Rare earth elements (REEs) in the tropical South Atlantic and quantitative deconvolution of their non-conservative behavior

Zheng, Xin-Yuan; Plancherel, Yves; Saito, Mak A.; Scott, Pete; Henderson, Gideon M.

doi:10.1016/j.gca.2016.01.018

Cited by 97 publications

(108 citation statements)

References 115 publications

(1 reference statement)

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“…Such apparent dichotomy will require further data, such as will be generated by GEOTRACES, an international study of the marine biogeochemical cycles of trace elements and their isotopes, where contemporaneous measurements of indicators of particulate scavenging (i.e., 230 Th and 231 Pa) and the REEs can be directly correlated. Despite these conflicting behavior profiles of the REEs, there is growing evidence for the conservative behavior of REEs in the South Atlantic [ Zheng et al ., ] and Gulf of Alaska [ Haley et al ., ] and we suggest that the Arctic represents another conservative REE environment.…”

Section: Discussionmentioning

confidence: 76%

“…The suggestion that the REE signature in the Canada Basin is equivalent to that of the Atlantic source waters also carries the implication that REE behavior in the Arctic Ocean is relatively conservative; REE concentrations in the intermediate and deep waters of the Arctic are more of a function of water mass mixing rather than biogeochemical processes such as reverse‐scavenging on particles. The dominance of “preformed” REE concentrations has also been observed in the Gulf of Alaska [ Haley et al ., ] as well as in the South Atlantic [ Zheng et al ., ], where “preformed” REEs are estimated to contribute >75% of the dissolved REE concentrations. In the Canada Basin, the lack of change in dissolved REE concentrations with depth and the matching signature with Atlantic intermediate waters suggest that here the “preformed” concentrations of the REEs constitute virtually 100% of the dissolved signal.…”

Section: Discussionmentioning

confidence: 99%

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The profile of the rare earth elements in the Canada Basin, Arctic Ocean

Yang

Haley

2016

Geochem Geophys Geosyst

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We analyzed the dissolved rare earth element (REE) content of three water column profiles (two shelf sites and one deep basin site) in the Canada Basin in order to better constrain the behavior of REEs in the Arctic Ocean. Dissolved concentrations of the REEs in the surface are 1.3–1.9 times higher than deep water (>500 m) concentrations, which are constant with depth (La: 19–23 pM, Nd: 14–17 pM, Yb: 4.0–4.3 pM). The dominant source of REEs to the surface waters of the Canada Basin is most likely Pacific water flowing through the Bering Strait and Chukchi Sea and/or the Mackenzie River. Dissolved REEs in the intermediate and deep waters are constant and appear to behave conservatively, allowing us to investigate this aspect of REE behavior in the oceans. Calculated deep ocean residence times of the REEs in the Canada Basin range from 450 to 700 years and match the age of these waters. We postulate that these values are likely applicable to global deep ocean reservoirs and that observed deviations from this conservative value can help to constrain nonconservative processes acting on the REEs.

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Section: Discussionmentioning

confidence: 76%

Section: Discussionmentioning

confidence: 99%

The profile of the rare earth elements in the Canada Basin, Arctic Ocean

Yang

Haley

2016

Geochem Geophys Geosyst

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“…2014). Adding additional ambiguity to the assessment of reverse scavenging is the issue of preformed REEs at depth that are likely conservative in nature Zheng et al, 2016). Such preformed REEs must be an important component of deep water REEs (at least on basinal scales), such that REE profiles cannot be taken at face value: de-convolution of the conservative and non-conservative REEs is needed for accurate interpretation (Bertram and Elderfield, 1993;Haley et al, 2014;Zheng et al, 2016).…”

Section: Modern Ocean Rees and Nd Isotopesmentioning

confidence: 99%

“…Adding additional ambiguity to the assessment of reverse scavenging is the issue of preformed REEs at depth that are likely conservative in nature Zheng et al, 2016). Such preformed REEs must be an important component of deep water REEs (at least on basinal scales), such that REE profiles cannot be taken at face value: de-convolution of the conservative and non-conservative REEs is needed for accurate interpretation (Bertram and Elderfield, 1993;Haley et al, 2014;Zheng et al, 2016). Such efforts, either using a water mass approach (e.g., Bertram and Elderfield, 1993;Grasse et al, 2012;Stichel et al, 2012Stichel et al, , 2015 or a more statistical approach (Singh et al, 2012;Haley et al, 2014;Zheng et al, 2016), are critical in evaluating the importance of scavenging on water column REEs.…”

Section: Modern Ocean Rees and Nd Isotopesmentioning

confidence: 99%

The Impact of Benthic Processes on Rare Earth Element and Neodymium Isotope Distributions in the Oceans

Haley

Abbott

et al. 2017

Front. Mar. Sci.

