Turner td 700 fluorometer

To extract Chl a, 500 mL of melt pond water was filtered onto GF/F filters (Whatman) and the filters were placed in test tubes containing 10 mL ethanol (96%). The samples were stored in darkness at −18 °C until analysis using a fluorometer (Turner TD-700 fluorometer, Turner Designs, California, USA). For POC determination, an additional 500 ml was filtered through separate pre-combusted GF/F filters (Whatman). These filters were stored frozen (−18 °C) in pre-combusted aluminum foil packages. For analysis, the filters were acidified to remove inorganic carbon and thereafter packed into tin capsules for determination of the organic carbon content using a solid phase elemental analyzer (CHN EA1108-Elemental analyzer, CARLO ERBA). For determination of PO₄³⁻, NO₃⁻ and Br⁻ concentrations, 50 mL of the filtrate was stored frozen (−18 °C). PO₄³⁻ and NO₃⁻ concentrations were measured by standard procedures as described in Grasshoff et al. (1983 ) and García-Robledo et al. (2014 (link)), respectively, while Br⁻ concentrations were measured using ion chromatography (IC, Dionex IC S-1500; Forster et al. 1999 (link)).

Chlorophyll-a was measured following filtration onto 0.2 μm polycarbonate membranes (Millipore) and extraction with Dimethyl sulfoxide (DMSO) at room temperature. After a 30 s sonification, each sample was left to extract overnight, followed by a centrifugation and measurement by fluorometry on a Turner TD-700 fluorometer (Turner Designs, Sunnyvale, CA) calibrated with a solid standard.

Samples for the measurement of NO₃⁻ + NO₂⁻, PO₄^3-, and Si(OH)₄ concentrations were filtered through precombusted (450 °C for 4.5 h) 25 mm GF/F filters and stored in acid-cleaned Falcon^TM tubes (Thermo Fisher Scientific) at −20 °C until analysis using standard techniques [30 ] on a Lachat QuikChem 8000 Flow Injection Analyzer. Samples for the analysis of POC and PON were filtered onto precombusted (4 h @ 450 °C) 25 mm Whatman GF/F filters. Blank filters were made by filtering ca. 25 ml filtered (0.2 µm) seawater and were processed the same as the particulate samples. The filters were dried (60 °C) and stored at room temperature until analysis. Prior to analysis the samples were fumed with concentrated HCl, dried at 60 °C for 24 h, packed into tin capsules (Costech Analytical Technologies Inc. Valencia, CA) and analyzed on an Elemental Combustion System (Costech Analytical Technologies) interfaced to a Thermo Finnigan Delta V Advantage isotope ratio mass spectrometer (Thermo Fisher Scientific) at the SOEST Biogeochemical Stable Isotope Facility at the University of Hawai’i, Manoa. Fluorometric analysis of Chl a was measured [31 ] using a Turner Fluorometer TD-700 (Turner Designs, Inc., San Jose, CA).