The non-steric contribution to sea surface height (SSH) variability hampers the use of satellite altimeter data in mapping steric-related variability. Here, two eddy-resolving 1/16¿ world ocean simulations are used to investigate the effects of mesoscale flow instabilities on the non-steric (or abyssal ocean) contribution to the global barotropic mode. Model results show the non-steric component accounting for >50% of the total SSH variability over 37% of the world ocean in the model, predominantly at mid and high latitudes. Most of this is either wind-driven and deterministic or eddy-driven and nondeterministic. Upper ocean flow instabilities drive deep flows and generate non-steric SSH variability maxima (5--10 cm rms or more) in many major current systems throughout the world ocean. Resulting ocean anomalies are a nondeterministic response to atmospheric forcing and an eddy-resolving data-assimilative ocean model that demonstrates the essential dynamics is needed to depict their evolution. ¿ 2000 American Geophysical Union