Extracting foraminiferal sea water Nd isotope signatures from bulk deep sea sediment by chemical leaching

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doi: 10.1016/j.chemgeo.2016.06.024
Author(s): Blaser, Patrick; Lippold, Jörg; Gutjahr, Marcus; Frank, Norbert; Link, Jasmin M.; Frank, Martin
Author Affiliation(s): Primary:
Heidelberg University, Institute of Environmental Physics, Heidelberg, Germany
Other:
University of Bern, Switzerland
GEOMAR-Helmholtz Centre for Ocean Research, Germany
Volume Title: Chemical Geology
Source: Chemical Geology, Vol.439, p.189-204. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0009-2541 CODEN: CHGEAD
Note: In English. Includes appendices. 127 refs.; illus., incl. 1 table, sketch map
Summary: The seawater radiogenic neodymium (143Nd/144Nd) isotope signature is an invaluable tool for the reconstruction of past deep water provenance. Sedimentary foraminifera or fish teeth are among the most reliable archives known for Nd isotope based reconstructions of past seawater. As the distribution and preservation of these archives are limited, the extraction of hydrogenetic ferromanganese oxyhydroxides from bulk sediments provide an easily applicable alternative. This method, however, implies the risk of generating artefacts due to the possible release of non-seawater derived Nd during the extraction procedure. Here we revisit and further investigate the reliability of the extraction of seawater derived Nd isotope signatures via leaching of bulk deep sea sediments with two commonly used buffered acetic acid and acid-reductive mix solutions. Repeated application of such stepwise leaching procedures to different non-decarbonated sediments from distinct settings across the deep Atlantic Ocean shows pronounced elemental and Nd isotope trends during the leaching process in the laboratory. Our results show that seawater Nd isotope compositions are extracted together with carbonates and manganese oxides only at the beginning of the leaching series. During chemical extraction, the carbonates effectively work as a buffer preventing acid-induced mobilisation of Fe oxides and volcanogenic material. Once this buffer is consumed, potentially present volcanogenic phases are considerably attacked, leading to shifts in the extracted Nd isotope signal of up to + 12 epsilon units. Such volcanogenic phases are a significant source of contaminant Nd reflected by markedly elevated Al/Nd signatures. We consequently propose a revised weak leaching protocol for carbonate bearing deep sea sediments, which is simple to use, provides excellent agreement with data obtained from uncleaned foraminifera, and can be easily screened for contamination.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 02 Geochemistry; 06 Petrology, Sedimentary; Atlantic Ocean; Cenozoic; Crystal chemistry; Deep-sea sedimentation; Diagenesis; Early diagenesis; Expedition 303; Expedition 306; Expeditions 303/306; Ferromanganese composition; Foraminifera; Holocene; Hydroxides; ICP mass spectra; IODP Site U1302; IODP Site U1304; IODP Site U1308; IODP Site U1313; Integrated Ocean Drilling Program; Invertebrata; Isotope ratios; Isotopes; Laboratory studies; Leaching; Marine sedimentation; Marine sediments; Mass spectra; Metals; Microfossils; Mid-Atlantic Ridge; Nd-144/Nd-143; Neodymium; North Atlantic; Northeast Atlantic; Northwest Atlantic; Oxides; Paleo-oceanography; Paleoenvironment; Protista; Provenance; Quaternary; Rare earths; Sea water; Sedimentation; Sediments; Spectra; Stable isotopes; Volcaniclastics
Coordinates: N495300 N495300 W0241400 W0241400
Record ID: 2016081406
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands