Rare earth element and neodymium isotopes of the eastern US GEOTRACES Equatorial Pacific Zonal Transect (GP16)

Abstract Dissolved rare earth element ([REE]) and neodymium isotopic (eNd) data from the US GEOTRACES Eastern Equatorial Pacific Transect (EPZT) are presented. These data are compared to watermass distributions ( Peters et al., 2018 ), particulate data ( Lam et al., 2018 ) and carbonate species data ( Bates, 2018 ) to evaluate present theories of REE and eNd geochemistry, given that the Pacific has been notably intractable in relation to these ideas ( Jones et al., 2008 ). The [REEs] have typical depth profile distributions (e.g., [La] ranges from ∼5 to 15 pmol/kg in the surface, increasing with depth to values of ∼40 pmol/kg), as does eNd (ranging from ∼-1 to -6 eNd; similar to previous Pacific data). However, despite the unsurprising nature of these data, several apparent inconsistencies with respect to current models for REE/eNd geochemistry arise. These are: (1) While eNd remarkably maintains watermass distribution information, there is a significant (+1.4 eNd) offset in the data compared to published end-member compositions, indicating a strong but largely consistent non-conservative component; (2) Reversible scavenging seems an unlikely mechanism for redistribution of [REE] and eNd in the water column; (3) There does not appear to be any correlation of [REE] to carbonate ion concentration, and; (4) There are indications of influence from a benthic flux, but the evidence is ambiguous.