Age models of sediment cores from the North-West African continental margin

A statistical analysis ol 15 deep sea cores in the eastern North Atlantic off NW Africa revealed the typical fluctuation pattern of distinct species proups as has been described from various parts of the world ocean. Only the "WBF-group" appears to be correlated with global climatic changes, i.e. warmer periods as the Eemian and the Atlanticum. A partly antagonistic "High Productivity group" (HPR-group) is in general not linked with global changes but times of increased fertility in the surface water and the resulting flux of organic matter reaching the bottom. The groups were extracted from cluster analysis of more than 150 surface samples (HPR-group) and a factor analysis of selected cores (WBF-group). In contrast to previous studies the observed fluctuations can not be explained by drastic changes in bottom water masses, but by the pulsation of a distinct "High Productivity Patch" in space and time. At present, this patch is located below the well known upwelling area between 22° and 12° northern latitude. It shifted to the north (up to 27 °N) during the latest glacial period ( 18 ky), indicating an equivalent shift of upwelling productivity caused by advection of nutrient rich upwelling SACW-waters, probably during most of isotopic stages 2 and 3.

Sedimentology and faunal compositions of surface sediments from the southern Florida Strait

The water masses in the Florida Straits and Bahamas region are important sources for the Northern Atlantic surface ocean circulation. In this study, we analyse carbonate preservation in surface sediments located above the chemical lysocline in the Florida Straits and Bahamas region and discuss possible reasons for supralysoclinal dissolution. Calcite dissolution proxies such as the variation of the foraminiferal assemblage, Fragmentation Index, Benthic Foraminifera Index, and Resistance Index displayed a good preservation in both areas. The pteropod species Limacina inflata showed very good preservation in sediments of inter-platform channels from the Great Bahama Bank (Providence Channel, Exuma Sound) above the aragonite lysocline. Supralysoclinal aragonite dissolution, however, was observed at two water depth levels (800-1000 m and below 1500 m) in the Florida Straits. Our observations suggest that the supralysoclinal dissolution in the Florida Straits is due to the degradation of organic material. The presence of Antarctic Intermediate Water (AAIW) may be a contributing factor for the significant aragonite dissolution in 800-1000 m. The comparison of modern preservation patterns of the surface sediments with hydrographical measurements shows that the L. inflata Dissolution Index (LDX) might be an adequate proxy to reconstruct paleo-water mass conditions in an area which is highly saturated with respect to calcium carbonate.