Not good

Observed decreases in oxygen content of the global ocean – Helm et al. (2011) “Comparing the high-quality oxygen climatology from the World Ocean Circulation Experiment to earlier data we reveal near-global decreases in oxygen levels in the upper ocean between the 1970s and the 1990s. This globally averaged oxygen decrease is -0.93{plus minus}0.23 μmol l-1, which is equivalent to annual oxygen losses of -0.55{plus minus}0.13×1014 mol yr-1 (100-1000 m). The strongest decreases in oxygen occur in the mid-latitudes of both hemispheres, near regions where there is strong water renewal and exchange between the ocean interior and surface waters. Approximately 15% of global oxygen decrease can be explained by a warmer mixed-layer reducing the capacity of water to store oxygen, while the remainder is consistent with an overall decrease in the exchange between surface waters and the ocean interior. Here we suggest that this reduction in water mass renewal rates on a global scale is a consequence of increased stratification caused by warmer surface waters. These observations support climate model simulations of oxygen change under global warming scenarios.” Helm, K. P., N. L. Bindoff, and J. A. Church (2011), Geophys. Res. Lett., doi:10.1029/2011GL049513, in press.

H/t AGWObserver.

In recent years we have seen less accumulation of thermal energy than we expect to see in the upper ocean. This is the "missing heat." Some of the "missing" heat can be found by taking measurements of the deeper ocean.

Climate models grimly predict that increased warming of the surface ocean will strength the stratification of the ocean's layers, slowing the exchange of heat between the surface and the deep.

But "losing" heat to the deep ocean raised for me the hopeful speculation that heat might be settling into the deep faster than climate models predict, potentially buying humanity a itsy-bitsy piece of time to get serious about global warming.

But if we are already detecting the hypoxia caused by "an overall decrease in the exchange between surface waters and the ocean interior" then the real-world observations are supporting the models. The huge heat sink of the icy abyssal waters of the deep ocean will help us less and less as we heat the surface, meaning we end up with more surface warming for the same amount of retained heat.