Zooplankton and the discontinuity layer in relation to echo traces in the Oslofjord

Abstract

1. Using high amplification on the 38.5 Kc/sec. echosounder echoes from the depth of the discontinuity layer in the inner Oslofjord were mostly observable. 2. The distribution of zooplankton was analysed from samples taken with a plankton pump and tow nets. 3. The vertical distribution of zooplankton, biomass, total number and number of the different species demonstrated that such organisms were not responsible for the echoes. 4. Calculations made from hydrographic data are the bases for assuming that these special echo traces are caused by the border layer between two water masses.