Relations between the thermocline meso and microzooplankton,chlorophyll a and primary production distributions in Lancaster Sound

Summary Primary productivity in Lancaster Sound was estimated from chlorophyll and light irradiance profiles and light saturation measurments. Mesozooplankton concentrations were measured using an in situ zooplankton counter mounted on a Batfish and with the BIONESS. Microzooplankton concentrations were estimated from samples taken with the BIONESS. The horizontal and vertical distribution of the two groups of zooplankton are described and related to the distribution of chlorophyll primary production and physical features of the Sound. A westward intrusion of Baffin Bay water along the north shore of the sound which mixed with Arctic water flowing easterly resulted in a complex physical environment in the sound. The admixing of these water masses resulted in a highly variable biological structure. The thermocline was the main physical feature that affected the depth of the chlorophyll layer and the levels of primary production, with a shallow thermocline resulting in higher primary production. The admixing of Baffin Bay water with Arctic water at different areas of the sound combined with the different times of appearance of open water resulted in the populations of Calanus hyperboreus and C. glacialis showing different age structures, the youngest being in the Arctic water at the western end of the Sound. Microzooplankton populations were concentrated at various depths depending on the species. Oithona juveniles preferred the upper 10 m when the thermocline was near the surface. Most macrozooplankton were found below the thermocline and the primary production maxium. The largest concentrations of microzooplankton were found at the western end of the Sound in the Arctic water believed to be still in the biological spring.