Scientists at the Jet Propulsion Laboratory have found that the deep oceans below 2000 meters have warmed little, if any, since 2005. This was a very neat study using in situ measurements as well as satellite data. What they did was to measure the increase in total ocean heat content and then subtract what has been measured in the top 2000 meters. What was left over was the amount of warming occurring in the oceans below 2000 meters and they found that it was small, if any.
I am not at all surprised by this result. I know that many people have been saying heat is being stored in the lower levels of the ocean, but my review of the literature did not lead me to that conclusion. There are many reasons, but the fact is that the majority of the deep ocean water originates in the polar areas. As sea water freezes it extrudes the salt, creating a briny soup which is heavier than the surrounding sea water and sinks. Nearly all deep ocean currents originate in the vicinity of Antarctica. For this reason alone, I would have been surprised that the deep ocean was warming. The ocean water around Antarctica is warming, but the briny water will still be nearly freezing because it originates from freezing water. Of course, it is much more complicated than that and there are many other factors involved, but this is the starting point. I just don't see any mechanism to transport heat from the upper-levels to the lower. It all has led me to the conclusion that I was not expecting to find much deep ocean heating.
Now, I know many contrarians are going to point at this study and claim that the oceans are not warming and that is NOT what this study says. What they found is that the DEEP ocean is not warming a perceptible amount. But, note that the only way you can get that result is by finding the upper levels are warming. The way they measured the lower heating is by taking the total heating and subtracting the known amount of upper-level heating. So, this result is only possible with the existence of that upper-level heating.
So, this is a very neat and important study. It does nothing to contradict anything we know about anthropogenic climate change, but it does illustrate we still have lots to learn - and that is not really news.