Holocene Paleoenvironments in the Western Mediterranean Sea: palynological evidences on the Algerian coast and climatic reconstructions

Past and present oceanographic and climatic conditions along the Algerian coast involve complex mechanisms. Atlantic Ocean surface waters enter the Mediterranean Sea by the Gibraltar strait and become the Algerian current flowing along the North African coast forming a succession of eddies. Deep-water upwelling plumes is another recurrent feature of the ocean circulation along the Algerian margin. Past vegetation changes and the role of paleohydrological changes have been poorly described in this region. This work combines palynological (pollen and dinoflagellate cysts) and biomarker data to assess changing environmental and climatic conditions over the past 14 ka BP (late glacial and Holocene) acquired from the marine core MD04-2801 (Algerian coast, 2067 m water depth, Prisma cruise).

A total of 79 samples have been analyzed over the last 14 000 years BP. Palynological and organic biomarker proxy data were used to investigate the links between past sea surface temperature (SSTs) and hydrological changes on the observed regional environmental changes documented at centennial timescale resolution. Our data indicate (i) recurrent upwelling cells during relatively dry climatic 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) an increase of fluvial discharges between 8.2 and 6 ka BP during the African Humid Period, and the concomitant colonization of coastlands by the Mediterranean forest. The comparison between our results and other western Mediterranean palynological records underlines the singularity of our results along the Algerian margin in terms of dinocyst assemblages and notably the over-representation of heterotrophic taxa. Palynological data shows direct links between continental dryness and marine hydrological conditions. Finally, we applied the Modern Analogue Technique to our pollen assemblages along the core in order to reconstruct seasonal and annual precipitations and temperatures and compare our local climatic patterns to regional climate signals at basin scale for the Holocene period.