Reconstruction of the sedimentary history offshore NW Africa: Application of core-logging tools

Abstract

The goal of this thesis is to reconstruct, with high spatial resolution, the influence of coastal upwelling and terrigeneous input on the magnitude and composition of sediment accumulation off NW Africa, and to investigate how this influence has varied through the last glacial and interglacial periods. To achieve dense coverage for paleoceanographic reconstruction in the investigation area, a large number of sediment cores has been analyzed with rapid and non-destructive core-logging systems. The results of this thesis show that even the small region of the Canary Islands can be separated into several areas, with each reflecting its own sediment characteristics. Recent remote sensing images of chlorophyll concentration reflecting the present upwelling conditions are mirrored by the accumulation rates of the underlying sediment. The variation and distribution of the sediment accumulation rates in the past provides information about paleoceanographic features, such as upwelling conditions and sea-level fluctuations. The contribution of terrigeneous material to the marine sediments can be separated into eolian and a fluvial portions. Three characteristic areas could be delineated within the Canary Islands region. The ratio of eolian to fluvial transport of the terrigeneous material increases with wider distance to the coast. The fluvial contribution reflects river activity generally at near-coastal sites, whereas south of 30° N fluvial input occurs only during wet phases of interglacial time intervals. Holocene climate is characterized by significant environmental changes at 8,500 years B.P. in the northern part of the investigation area, whereas the abrupt change from the African humid period to modern desert environmental conditions occurred at 5,000 years B.P.. These findings document the separation of the climatic regime dominating the area north of 30° N from influences of the NW African monsoonal system further to the south.