Deep zonal jets in the western Pacific are geostrophic in character at latitudes of a fraction of a degree. This evidence corroborates the interpretation that deep jets very close to the equator take the form of Kelvin waves. Vertical displacements inferred from GEOSECS density profiles in the Pacific and Atlantic suggest deep jets are a general feature of equatorial oceans.
Eriksen, Charles C.. 1982. "Geostrophic equatorial deep jets." Journal of Marine Research 40, (S). https://elischolar.library.yale.edu/journal_of_marine_research/1637