Dissolved scandium, yttrium, and lanthanum in the surface waters of the North Atlantic: Potential use as an indicator of scavenging intensity

Abstract

Recent work has begun to elucidate the biogeochemical cycling of scandium (Sc) in the open ocean, but so far no surface distribution data have been reported of dissolved Sc, and no basin‐scale surface distributions have been reported of yttrium (Y) or lanthanum (La). This work presents basin‐wide surface Sc, Y, and La data in a section across the North Atlantic subtropical gyre (2011 GEOTRACES GA03) and investigates the potential utility of these distributions. This work uses dissolved and aerosol concentration data for La and Sc to estimate their surface ocean residence times in both the center of the oligotrophic gyre and near the African coastline. This work additionally shows that the surface distribution of Sc in the North Atlantic correlates with the shape of the gyre as inferred by isotherm depth, with lower Sc concentrations at the gyre boundaries. This pattern suggests that Sc could be drawn down by the elevated particle flux at the gyre boundaries. In this case, Sc removal could be used as an indicator of scavenging intensity. In order to account for variable input of Sc to the surface ocean, we propose normalizing the Sc distribution to that of Y or La, which are much less particle reactive and are input via dust to the surface North Atlantic in constant ratios with Sc. Such normalization improves the correlation with isotherm depth. We propose that the variations in dissolved Y/Sc and La/Sc ratios may be due to preferential Sc scavenging and could therefore indicate scavenging intensity.

Exposing the Distributions and Elemental Associations of Scavenged Particulate Phases in the Ocean Using Basin‐Scale Multi‐Element Data Sets

“…Below 300 m (i.e., after remineralization has degraded most‐biogenic V), the V:Fe ratio of ~ 5 mmol:mol observed in Fe‐oxide‐rich hydrothermal samples can be seen emerging as a lower limit for all transect Fe‐oxides by using a quasi‐mixing diagram that considers both Factor 1 and Factor 2 (biomass) abundances (Figure e). Similarly, Fe‐oxides also appear to be a potential carrier of the scavenged elements La and Y (Table , Till et al, ).…”

Dissolved Trace Metals in the Ross Sea

“…The stoichiometric relationships between dissolved (D) metals [e.g., zinc (Zn), cadmium (Cd), cobalt (Co), copper (Cu) and nickel (Ni)] and macro-nutrients {e.g., nitrate (NO 3 − ), silicate (Si(OH) 4 ), and phosphate (PO 4 3− )} indicate that their concentrations are regulated by phytoplankton uptake (de Baar, 1994;Löscher et al, 1998;Cullen and Sherrell, 2005;Cullen, 2006;Lai et al, 2008;Bruland et al, 2014;Dulaquais et al, 2014a;Wyatt et al, 2014;Saito et al, 2017;Till et al, 2017;Middag et al, 2018Middag et al, , 2019Middag et al, , 2020. For example, Zn is used for protein repair, in the enzyme alkaline phosphatase, and for the uptake of CO 2 via the enzyme carbonic anhydrase (Morel et al, 1994;Buitenhuis et al, 1999;Hu et al, 2003;Shaked et al, 2006;Montsant et al, 2007).…”

“…This difference might be due to the smaller size of Y, probably causing it to be more strongly complexed with organic ligands and therefore less susceptible to scavenging compared to La (Shannon, 1976;Nozaki, 2001;Parker et al, 2016). Rivers and dust are known sources for both elements (Till et al, 2017), however, these sources play a minor role in the Southern Ocean.…”

A Lagrangian View of Trace Elements and Isotopes in the North Pacific

“…Dissolved scandium (dSc) and thorium‐232 (d 232 Th) are both abiotic indicators of continental dust input to the ocean, as well as metal scavenging by adsorption on to particles (Hayes, Anderson, Fleisher, et al, 2013; Till et al, 2017) and can serve as abiotic analogues of the bioactive metals such as Fe. Dissolved Sc displayed profiles of about 2 pmol/kg with a slight minimum of 1.5 pmol/kg at 75‐ to 125‐m depth (Figure 8).…”