Land-sea linkages on the Algerian Margin over the last 14 kyrs BP: climate variability at orbital to centennial timescales

Past and present environmental conditions over the Holocene along the Algerian coast involve complex atmosphere-hydrosphere-biosphere interactions and anthropogenic activities on adjacent watersheds. Atlantic Ocean surface waters entering the western Mediterranean Sea at the Gibraltar Strait leads to the Algerian Current, which flows along the North African coast in a succession of strong and large-scale eddies. Deep-water upwelling plumes are other recurrent hydrological features of the Algerian margin impacting on regional environmental features. However, vegetation and paleohydrological changes that occurred over the Holocene have not been described so far. To fill this gap, a suite of paleoclimate proxies was analysed in the marine core MD04-2801 (2,067 m water depth) at a secular-scale resolution over the last 14 kyrs BP. Terrestrial (pollen grains) and marine (dinoflagellate cysts or dinocysts) palynological assemblages, as well as sedimentological (grain-size analysis and XRD-based quantitative analysis of clay minerals) and biomarkers (alkenones and n-alkanes), were determined to explore the links between past sea surface hydrological conditions and regional environmental changes on nearby watersheds. Our data underline the unique character of our results in terms of dinocyst assemblages including the over-representation of heterotrophic dinocyst taxa (Brigantedinium spp.) signing for strong planktonic productivity in the study area. The Modern Analogue Technique applied to the new pollen and dinocyst assemblages reconstructed in this study also provides unique climatic and hydrological quantifications, respectively. We then discuss the links between dryness on land and surface hydrological conditions, and notably : (i) recurrent upwelling cells during the relatively dry climate conditions of the Younger Dryas (12.7 to 11.7 ka BP), the Early Holocene (11.7 to 8.2 ka BP) and from 6 ka BP onwards, (ii) enhanced fluvial discharges between 8.2 and 6 ka BP during the African Humid Period concomitant with the colonization of coastlands by the Mediterranean forest.