Due to time lags in moving energy / heat around, there is no reason to think that deeper ocean temperature changes will be in lock - step with surface changes. (skepticalscience.com)
The observational record of deep - ocean variability is short, which makes it difficult to attribute the recent rise in deep ocean temperatures to anthropogenic forcing. (notrickszone.com)
The very first measurements of deep ocean temperatures were performed with instruments lowered from a ship down into the ocean. (skepticalscience.com)