Ocean Science www.ocean-sci.net 1812-0784 1812-0792 6 3 2010 10.5194/os-6-621-2010 http://www.ocean-sci.net/6/621/2010/ http://www.ocean-sci.net/6/621/2010/os-6-621-2010.html http://www.ocean-sci.net/6/621/2010/os-6-621-2010.pdf 621 631 2010-07-02 Seismic imaging of a thermohaline staircase in the western tropical North Atlantic I. Fer ilker.fer@gfi.uib.no P. Nandi W. S. Holbrook R. W. Schmitt P. Páramo Geophysical Institute, University of Bergen, Allégaten 70, 5007, Bergen, Norway BP America, Inc., 501 Westlake Park Blvd, Houston, TX 77079, USA Dept. of Geology and Geophysics, University of Wyoming, Laramie, WY 82071, USA Dept. of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA BP Exploration, Bldg H, Chertsey Road, Sunbury-on-Thames, TW16 7LN, UK Multichannel seismic data acquired in the Lesser Antilles in the western tropical North Atlantic indicate that the seismic reflection method has imaged an oceanic thermohaline staircase. Synthetic acoustic modeling using measured density and sound speed profiles corroborates inferences from the seismic data. In a small portion of the seismic image, laterally coherent, uniform layers are present at depths ranging from 550–700 m and have a separation of ~20 m, with thicknesses increasing with depth. The reflection coefficient, a measure of the acoustic impedance contrasts across these reflective interfaces, is one order of magnitude greater than background noise. Hydrography sampled in previous surveys suggests that the layers are a permanent feature of the region. Spectral analysis of layer horizons in the thermohaline staircase indicates that internal wave activity is anomalously low, suggesting weak internal wave-induced turbulence. Results from two independent measurements, the application of a finescale parameterization to observed high-resolution velocity profiles and direct measurements of turbulent dissipation rate, confirm these low levels of turbulence. 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