CarbonBridge 2014: Physical oceanography and microorganism composition during 5 cruises (Jan, March, May, August, Nov 2014) on and off the shelf northwest of Svalbard in 2014

Data were collected on and off the shelf northwest of Svalbard during cruises in January, March, May, August and November 2014. The sampling depths were 1, 5, 10, 20, 30, 50, 100, 200, 500, 750, and 1000 m, as well as at the depth of the Chl a maximum. The sampling concentrated on the core of the northwards drifting warm Atlantic water, which enters the Arctic Ocean north of Svalbard either south or north of the Yermark plateau. Transects were sampled across the core of the Atlantic water inflow at 79N, and additionally at 79.4N in May and August. Heavy drift ice restricted the sampling to the shelf and shelf-break in May and August 2014. During January, March, and November, the area north of Svalbard was largely ice-free, which allowed sampling off the shelf-break into the Arctic Ocean during winter. At all stations, depth profiles of temperature, salinity and fluorescence were taken with a CTD (Seabird SBE 911 plus). Water was sampled with Niskin bottles from discrete depths for analysis of inorganic nutrients, chlorophyll a (Chl a), microbial abundance, bacterial production (BP), as well as DOM and POM. In May and August, three process stations each (in datasheet referred to as P-stations: P1, P3, P4 in May, and P5, P6, P7 in August, at these stations more time-demanding processes were investigated, such as in situ primary production and vertical export of POM. Chl a was determined by filterig 100-500mL water onto Whatmann GF/F glass fiber filters. Chl a was determined fluorometrically (10-AU, Turner Designs) from triplicates of each filter type after extraction in 5 mL methanol at room temperature in the dark for 12 h without grinding. Abundances of microorganisms: picophytoplankton, nanophytoplankton, virus, heterotrophic bacteria, and heterotrophic nanoflagellates were determined on an Attune(R) Focusing Flow Cytometer (Applied Biosystems by Life technologies) with a syringe-based fluidic system and a 20 mW 488 nm (blue) laser. Samples were fixed with glutaraldehyde (0.5% final conc.) at 4°C for minimum 2 h, shock frozen in liquid nitrogen, and stored at -80 °C until analysis. Total organic carbon (TOC) in unfiltered seawater was analyzed by high temperature combustion using a Shimadzu TOC-VCSH. All samples were acidified with HCl (to a pH of around 2) and bubbled with pure N2 gas in order to remove any inorganic carbon. Calibration was performed using deep seawater and low carbon reference waters. A blank consisting of milliQ water was analyzed every eighth sample to assess the day-to-day instrument variability. Concentration of total nitrogen (TN) was determined simultaneously by high temperature combustion using a CPH-TN nitrogen analyzer. Total organic nitrogen (TON) was calculated by subtracting the inorganic nitrogen (NOx = NO3 + NO2 + NH4+) measured from parallel nutrient samples. The instrument was calibrated using a standard series of acetoanilide and the accuracy of the instrument was evaluated using seawater reference material provided by the Hansell CRM (consensus reference material) program. For analysis of particulate organic carbon (POC) and particulate organic nitrogen (PON), triplicate subsamples (100 - 500 mL) were filtered onto precombusted Whatman GF/F glass-fibre filters (450°C for 5 h), dried at 60°C for 24 h and analyzed on-shore with a Leeman Lab CEC 440 CHN analyzer. Prior to analysis, the dried samples were fumed by concentrated HCl in 24 h before re-drying at 60°C for 24 h to remove inorganic carbon. Unfiltered seawater was filled directly from the Niskin bottles into 30 mL acid washed HDPE bottles and stored at -20°C. Nitrite and nitrate (NO-2 + NO- 3 ), phosphate (PO3- 4 ) and silicic acid (H4SiO4) were measured on a Smartchem200 (by AMS Alliance) autoanalyser following procedures as outlined in Wood et al. (1967) for NO-3 + NO-2 , Murphy and Riley (1962) for PO3-4 and Koroleff (1983) for the determination of H4SiO4. The determination of NO-3 was done by reduction to NO-2 on a built-in cadmium column, which was loaded prior to every sample run. Seven-point standard curves were made prior to every run. Two internal standards and one blank were inserted for every 8 samples and these were used to correct for any drift in the measurements. Concentration of NH+4 was determined directly in fresh samples using ortho-phthaladehyde according to Holmes et al. (1999)