Sedimentation of pteropods in the Norwegian Sea in autumn

Abstract

Pteropod vertical distribution on the Vøring Plateu (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 zooplankton and reached maximum values (>13,600 individuals m −3) in the upper 25 m of the water column; the size spectrum shifted from small (< 1 mm) towards large (> mm) specimens during the study. Vertical flux at 100 m depth increased from 600 mg dry weight m −2 day −1 to 1000 mg dry weight m −2 day −1 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 was 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 Cm −2 and 1.4 g carbonate m −2 equivalent to 8 and 15% of annual flux recorded in the area in 1988. Through their feeding, reproduction and subsequent mortality pteropods were the main contributors to vertical particle flux in the eastern Norweigian Sea during 1988.