Bioactive Trace Metals and Their Isotopes as Paleoproductivity Proxies: An Assessment Using GEOTRACES‐Era Data

Abstract

1. What is the modern marine distribution of this TEI system? 104 2. Which biological, chemical, and physical processes are most important for maintaining this 105 distribution? 106 3. In what form is this TEI system incorporated into sediments? 107 4. Are there clear priorities for improving the utility of this system to track paleoproductivity? 108 This structure results in some repetition of the main distributions, drivers, and sedimentary archives 109 between individual TEI systems. This redundancy is deliberate: each section can be read independently 110 without reference to other TEIs. We close our review by assessing the 'maturity' of each system based on 111 a comparison to more established productivity proxies, offer suggestions for future studies, and discuss 112 prospects for paleoproductivity reconstructions using bioactive TEI isotope systems.

Strong Margin Influence on the Arctic Ocean Barium Cycle Revealed by Pan‐Arctic Synthesis

“…In this scenario, the observed composition is the result of mixing the initial Atlantic‐derived seawater with a single source (which realistically may be the net composition of multiple sources). This calculation assumes no mechanism for the additional source (or net isotopes of several sources); however, a δ 138 Ba source of ∼0.06‰ is consistent with pelagic barite derived from surface waters possessing a δ 138 Ba ≈ 0.5, assuming a Ba isotope fractionation during barite precipitation of roughly −0.5‰ (Horner et al., 2021 ).…”

“…Geochemical tracers have played a central role in unraveling the distributions of water types within the Arctic Ocean, though nonconservative processes have often complicated interpretations (e.g., Whitmore et al., 2020 and references therein). Barium (Ba) is a widely applied tracer of biogeochemistry and has been used as a tracer of freshwater inputs (e.g., Guay et al., 2009 ), mixing (e.g., Hsieh & Henderson, 2017 ), and paleoceanographic conditions (e.g., Horner et al., 2021 ). The distribution of dissolved Ba (dBa) in the Arctic Ocean is unique in that high concentration, river‐derived dBa can be observed in the surface (Guay et al., 2009 ; Guay & Falkner, 1997 ).…”

Dissolved and Particulate Barium Distributions Along the US GEOTRACES North Atlantic and East Pacific Zonal Transects (GA03 and GP16): Global Implications for the Marine Barium Cycle

“…With an estimated inventory of ∼150 Tmol, the residence time of dBa in the ocean is ∼8.5 ky (Dickens et al., 2003; Paytan et al., 1996). Considering present‐day approximations, the estimated stable Ba isotopic compositions of sources and sinks of Ba imply an imbalance in the conceptual marine budget, where purported sources are significantly enriched in the heavier stable isotope than major sinks (Bridgestock et al., 2018; Cao et al., 2016, 2020; Horner & Crockford, 2021; Horner et al., 2021; Hsieh & Henderson, 2017; Mayfield et al., 2021). Evidence suggests that there should be one or more sources with a light isotopic signature to balance the budget, unaccounted sinks with a heavy isotopic signature, or a combination of both.…”

Earth system science applications of next-generation SEM-EDS automated mineral mapping

“…Frontiers in Earth Science frontiersin.org isotopic analytical techniques largely rely on operationally defined recovery methods such as sequential leaching to infer the target phase rather than direct observation (Du et al, 2016;Abbott et al, 2019;Horner et al, 2021). We explore the importance of constraining the context of geochemical records by considering two recent studies which combined SEM-EDS mineral mapping with traditional sediment leaching.…”