Interpretation of the paleo-primary production record in the NW African coastal upwelling system as potentially biased by sea level change

Xavier Giraud (1) , Andre Paul

1 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement

Using a regional circulation-ecosystem model subject to a set of boundary conditions that reflect present-day (PD) and Last Glacial Maximum (LGM) conditions, we investigate how changes in preformed subsurface nutrient concentrations as opposed to a local drop in sea level or increase in wind stress influence the biological productivity off the northwest African coastal upwelling area. A reduction of subsurface nutrient concentration at LGM reduced the zonally averaged primary production (PP). The sea level change modifies the shelf morphology, the upwelling circulation, and the productivity and displaces the high-productivity zone. According to our model results, the sedimentary record of PP is best explained by a simulation considering a doubled wind stress over NW Africa. We conclude that production regionally along the coast of NW Africa during the LGM may have been lower than today, despite the fact that most of the sediment cores north of 22°N show local increases in PP during the last glacial period. This paradox may be due to the sea level change and the associated eastward shift of the coastline and upwelling system.

Domaines: Océanographie

Xavier Giraud, Andre Paul. Interpretation of the paleo-primary production record in the NW African coastal upwelling system as potentially biased by sea level change. Paleoceanography, 2010, 25, pp.PA4224. ⟨10.1029/2009PA001795⟩. ⟨hal-00765326⟩