Secular changes in the density structure of selected regions of the upper ocean are investigated to see if they can explain the apparent rise in sea level observed along the continental margins of the world's oceans. The time rate of change of dynamic height is estimated to be -0.8 dyn cm/century, a value that is indistinguishable statistically from 0. Further, the distribution of individual values entering the grand average are distributed normally to a high degree of approximation. Assuming the change in relative sea level is real, then is could be due to either melting of the polar caps or warming of the upper ocean. Warming, since the turn of the century, of the magnitude suggested in much of the literature would have been detectable in the density structure of the upper ocean. This signal was not seen in the current analysis. A more modest warming, allowing for instrumental biases over the last 50 years or melting of the polar caps by just enough to give the observed change in relative sea level, would have signatures in the upper ocean density field that would barely be detectable in the current study. A combination of warming and melting shold have had a signal that was marginally detectable. This latter signal was not observed. A final possibility is that the ocean gyres have ''spun up'' causing increased sea level along the continental margins. The current analysis, while not designed to investigate this possibility, suggests further work is justified to test this idea. Explaining secular changes in the density field of the upper ocean will require long-time series of hydrographic observations taken at key locations in the world's oceans. The temporal sampling must be particularly intense to filter the relatively small expected signal from the high background noise levels.