global warming and dilute deep ocean currents
The pacific decadal oscillation occurs every 10 -20 twenty years and the southern pacific ocean gets particularly warmer than normal.I have never seen an explanation for this phenomenon.But here is one possibility: cold dense sinking water from anatarctica heading north into the pacific every ten years gets less solutes added to it ( perhaps because there are alternating layers of rock/sediment on its route of alternating composition - each layer taking 10 years or more to "dissolve" in the cold sinking current, perhaps because mid-ocean ridges are pumping less solutes into the sea than usual,perhaps because less sediment has passed from the surface of antarctica's landmass into the sea).With less solutes the water is more dilute.As it heads north towards the equator and along the sea floor this less dense, more dilute water picks up solutes from the layers of water above it.When it rises at the equator the surface of the sea has been depleted of solutes and is less dense and offers less resistance
to the rising cold current which rises higher than normal.This would explain why the equatoral water has been observed by NASA to be bulging noticeably during the Pacific Decadal oscillation.In a similar manner El Nino could be explained but this time by more solutes being removed from the sea by the trench off the west coast of Chile.
With solutes moving from the surface to the lower depths to compensate the vapour pressure of the surface water would be higher and more water would evaporate and act like a greenhouse gas, heating the sea and encouraging CO2 to leave it too.
But why do "warm" events of the scale and severity of El Nino and the pacific decadal oscillation only happen in the pacific? The pacific has far more ocean ridges (total length) than the atlantic
and faces a wider area of the antarctic, so perhaps part of the answer lies here.