| |
| |
|
|
|
|
| |
 |
Circulation, biogeochemistry and carbon cycling in ocean margins
|
| |
|
|
Controls on molybdenum and uranium isotopic signatures in pore waters and sediments on continental margin off Namibia
P-M1-03-S
Zhiwei He* , CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, Anhui, China
M. O. Clarkson, Institute of Geochemistry and Petrology, Department of Earth Sciences, ETH Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland
Corey Archer, Institute of Geochemistry and Petrology, Department of Earth Sciences, ETH Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland
Derek Vance, Institute of Geochemistry and Petrology, Department of Earth Sciences, ETH Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland
Presenter Email: hezw@mail.ustc.edu.cn |
| The abundance and isotope composition of molybdenum (Mo) and uranium (U) in ancient sedimentary rocks are widely used to reconstruct the redox evolution of paleo-marine systems. The application of Mo-U systematics generally relies upon our understanding of their behavior in modern oceanic settings. However, although a broad framework currently exists for understanding the mechanisms leading to sedimentary accumulation of Mo, U and the associated isotopic fractionations, the extent of Mo and U isotope variation of sediment pore waters in ocean margin regions has not yet been examined. Here we have measured coupled Mo and U data for pore waters and sediments from 3 sites along a transect across the Namibia upwelling area (26 oS), which crosses a redox gradient in bottom water conditions. With the site becoming more reducing, the average Mo concentration in the sediments increases from 2.6 ppm to 6.5 ppm with average d98Mo increasing from 0.85‰ to 1.5‰ approaching modern seawater value (2.3‰). Meanwhile, the average U concentration in the sediments decreases from 11 ppm to 8 ppm with average d238U increasing from -0.26‰ to -0.10‰ positively shifting from the modern seawater value ( -0.40‰). The variation patterns of Mo and U concentration and isotope composition in the pore water profiles reveal that the mechanisms controlling the Mo and U signatures of the sediments are strongly dependent on the early diagenetic behaviors of Mo and U within the pore waters in context of different redox conditions. |
|
|
|
|
|
|
|
|