Contributions From Compound-specific Radiocarbon and Size Fraction-specific Th-230 Excess Data Towards Understanding of Sediment Redistribution Processes in the Panama Basin


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Gesine.Mollenhauer [ at ] awi.de

Abstract

Despite considerable efforts in the recent years, the sedimentation processes in the Eastern Equatorial Pacific, namely the Panama Basin, remain the subject of considerable uncertainty. In particular, the occurrence of lateral sediment redistribution as suggested by constant flux proxies like Th-230 excess is the subject of much debate. Th-230 excess measurements performed on bulk samples imply strong sediment focusing, leading to up to 8-fold higher accumulation than vertical flux rates. Arguments have been put forward suggesting that the assumptions behind the Th-230 excess method may not be entirely valid. In several other regions of the world, comparison of compound-specific radiocarbon ages of marine algal biomarkers with those of co-occurring coarse-grained sediment constituents like planktonic foraminifera have provided independent evidence for the occurrence of lateral supply of allochthonous, pre-aged sediment. The interpretation of those data is based on the assumption that organic biomarkers primarily reside in the fine-grained sediment fraction, which is more susceptible to resuspension and lateral transport processes than foraminifera. Here we present results from a study combining both methods to assess lateral sediment supply. Using samples from sediment cores Y69-71P and ME0005-24JC from the SW Panama Basin, we performed compound-specific radiocarbon analyses of marine phytoplankton-derived organic biomarkers (alkenones) and co-occurring planktonic foraminifera. In addition, we examined the Th-230 excess distribution in individual sediment grain size fractions of selected radiocarbon-dated horizons in both cores, testing the hypothesis that laterally advected fine-grained material contributes more strongly to the total inventory of Th-230 excess than coarse-grained material. We found higher Th-230 inventories in the smaller grain size fractions than in coarse silt and sand sized material. Down-core variations in grain-size distribution may thus partly explain the observed Th-230 excess inventory. In contrast, radiocarbon data indicate no supply of pre-aged organic matter.



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Conference (Poster)
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Not peer-reviewed
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Published
Event Details
American Geophysical Union, Fall Meeting 2008, San FranciscoDec 2008..
Eprint ID
19782
Cite as
Mollenhauer, G. , Kretschmer, S. , Kusch, S. , Mix, A. C. and Eglinton, T. I. (2008): Contributions From Compound-specific Radiocarbon and Size Fraction-specific Th-230 Excess Data Towards Understanding of Sediment Redistribution Processes in the Panama Basin , American Geophysical Union, Fall Meeting 2008, San FranciscoDec 2008. .


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