.Earth and Planetary Science Letters 155 1998 15–28 Secular variation of Nd and Pb isotopes in ferromanganese crusts from the Atlantic, Indian and Pacific Oceans

• Main Authors: R. K. O’nions, M. Frank, F. Von Blanckenburg, H. -f. Ling
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1997
• Subjects: Pacific; Indian; Burton; North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.556.8087; http://www.geomar.de/fileadmin/personal/fb1/p-oz/mfrank/Onions_et_al_1998.pdf

Two ferromanganese crusts from the Indian Ocean and one from the Atlantic Ocean have been analysed for 10Ber 9Be, 143Ndr 144Nd and 208,207,206Pbr 204Pb ratios as a function of depth beneath their growth surfaces. 10Ber 9Be ratios provide growth rate estimates for these crusts between 1.55 and 2.82 mm May1 and further suggest that 87Srr 86Sr in crusts do not in any case examined so far provide reliable estimates for growth rates. A crust ALV-539 from 358N in the western N. wAtlantic has e and Pb-isotope variations indistinguishable from crust BM-1969.05 from 398N in the N. Atlantic K.W.Nd Burton, H.-F. Ling, R.K. O’Nions, Closure of the central American isthmus and its impact on North Atlantic deepwater . . x 10 10circulation, Nature London 386 1997 382–385 when Ber Be ratios are used to estimate growth rates. Both crusts provide evidence for a marked change in deepwater composition in the western N. Atlantic with a reduction in e and anNd increase in 206Pbr 204Pb from;8 Ma ago towards the present day. The two crusts from the Indian Ocean show comparatively small variations in e between y8.0 and y7.0 over the last 20 Ma and do not show the large shift in eNd Nd wseen in the Atlantic crusts. Comparison of e in the crusts analysed here with those published previously H.-F. Ling, K.W.Nd