Effects of sediment storage conditions on pigment analyses

Sediment pigments as an indicator of water column and benthic processes have become widely used during the last decades. However, the effect of different storage and handling conditions on the accuracy of sediment pigment analyses has not been adequately evaluated. This can potentially make comparisons between studies difficult and, at worst, call into question the validity of some studies. Even though sediment pigment studies often rely on relative changes of individual pigments with depth, the effect of storage and handling is a critical consideration in any investigation. Based on testing of a number of different protocols, this study recommends that all sediment samples should be frozen at -20 degrees C or colder as soon as possible after sampling and stored at this temperature without additional treatment (e.g., freeze-drying) until just before analysis of pigments. Freezing at a lower temperature than -20 degrees C or flushing with nitrogen gas did not improve preservation. Our results showed that, if dictated by other proxy analyses, raw sediment can be stored at 3 degrees C for up to 6 months, whereas freeze-dried sediment should always be stored frozen. In addition, the use of an internal standard (for example, beta-apo-8-carotenal) for normalizing pigment concentrations is highly recommended as it significantly reduces variability between runs.