X-ray magnetic circular dichroism (XMCD) studies at the Er L_{2,3} edges of Er_{3}Fe_{5}O_{12} exhibit a change of the spectral shape as a function of temperature and magnetic field. Using singular value decomposition, this variation is understood as a linear combination of two components. The dominating component is associated with the Er magnetization, while the second contribution is identified as an induced signal from the Fe sites. XMCD at either of the L edges in Er_{3}Fe_{5}O_{12} provides information on the net magnetization of both sublattices. Their evolution in fields up to 30 T reveals details of the ferrimagnetic interactions on two very different scales.