  We report on observations of six giants in the globular cluster M15 (NGC
7078) using the Subaru Telescope to measure neutron-capture elemental
abundances. Our abundance analyses based on high-quality blue spectra confirm
the star-to-star scatter in the abundances of heavy neutron-capture elements
(e.g., Eu), and no significant s-process contribution to them, as was found in
previous studies. We have found, for the first time, that there are
anti-correlations between the abundance ratios of light to heavy
neutron-capture elements ([Y/Eu] and [Zr/Eu]) and heavy ones (e.g., Eu). This
indicates that light neutron-capture elements in these stars cannot be
explained by only a single r-process. Another process that has significantly
contributed to the light neutron-capture elements is required to have occurred
in M15. Our results suggest a complicated enrichment history for M15 and its
progenitor.
