Authigenic oxide Neodymium isotopic composition as a proxy of seawater; applying multivariate statistical analyses

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http://abstractsearch.agu.org/meetings/2016/FM/PP11A-2003.html
Author(s): McKinley, Claire Cecilia; Scudder, Rachel; Thomas, Deborah Jane
Author Affiliation(s): Primary:
Texas A&M University College Station, College Station, TX, United States
Volume Title: AGU 2016 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2016; American Geophysical Union 2016 fall meeting, San Francisco, CA, Dec. 12-16, 2016. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The Neodymium Isotopic composition (Nd IC) of oxide coatings has been applied as a tracer of water mass composition and used to address fundamental questions about past ocean conditions. The leached authigenic oxide coating from marine sediment is widely assumed to reflect the dissolved trace metal composition of the bottom water interacting with sediment at the seafloor. However, recent studies have shown that readily reducible sediment components, in addition to trace metal fluxes from the pore water, are incorporated into the bottom water, influencing the trace metal composition of leached oxide coatings. This challenges the prevailing application of the authigenic oxide Nd IC as a proxy of seawater composition. Therefore, it is important to identify the component end-members that create sediments of different lithology and determine if, or how they might contribute to the Nd IC of oxide coatings. To investigate lithologic influence on the results of sequential leaching, we selected two sites with complete bulk sediment statistical characterization. Site U1370 in the South Pacific Gyre, is predominantly composed of Rhyolite (∼60%) and has a distinguishable (∼10%) Fe-Mn Oxyhydroxide component (Dunlea et al., 2015). Site 1149 near the Izu-Bonin-Arc is predominantly composed of dispersed ash (∼20-50%) and eolian dust from Asia (∼50-80%) (Scudder et al., 2014). We perform a two-step leaching procedure: a 14 mL of 0.02 M hydroxylamine hydrochloride (HH) in 20% acetic acid buffered to a pH 4 for one hour, targeting metals bound to Fe- and Mn- oxides fractions, and a second HH leach for 12 hours, designed to remove any remaining oxides from the residual component. We analyze all three resulting fractions for a large suite of major, trace and rare earth elements, a sub-set of the samples are also analyzed for Nd IC. We use multivariate statistical analyses of the resulting geochemical data to identify how each component of the sediment partitions across the sequential extractions. Here we present results comparing the two sites, and examine how the composition of the sediment impacts the resulting Nd IC.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; East Pacific; Expedition 329; IODP Site U1370; Integrated Ocean Drilling Program; Leg 185; North Pacific; Northwest Pacific; ODP Site 1149; Ocean Drilling Program; Pacific Ocean; South Pacific; Southeast Pacific; West Pacific
Coordinates: S415107 S415107 W1530623 W1530623
N312030 N312030 E1432100 E1432100
Record ID: 2018010330
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