Mixing hotspots transform North Atlantic water masses along overturning pathways

Speaker: Maya Jakes, University of Southampton
Series: Quantitative Climate and Environmental Science Seminars

Ocean mixing continuously modifies water-mass properties by redistributing heat, salt and other tracers throughout the ocean interior, playing a critical role in regulating Earth's climate. Yet the magnitude and spatial distribution of mixing-driven water-mass transformations remain poorly constrained by observations. Here we combine a new theoretical framework with Argo float observations to produce the first basin-scale maps of mixing-driven transformations in the North Atlantic. At the basin scale, mixing drives peak diathermal and diahaline fluxes of ~62 TW and 4.3x106 kg s-1, respectively, transferring heat and salt towards colder and fresher classes. These fluxes erode the thermohaline extremes and form ~5 Sv of water within intermediate temperature classes and ~10 Sv of water within intermediate salinity classes. Three hotspot regions - the Western Tropics, Grand Banks and Mediterranean Outflow regions - account for ~50% of the peak basin-integrated heat and salt fluxes despite occupying only ~20% of the sampled area. These hotspots occur where major currents and distinct water masses converge, and isopycnal mixing dominates the thermohaline fluxes. Our results reveal how geographically localised mixing processes collectively shape the evolution of North Atlantic water masses along overturning pathways and help maintain the basin-scale thermohaline structure.