Ocean Mass Redistribution & Corresponding Frequency Offsets for Precise   Timing Applications
  The relativistic timing affects of tidally redistributed ocean mass are investigated. The Sun, Moon, and Earth hurl through space, and their gravitational fields cause the tides which is a slight redistribution of ocean mass. This redistributed mass perturbs the Earth's gravitational potential affecting atomic clocks. The magnitude of this perturbation will be quantified, correcting for this effect. The predicted fractional frequency offset (10-19) is too small to be detected, but this effect may become visible in the future. 
Scott Czopek
gr-qc astro-ph.IM