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Special Session 4: Biogeochemical cycling of trace elements in the ocean: GEOTRACES and beyond |
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Cycling of rare earth elements (REEs) in the South Atlantic
Monday 9th @ 1115-1135
Room 4
Xin-Yuan Zheng* , Department of Geoscience, University of Wisconsin-Madison
Peter Scott, Department of Earth Sciences, University of Cambridge
Yves Plancherel, Department of Earth Sciences, University of Oxford
Gideon Henderson, Department of Earth Sciences, University of Oxford
Presenter Email: xzheng75@wisc.edu
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| Rare earth elements (REEs) and their isotopes, particularly, Nd isotopes, have been used extensively to trace a wide range of processes in modern and past oceans, but a full appreciation of their strengths and limitations as geochemical tracers is still limited by the incomplete understanding of REE cycling in the modern ocean. This is exemplified notably by the poor constraint on REE fluxes at the continent¨Cocean interface, and the so-called ˇ°Nd paradoxˇ±¨Cthe apparent inconsistency between nutrient-like Nd concentration profiles and circulation-controlled Nd isotope composition profiles in seawater. In contrast to the majority of early studies that were focused on local cycling of REEs, the growing REE dataset acquired through the effort of GEOTRACES program provides an opportunity to investigate the REE cycling on the basinal to global scale. Here we will present results of dissolved REE concentrations from two full-depth, east-west sections along ~12ˇăS (CoFeMUG, GAc01)[1] and ~40ˇăS (UK GEOTRACES GA 10) in the South Atlantic, and demonstrate how the relative contribution of physical transport (i.e., preformed) and biogeochemical regeneration in controlling the REE cycle in the South Atlantic can be quantified for the first time using the new dataset and a multi-parameter mixing model that we have developed. Our results show that the preformed REEs are the dominant component in the deep South Atlantic, and small but significant non-conservative REEs concentrations can be found and quantified near the continent¨Cocean interface. The unique geochemical properties of REEs allow for tracing of sources for the observed non-conservative behaviors. These results significantly improve our understanding of REE cycling in the South Atlantic. With increasing, publically-available trace-element data through the GEOTRACES Intermediate Data Product (IDP), the modeling technique developed here can be also useful in studying marine cycling of trace elements beyond REEs.
Reference
[1] Zheng et al., GCA, 2016
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