Spatial Variation of Diapycnal Diffusivity Estimated From Seismic Imaging of Internal Wave Field, Gulf of Mexico

Dickinson, N. A. and White, N. J. and Caulfield, C. P. (2017) Spatial Variation of Diapycnal Diffusivity Estimated From Seismic Imaging of Internal Wave Field, Gulf of Mexico. Journal of Geophysical Research: Oceans, 122 (12). pp. 9827-9854. ISSN 2169-9291 DOI https://doi.org/10.1002/2017JC013352

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Abstract

Bright reflections are observed within the upper 1,000 m of the water column along a seismic reflection profile that traverses the northern margin of the Gulf of Mexico. Independent hydrographic calibration demonstrates that these reflections are primarily caused by temperature changes associated with different water masses that are entrained into the Gulf along the Loop Current. The internal wave field is analyzed by automatically tracking 1,171 reflections, each of which is greater than 2 km in length. Power spectra of the horizontal gradient of isopycnal displacement, , are calculated from these tracked reflections. At low horizontal wave numbers ( cpm), , in agreement with hydrographic observations of the internal wave field. The turbulent spectral subrange is rarely observed. Diapycnal diffusivity, K, is estimated from the observed internal wave spectral subrange of each tracked reflection using a fine‐scale parametrization of turbulent mixing. Calculated values of K vary between and m2 s−1 with a mean value of m2 s−1. The spatial distribution of turbulent mixing shows that m2 s−1 away from the shelf edge in the upper 300 m where stratification is strong. Mixing is enhanced by up to 4 orders of magnitude adjacent to the shoaling bathymetry of the continental slope. This overall pattern matches that determined by analyzing nearby suites of CTD casts. However, the range of values recovered by spectral analysis of the seismic image is greater as a consequence of significantly better horizontal resolution.

Item Type:	Article
Uncontrolled Keywords:	2017AREP; IA72
Subjects:	02 - Geodynamics, Geophysics and Tectonics
Divisions:	02 - Geodynamics, Geophysics and Tectonics 08 - Green Open Access 12 - PhD
Journal or Publication Title:	Journal of Geophysical Research: Oceans
Volume:	122
Page Range:	pp. 9827-9854
Identification Number:	https://doi.org/10.1002/2017JC013352
Depositing User:	Sarah Humbert
Date Deposited:	03 Dec 2018 12:57
Last Modified:	03 Dec 2018 12:57
URI:	http://eprints.esc.cam.ac.uk/id/eprint/4367

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