Homoky William B.

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William B.

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  • Article
    Eddy-driven sediment transport in the Argentine Basin : is the height of the Zapiola Rise hydrodynamically controlled?
    (John Wiley & Sons, 2015-03-27) Weijer, Wilbert ; Maltrud, Mathew E. ; Homoky, William B. ; Polzin, Kurt L. ; Maas, Leo R. M.
    In this study, we address the question whether eddy-driven transports in the Argentine Basin can be held responsible for enhanced sediment accumulation over the Zapiola Rise, hence accounting for the existence and growth of this sediment drift. To address this question, we perform a 6 year simulation with a strongly eddying ocean model. We release two passive tracers, with settling velocities that are consistent with silt and clay size particles. Our experiments show contrasting behavior between the silt fraction and the lighter clay. Due to its larger settling velocity, the silt fraction reaches a quasisteady state within a few years, with abyssal sedimentation rates that match net input. In contrast, clay settles only slowly, and its distribution is heavily stratified, being transported mainly along isopycnals. Yet, both size classes display a significant and persistent concentration minimum over the Zapiola Rise. We show that the Zapiola Anticyclone, a strong eddy-driven vortex that circulates around the Zapiola Rise, is a barrier to sediment transport, and hence prevents significant accumulation of sediments on the Rise. We conclude that sediment transport by the turbulent circulation in the Argentine Basin alone cannot account for the preferred sediment accumulation over the Rise. We speculate that resuspension is a critical process in the formation and maintenance of the Zapiola Rise.
  • Article
    Coastal ocean and shelf-sea biogeochemical cycling of trace elements and isotopes : lessons learned from GEOTRACES
    (The Royal Society, 2016-10-17) Charette, Matthew A. ; Lam, Phoebe J. ; Lohan, Maeve C. ; Kwon, Eun Young ; Hatje, Vanessa ; Jeandel, Catherine ; Shiller, Alan M. ; Cutter, Gregory A. ; Thomas, Alex ; Boyd, Philip ; Homoky, William B. ; Milne, Angela ; Thomas, Helmuth ; Andersson, Per S. ; Porcelli, Don ; Tanaka, Takahiro ; Geibert, Walter ; Dehairs, Frank ; Garcia-Orellana, Jordi
    Continental shelves and shelf seas play a central role in the global carbon cycle. However, their importance with respect to trace element and isotope (TEI) inputs to ocean basins is less well understood. Here, we present major findings on shelf TEI biogeochemistry from the GEOTRACES programme as well as a proof of concept for a new method to estimate shelf TEI fluxes. The case studies focus on advances in our understanding of TEI cycling in the Arctic, transformations within a major river estuary (Amazon), shelf sediment micronutrient fluxes and basin-scale estimates of submarine groundwater discharge. The proposed shelf flux tracer is 228-radium (T1/2 = 5.75 yr), which is continuously supplied to the shelf from coastal aquifers, sediment porewater exchange and rivers. Model-derived shelf 228Ra fluxes are combined with TEI/ 228Ra ratios to quantify ocean TEI fluxes from the western North Atlantic margin. The results from this new approach agree well with previous estimates for shelf Co, Fe, Mn and Zn inputs and exceed published estimates of atmospheric deposition by factors of approximately 3–23. Lastly, recommendations are made for additional GEOTRACES process studies and coastal margin-focused section cruises that will help refine the model and provide better insight on the mechanisms driving shelf-derived TEI fluxes to the ocean.