This project began an evaluation of nutrients and phytoplankton standing stocks in the central Arctic Ocean based on sampling at the North Pole Environmental Observatory (NPEO). The first sampling occurred in April 2005, the second in April 2006, where eight vertical profiles of hydrographic properties (salinity, temperature, sigma-t), in-situ fluorescence, and nutrients in the region of the NPEO were determined.

Vertical profiles of hydrographic, fluorescence, and nutrients over the upper 150 m were obtained using a Sea-Bird SBE-19 CTD (serial number 1923347-2995) combined with a Wetstar model WS3S miniature flow-through fluorometer (serial number 646P), which had an excitation wavelength of 460 nm and an emission wavelength of 695 nm. The continuous CTD profiles were processed using standard SeaSoft software with the results being binned into 0.5 m depth intervals. The fluorometer was calibrated in the laboratory with aqueous solutions of resorufin (Christensen, 2006a). The fluorescence of resorufin was compared with the fluorescence of purified chlorophyll-a (from the algae Anacystis nidulans) dissolved in buffered acetone (10 ml of 1% (weight per volume) magnesium carbonate per L of 90% acetone). These chlorophyll solutions showed a fluorescence of 40.0 times that of resorufin for the same molar concentrations. The output of the fluorometer was first converted to fluorescence of resorufin (mmol/L) and then to that of chlorophyll-a (expressed in microgram-chl/L) using this factor and the molecular weight of chlorophyll-a (893.5 g/mole).