Short-term variability in the flux of rapidly sinking particles in the Antarctic marginal ice zone

A sediment trap deployment was made at a station (64 degrees 42 'S, 139 deg rees 59 'E) at five depths (537, 796, 1,259, 1,722, 2,727 m) in the margina l ice zone (MIZ) of the Antarctic Ocean during a summer productive period f rom 26 December 1994 to 20 January 1995. This aim of the study was to revea l a possible occurrence of a sporadic bloom in surface layers and to evalua te the role of fast-sinking particles in transportation processes of bloom- derived material down to mesopelagic and bathypelagic layers. During the ob servation, a marked flux increase (70.5 mg C m(-2) day(-1), 7.7 mg N m(-2) day(-1)) was observed at the depth of 537 rn on 7-9 January. The increased flux at 537 m decreased with depth and time. The same mass of sinking parti cles forming the flux maximum at each depth sank down from the shallowest t rap (537 m) to the deepest trap (2,727 m) within 4-11 days, indicating that these particles were transported downward to the bottom with the sinking r ate of > 200 m day(-1). Collected particles were composed of two major part icle fractions; one was dominated by fecal pellets of macrozooplankton (mai nly Euphausia super a) with relatively fast sinking rates (FSP; fast-sinkin g particles) and the other by minute diatoms of Fragilariopsis curta with s low sinking rates (SSP; slowly sinking particles). According to the compari son of time depth changes of these two fractions, the SSP had unexpectedly faster sinking rates comparable with the FSP during the periods of maximum fluxes. probably indicating the SSP were transformed from the FSP during si nking. The present result strongly suggests that a local bloom of F. curta and intensified zooplankton grazing activities occurred in surface layers i n a few days in the MIZ, and then the egested fecal pellets were rapidly tr ansported downward with fragmentation processes into small-sized minute par ticles in mesopelagic and bathypelagic layers.