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    On the estimation of deep Atlantic ventilation from fossil radiocarbon records. part I: modern reference estimates

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    Article (3.968Mb)
    Date
    2021-05-18
    Author
    Marchal, Olivier  Concept link
    Zhao, Ning  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/28631
    As published
    https://doi.org/10.1175/JPO-D-20-0153.1
    DOI
    10.1175/JPO-D-20-0153.1
    Keyword
     Atlantic Ocean; Abyssal circulation; Tracers; Inverse methods 
    Abstract
    Radiocarbon dates of fossil carbonates sampled from sediment cores and the seafloor have been used to infer that deep ocean ventilation during the last ice age was different from today. In this first of two companion papers, the time-averaged abyssal circulation in the modern Atlantic is estimated by combining a hydrographic climatology, observational estimates of volume transports, Argo float velocities at 1000 m, radiocarbon data, and geostrophic dynamics. Different estimates of modern circulation, obtained from different prior assumptions about the abyssal flow and different errors in the geostrophic balance, are produced for use in a robust interpretation of fossil records in terms of deviations from the present-day flow, which is undertaken in Part II. We find that, for all estimates, the meridional transport integrated zonally and averaged over a hemisphere, ⟨Vk⟩, is southward between 1000 and 4000 m in both hemispheres, northward between 4000 and 5000 m in the South Atlantic, and insignificant between 4000 and 5000 m in the North Atlantic. Estimates of ⟨Vk⟩ obtained from two distinct prior circulations—one based on a level of no motion at 4000 m and one based on Argo float velocities at 1000 m—become statistically indistinguishable when Δ14C data are considered. The transport time scale, defined as τk=Vk/⟨Vk⟩, where Vk is the volume of the kth layer, is estimated to about a century between 1000 and 3000 m in both the South and North Atlantic, 124 ± 9 yr (203 ± 23 yr) between 3000 and 4000 m in the South (North) Atlantic, and 269 ± 115 yr between 4000 and 5000 m in the South Atlantic.
    Description
    Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 51(6),(2021): 1842–1872, https://doi.org/10.1175/JPO-D-20-0153.1.
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    • Geology and Geophysics (G&G)
    Suggested Citation
    Marchal, O., & Zhao, N. (2021). On the estimation of deep Atlantic ventilation from fossil radiocarbon records. part I: modern reference estimates. Journal of Physical Oceanography, 51(6), 1842–1872.
     

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