) was used to analyze chlorophyll fluorescence according to UNESCO (1994). Microscopy To quantify the abundance and biomass of sea ice diatoms, the inverted microscopy method was applied (Utermöhl 1931). Samples fixed with Lugol’s solution were settled for 24 hours using a 10-ml settling column (Utermöhl 1931) onto a slide chamber. The diatoms were counted using an Olympus inverted microscope and a 40x phase contrast objective. Diatoms were counted using 11 broad categories based on common Arctic diatom genera, most of them pennate (as in Horner & Schrader 1982, Lund-Hansen et al. 2014, Hsaio 1980, Poulin et al. 2010, von Quillfeldt et al. 2003). These categories included: Gyrosigma, Amphiprora, Navicula, Luticola, Nitzschia frigida, Thalassiothrix, Cylindrotheca, Pseudogomphonema, Fragilariopsis, Pinnularia, Nitzschia spp, and. The centric diatoms, while only counted in one category (“centric”), included representatives of the genera Melosira, Chaetoceros and Thalassiosira; the latter genus was the one most commonly found. In most cases a minimum of 30 cells in each category was counted. The size range among all categories ranged from 5 µm to 210 µm, and was determined based on the largest dimension of the cell. Cell dimensions were measured in the x-y plane using a calibrated ocular grid. The hidden (z) dimension was calculated based on the geometric shape of the cell. To confirm that the hidden dimension was correctly calculated, some cells were turned using a fine needle and the third dimension was measured directly. Biovolume (µm3 L-1) for each of the categories was calculated by averaging size in the respective size classes and approximating geometric shapes based on recommendations from HELCOM (Hillebrand et al.1999, Olenina et.al. 2006). The biovolume (µm3 L-1) was calculated by multiplying cell abundance by the cell-specific biovolume. Using a carbon to volume factor specific for diatoms based on cell volume (<3000 µm3 and >3000 µm3), the biovolume was converted to biomass (mg C L-1; Menden-Deuer et al. 2000).
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