Sources of variability in geographical and seasonal differences in particulate fluxes from short-term sediment trap deployments, east of New Zealand

Abstract

Free-floating sediment traps were used to measure total mass and particulate phosphorus fluxes from the upper ocean (>100–550 m) at two stations in each of three water types (subantarctic, Subtropical Convergence and subtropical), east of New Zealand, in winter and spring 1993. Despite marked changes in ecosystem community structure and function between water types and occasionally between stations, there were no significant differences in export flux either across water masses, between stations or with increasing water depth. One exception was in the Subtropical Convergence where significant increases in particulate flux with depth at one station in spring are inferred to be caused by tidal current resuspension of bottom sediments on the crest of the Chatham Rise. High degrees of variation between mass fluxes calculated from individual cylinders observed in winter (coefficients of variation ranging from 10 to 123%) may have been due to inter-trap hydrodynamic interactions or sample processing errors. In spring, overall coefficients of variation of mass flux were smaller than in winter (6–87%), but variations due solely to sub-sampling procedures were significant (<1–83%). The ranges of variability for the New Zealand traps are similar to other published sediment trap studies, suggesting that the use of single, free-floating sediment trap arrays to characterise fluxes for specific oceanic provinces is unlikely to be valid statistically. Based on the results from east of New Zealand, more than two arrays would be required to improve the power of the chosen statistical test in order to determine significant differences in particulate flux between physically and biologically distinctive oceanic water masses.