Uranium isotope systematics of ferromanganese crusts in the Pacific Ocean: Implications for the marine 238U/235U isotope system

Uranium isotopic compositions of the crust and ocean: Age corrections, U budget and global extent of modern anoxia

“…Each sample measurement was bracketed by standards spiked to the same level as the sample. The U procedural blanks after removal of organics from the resin by drying in $0.2 mL of HNO 3 /H 2 O 2 (1:1) Goto et al, 2014;Murphy et al, 2014;Andersen et al, 2015;Goldmann et al, 2015) vary from 4 to 13 pg. This represents 0.02-0.05& of the signal measured.…”

“…Therefore, samples dated by these techniques need to have their U isotopic compositions measured (Stirling et al, 2005(Stirling et al, , 2006Weyer et al, 2008;Amelin et al, 2010;Brennecka et al, 2010b;Brennecka and Wadhwa, 2012;Connelly et al, 2012;Goldmann et al, 2015) or uncertainties on the U isotopic composition should be propagated into age calculations. (iii) In low temperature aqueous geochemistry, U isotopic fractionation between U 4+ and U 6+ (driven in part by nuclear field shift effects; Bigeleisen, 1996;Schauble, 2007;Abe et al, 2008), makes U isotopes potential tracers of paleoredox conditions (Montoya-Pino et al, 2010;Brennecka et al, 2011a;Kendall et al, 2013Kendall et al, , 2015Asael et al, 2013;Andersen et al, 2014;Dahl et al, 2014;Goto et al, 2014;Noordmann et al, 2015).…”

“…The contrasting behaviors of the two oxidation states of uranium explains why the disappearance of detrital uraninite after the Archean marks the rise of oxygen in Earth's atmosphere/hydrosphere (Ramdohr, 1958;Rasmussen and Buick, 1999;Frimmel, 2005). More recently, significant effort has focused on using U isotopes to constrain the past extents of anoxic/euxinic vs. oxic or suboxic sediments in modern and ancient oceans (Montoya-Pino et al, 2010;Brennecka et al, 2011a;Asael et al, 2013;Kendall et al, 2013Kendall et al, , 2015Andersen et al, 2014;Dahl et al, 2014;Goto et al, 2014;Noordmann et al, 2015). A virtue of this system is that it can potentially reflect the global redox state of Earth's oceans.…”

Continuous growth of hydrogenetic ferromanganese crusts since 17 Myr ago on Takuyo-Daigo Seamount, NW Pacific, at water depths of 800–5500 m

“…We tried several different radiometric dating methods for the northwest Pacific Fe-Mn crusts for crosschecking using Os-Re (Tokumaru et al, 2015) and U series (Goto et al, 2014;Yamaoka et al, …”

Combining benthic foraminiferal ecology and shell Mn/Ca to deconvolve past bottom water oxygenation and paleoproductivity

“…uranium stable isotope ratios in Fe-Mn crusts (e.g. Goto et al, 2014), but yield information of global oceanic state rather than local conditions. In foraminiferal research, bottom-water oxygen concentrations have traditionally been reconstructed using transfer functions, which are based on relative abundance of specific marker species (e.g.…”