Press release:

 

http://www.cam.ac.uk/research/news/first-global-map-of-flow-within-the-earths-mantle-finds-the-surface-is-moving-up-and-down-like-a-yo

 

Or go straight to the paper:

 

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2709.html

 

My own perspective:

 

We already knew that the Earth's surface moves up and down, and that one way this can happen is because the mantle pushes the land up from underneath. In this paper a new dataset of observations is presented measuring this type of topography ("dynamic topography"). What's interesting is that the "shape" of the bulges is different from what has been previously been predicted. They are narrower than the broad peaks predicted by previous modelling. They also form more quickly. The authors demonstrate how hot buoyant material confined to channels in the asthenosphere can fit the data.

Why does the moon and sun's tidal influence not explain this effect?

I guess the wavelengths don't fit.

 

The spatial wavelength is far too short. These bulges are of order +/-1 km elevation with 10^3 km lateral wavelength.

The temporal wavelength is far too long. Geological evidence shows this topography develops over millions of years.

Sorry; I thought this was about earth tides.