http://ocean.mit.edu...Phys. Oc., (pdf)
Two of the world’s premiere ocean scientists from Harvard and MIT have addressed the data limitations that currently prevent the oceanographic community from resolving the differences among various estimates of changing ocean heat content (in print but available here).3 They point out where future data is most needed so these ambiguities do not persist into the next several decades of change. As a by-product of that analysis they 1) determined the deepest oceans are cooling, 2) estimated a much slower rate of ocean warming, 3) highlighted where the greatest uncertainties existed due to the ever changing locations of heating and cooling, and 4) specified concerns with previous methods used to construct changes in ocean heat content, such as Balmaseda and Trenberth’s re-analysis (see below). 13 They concluded, “Direct determination of changes in oceanic heat content over the last 20 years are not in conflict with estimates of the radiative forcing, but the uncertainties remain too large to rationalize e.g., the apparent “pause” in warming.”
Their results (Figure 18. below) suggest a flattening or slight cooling in the upper 100 meters since 2004, in agreement with the -0.04 Watts/m2 cooling reported by Lyman (2014).6 The consensus of previous researchers has been that temperatures in the upper 300 meters have flattened or cooled since 2003,4 while Wunsch and Heimbach (2014) found the upper 700 meters still warmed up to 2009.
The deep layers contain twice as much heat as the upper 100 meters, and overall exhibit a clear cooling trend for the past 2 decades. Unlike the upper layers, which are dominated by the annual cycle of heating and cooling, they argue that deep ocean trends must be viewed as part of the ocean’s long term memory which is still responding to “meteorological forcing of decades to thousands of years ago”. If Balmaseda and Trenberth’s model of deep ocean warming was correct, any increase in ocean heat content must have occurred between 700 and 2000 meters, but the mechanisms that would warm that “middle layer” remains elusive.