Land surface heating faster than sea surface. Why?

The climate action delayers claim that global warming has stalled since 1998.
Climatologists respond that global surface increase heat has slowed because heat is going into the deep oceans. This is backed by observation.
The delayers respond that this is new science to them, and they doubt it.

I have been comparing sea surface temperatures (SST) with land surface temperatures on the excellent WoodforTrees website, which enables you to play with graphs.

Here is a comparison of global SST with the Crutem3 land surface data:

In case delayers do not trust Crutem data, here is the BEST data:

And here is the Hadcrut data:

Note that the green line in each case is of dry land temperatures alone, so we are comparing land and sea surface temperatures. All three datasets show land and sea temperatures pretty much on the same upward slope until 1980, when the land surface heating rate increases, while the ocean continues on the same upward slope it had been on since the late 1940s.

Now this must mean that either the sea has not been receiving the same amount of sun as the land, or it means that the heat from the sea has transferred downwards to the deeper levels of the ocean. Or a bit of both.

If the cooling low cloud cover over the sea has increased more than it has increased over the land, the former could be the explanation.

However, Eastman et al. showed that marine strato-cumulus (MSC) cover is inversely proportional to SST in most parts of the world's oceans, the exception being in the central Pacific, where MSC increased as SST increased. Cirrus clouds increases with SST, but cirrus clouds have a warming effect.

So cannot be claimed that the slowed rate of SST increase is due to cloud screening.

Therefore it must be that heat is being lost from the surface to the deep ocean.

These heat transfers occur at several points in the ocean where downwelling occurs. One delayer I encountered even cast doubt on downwelling, based on his observation of small pieces of toilet paper from his sailing boat (they did not sink).

Against this interesting, but somewhat limited evidence, we can put our knowledge of the Thermohaline Circulation, a mighty system of currents that connects the oceans of the world.

The main point of change from superficial to deep occurs in the north Atlantic near Greenland, but other points of downwelling are shown in this map:

"U" indicates areas of upwelling water. The red spots mark downwelling areas.  At these sites, warm surface waters have been drawn down to deep levels of the ocean. That is where the heat is going.  Some recently published work by Kosaka and Xie confirms this.