Maas Leo R. M.

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Maas
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Leo R. M.
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  • Article
    Internal solitary waves in the Red Sea : an unfolding mystery
    (The Oceanography Society, 2012-06) da Silva, Jose C. B. ; Magalhaes, Jorge M. ; Gerkema, Theo ; Maas, Leo R. M.
    The off-shelf region between 16.0° and 16.5°N in the southern Red Sea is identified as a new hotspot for the occurrence of oceanic internal solitary waves. Satellite observations reveal trains of solitons that, surprisingly, appear to propagate from the center of the Red Sea, where it is deepest, toward the continental shelf, but they do not survive as coherent structures over the shelf. These solitons are characterized by coherent crest lengths exceeding 80 km and crest-to-crest distances of more than 2 km, compatible with signatures of large-amplitude solitary waves. Despite the fact that these Red Sea solitons have large amplitudes, they appear to be generated by very weak surface tides. Tidal current velocity is only about 5 cm s–1 over the shelf, much weaker than over other ocean shelves where similar solitary waves have been reported. The appearance of these waves over this particular geographical stretch suggests generation by a locally amplified internal tide on the main pycnocline. We consider three possible explanations for soliton generation in the Red Sea: interfacial tide resonance, local generation by internal tidal beams generated at the shelf breaks, and local generation by internal tidal beams generated at the shelf breaks but first amplified by repeated focusing reflections.
  • 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.