Variability in the vertical flux of microorganisms and biogenic material in the epipelagic zone of a North Pacific central gyre station

Abstract

Free-floating particle interceptor trap arrays were deployed at a single station (26°N, 155°W) in the North Pacific central gyre for three consecutive periods (I: 24–31 March 1986; II: 31 March to 12 April 1986; III: 14–17 April 1986). Temporal changes in plankton biomass and biogenic vertical fluxes coincided with a 10 day storm that produced up to 35 kn winds and 3.5 m swells. Mean wind speed increased during the study period as did suspended adenosine triphosphate (sus-ATP) concentrations in the upper 120 m. Vertical fluxes of total particulate carbon (PC), ATP, diatoms, dinoflagellates, bacteria, mastigotes and fecal pellets were greatest during the post-storm period, whereas ciliate fluxes were nearly equal in all three trap sets. Aloricate ciliates were the dominant taxonomic group, accounting for 45–79% of the total microbial biomass in the traps. Carbon estimates revealed that most of the PC flux was amorphous material and that fecal pellets and microorganisms represented a small proportion of the PC flux; 0.2–1.2 and 6.0–8.0% of total PC, respectively. Relative abundances, diversity, equitability and taxon rank order of diatoms, dinoflagellates, aloricate ciliates and tintinnid ciliates varied between trap sets, depths and taxonomic groups. Findings from this study support the hypothesis that physical forcing by the storm stimulated planktonic production and altered assemblage structure in the epipelagic zone and consequently stimulated efflux of biogenic materials and organisms from this zone.