Research by an Australian biologist suggests that when elephant seals like this one (a juvenile on Humble Island, Antarctica) forage at sea they sometimes remain motionless deep under water for as long as 20 minutes. What's unclear is whether that chillaxing break is simply a way for them to rest in the ocean or an aid in digestion.
Either way, the blubber that insulates them from cold also delivers buoyancy. Sufficiently fattened elephant seals will float gently back to the surface. If they're too skinny (it's a relative thing), they sink to the bottom.
New tags developed and deployed off eastern Antarctica and put on the elephant seals' heads not only will track the chubby mammals habits, but record water temperature and salinity -- valuable information for piecing together the world's shifting climate puzzle.