The presence of heavy ions in a plasma introduces additional characteristic frequencies one of which is a crossover frequency between each adjacent pair of gyrofrequencies of the ions present. The crossover frequency is controlled by the fractional ion charge densities. The phase speed of the L and R wave modes have the same phase velocity at this frequency. For oblique propagation waves become linearly polarized at the crossover frequency. They reverse their natural polarization from left to right (or vice versa) as the wave frequency transverses the crossover frequency. Here we present polarization analysis of a portion of the Ulysses magnetometer observations in the middle Jovian magnetosphere during the inbound pass and close to a plasma sheet approach. The analysis show transverse waves with frequency between the gyrofrequencies of SO+ and S+. We observe polarization reversal at this frequency, which could be an indication of wave observations at the crossover frequency. On this assumption these observations can then be used to derive heavy ion composition of the resident plasma. ¿ 2001 American Geophysical Union