What causes the "ripples" that extend east-west along the mid-atlantic ridge?
These are transform faults that result from differential spreading rates of the middle ocean ridge. As such they are part of the plate boundary. Possible causes are different production rates of magma, thermal differences of the sea floor, differences of relative plate movement.

https://en.wikipedia.org/wiki/Transform_fault

https://en.wikipedia.org/wiki/Mid-ocean_ridge

Paywalled:
Dynamical Instability Produces Transform Faults at Mid-Ocean Ridges

And:
Wilson, 1965: A New Class of Faults and their Bearing on Continental Drift

Inactive transform faults extending beyond the spreading zone are sometimes generally named "fracture zone".

But transform faults can also reach all the way to the next subduction zone (e.g. Azores-Gibraltar fault zone) and be responsible for devastating earthquakes.