The use of foraminifera as a record of the past neodymium isotope composition of seawater

Abstract

[1] We present new isotopic data for sedimentary planktonic foraminifera, as well as for potential water column and sedimentary sources of neodymium (Nd), which confirm that the isotopic composition of the foraminifera is the same as surface seawater and very different from deep water and sedimentary Nd. The faithfulness with which sedimentary foraminifera record the isotopic signature of surface seawater Nd is difficult to explain given their variable and high Nd/Ca ratios, ratios that are often sedimentary foraminifera, ratios that are often much higher than is plausible for direct incorporation within the calcite structure. We present further data that demonstrate a similarly large range in Nd/Ca ratios in plankton tow foraminifera, a range that may be controlled by redox conditions in the water column. Cleaning experiments reveal, in common with earlier work, that large amounts of Nd are released by cleaning with both hydrazine and diethylene triamine penta-acetic acid, but that the Nd released at each step is of surface origin. While further detailed studies are required to verify the exact location of the surface isotopic signature and the key controls on foraminiferal Nd isotope systematics, these new data place the use of planktonic foraminifera as recorders of surface water Nd isotope ratios, and thus of variations in the past supply of Nd to the oceans from the continents via weathering and erosion, on a reasonably sure footing.

Vertical distribution of scandium in the north central Pacific

“…Although intensive studies have investigated the North Pacific, almost no data related to seawater have been reported for the north central Pacific region near the Hawaiian Islands. Vertical distributions of Ln reported so far were only those for Nd and Sm, whose vertical profiles were compiled from data obtained at various stations close to the HOT station [Vance et al, 2004]. The Nd concentrations at BO-3 station and the various stations show the same range in values at depths of less than 3000 m ( Figure S2).…”

Neodymium isotopic composition of the oceans: A compilation of seawater data

“…All seawater Nd IC data published up to September 2011 to our knowledge are reported here [Piepgras et al, 1979;Piepgras and Wasserburg, 1980, 1982, 1983Stordal and Wasserburg, 1986;Piepgras and Wasserburg, 1987;Piepgras and Jacobsen, 1988;Spivack and Wasserburg, 1988;Bertram and Elderfield, 1993;Jeandel, 1993;Henry et al, 1994;Shimizu et al, 1994;Jeandel et al, 1998;Tachikawa et al, 1999;Amakawa et al, 2000;Lacan and Jeandel, 2001;Lacan, 2002;Amakawa et al, 2004aAmakawa et al, , 2004bLacan and Jeandel, 2004a, 2004cTachikawa et al, 2004;Vance et al, 2004;Dahlqvist et al, 2005;Lacan andJeandel, 2005a, 2005b;Tazoe et al, 2007aTazoe et al, , 2007bAndersson et al, 2008;Amakawa et al, 2009;Godfrey et al, 2009;Porcelli et al, 2009;Rickli et al, 2009;Zimmermann et al, 2009aZimmermann et al, , 2009bRickli et al, 2010;Copard et al, 2011;Tazoe et al, 2011]. When Nd concentration is also available, it is also reported.…”

A boundary exchange influence on deglacial neodymium isotope records from the deep western Indian Ocean

“…Bayon et al, 2002;Gutjahr et al, 2007;Martin et al, 2010), but may not reliably recover bottom water compositions in all locations. This has been variously attributed to the presence of continental 'preformed' ferromanganese oxides (Bayon et al, 2004;Bayon et al, 2009), the downslope transport of authigenic ferromanganese oxides Stumpf et al, 2010), or the laboratory leaching of detrital volcanic material (Vance et al, 2004;Roberts et al, 2010;Elmore et al, 2011). Therefore, we additionally measured the ε Nd composition of uncleaned planktonic foraminifera, which have been cleaned of detritus but not chemically cleaned; in this case, given the low Nd concentration in biogenic calcite, a mass balance dictates that their ε Nd composition should be dominated by authigenic ferromanganese oxide coatings derived from bottom water (Palmer, 1985;Palmer and Elderfield, 1986;Pomies et al, 2002;Roberts et al, 2010).…”