What keeps the cerebrospinal fluid circulating? Is it pumped by something?
This picture from wikipedia seems to indicate that it pulsates as though it is pumped:
There is no evidence that the CSF has a pump, especially not a spinal pump as suggested by Dr. Jockers in the above answer. Dr. Jockers calls himself a "Maximized Living Doctor" but does not list his credentials. It is likely that he is a Doctor of Chiropractic; his references for the CSF pump article are dead ends: One is a dead link, two are references back to his Natural News page and one is a link to a Chiropract Medicine page (a good one, from my reading) in which the author himself states:
This is in keeping with the findings of decades of research in western medicine (M.D., Ph.D., D.O., etc.)
The "circulation" of the CSF, as already mentioned, is something of a misnomer. CSF is not known to "circulate" in the manner of blood. It does get agitated by pressure differentials, and it is 'circulated' in terms of being reabsorbed and replaced every 6-7 hours. Other than that, no circulation occurs.
Blood circulation is not generated only by the heart. Pressure differentials throughout the body affect the circulation of blood as well. One that is easily demonstrated (first documented in 1733) is the effect of intrathoracic (chest) pressure on circulation. The blood pressure of healthy people falls during spontaneous inspiration. When someone takes a deep breath, the blood return to the heart via the vena cava decreases, and pressure is exerted on the right atrium. Both cause decreased filling, which will drop blood pressure. Although this is best demonstrated with a blood pressure cuff, it can be demonstrated without. An unrecommended method is exemplified in a childhood game of passing out. A Valsalva maneuver (deep breath and glottal closure) decreases blood flow to the heart. Squeezing the chest further decreases return, resulting in fainting.
The same pressure differentials agitate the CSF. Additionally, smaller movements were seen with pressure differentials caused by the beating of the heart.
The image in the OP's question is of a patient with normal pressure hydrocephalus (NPH) showing pulsations of CSF with heartbeat, nothing more.
There are other factors that cause movement of CSF, but they are intermittent and variable.