  A large fraction of the stellar mass in galaxy clusters is thought to be
contained in the diffuse low surface brightness intracluster light (ICL). Being
bound to the gravitational potential of the cluster rather than any individual
galaxy, the ICL contains much information about the evolution of its host
cluster and the interactions between the galaxies within. However due its low
surface brightness it is notoriously difficult to study. We present the first
detection and measurement of the flux contained in the ICL at z~1. We find that
the fraction of the total cluster light contained in the ICL may have increased
by factors of 2-4 since z~1, in contrast to recent findings for the lack of
mass and scale size evolution found for brightest cluster galaxies. Our results
suggest that late time buildup in cluster cores may occur more through
stripping than merging and we discuss the implications of our results for
hierarchical simulations.
