Organic carbon and nitrogen concentrations on vertical profiles in waters of the North Atlantic in June-July 1996

Not filtered water samples were taken in 10 ml ampoules (sealed immediately after being acidified with phosphoric acid to pH<2, sampling), or 40 ml screw-lid vials, and measured onboard at sampling or next days, or frozen (-20°C) until being acidified and measured in home labs. Carbon measurement was by high-temperature catalytic oxydation in a 10 cm column packed with 5% Pt on aluminum oxide beads at 900°C in a stream of oxygen, and CO2 detection by infrared extinction after the removal of moisture and SO2 by appropriate traps (cold trap, Mg-percarbonate, Na-pyrophosphate, tin, bronze or Sulfix). The apparatus was the dual channel Dimatek 2000 equipped with a Binos 200 detector. Nitrogen was measured by chemoluminescence detection of NO2 in the combustion gases after leaving the Binos detector in one of the two channels of the setup. Most measurements of samples containing high nitrate were discarded, when data were inconsistent. The nature of nitrate interference is not clear.