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  • Iron  (2)
  • Geochemical cycles  (1)
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  • 1
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    Ironing out Fe residence time in the dynamic upper ocean (2020)
    American Geophysical Union
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    Publication Date: 2022-10-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Black, E. E., Kienast, S. S., Lemaitre, N., Lam, P. J., Anderson, R. F., Planquette, H., Planchon, F., & Buesseler, K. O. Ironing out Fe residence time in the dynamic upper ocean. Global Biogeochemical Cycles, 34(9), (2020): e2020GB006592, doi:10.1029/2020GB006592.
    Description: Although iron availability has been shown to limit ocean productivity and influence marine carbon cycling, the rates of processes driving iron's removal and retention in the upper ocean are poorly constrained. Using 234Th‐ and sediment‐trap data, most of which were collected through international GEOTRACES efforts, we perform an unprecedented observation‐based assessment of iron export from and residence time in the upper ocean. The majority of these new residence time estimates for total iron in the surface ocean (0–250 m) fall between 10 and 100 days. The upper ocean residence time of dissolved iron, on the other hand, varies and cycles on sub‐annual to annual timescales. Collectively, these residence times are shorter than previously thought, and the rates and timescales presented here will contribute to ongoing efforts to integrate iron into global biogeochemical models predicting climate and carbon dioxide sequestration in the ocean in the 21st century and beyond.
    Description: We would like to thank S. Albani for providing the dust model results (Community Atmosphere Model, C4fn) and the three anonymous reviewers for their constructive comments. The U.S. GEOTRACES work was supported by the National Science Foundation (OCE‐1232669 and OCE‐1518110) and E. Black was also funded by a NASA Earth and Space Science Graduate Fellowship (NNX13AP31H) and the Ocean Frontier Institute. The GEOVIDE work was funded by the Flanders Research Foundation (G071512N), the Vrije Universiteit Brussel (SRP‐2), the French ANR Blanc GEOVIDE (ANR‐13‐BS06‐0014), ANR RPDOC BITMAP (ANR‐12‐PDOC‐0025‐01), IFREMER, CNRS‐INSU (programme LEFE), INSU OPTIMISP, and Labex‐Mer (ANR‐10‐LABX‐19).
    Keywords: Thorium‐234 ; Iron ; Export ; GEOTRACES ; Residence time
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    Strong margin influence on the Arctic Ocean Barium Cycle revealed by pan‐Arctic synthesis (2022)
    American Geophysical Union
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    Publication Date: 2022-10-26
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Whitmore, L., Shiller, A., Horner, T., Xiang, Y., Auro, M., Bauch, D., Dehairs, F., Lam, P., Li, J., Maldonado, M., Mears, C., Newton, R., Pasqualini, A., Planquette, H., Rember, R., & Thomas, H. Strong margin influence on the Arctic Ocean Barium Cycle revealed by pan‐Arctic synthesis. Journal of Geophysical Research: Oceans, 127(4), (2022): e2021JC017417, https://doi.org/10.1029/2021jc017417.
    Description: Early studies revealed relationships between barium (Ba), particulate organic carbon and silicate, suggesting applications for Ba as a paleoproductivity tracer and as a tracer of modern ocean circulation. But, what controls the distribution of barium (Ba) in the oceans? Here, we investigated the Arctic Ocean Ba cycle through a one-of-a-kind data set containing dissolved (dBa), particulate (pBa), and stable isotope Ba ratio (δ138Ba) data from four Arctic GEOTRACES expeditions conducted in 2015. We hypothesized that margins would be a substantial source of Ba to the Arctic Ocean water column. The dBa, pBa, and δ138Ba distributions all suggest significant modification of inflowing Pacific seawater over the shelves, and the dBa mass balance implies that ∼50% of the dBa inventory (upper 500 m of the Arctic water column) was supplied by nonconservative inputs. Calculated areal dBa fluxes are up to 10 μmol m−2 day−1 on the margin, which is comparable to fluxes described in other regions. Applying this approach to dBa data from the 1994 Arctic Ocean Survey yields similar results. The Canadian Arctic Archipelago did not appear to have a similar margin source; rather, the dBa distribution in this section is consistent with mixing of Arctic Ocean-derived waters and Baffin Bay-derived waters. Although we lack enough information to identify the specifics of the shelf sediment Ba source, we suspect that a sedimentary remineralization and terrigenous sources (e.g., submarine groundwater discharge or fluvial particles) are contributors.
    Description: This research was supported by the National Science Foundation [OCE-1434312 (AMS), OCE-1436666 (RN), OCE-1535854 (PL), OCE-1736949, OCE-2023456 (TJH), and OCE-1829563 (R. Anderson for open access support)], Natural Sciences and Engineering Research Council of Canada (NSERC)-Climate Change and Atmospheric Research (CCAR) Program (MTM), and LEFE-CYBER EXPATE (HP). HT acknowledges support by the Canadian GEOTRACES via NSERC-CCAR and the German Academic Exchange Service (DAAD): MOPGA-GRI (Make Our Planet Great Again—Research Initiative) sponsored by BMBF (Federal German Ministry of Education and Research; Grant No. 57429828).
    Keywords: GEOTRACES ; Barium isotopes ; Geochemical cycles ; Climate ; Continental shelves
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    Radium isotopes as tracers of iron sources fueling a Southern Ocean phytoplankton bloom (2008)
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 54 (2007): 1989-1998, doi:10.1016/j.dsr2.2007.06.003.
    Description: Elevated levels of productivity in the wake of Southern Ocean island systems are common despite the fact that they are encircled by high nutrient low chlorophyll (HNLC) waters. In the Crozet Plateau region, it has been hypothesized that iron from island runoff or sediments of the plateau could be fueling the austral summer phytoplankton bloom. Here, we use radium isotopes to quantify the rates of surface ocean iron supply fueling the bloom in the Crozet Plateau region. A 1-D eddy-diffusion-mixing model applied to a 228Ra profile (t1/2 = 5.75 yr) at a station north of the islands suggested fast vertical mixing in the upper 300 m (Kz = 11-100 cm2 s- 1) with slower mixing between 300 and 1000 m (Kz = 1.5 cm2 s-1). This estimate is discussed in the context of Kz derived from the CTD/LADCP data. In combination with the dissolved Fe profile at this location, we estimated a vertical flux of between 5.6 and 31 nmol Fe m-2 d-1. The cross-plateau gradients in the short-lived radium isotopes, 224Ra (t1/2 = 3.66 d) and 223Ra (t1/2 = 11.4 d), yielded horizontal eddy diffusivities (Kh) of 39 m2 s-1 and 6.6 m2 s-1, respectively. If we assume that the islands (surface runoff) alone were supplying dissolved Fe to the bloom region, then the flux estimates range from 2.3 to 14 nmol Fe m-2 d-1. If the plateau sediments are considered a source of Fe, and conveyed to the bloom region through deep winter mixing combined with horizontal transport, then this flux may be as high as 64 to 390 nmol Fe m-2 d-1. Combined, these Fe sources are sufficient to initiate and maintain the annual phytoplankton bloom.
    Description: This work was funded by grants from the Natural Environment Research Council [NE/B502844/1] and the National Science Foundation (ANT-0443869 to M.A.C).
    Keywords: Radium isotopes ; Iron ; Productivity ; Ocean mixing ; Southern Ocean
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
    Format: application/pdf
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