Actinium and radium fluxes from the seabed in the northeast Pacific Basin

Kemnitz, Nathaniel; Hammond, Douglas E.; Henderson, Paul B.; Roy, Emilie Le; Charette, Matthew A.; Moore, Willard S.; Anderson, Robert F.; Fleisher, Martin Q.; Leal, Anne; Black, Erin; Hayes, Christopher T.; Adkins, Jess F.; Berelson, William M.; Bian, Xiaopeng

doi:10.1016/j.marchem.2022.104180

Cited by 9 publications

(24 citation statements)

References 51 publications

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“…In addition, interpretation of its distribution requires the knowledge of its 231 Pa parent distribution. As a result, the use of dissolved excess 227 Ac as an oceanic tracer has been reported in few studies to date (Dulaiova et al, 2012;Geibert et al, 2002Geibert and Vöge, 2008;Kipp et al, 2015;Le Roy et al, 2019;Koch-Larrouy et al, 2015;Nozaki, 1984Nozaki, , 1993Nozaki et al, 1990;Levier et al, 2021;Kemnitz et al, 2022). In the present study, we report nine vertical profiles of 227 Ac from a largescale section in the North Atlantic Ocean and the Labrador Sea.…”

Section: Introductionmentioning

confidence: 54%

“…It is then transported to the seafloor and thus, accumulates slowly in the sediments (Anderson et al, 1983). In the sediment, 231 Pa decays to 227 Ac which is then released to the overlying water column due to its higher solubility (Anderson et al, 1983;Nozaki, 1984;Nozaki et al, 1990;Nozaki, 1993, p.199;Geibert et al, 2002;Kemnitz et al, 2022). 227 Ac that diffuses out of the sediments is then redistributed in the ocean by transport (advection and upwelling) and mixing (Nozaki, 1984;Geibert et al, 2002;Koch-Larrouy et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

“…Nozaki (1984) proposed estimating vertical eddy diffusivity coefficients (K z ) from the 227 Ac ex vertical distribution. 227 Ac ex has also been used to estimate upwelling rates, since this process also brings 227 Ac toward the surface (Geibert et al, 2002;Haskell et al, 2015;Kemnitz et al, 2022). Finally, Kipp et al (2015) showed that hydrothermal vents constituted a source of 227 Ac to the deep Atlantic Ocean that was equivalent to ~2 -6% of the deep-sea sediment flux.…”

Section: Introductionmentioning

confidence: 99%

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The distribution of 227Ac along the GA01 section in the North Atlantic

et al. 2023

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Section: Introductionmentioning

confidence: 54%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The distribution of 227Ac along the GA01 section in the North Atlantic

et al. 2023

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“…(2015) also reported that 8%–12% of the total 227 Ac was present in the particulate phase near a hydrothermal vent in the North Atlantic Ocean, similar to the proportion of particulate La (up to 14%) in the same region (German et al., 1990). The partitioning coefficient of Ac in porewater was also observed to be 2–11 times higher than that of Ra (Kemnitz et al., 2023), indicating that Ac is much more particle‐reactive than Ra. In addition, we note that if the scavenging model assumes the particle scavenging of Ra, larger amounts of 227 Ac would have to be removed (Figure S2 in Supporting Information ).…”

Section: Resultsmentioning

confidence: 98%

New Insight Into the Source and Sink of ²²⁷Ac in the Ocean

Seo,

Lee,

Kim

2024

Geophysical Research Letters

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Actinium‐227 (227Ac) has been used as a powerful tracer of diapycnal mixing in the ocean, assuming that it is conservative and originates mainly from deep‐sea sediments. However, here we show an unexpectedly large source (continental margin) and sink (scavenging) of 227Ac in the ocean, based on high‐resolution 227Ac distributions obtained for the first time by mooring Mn‐fibers in the East Sea (Japan Sea). Although we expected a decrease in radium‐228 (228Ra) to 227Ac ratios with depth owing to their different half‐lives, the ratios increased with depth in the upper layer, indicating efficient removal of 227Ac by particle scavenging. In addition, unusually high 227Ac activities (∼15 dpm m−3) were observed in the surface layer, likely due to the horizontal transport of 227Ac‐enriched shelf water. Thus, our results suggest refining our understanding of the geochemical cycle and application of 227Ac in the ocean.

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“…A different sedimentary regime at Station 5 is also reflected by a lower bulk sediment aluminum (Al) content compared to the other stations (Figure 2d). Sediment accumulation rates vary between 0.11 cm ka −1 at Station 2 to ∼0.6 cm ka −1 at Station 5 (Kemnitz et al., 2022); these sedimentation rates are within the range characteristic of North Pacific red clays (0.05–0.6 cm ka −1 ), and higher than the average sedimentation rates of South Pacific red clays (∼0.04 cm ka −1 ) (Glasby, 1991).…”

Section: Resultsmentioning

confidence: 99%

Trace Element Geochemistry in North Pacific Red Clay Sediment Porewaters and Implications for Water‐Column Studies

Steiner,

Antler,

Berelson

et al. 2023

Global Biogeochemical Cycles

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Geochemical analyses of trace elements in the ocean water column have suggested that pelagic clay‐rich sediments are a major source of various elements to bottom‐waters. However, corresponding high‐quality measurements of trace element concentrations in porewaters of pelagic clay‐rich sediments are scarce, making it difficult to evaluate the contributions from benthic processes to global oceanic cycles of trace elements. To bridge this gap, we analyzed porewater and bulk sediment concentrations of vanadium, chromium, cobalt, nickel, copper, arsenic, molybdenum, barium and uranium, as well as concentrations of the major oxidants nitrate, manganese, iron, and sulfate in the top 30 cm of cores collected along a transect from Hawaii to Alaska. The data show large increases in porewater concentrations of vanadium, manganese, cobalt, nickel, copper, and arsenic within the top cm of the sediment, consistent with the release of these elements from remineralized organic matter. The sediments are a sink for sulfate, uranium, and molybdenum, even though conditions within the sampled top 30 cm remain aerobic. Porewater chromium concentrations generally increase with depth due to release from sediment particles. Extrapolated to the global aerial extent of pelagic clay sediment, the benthic fluxes in mol yr−1 are Ba 3.9 ± 3.6 × 109, Mn 3.4 ± 3.5 × 108, Co 2.6 ± 1.3 × 107, Ni 9.6 ± 8.6 × 108, Cu 4.6 ± 2.4 × 109, Cr 1.7 ± 1.1 × 108, As 6.1 ± 7.0 × 108, V 6.0 ± 2.5 × 109. With the exception of vanadium, calculated fluxes across the sediment–water interface are consistent with the variability in bottom‐water concentrations and ocean residence time of the studied elements.

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Actinium and radium fluxes from the seabed in the northeast Pacific Basin

Cited by 9 publications

References 51 publications

The distribution of 227Ac along the GA01 section in the North Atlantic

The distribution of 227Ac along the GA01 section in the North Atlantic

New Insight Into the Source and Sink of ²²⁷Ac in the Ocean

Trace Element Geochemistry in North Pacific Red Clay Sediment Porewaters and Implications for Water‐Column Studies

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Actinium and radium fluxes from the seabed in the northeast Pacific Basin

Cited by 9 publications

References 51 publications

The distribution of 227Ac along the GA01 section in the North Atlantic

The distribution of 227Ac along the GA01 section in the North Atlantic

New Insight Into the Source and Sink of 227Ac in the Ocean

Trace Element Geochemistry in North Pacific Red Clay Sediment Porewaters and Implications for Water‐Column Studies

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Product

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New Insight Into the Source and Sink of ²²⁷Ac in the Ocean