Vertical mixing and heat fluxes conditioned by a seismically imaged oceanic front

Gunn, Kathryn L. and Dickinson, N. A. and White, N. J. and Caulfield, C. P. (2021) Vertical mixing and heat fluxes conditioned by a seismically imaged oceanic front. Frontiers in Earth Science. ISSN 2296-6463 DOI https://doi.org/10.3389/fmars.2021.697179

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Abstract

The southwest Atlantic gyre connects several distinct water masses, which means that this oceanic region is characterized by a complex frontal system and enhanced water mass modification. Despite its significance, the distribution and variability of vertical mixing rates have yet to be determined for this system. Specifically, potential conditioning of mixing rates by frontal structures, in this location and elsewhere, is poorly understood. Here, we analyze vertical seismic (i.e., acoustic) sections from a three-dimensional survey that straddles a major front along the northern portion of the Brazil-Falkland Confluence. Hydrographic analyses constrain the structure and properties of water masses. By spectrally analyzing seismic reflectivity, we calculate spatial and temporal distributions of the dissipation rate of turbulent kinetic energy, ε, of diapycnal mixing rate, K, and of vertical diffusive heat flux, FH. We show that estimates of ε, K, and FH are elevated compared to regional and global mean values. Notably, cross-sectional mean estimates vary little over a 6 week period whilst smaller scale thermohaline structures appear to have a spatially localized effect upon ε, K, and FH. In contrast, a mesoscale front modifies ε and K to a depth of 1 km, across a region of O(100) km. This front clearly enhances mixing rates, both adjacent to its surface outcrop and beneath the mixed layer, whilst also locally suppressing ε and K to a depth of 1 km. As a result, estimates of FH increase by a factor of two in the vicinity of the surface outcrop of the front. Our results yield estimates of ε, K and FH that can be attributed to identifiable thermohaline structures and they show that fronts can play a significant role in water mass modification to depths of 1 km.

Item Type: Article
Uncontrolled Keywords: 2021AREP; IA77
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
02 - Geodynamics, Geophysics and Tectonics
Divisions: 02 - Geodynamics, Geophysics and Tectonics
08 - Green Open Access
12 - PhD
01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title: Frontiers in Earth Science
Identification Number: https://doi.org/10.3389/fmars.2021.697179
Depositing User: Sarah Humbert
Date Deposited: 25 Mar 2022 14:57
Last Modified: 25 Mar 2022 14:57
URI: http://eprints.esc.cam.ac.uk/id/eprint/6032

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