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Neodymium (Nd) isotopes are considered a valuable tracer of modern and past ocean circulation. However, the promise of Nd isotope as a water mass tracer is hindered because there is not an entirely self-consistent model of the marine geochemical cycle of rare earth elements (REEs, of which Nd is one). That is, the prevailing mechanisms to describe the distributions of elemental and isotopic Nd are not completely reconciled. Here, we use published [Nd] and Nd isotope data to examine the prevailing model assumptions, and further compare these data to emergent alternative models that emphasize benthic processes in controlling the cycle of marine REEs and Nd isotopes. Our conclusion is that changing from a "top-down" driven model for REE cycling to one of a "bottom-up" benthic source model can provide consistent interpretations of these data for both elemental and isotopic Nd distributions. We discuss the implications such a benthic flux model carries for interpretation of Nd isotope data as a tracer for understanding modern and past changes in ocean circulation.

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“…Within the Classical Labrador Seawater (CLSW), at 2,100 and 2,990 m, the isotopic composition is more radiogenic and constant at around −12.1 ± 0.1. From 420 m, [Nd] is constant to 2,100 m and increases from 17.5 ± 0.5 to 19.6 pmol/kg at 2,990 m. The typical increase below 2,000 m was documented in other studies in the Atlantic Ocean and most recently, based on high resolution profiles, has been attributed to a combination of increase from particle release and lateral advection of preformed REE along with reversible scavenging (Siddall et al, 2008;Stichel et al, 2015;Lambelet et al, 2016;Zheng et al, 2016). This increasing slope in [Nd] is interrupted by a sudden decrease at 3,184 m, coinciding with the upper FIGURE 2 | Vertical distribution of dissolved Nd concentration (A), Nd isotopic composition (B) and (C) mantle derived excess He (xs 3 He, Jenkins et al, 2015a).…”

Section: Vertical and Lateral Distribution Of Water Masses At Tagmentioning

confidence: 53%

TAG Plume: Revisiting the Hydrothermal Neodymium Contribution to Seawater

et al. 2018

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We present results on the distribution of ε Nd and [Nd] from the TAG hydrothermal vent field and adjacent locations collected during the GEOTRACES GA03 cruise in October 2011. Our results show that Nd isotopes directly below and above the plume do not significantly deviate from average NADW (ε Nd = −12.3 ± 0.2). Within the plume, however, isotope values are shifted slightly toward more radiogenic values up to ε Nd = −11.4. Interestingly at the same time a significant decrease in [Nd] along with rare earth element (REE) fractionation is observed, indicating enhanced scavenging within the plume despite the change in Nd isotopes. Elemental concentrations of Nd are reduced by 19.6-18.5 pmol/kg, coinciding with the maximum increase of mantle derived helium (xs 3 He) from 0.203 to 0.675 fmol/kg, resulting in an average 1.8 pmol/kg decrease in [Nd] relative to an expected linear increase with depth. The inventory loss of Nd within the plume sums up to 614 nmoles/m 2 , or 6%, if a continuous increase of [Nd] with depth is assumed. Compared to BATS and the western adjacent station USGT11-14, the local inventory loss is even higher at 10%. The tight relationship of xs 3 He increase and [Nd] decrease allows us to estimate scavenging rates at TAG suggesting 40 mol/year are removed within the TAG plume. A global estimate using power output along ocean ridges yields an annual Nd removal of 3.44 × 10 6 mol/year, which is about 71% of riverine and dust flux combined or 6-8% of the estimated global flux of Nd into the ocean. The change in Nd isotopic composition of up to 0.7 more radiogenic ε Nd values suggests an exchange process between hydrothermally derived particles and seawater in which during the removal process an estimated 1.1 mol/year of hydrothermal Nd is contributed to the seawater at the TAG site. This estimate is only 0.1% of the global Nd signal added to the ocean by boundary exchange processes at ocean margins, limiting the ability of changing the Nd isotopic composition on a global scale in contrast to the more significant estimated sink of elemental Nd in hydrothermal plumes from this study.

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Rare earth elements (REEs) in the tropical South Atlantic and quantitative deconvolution of their non-conservative behavior

Cited by 97 publications

References 115 publications

The profile of the rare earth elements in the Canada Basin, Arctic Ocean

The profile of the rare earth elements in the Canada Basin, Arctic Ocean

The Impact of Benthic Processes on Rare Earth Element and Neodymium Isotope Distributions in the Oceans

TAG Plume: Revisiting the Hydrothermal Neodymium Contribution to Seawater

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