Water Sample Collection
Water samples for both NO2 and NH4 analyses were collected using a 24 x 10-liter Niskin bottle rosette sampler equipped with a conductivity, temperature, and pressure instrument package (SBE9, Sea-Bird Electronics, Bellevue, Washington, U.S.A.). The sampler was also equipped with sensors for dissolved oxygen (SBE43, Sea-Bird) and chlorophyll fluorescence (FluoroSeatechWetlabsFLF Sensor). NH4 and NO2 were measured on board immediately after sample collection.
NO2 Analysis
Nitrite concentration was measured manually colorimetrically using standard methods (Hansen and Koroleff, 1999).
NH4 Analysis
Duplicate samples for ammonium concentration were measured immediately upon retrieval and were not filtered prior to analysis. Ammonium concentration was measured manually fluorometrically using standard methods (Holmes et al. 1999).