Rare earth elements in the North Atlantic, part I: Non-conservative behavior reveals margin inputs and deep waters scavenging

Abstract

Dissolved concentrations of 14 Rare Earth Elements (dREE) were measured in seawater samples collected during the GEOVIDE cruise (GEOTRACES GA01, May–June 2014) in the North Atlantic. This is the first dREE dataset produced using the manually operated self-built preconcentration system, made of eight columns of Nobias chelate PA-1® resin (Hitachi High-Technologies) in parallel. Concentration profiles differ from the typical “nutrient-like” dREE vertical distributions. Instead, we observe surface enrichment, especially close to the Iberian margin, and constant or decreasing concentrations below 500 m. An extended Optimum Multiparameter Analysis applied to the GEOVIDE section allowed disentangling the conservative signal brought by water masses from the non-conservative signal produced by inputs or subtractions along the water pathways. Results show i) strong dissolved inputs from the Iberian margin from resuspended particle dissolution, ii) that surprisingly, rather than mixing, scavenging in deep water masses is responsible for the decreasing concentrations at depth, especially in the lower North East Atlantic Deep Water and the Iceland Scotland Overflow Water, and iii) that in the Irminger and Labrador Seas, biological uptake is compensated by external inputs. The combination of lithogenic inputs from the Iberian margin, due to partial dissolution, with scavenging in deep water masses supports that mechanisms occurring at the land-ocean interface explain part of the observations of boundary exchange.