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  • Instability  (1)
  • Inverse modeling  (1)
  • 2015-2019  (2)
  • 1
    Publication Date: 2016-05-12
    Description: Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 30 (2015): 1470-1489, doi:10.1002/2014PA002743.
    Description: The ocean circulation modifies mixed layer (ML) tracer signals as they are communicated to the deep ocean by advection and mixing. We develop and apply a procedure for using tracer signals observed “upstream” (by planktonic foraminifera) and “downstream” (by benthic foraminifera) to constrain how tracer signals are modified by the intervening circulation and, by extension, to constrain properties of that circulation. A history of ML equilibrium calcite δ18O (δ18Oc) spanning the last deglaciation is inferred from a least-squares fit of eight benthic foraminiferal δ18Oc records to Green's function estimated for the modern ocean circulation. Disagreements between this history and the ML history implied by planktonic records would indicate deviations from the modern circulation. No deviations are diagnosed because the two estimates of ML δ18Oc agree within their uncertainties, but we suggest data collection and modeling procedures useful for inferring circulation changes in future studies. Uncertainties of benthic-derived ML δ18Oc are lowest in the high-latitude regions chiefly responsible for ventilating the deep ocean; additional high-resolution planktonic records constraining these regions are of particular utility. Benthic records from the Southern Ocean, where data are sparse, appear to have the most power to reduce uncertainties in benthic-derived ML δ18Oc. Understanding the spatiotemporal covariance of deglacial ML δ18Oc will also improve abilities of δ18Oc records to constrain deglacial circulation.
    Description: 2016-05-12
    Keywords: Oxygen isotopes ; Inverse modeling ; Deglaciation ; Tracers ; Ocean circulation ; Green's function
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 2
    American Meteorological Society
    Publication Date: 2020-02-18
    Description: Author Posting. © American Meteorological Society, 2019. 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, 49 (2), (2019): 607-630, doi:10.1175/JPO-D-18-0166.1.
    Description: The Lagrangian motion in the eddy field produced from an unstable retrograde jet along the shelf break is studied from idealized numerical experiments with a primitive equation model. The jet is initially in thermal wind balance with a cross-isobath density gradient and is not subjected to any atmospheric forcing. Over the course of the model integration, the jet becomes unstable and produces a quasi-stationary eddy field over a 2-month period. During this period, the cross-slope flow at the shelf break is characterized by along-slope correlation scales of O(10) km and temporal correlation scales of a few days. The relative dispersion of parcels across isobaths is found to increase with time as tb, where 1 〈 b 〈 2. This mixed diffusive–ballistic regime appears to reflect the combined effects of (i) the short length scales of velocity correlation at the shelf break and (ii) the seaward excursion of monopolar and dipolar vortices. Cross-slope dispersion is greater offshore of the front than inshore of the front, as offshore parcels are both subducted onshore below density surfaces and translated offshore with eddies. Nonetheless, the exchange of parcels across the jet remains very limited on the monthly time scale. Particles originating from the bottom experience upward displacements of a few tens of meters and seaward displacements of O(100) km, suggesting that the eddy activity engendered by an unstable along-slope jet provides another mechanism for bottom boundary layer detachment near the shelf edge.
    Description: The author expresses his gratitude to the researchers who contributed to the development and public dissemination of POM [for a list of contributors, see Mellor (2002) and comments in the source code]. Discussions with Kenneth Brink, Hyodae Seo, and Weifeng Zhang have been helpful. Comments provided by Kenneth Brink on a draft are gratefully acknowledged. The criticism from two anonymous reviewers allowed us to better focus the manuscript and to significantly improve its clarity. This work has been supported by Grant OCE-1556400 from the U.S. National Science Foundation.
    Description: 2020-02-18
    Keywords: Dispersion ; Eddies ; Frontogenesis/frontolysis ; Instability ; Lagrangian circulation/transport ; Jets
    Repository Name: Woods Hole Open Access Server
    Type: Article
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