jats:pThe 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:italicK</jats:italic>, and of vertical diffusive heat flux, jats:italicF</jats:italic>jats:subjats:italicH</jats:italic></jats:sub>. We show that estimates of ε, jats:italicK</jats:italic>, and jats:italicF</jats:italic>jats:subjats:italicH</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:italicK</jats:italic>, and jats:italicF</jats:italic>jats:subjats:italicH</jats:italic></jats:sub>. In contrast, a mesoscale front modifies ε and jats:italicK</jats:italic> to a depth of 1 km, across a region of jats:italicO</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:italicK</jats:italic> to a depth of 1 km. As a result, estimates of jats:italicF</jats:italic>jats:subjats:italicH</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:italicK</jats:italic> and jats:italicF</jats:italic>jats:subjats:italicH</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>