Ionospheric ion upwelling in the vicinity of the dayside cleft has been studied, based primarily on data from the Dynamics Explorer 1 spacecraft. Using retarding ion mass spectrometer low-energy ion data and plasma wave instrument dc electric field data, bulk ion plasma parameters, including ion species density and field-aligned bulk velocity and flux, have been derived at points within a number of observed upwelling ion events for the ion species H+, He+, O+, and O++. The ion species bulk parameters near the source latitude are examined and compared. We find that the upwelling plasma is rich in O+, which typically comprises ~90% of the particle density, followed by H+ at somewhat less than 10%, and then He+ and O++, each comprising ~1% of the upwelling ion particle density. The upwelling O+ ion flux is also commonly dominant over that associated with the other species, with normalized values near the source region which are typically near 109 cm-2 s-1. The fractional upward H+ flux is not as small as the fractional H+ density due to the much larger H+ upward flow velocities. Integration of the product of the normalized upward ion species flux and the upwelling ion occurrence probability (Lockwood et al., 1985) over the source area yields an estimate of the source strength of this low-altitude cleft region magnetospheric plasma source of 2.6¿1025 ions s-1. ¿American Geophysical Union 1990