Marine records of environmental change in the NE Atlantic (West coast of the Iberian Peninsula) over the past 150 years- a dinoflagellate cyst perspective

The west coast of the Iberian Peninsula is part of the Canary upwelling system, one of the most productive marine areas worldwide. Here, wind-driven transport of nutrients from depth to the photic zone contributes largely to phytoplankton growth. Upwelling leads to mixing and nutrient-enrichment, favouring diatom blooms, while dinoflagellate blooms are typically restricted to warmer and more stratified waters, associated with upwelling relaxation and other stratification-inducing processes.

We have studied the sedimentary record of dinoflagellate cysts from three areas along the west coast of the Iberian Peninsula. The aim of this study was to reconstruct past environmental changes and evaluate the relative contribution of climate variability and human impact in this area, which is influenced by both river input and coastal upwelling.

A major shift in the cyst assemblages was recorded off the Douro and Lis rivers after the 1940’s. This shift included a marked increase in total cyst concentrations and Lingulodinium machaerophorum (accompanied by an increase in Operculodinium centrocarpum), previously proposed to indicate cultural eutrophication. However, this community change is also concomitant with a large excursion of the North Atlantic Oscillation (NAO) towards negative indices, unique in the context of the past ca. 150 years, which, among other effects, is related to increased river runoff. Contrary to the cyst signal registered in the two cores collected from the NW sector of the west Iberian shelf, the southernmost record shows an increase in Protoperidinioid cysts possibly related to an intensification of the upwelling.

This study indicates that the observed changes in the cyst-forming dinoflagellate community off west Iberia have been driven by regional climate variability, which exerts a large influence in water stability and nutrient availability by modulating river flow and upwelling in the area.