Particulate rare earth element behavior in the North Atlantic (GEOVIDE cruise)

Abstract

Abstract. Particulate concentrations of the 14 Rare Earth Elements (PREE), yttrium, and 232-thorium were measured in 200 samples collected in the epipelagic (ca. 0–200 m) and mesopelagic (ca. 200–1500 m) zones of the North Atlantic during the GEOVIDE cruise (May/June 2014, R/V Pourquoi Pas?, GEOTRACES GA01), providing the most detailed snapshot of the PREE distribution in the North Atlantic so far. Concentrations of particulate cerium (PCe) varied between 0.2 and 16 pmol L−1, while particulate neodymium (PNd) concentrations ranged between 0.1 and 6.1 pmol L−1. Particulate ytterbium (PYb) concentrations ranged between 0.01 and 0.50 pmol L−1. In addition, this study showed that PREE distributions were also controlled by the biological production in the upper sunlit ocean and by remineralization processes in the mesopelagic area. Low surface concentrations combined with normalized PREE patterns displaying a negative Ce anomaly and HREE enrichments pointed to freshly formed biogenic particles imprinting the seawater signature. A significant relationship between biogenic silica (BSi) and PHREE was also observed in the Labrador and Irminger seas, due to the occurrence of strong diatom blooms at the sampling time. In order to identify dissolved-particulate processes independent of the ionic radius, we used PHo∕PY ratios and showed that absorption processes were predominant in the upper ocean, while adsorption processes dominated at deeper depths. This study highlighted different lithogenic fractions of PREE and dispersion depending on the shelf: off the Iberian margin, up to 100 % of the PREE were determined to have a lithogenic origin. This lithogenic input spread westward along an intermediate nepheloid layer (INL), following isopycnals up to 1700 km away from the margin. In contrast, along the Greenland and Newfoundland margins, the circulation maintained lithogenic inputs of PREE along the coasts.

Seawater‐Particle Interactions of Rare Earth Elements and Neodymium Isotopes in the Deep Central Arctic Ocean

“…Hence, it was suggested that particles introduced to surface waters by river input or biological production are removed by surface advection (Yang and Haley, 2016) and possibly recycled/remineralized in the mixed layer, minimizing export to the deeper water column. Our new [pREE] data, however, show pREEs are still present in the deeper water column and that the pREE concentration range is similar to that at several locations in the Atlantic Ocean, for which [pREE] data exist (e.g., Sholkovitz et al, 1994;Tachikawa et al, 1999;van de Flierdt et al, 2012;Garcia-Solsona et al, 2014;Lagarde et al, 2020). The pREE concentration range in this study over the entire water column at the open ocean stations (stations 50-101) is from 0.1 to 0.9 pmol/kg Nd.…”

“…All rights reserved. Elderfield (1993), Sholkovitz et al (1994), Tachikawa et al (1999), van de Flierdt et al (2012), Garcia-Solsona et al (2014) and Lagarde et al (2020); (b) particulate HREE/LREE ratios and (c) particulate Ce-anomaly of this study and Garcia-Solsona et al (2014).…”

“…Highest [pREE] are found in eutrophic areas with 0.7-10 pmol/kg pNd compared to oligotrophic areas with 0.1-0.7 pmol/kg pNd in the tropical northeastern Atlantic (Tachikawa et al, 1999). Recently, Lagarde et al (2020) reported [pNd] concentrations in the range of 0.15 to 6.08 pmol/kg in the North Atlantic (Figure 6a). Leaching or digestion methods vary in these studies, which limits the comparability, but overall it suggests that the [pREE] in these areas are of the same order of magnitude as those in the central Arctic Ocean despite previous suggestions of very low particle fluxes in the Arctic Ocean (Yang and Haley, 2016).…”

Internal tides responsible for lithogenic inputs along the Iberian continental slope

“…They observed a continuous propagation of intermediate nepheloid layers up to 2000 km away following isopycnal layers at the following depths: 180 m, 220 m, 500 m and 800 m (corresponding to potential density anomalies σ = 27.00, 27.05, 27.18 and 27.39 kg.m −3 respectively, Fig. 1b, Lagarde et al, 2020). These results suggest intense resuspension along the Iberian continental slope (further named slope, Fig.…”

“…Suspended particles were sampled between the surface and 1000m at several stations during the cruise by in situ seawater filtration. Particulate Rare Earth Elements (REE) concentrations and particulate iron concentrations (Gourain et al, 2019, Lagarde et al, 2020 measured in these suspended particles were higher close to the Iberian margin. These authors revealed that these particles contain 40% to 100% of lithogenic material.…”