DtflD-.K"a Re~tu~rh. Vol 38. No. I0. PP. L.'M.I-I~L 1~'I1. 01~a,--Ol4qV~l $3.1111 ~,. 0AIO Pllnted m Great BrtUun. ~ 1991 Pergamon Pre-..t ok: Sedimentation of pteropods in the Norwegian Sea in autumn ULRICH V. BATHMANN,* TOM T. NoJli" and Booo VON BODUNGEN~ (Received 8 June 1990: in revised form 9 Januarv 1991: accepted 15 January 199 l) Abstraet--Pteropod vertical distribution on the Voting Plateau (eastern Norwegian Sea) was recorded during a 3 week drifting experiment during August 1988. Parallel to sampling of hydrographical, chemical and biological properties of the water column, sediment traps recorded vertical pelagic flux at five depth strata. Pteropods (Limacina retroversa) dominated the zooplank- ton and reached maximum values (>!3.600 individuals m -~) in the upper 25 m of the water column: the size spectrum shifted from small (< l ram) towards large (>3 ram) specimens during the study. Vertical flux at 100 m depth increased from 6110mg dry weight m-" day- I to 1(100tug dry weight m-: day- I at the end of the experiment. Trap material during the first sampling intervals consisted primarily of phytoplankton and protozoans aggregated within pteropod feeding nets. Thereafter, the increase in flux rates wits associated with empty shells of pteropods in the size class 1-3 mm indicating mortality prior to mass sinking. Particle flux during the investigation period totalled 0.2 g organic C m-2 and [ .4 g carbonate m-: equivalent to 8 and 15% of annual flux recorded in the area in 1988. Through their feeding, reproduction and subsequent mortality ptcropods were the main contributors to vertical particle flint in the eastern Norwegian Sea during 1988. INTRODUCTION LONG-TERM records of vertical particle flux in the Norwegian Sea demonstrate that the annual cycle of pelagic sedimentation is related to successional patterns within the pelagic community with peak fluxes during summer and autumn (BaTtIMANN et al., 1990). In the central Atlantic spring maxima characterize annual flux patterns (Deoseg, 1987); appar- ently biological factors are responsible for the shift of the annual maxima to other seasons in the eastern Norwegian Sea. Grazing of copepods was shown to prevent development of a phytoplankton spring bloom and its subsequent sedimentation (PeI~ERT et al., 1987). A few weeks later the ontogenctic downward migration of these copepods enhanced vertical faecal pellet flux (BATHmAtS et al., 1987) which triggered increased respiration at the sea- floor (GRaF, 1989). The high autumn flux rates in the eastern Norwegian Sea (HoNJo etal., 1988; BATHmANN et al., 1990) coincide with the annual maximum abundance of the euthecosomateous pteropod Lhnacbm retroversa (WlaORG, 1955; NoJL 1989). The population originates from surface waters of the North Atlantic (REDFIELD, 1939; ~STVEDT, 1955) where they arc "Alfrcd-Wcgencr-lnstitut fiir Polar- und Mccrcsforschung. 285 Brcmcrhavcn, F.R.G. tlnstitutc of Marine Research, P.O. Box 1870-Nordncs, N-5(}24 Bergen. Norway. :[:Sondcrforschungsbcrcich 313, Univcrsitfit Kicl, 23 Kicl 1, F.R.G. 1341