Chaetognaths are among the most abundant predators in the Southern Ocean and are potentially important components in the biological carbon pump due to the production of large, fast-sinking fecal pellets. In situ S. gazellae abundance, fecal pellet production, sinking rates, carbon content, and vertical carbon fluxes were measured at the Lazarev Sea between December 2005 and January 2006. Sagitta gazellae produce fecal pellets that sink at speeds of 33-600 m day(-1) and have carbon contents of 0.01-0.8 mg C pellet(-1). Vertical carbon flux was later compared with the total carbon flux measured at 360 m depth at the study area. Rough estimates using published seasonal abundance of S. gazellae indicate that, at 360 m depth in the Lazarev Sea, this specie may contribute 12 and 5% of the total vertical carbon flux in winter (ice-covered) and summer (ice-free), respectively. Thus, the role of chaetognaths in the downward transport of organic matter may be far more important than previously thought.