Seasonal variation in the biochemical composition of particulate material collected by sediment traps at Signy Island, Antarctica

Particulate material recovered over an 18-month period from sediment traps deployed at a shallow-water nearshore Antarctic site was analysed for photo synthetic pigments, aliphatic hydrocarbons and fatty acids. All components showed a distinct seasonal variation, with high recovery rates during the s ummer open-water phytoplankton bloom and low rates under winter fast ice. T he amount of trapped material differed between the two summers, indicating inter-annual variability of vertical flux associated with differences in th e intensity of the summer phytoplankton bloom. Particulate material trapped in summer was dominated by that which originated in diatoms. High recoveri es of chlorophyll a, fucoxanthin, n-C-21:6 hydrocarbon, 20:5(n-3) fatty aci d and shorter chain (C-15-C-24) aliphatic hydrocarbons all pointed to a sig nificant summer flux of ungrazed diatoms. There were, however, also signals of zooplankton grazing activity (notably pyrophaeophorbide a), and the pre sence of C18:4(n-3) and C23:6(n-3) fatty acids suggested a small flux of ma terial from flagellates and other sources. Longer chain n-alkanes (C-25-C-3 4) indicative of nanoplankton were detected all year, but there was no sign ificant deposition of zooplankton material in ally sample. The major recove ry rate of photosynthetic pigments was in late summer (February to April), and the major grazing signal occurred after the peak of the summer diatom b loom. Most of the diatom bloom appeared to settle out from the water column without being grazed. The major seasonal contrast in the biochemistry of t he trapped material was the dominance of the diatom signature in summer, an d in winter the predominance (but at much lower recovery rates) of material from nanoplankton.