American Geophysical Union Become an AGU Member
Subscribe to AGU Journals		 AGU Home AGU Publications

Subscriber Access to Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 608348 bytes)

GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, VOL. 9, Q02007, doi:10.1029/2007GC001766, 2008

New constraints on the Pb and Nd isotopic evolution of NE Atlantic water masses

S. B. Muiños

Instituto Nacional de Engenharia, Tecnologia e Inovação, Departamento de Geologia Marinha, Estrada da Portela, Apartado 7586, P-2721-866, Alfragide, Portugal
Leibniz Institute for Marine Sciences, IFM-GEOMAR, Wischhofstrasse, 1-3, D-24148 Kiel, Germany


M. Frank

Institute for Isotope Geology and Mineral Resources, Department of Earth Sciences, ETH Zurich, Zurich, Switzerland


C. Maden

Institute for Particle Physics, ETH Zurich, Zurich, Switzerland


J. R. Hein

U.S. Geological Survey, 345 Middlefield Road, MS 999, Menlo Park, California 94024, USA


T. van de Flierdt

Institute for Isotope Geology and Mineral Resources, Department of Earth Sciences, ETH Zurich, Zurich, Switzerland


S. M. Lebreiro

Instituto Nacional de Engenharia, Tecnologia e Inovação, Departamento de Geologia Marinha, Estrada da Portela, Apartado 7586, P-2721-866, Alfragide, Portugal


L. Gaspar

Instituto Nacional de Engenharia, Tecnologia e Inovação, Departamento de Geologia Marinha, Estrada da Portela, Apartado 7586, P-2721-866, Alfragide, Portugal


J. H. Monteiro

Instituto Nacional de Engenharia, Tecnologia e Inovação, Departamento de Geologia Marinha, Estrada da Portela, Apartado 7586, P-2721-866, Alfragide, Portugal


A. N. Halliday

Institute for Isotope Geology and Mineral Resources, Department of Earth Sciences, ETH Zurich, Zurich, Switzerland


Abstract

Time series of lead (Pb) and neodymium (Nd) isotope compositions were measured on three ferromanganese crusts recording the evolution of NE Atlantic water masses over the past 15 Ma. The crusts are distributed along a depth profile (∼700–4600 m) comprising the present-day depths of Mediterranean Outflow Water and North East Atlantic Deep Water. A pronounced increase of the 206Pb/204Pb in the two deeper crusts starting at ∼4 Ma and a decrease in 143Nd/144Nd in all three crusts took place between ∼6–4 Ma and the present. These patterns are similar to isotope time series in the western North Atlantic basin and are consistent with efficient mixing between the two basins. However, the changes occurred 1–3 Ma earlier in the eastern basin indicating that the northeastern Atlantic led the major change in Pb and Nd isotope composition, probably due to a direct supply of Labrador Seawater via a northern route. The Pb isotope evolution during the Pliocene-Pleistocene can generally be explained by mixing between two end-members corresponding to Mediterranean Outflow Water and North East Atlantic Deep Water, but external sources such as Saharan dust are likely to have played a role as well. The Pb isotope composition of the shallowest crust that grew within the present-day Mediterranean Outflow Water does not show significant Pb isotope changes indicating that it was controlled by the same Pb sources throughout the past 15 Ma.

Received 25 July 2007; accepted 7 November 2007; published 12 February 2008.

Keywords: ferromanganese crusts; radiogenic isotopes; seawater chemistry; northeastern Atlantic; Mediterranean Outflow Water; North East Atlantic Deep Water.

Index Terms: 1040 Geochemistry: Radiogenic isotope geochemistry; 1050 Geochemistry: Marine geochemistry (4835, 4845, 4850); 4835 Oceanography: Biological and Chemical: Marine inorganic chemistry (1050).

Subscriber Access to Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 608348 bytes)

Citation: Muiños, S. B., M. Frank, C. Maden, J. R. Hein, T. van de Flierdt, S. M. Lebreiro, L. Gaspar, J. H. Monteiro, and A. N. Halliday (2008), New constraints on the Pb and Nd isotopic evolution of NE Atlantic water masses, Geochem. Geophys. Geosyst., 9, Q02007, doi:10.1029/2007GC001766.