The effect of frozen storage of open-ocean seawater samples on the concentration of dissolved phosphate and nitrate

Filtered seawater samples which were stored at −20°C in containers of different surface area to volume ratios were analysed for the effects of surface adsorption of nitrate and phosphate during storage for a maximum of 24 months. The results for nitrate showed no significant change in concentration over the duration of the experiment. However, the concentration of phosphate steadily decreased in samples stored for longer than 4 months. The loss of phosphate after this time cannot be explained at present, but this study showed that it was not due to the effects of surface adsorption.