Term used when surface and deep water swap in the ocean?

I'm writing a paper on global warming and part of it includes how CO2 cycles through the ocean and I remember reading this article talking about how the salinity and temperature affect the water densities and every now and then the deep water and surface water sort of flip flop. I could of swore there was a certain term for that but I'm having a total brain fart and mad case of writer's block right now. Thanks all :)