Actual timing of neodymium isotopic variations recorded by Fe-Mn crusts inthe western North Atlantic

Hydrogenetic ferromanganese (Fe-Mn) crusts from the western North Atlantic record variations in the Nd and Pb isotopic composition of Cenozoic deep wa ter preserved during their growth. The timing and cause of the most strikin g change have been the subject of debate. Some have proposed that the shift took place after 4 Ma in response to the closure of the Panama gateway. Ot hers have argued that the major change in isotope composition occurred as e arly as 8 Ma. This study presents high-resolution Nd isotope records fbr cr usts previously dated using Be-10/Be-9 chronology. These data confirm that the shifts in Nd occurred after 4 Ma, consistent with a likely relationship with the closure of the Central American Isthmus and intensification of No rthern Hemisphere Glaciation, and in accordance with changes seen in other physical and chemical records. These results illustrate the need for both a robust chronological framework and high-resolution records before a reliab le paleoceanographic interpretation can be made of the variations recorded by Fe-Mn crusts. (C) 1999 Elsevier Science B.V. All rights reserved.