he detection of quasi-periodic oscillations in the brightest X-ray sources has opened up a new window on the properties of accreting neutron stars. All six of the highest accretion rate (M greater than or similar to 10(-9) M. yr(-1)) sources have exhibited oscillations in the 5-7 Hz range. We explore the possibility that the underlying clock for this feature is a low I nonradial oscillation in the neutron star ''ocean.'' The composition of the ocean at densities greater than or similar to 10(7) g cm(-3) depends on how the accreted hydrogen and helium is burned to heavier elements, which in turn depends on the accretion rate. In particular, the high accretion rate sources develop deep, massive oceans of light elements (C, O, Ne, Mg, ...). In contrast, low accretion rate sources burn the accreted matter to iron group elements at low densities through type I X-ray bursts. The stronger Coulomb forces in the iron plasma leads to crystallization just beneath the burning region, and therefore lower accretion rate sources have much shallower, less massive oceans than the higher accretion rate sources. Our adiabatic nonradial mode calculations show that the deep ocean of light elements supports g-modes (basically shallow water waves) with frequencies (for l = 1) that are a compelling match to the observed approximate to 5-7 Hz quasi-periodic X-ray oscillations. In addition, these modes can contain up to 10(37)-10(38) ergs of energy and still be in the linear regime at the density where the frequency is set. The successful identification of a few nonradial modes with their observed frequencies would yield new information about the thermal and compositional makeup of the neutron star at densities in excess of 10(9) g cm(-3). Our initial results are in the limit of slow rotation (i.e., P-s greater than or similar to 1/6 s) and weak magnetic fields (B less than or similar to 10(11) G) and we mention the differences rapid rotation might make. We also emphasize the promise afforded by ''oceanography'' of accreting neutron stars with the X-Ray Timing Explorer and USA satellites.
