Influence of the Amazon River on the Nd isotope composition of deep water in the western equatorial Atlantic during the Oligocene–Miocene transition

• Published in: Earth and Planetary Science Letters
• Main Authors: Stewart, Joseph A., Gutjahr, Marcus, James, Rachael H., Anand, Pallavi, Wilson, Paul A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2016
• Subjects: North Atlantic; Planktonic foraminifera
• Online Access: https://oceanrep.geomar.de/id/eprint/34075/; https://oceanrep.geomar.de/id/eprint/34075/1/Stewart.pdf; https://oceanrep.geomar.de/id/eprint/34075/2/Stewart_Supp.doc; https://doi.org/10.1016/j.epsl.2016.08.037

Highlights • Records of seawater εNdεNd are highly unradiogenic across the OMT at Ceara Rise. • Strong influence of Amazon particulate Nd on seawater εNdεNd at Ceara Rise. • Point-sourced riverine Nd influences seawater far from continental shelf. • Regional sedimentary Nd flux can be confused with water mass mixing signals. Abstract Dissolved and particulate neodymium (Nd) are mainly supplied to the oceans via rivers, dust, and release from marine sediments along continental margins. This process, together with the short oceanic residence time of Nd, gives rise to pronounced spatial gradients in oceanic 143Nd/144Nd ratios (εNdεNd). However, we do not yet have a good understanding of the extent to which the influence of riverine point-source Nd supply can be distinguished from changes in mixing between different water masses in the marine geological record. This gap in knowledge is important to fill because there is growing awareness that major global climate transitions may be associated not only with changes in large-scale ocean water mass mixing, but also with important changes in continental hydroclimate and weathering. Here we present εNdεNd data for fossilised fish teeth, planktonic foraminifera, and the Fe–Mn oxyhydroxide and detrital fractions of sediments recovered from Ocean Drilling Project (ODP) Site 926 on Ceara Rise, situated approximately 800 km from the mouth of the River Amazon. Our records span the Mi-1 glaciation event during the Oligocene–Miocene transition (OMT; ∼23 Ma). We compare our εNdεNd records with data for ambient deep Atlantic northern and southern component waters to assess the influence of particulate input from the Amazon River on Nd in ancient deep waters at this site. εNdεNd values for all of our fish teeth, foraminifera, and Fe–Mn oxyhydroxide samples are extremely unradiogenic (εNd≈−15εNd≈−15); much lower than the εNdεNd for deep waters of modern or Oligocene–Miocene age from the North Atlantic (εNd≈−10εNd≈−10) and South Atlantic (εNd≈−8εNd≈−8). This finding suggests that ...