10Be and Ba concentrations in West African sediments trace productivity in the past

Autor: Augusto Mangini, Marc J.-F. Suter, G. Bonani, Beate Dittrich-Hannen, H.-J. Rutsch, Monika Segl, P. W. Kubik
Rok vydání: 1995
Předmět:
Zdroj: Earth and Planetary Science Letters. 133:129-143
ISSN: 0012-821X
DOI: 10.1016/0012-821x(95)00069-o
Popis: Particle reactive elements are scavenged to a higher degree at ocean margins than in the open ocean due to higher fluxes of biogenic and terrigenous particles. In order to determine the influence of these processes on the depositional fluxes of10Be and barium we have performed high-resolution measurements on sediment core GeoB 1008-3 from the Congo Fan. Because the core is dominated by terrigenous matter supplied by the Congo River, it has a high average mass accumulation rate of 6.5 cm/kyr. Biogenic10Be and Ba concentrations were calculated from total concentrations by subtracting the terrigenous components of10Be and Ba, which are assumed to be proportional to the flux of Al2O3. The meanBa/Al weight ratio of the terrigenous component was determined to be 0.0045. The unusualy high terrigenous10Be concentrations of 9.1 × 109 atoms/g Al2O3 are either due to input of particles with high10Be content by the Congo River or due to scavenging of oceanic10Be by riverine particles. The maxima of biogenic10Be and Ba concentrations coincide with maxima of the paleoproductivity rates. Time series analysis of the10Be and of Ba concentration profiles reveals a strong dominance of the precessional period of 24 kyr, which also controls the rates of paleoproductivity in this core. During the maxima of productivity the flux of biogenic Ba is enhanced to a larger extent than that of biogenic10Be. Applying a model for coastal scavenging, we ascribe the observed higher sensitivity of Ba to biogenic particle fluxes to the fact that the ocean residence time of Ba is approximately 10 times longer than that of10Be.
Databáze: OpenAIRE
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