Solar cycle variations in the intensity of geomagnetically trapped anomalous cosmic ray (ACR) oxygen are demonstrated by ~7 years of data from the SAMPEX satellite. They correspond to similar variations in the interplanetary ACR source. Trapped particle losses during the approach to solar maximum are not associated with geomagnetic activity and may be consistent with atmospheric energy degradation. The average trapped particle pitch angle distribution and energy spectra support this interpretation in which both source and loss rates are proportional to atmospheric density. ¿ 2000 American Geophysical Union