Large-scale (greater than 100 kilometer radius) ocean eddies within the Loop Current of the Gulf of Mexico are an important conveyor of water from the subtropics to the tropics. These Loop Current Eddies trap the well mixed subtropical warm and salty water within their core that is separate and distinct from the local water masses surrounding the eddies.
Meunier et al.  describe a recent glider survey with high resolution temperature and salinity profiles in both horizontal and vertical space, which not only observed a Loop Current Eddy as it traversed northwestward through the Gulf of Mexico, but also remarkably observed three smaller (20 to 30 kilometer radii) eddies embedded within the larger eddy. These smaller eddies share the same water mass properties as the larger eddy but are distinctly located within the higher stratification of the density gradient at the base of the larger eddy.
This feature makes the so-called intra-thermocline eddies difficult to observe because they are small and have little surface signature that might be detectable, for example, from remotely sensed sea surface height measurements. Hence it may be that intra-thermocline eddies are much more prevalent than we realize, and potentially play a significant role in the redistribution of heat, freshwater, and biogeochemical properties of subtropical water masses that transit the Gulf of Mexico.
Citation: Meunier, T., Tenreiro, M., Pallàs‐Sanz, E., Ochoa, J., Ruiz‐Angulo, A., Portela, E., et al. . Intrathermocline eddies embedded within an anticyclonic vortex ring. Geophysical Research Letters, 45. https://doi.org/10.1029/2018GL077527
—Janet Sprintall, Editor, GRL