Separating biogeochemical cycling of neodymium from water mass mixing in the Eastern North Atlantic

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

“…One positive test for REE adsorption in the oceans may be seen in conservative Arctic Ocean REE profiles where particles are near absent (Yang and Haley, 2016). We do note, however, that a counter-argument can be made in that there does not appear to be an appreciable difference in the [Nd] profiles relating to marginal sites vs. distal sites, where particle loading may be very different (German and Elderfield, 1990;Grasse et al, 2012;Goswami et al, 2014;Haley et al, 2014;Abbott et al, 2015b;Stichel et al, 2015).…”

“…The thermodynamics of desorption become even less favorable as the increasing dissolved concentration at depth would tend to push the equilibrium toward further adsorption (reiterating arguments posed by Elderfield, 1988). Moreover, given free Nd is <16% of the total dissolved Nd (Millero, 1992;Schijf et al, 2015), and surface adsorption coefficients are typically not exceptionally high (in the range of 3 to 5 onto carboxyl and moncarboxylic groups; Smith and Martell, 1989;Byrne and Kim, 1990;Ngwenya et al, 2010), the potential for REE transfer from the shallow to deep ocean via particle surface scavenging should be limited (Elderfield and Greaves, 1982;Stichel et al, 2015).…”

“…It was originally held that the REEs are input to the oceans predominantly via rivers, with potential additions via dust where such inputs are relatively high (Byrne and Sholkovitz, 1996;Greaves et al, 1999;Tachikawa et al, 1999b;Goswami et al, 2014;Dunlea et al, 2015;Stichel et al, 2015; also see Bayon et al, 2004 for the alternative view that dust is a sink term). 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).…”

“…This model implies that [Nd] should behave much like δ 13 C in the water column, wherein their distributions reflect a preformed signal modified by top-down uni-directional input additions related to POC remineralization. Available GEOTRACES data allow us to make an initial comparison of water column [Nd] and δ 13 C (Mawji et al, 2015;Stichel et al, 2015; Figure 1). We consider the comparison inconclusive; these data appear to share many similarities (e.g., at Stations 12, 24, 10, especially in the upper 1,000 m) but not everywhere (e.g., at Stations 1, 3, and 7).…”

Neodymium isotopic characterization of Ross Sea Bottom Water and its advection through the southern South Pacific

“…Filters were pre-cleaned with 1N HCl and rinsed with MilliQ water, followed by flushing with seawater prior to first use. The same sampling procedure was used on the US GEOTRACES North Atlantic cruise (GA03) and intercalibration at crossover stations shows that carry-over from the previous station does not pose a problem with the measured seawater Nd isotope values or concentrations (see Stichel et al, 2015). Following filtration, the water samples were acidified with quartz-distilled 6N hydrochloric acid (HCl) to a target pH of 3.5 for Nd isotopes and a pH of ≤2 for [Nd] analyses.…”