Pity to see two intellectually competent people at each other over what appears to me to be a very slight difference in interpretation of part of the OP.
Here's the bit from the OP where I think there are differing interpretations.
"At a global level, the research showed upper-ocean warming has been underestimated by 24 per cent to 58 per cent, Dr Durack said."
I think there may be some confusion between ACTUAL heat content and CHANGE in heat content. I think it is the change in heat content that has been the focus of this research. The use of the term "warming" in the above quote does imply that it's the change in heat that has been underestimated.
If we were to examine a doubling of ACTUAL heat content of liquid water at 2C, we would first need to determine the actual heat at the temperature and (urk) pressure. First we would need to add up the heat energy needed to warm ice from absolute zero to whatever the melting point is between 2km deep in the salty ocean and the abyssal depths. (I don't want to do this hence my earlier "urk".) Then we would want to calculate the latent heat of melting, again an unpleasantly complicated calculation given the saltiness and the variable depth. Lastly we would need to perform the relatively straightforward calculation for the heat needed to warm the liquid water from its variable melting point to the 2C.
The more I look at the computation, the more it looks post doctoral rather than undergraduate. The undergraduate answer would be very likely around 8.4kJ per kilogram but unfortunately it would be wrong.
FWIW, I enjoy reading contributions from both janti and pseudo.
