Urea concentrations from multiple HOE-DYLAN cruises from July to September 2012 (C-MORE project)

Seawater samples were collected from Niskin bottles with acid-washed syringes to avoid ammonium contamination from air and ship fumes. Samples were kept frozen (-20 ºC) until analysis. Urea was measured at the nanomolar level with the diacetyl monoxime automated method (Aminot and Kérouel, 1982), using a flow-injection system coupled to a 2m Liquid Waveguide Capillary Cell to read the color. Low nutrient seawater exposed to daylight for twoo weeks was used for working standards preparation, blanks and carrier. The absorbance-concentration relationship was linear up to at least 800 nM Urea, with a method detection limit of 4.4 nM, and an error of 4.7% at 100nM.