From the subtropics to the central equatorial Pacific Ocean: Neodymium isotopic composition and rare earth element concentration variations

Abstract

[1] Neodymium isotopic compositions (e Nd ) and rare earth element (REE) concentrations were measured for filtered surface to deep waters (112 samples) in the Southern Tropical Pacific. The relatively detailed picture of these tracer distributions allowed us to refine the areas where oceanic e Nd variations occur. e Nd values increase for most of the water masses flowing from Samoa to the Solomon Sea and in the Papua New Guinea (PNG) area, as already observed. Furthermore, water masses arriving from the eastern equatorial Pacific (200-550 m depth) also revealed radiogenic values, possibly acquired in the vicinity of the South American coasts and Galapagos Islands. These e Nd variations affect the whole water column. The most likely process causing such variations is "boundary exchange" between the numerous radiogenic slopes/margins located in this area and seawater flowing past. Dissolution of atmospheric deposition and/or diffuse streaming of volcanic ash are also suggested to explain the radiogenic e Nd observed at the surface in the PNG area. Interestingly, a positive europium (Eu) anomaly characterizes the normalized REE patterns of most of the studied water masses. This anomaly is consistent with the REE patterns of sediment and rock samples that are potential sources for the local waters. Such consistency reinforces the hypothesis that lithogenic sources play a major role in the oceanic REE budget, thanks to "boundary exchange." The data set presented here is a good basis for further sampling that will be realized in the framework of the ongoing GEOTRACES program (www.geotraces.org).

The Impact of Benthic Processes on Rare Earth Element and Neodymium Isotope Distributions in the Oceans

“…Budgetary estimates from diffuse benthic REE fluxes, such as SGD or from sedimentary pore water Greaves et al, 1999;Haley and Klinkhammer, 2003;Tachikawa et al, 2003;Johannesson and Burdige, 2007;Schacht et al, 2010;Johannesson et al, 2011Johannesson et al, , 2017Abbott et al, 2015a;Fröllje et al, 2016), suggest that they may dominate the flux of REEs to the oceans. Importantly, such diffuse, or at least hard to quantify, sources are consistent with deep-water isopycnal mixing of ε Nd signals off margins that cannot be explained through surface water sources (Grasse et al, 2012;Grenier et al, 2013). However, while a diffuse benthic source of Nd appears to better describe the dominant flux of REEs to the ocean, outstanding questions remain.…”

“…More recently, the emphasis of REE input to the oceans has shifted to greater consideration of a benthic continental margin source for REEs, as we will discuss further later (Spivack and Wasserburg, 1988;Jeandel et al, 1998;Goldstein and Hemming, 2003;Tachikawa et al, 2003;Arsouze et al, 2009;Rickli et al, 2009Rickli et al, , 2010Rickli et al, , 2014Carter et al, 2012;Grasse et al, 2012;Singh et al, 2012;Grenier et al, 2013;Wilson et al, 2013;Garcia-Solsona et al, 2014).…”

Rare earth element distribution in the Atlantic sector of the Southern Ocean: The balance between particle scavenging and vertical supply

“…Rempfer et al, 2011). A number of studies have recently contributed to filling these data gaps (see Lacan et al, 2012 for the global database before most of these new efforts; Grenier et al 2013;Haley et al, 2014;Osborne et al, 2014;Molina-Kescher et al, 2014), many of which were conducted within the framework of the international GEOTRACES program, (Singh et al, 2012;Stichel et al, 2012a, b;Chen et al, 2013b;Garcia-Solsona et al, 2014, Goswami et al, 2014. However, not all of these studies reported the complete set of REEs thus not exploring their full potential.…”

Diatoms spread a high ^|^epsilon;Nd-signature in the North Pacific Ocean

“…Some recent observational studies promote Papua New Guinea as a typical area of boundary exchange of the high ε Nd sources to the Central Pacific Ocean (Amakawa et al, 2013;Grenier et al, 2013). This may be correct, but the involvement of diatoms cannot be ruled out, considering the higher ε Nd values near the surface and the depth of anomalous silica concentration.…”