NE Atlantic zooplankton wintering in fjord habitats responds to hemispheric climate

Abstract

This study addresses how local abiotic variability links zooplankton stocks to climate systems. Four zooplankton species and abiotic environmental data were sampled annually during October and February 1983–2005 in two northern Norwegian fjord basins. Inter-decadal change in abundance occurred in both fjords but differed between the two communities, presumably resulting from combinations of topography, specific life history strategies and preference for ambient water qualities before advective migration into the habitats. The shallow Mistfjord sill led to accumulation of coastal water in the fjord basin, while the deeper Saltfjord sill allowed frequent seasonal exchange of Atlantic basin water. Changes in basin water temperature and salinity were decadal in the Mistfjord basin, and inter-annual in the Saltfjord basin. Several biotic and abiotic variables co-varied with climate indices, which indicate causal relationships between hemispheric climate variability and abundance of over-wintering zooplankton, but the processes involved are not fully understood. Tropospheric processes generating North Atlantic Oscillation apparently forced vernal freshwater discharge from Norway, summer reproduction in neritic waters and geographic distribution of basin-scale population systems. Stratospheric forcing as indicated by the Arctic Oscillation seems to be involved in geophysical relationships that influence dynamic processes in zooplankton population systems within the Arctic Mediterranean.