Tropical mangrove forests as a source of dissolved rare earth elements and yttrium to the ocean

Type Article
Date 2021-08
Language English
Author(s) Dang Duc Huy1, 2, Zhang Zhirou1, Wang Wei1, Oursel Benjamin3, Juillot Farid4, 5, Dupouy Cecile3, 5, Lemonnier HuguesORCID6, Mounier Stephane7
Affiliation(s) 1 : Trent School of the Environment, Trent University, Peterborough, Canada
2 : Department of Chemistry, Trent University, Peterborough, Canada
3 : Aix Marseille Université, Université de Toulon, CNRS, IRD, MIO, Marseille, France
4 : Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Sorbonne Université, UMR CNRS 7590, MNHN, ERL IRD 206, Paris, France
5 : Institut de Recherche pour le Developpement (IRD), Centre IRD Noumea, Nouvelle-Calédonie, France
6 : IFREMER, IRD, Université de la Nouvelle-Calédonie, Université de La Réunion, UMR 92200 ENTROPIE, Nouméa, Nouvelle-Calédonie, France
7 : Université de Toulon, Aix Marseille Université, CNRS, IRD, MIO, Toulon, France
Source Chemical Geology (0009-2541) (Elsevier BV), 2021-08 , Vol. 576 , P. 120278 (12p.)
DOI 10.1016/j.chemgeo.2021.120278
WOS© Times Cited 4
Keyword(s) Rare earth elements, yttrium, water stable isotopes, mangrove, estuary

Rare earth elements (REEs) and Y, or REYs, are commonly used as geochemical proxies for water chemistry, history of the continental crust and provenance studies. At the continent-ocean interface, the estuarine geochemistry of REYs is commonly thought to be driven by large-scale removal of the dissolved fraction. Consequently, contributions of river-borne dissolved REYs to the marine budget are assumed to represent a minor fraction of the total flux. Here, we report a significant release of dissolved REYs, together with a fractionation between light REEs, heavy REEs and Y, in the tropical mangrove estuaries of New Caledonia. These observations were associated with biogeochemical processes of the redox-dynamic mangrove system, rather than a possible contribution of REYs from a fresh groundwater source, based on stable water isotope compositions. These findings imply that tropical mangrove estuaries may act as a sizeable source of REYs to the ocean rather than buffer zones, at least for the dissolved fraction. We also extrapolated our data to compute the contributions of dissolved REY fluxes from the mangroves to global oceans. This preliminary calculation suggests that the mangrove system supplies 2.6-5% of global river-borne dissolved Nd, an REE with the most comprehensive mass balance. Therefore, given that the ocean mass budget of REYs remains unbalanced with fluxes missing on a global scale, considering the mangrove system as an input of oceanic mass balance models may help improve our understanding of the global distribution of REYs.

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