TY - JOUR
T1 - Pelagic clays as archives of marine iron isotope chemistry
AU - Dunlea, Ann G.
AU - Tegler, Logan A.
AU - Peucker-Ehrenbrink, Bernhard
AU - Anbar, Ariel D.
AU - Romaniello, Stephen J.
AU - Horner, Tristan J.
N1 - Funding Information:
The authors acknowledge fruitful discussions with Sune Nielsen and Silke Severmann, laboratory assistance from Maureen Auro, and the MC-ICP-MS expertise of Jurek Blusztajn and Wang Zheng. This research used samples and data provided by the Integrated Ocean Drilling Program (IODP). This project was funded by NSF grants to A.D.A. and S.J.R. as well as A.G.D., T.J.H., and B.P.E. Additional funding was provided by the WHOI Summer Student Fellowship Program (L.A.T.), ASU NASA Space Grant (L.A.T.), and the National Science Foundation Graduate Research Fellowship (Grant # 1122374 ; L.A.T).
Funding Information:
The authors acknowledge fruitful discussions with Sune Nielsen and Silke Severmann, laboratory assistance from Maureen Auro, and the MC-ICP-MS expertise of Jurek Blusztajn and Wang Zheng. This research used samples and data provided by the Integrated Ocean Drilling Program (IODP). This project was funded by NSF grants to A.D.A. and S.J.R. as well as A.G.D. T.J.H. and B.P.E. Additional funding was provided by the WHOI Summer Student Fellowship Program (L.A.T.), ASU NASA Space Grant (L.A.T.), and the National Science Foundation Graduate Research Fellowship (Grant #1122374; L.A.T).
Publisher Copyright:
© 2021 Elsevier B.V.
PY - 2021/8/5
Y1 - 2021/8/5
N2 - Slowly accumulating pelagic clays are enriched in metals that were formerly in seawater, including iron, an important micronutrient. Because the metals are minimally remobilized in oxygenated porewater, pelagic clays may be a potential archive for records of past marine micronutrient cycling. Here, we present a record of changes in hydrogenous iron (Fe) isotopes since the late Cretaceous derived from pelagic clays that we dated with osmium isotope chronostratigraphy. To optimize the separation of the hydrogenous metal (oxy)hydroxides from bulk sediment, we repeatedly leached an oxic pelagic clay sample under variable conditions (HCl molarity, temperature, time) and measured the element concentrations, Fe isotopes, and Os isotopes. The common behavior of elements amidst the permutations of the leach experiment offers insight into which components were dissolved and we defined a range of successful leaches. We applied our optimal leach for Fe and Os isotopes (1 M HCl, for 24 h at 20 °C) to 45 samples at Site U1366 in the South Pacific Gyre. The resulting record suggests a dynamic Fe cycle in the water column overlying Site U1366 over the past 95 million years. Early in the site's history, trends in the Fe isotopes are interpreted as reflecting changes in hydrothermal Fe with distance from the ridge. Contributions from a background Fe source are identified as well as a transition to dust-like source after 50 Ma until present. Constructing similar records at multiple sites will provide a basin-wide perspective on how the marine Fe cycle has changed over million-year timescales.
AB - Slowly accumulating pelagic clays are enriched in metals that were formerly in seawater, including iron, an important micronutrient. Because the metals are minimally remobilized in oxygenated porewater, pelagic clays may be a potential archive for records of past marine micronutrient cycling. Here, we present a record of changes in hydrogenous iron (Fe) isotopes since the late Cretaceous derived from pelagic clays that we dated with osmium isotope chronostratigraphy. To optimize the separation of the hydrogenous metal (oxy)hydroxides from bulk sediment, we repeatedly leached an oxic pelagic clay sample under variable conditions (HCl molarity, temperature, time) and measured the element concentrations, Fe isotopes, and Os isotopes. The common behavior of elements amidst the permutations of the leach experiment offers insight into which components were dissolved and we defined a range of successful leaches. We applied our optimal leach for Fe and Os isotopes (1 M HCl, for 24 h at 20 °C) to 45 samples at Site U1366 in the South Pacific Gyre. The resulting record suggests a dynamic Fe cycle in the water column overlying Site U1366 over the past 95 million years. Early in the site's history, trends in the Fe isotopes are interpreted as reflecting changes in hydrothermal Fe with distance from the ridge. Contributions from a background Fe source are identified as well as a transition to dust-like source after 50 Ma until present. Constructing similar records at multiple sites will provide a basin-wide perspective on how the marine Fe cycle has changed over million-year timescales.
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U2 - 10.1016/j.chemgeo.2021.120201
DO - 10.1016/j.chemgeo.2021.120201
M3 - Article
AN - SCOPUS:85105355808
SN - 0009-2541
VL - 575
JO - Chemical Geology
JF - Chemical Geology
M1 - 120201
ER -