Vertical Mixing and Heat Fluxes Conditioned by a Seismically Imaged Oceanic Front
Authors
Gunn, KL
Dickinson, A
White, NJ
Caulfield, CCP
Publication Date
2021Journal Title
Frontiers in Marine Science
ISSN
2296-7745
Publisher
Frontiers Media SA
Volume
8
Language
en
Type
Article
This Version
VoR
Metadata
Show full item recordCitation
Gunn, K., Dickinson, A., White, N., & Caulfield, C. (2021). Vertical Mixing and Heat Fluxes Conditioned by a Seismically Imaged Oceanic Front. Frontiers in Marine Science, 8 https://doi.org/10.3389/fmars.2021.697179
Abstract
<jats:p>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, <jats:italic>K</jats:italic>, and of vertical diffusive heat flux, <jats:italic>F</jats:italic><jats:sub><jats:italic>H</jats:italic></jats:sub>. We show that estimates of ε, <jats:italic>K</jats:italic>, and <jats:italic>F</jats:italic><jats:sub><jats:italic>H</jats:italic></jats:sub> 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, <jats:italic>K</jats:italic>, and <jats:italic>F</jats:italic><jats:sub><jats:italic>H</jats:italic></jats:sub>. In contrast, a mesoscale front modifies ε and <jats:italic>K</jats:italic> to a depth of 1 km, across a region of <jats:italic>O</jats:italic>(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 <jats:italic>K</jats:italic> to a depth of 1 km. As a result, estimates of <jats:italic>F</jats:italic><jats:sub><jats:italic>H</jats:italic></jats:sub> increase by a factor of two in the vicinity of the surface outcrop of the front. Our results yield estimates of ε, <jats:italic>K</jats:italic> and <jats:italic>F</jats:italic><jats:sub><jats:italic>H</jats:italic></jats:sub> 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.</jats:p>
Keywords
Marine Science, seismic oceanography, diapycnal diffusivity, diffusive heat flux, fronts, Brazil-Falkland Confluence
Identifiers
External DOI: https://doi.org/10.3389/fmars.2021.697179
This record's URL: https://www.repository.cam.ac.uk/handle/1810/329625
Rights
Licence:
http://creativecommons.org/licenses/by/4.0/
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