A graph on page 69 shows measured pH from 1991 through 2006. I think that the sample period is interesting. http://wso.stanford.edu/gifs/Tilts.gif shows this to be a period encompassing 2 solar maximum when lower frequencies, deeper penetrating solar radiation may be a factor. Further, the graph on page 69 seems to confirm that during the solar minimum, pH declined at higher sea elevations.
I would love to see these results over a 22 year period, adding 2006-2012. My prediction as a lay person is that pH balances over that period with a slight time offset due to the lifecycles of various ocean life and heat accumulation/dissipation.