Dataset: Nutrients: EN532 and EN538
Deployment: EN538

Seawater for nutrient assays was collected from the Niskin bottles attached to the CTD/Rosette system into acid cleaned (10% HCl), ‘aged’, 60 ml HDPE (Nalgene) sample bottles. In most cases, samples were analysed immediately for nutrients, and always within 2-3 hours of collection. Nanomolar ammonium was analysed using the method by Holmes (1999) following its reaction with a fluorescent reagent. Nitrate, nitrite were detected using a NOx analyzer from Teledyne Instruments, based on the chemiluminescence reaction of nitric oxide and ozone using Vanadium (III) reduction (Braman and Hendrix 1989). Silicate concentrations were measured on 0.8 µm filtered samples according to Strickland and Parsons (1968), by Daniel Qian and Nicolas Van Oostende at Princeton University. The detection limits were estimated to be 20 nM for NH4, 10 nM for NO2, 50 nM for NO3+NO2 and 100 nM for Si(OH)4.

Clean handling techniques were employed to avoid any contamination of the samples, particularly for the ammonium samples. Dura-Touch gloves were used at all times and samples were not decanted or transferred, but were kept tightly closed until just before ammonium analysis in order to avoid any contamination from external sources. No water column nutrient samples were frozen or stored except for silicate. All sampling and handling techniques, whenever possible, followed the international nutrient GO-SHIP manual (Hydes et al. 2010).