Dominance of benthic flux of REEs on continental shelves: implications for oceanic budgets

Abstract

Rare earth elements (REEs) are powerful tools to track oceanic biogeochemical processes. However, our understanding of REE sources is incomplete, leading to controversial interpretations regarding their oceanic cycling. Continental margin sediments are often assumed to be a major source, but the sediment pore water data required to understand the processes controlling that potential source are scarce. Here, we measure and compile pore water and estuarine REE data from the Changjiang (Yangtze) estuary-East China Sea shelf. We show that release of REEs, from shallow pore water to overlying seawater, is coupled to Mn reduction. In contrast, REEs are removed in deep pore water, perhaps via formation of an authigenic REE-bearing phase. This sedimentary source can potentially explain REE addition in the estuary at mid-high salinity. Our calculations suggest that the benthic flux is the largest Nd source (∼40 %) on the East China Sea shelf. Globally, however, despite a higher benthic Nd flux on the advection-dominated shelf, the much more extensive deep ocean still dominates the total area-integrated benthic flux. Our results call for a more extensive investigation of the magnitude of the benthic flux of REEs to the oceans.

Simulating marine neodymium isotope distributions using Nd v1.0 coupled to the ocean component of the FAMOUS–MOSES1 climate model: sensitivities to reversible scavenging efficiency and benthic source distributions

“…This suggests that perhaps too much emphasis has been put on a widespread abyssal benthic flux to resolve the Nd paradox, and it may be that shallower and marginal regions pose a larger in magnitude and more distinct Nd source to seawater as opposed to an open-ocean benthic source. Recent pore water measurements by Deng et al (2022) on the East China continental shelf revealed larger benthic fluxes across the dynamic hydraulic environment of the continental shelf compared to deep pore water, which acted as a sink, likely due to authigenic precipitation. As such, spatial variations in the benthic flux are likely affected by multiple complex depth-related processes, although deep-ocean regions may still dominate the total area-integrated benthic flux.…”

“…The decoupled nature of marine [Nd] and ε Nd , which is yet to be fully understood, and new emerging observations (e.g. Stichel et al, 2020;Lagarde et al, 2020;Paffrath et al, 2021;Deng et al, 2022) emphasise the critical need to progress our understanding of modern marine Nd cycling in the light of continued use of ε Nd as a valuable tracer of ocean circulation. In this context, Nd-isotopeenabled ocean models remain an effective way to understand seawater measurements and to progress with testing and constraining processes governing marine Nd cycling, which can then feedback key information to the wider GEOTRACES and ocean tracer modelling community.…”

Dominance of benthic fluxes in the oceanic beryllium budget and implications for paleo-denudation records

“…Overlying bottom water was first drained and filtered. Pore-water was separated using methods previously described in detail ( 31 , 50 ) at ~cm resolution, either by centrifuging sliced core sediment under anaerobic conditions followed by filtration (Baltic Sea samples: 0.2-μm filters and Mexico-California margin samples: 0.45-μm filters) or by in situ extraction via precleaned Rhizon samplers (East China Sea samples: 0.15-μm filters). Water samples were acidified for storage (pH ≤ 2).…”

“…We developed a procedure that can separate three components, which are, salt matrix, Be, and other trace metals such as REE on the same sample, optimizing the usage of precious pore-water samples. To do so, we coupled a well-established REE preconcentration protocol ( 50 , 51 ) with an additional procedure for the preconcentration of Be from the remaining seawater matrix ( 14 , 52 ).…”

Rare earth elements in aeolian loess sediments from Menyuan Basin, northeastern Tibetan plateau: Implications for provenance

“…frontiersin.org proxies to reveal the source, genesis, and sedimentary environment (Jiang et al, 2019;Gallello et al, 2021;Romero et al, 2021;Zhang X et al, 2021;Deng et al, 2022a).…”