Ammonium (NH4) 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 contamination from air and ship fumes, and were kept frozen (-20 ºC) until analysis. Ammonium was measured at the nanomolar level with the phenol method (e.g. Hansen and Koroleff, 1999), using a flow-injection system coupled to a 2m Liquid Waveguide Capillary Cell to read the color. Low nutrient seawater was used for working standards preparation, blanks and carrier. All material and instruments was acid-washed before use. The absorbance-concentration relationship was lineal up to at least 500 nM ammonium, with a method detection limit of 3.7 nM and an error of 14% at 50 nM and 2% at 100-200 nM.