Anomalous conditions exist in the salinity, oxygen, and nutrient fields over the western flank of the Northern Hemisphere Mid-Atlantic Ridge. We examine possible advective sources for this anomaly, but determine that vertical mixing is the most likely cause. We proceed to use knowledge gained from the Brazil Basin Tracer Release Experiment in the South Atlantic (where microstructure and fine structure were obtained to explore the intensity, spatial distribution, and mechanisms of mixing in the deep ocean) to interpret density fine structure from common conductivity-temperature-depth data in the North Atlantic. These data support the hypothesis that the anomalous hydrographic conditions are associated with enhanced levels of vertical mixing. The inferred levels of vertical diffusivity over the Northern Hemisphere Mid-Atlantic Ridge are as high as in the South Atlantic: 1–10 × 10−4 m2/s.