Solar coronal plasma composition is typically characterized by first
ionization potential (FIP) bias. Using spectra obtained by Hinode's EUV Imaging
Spectrometer (EIS) instrument, we present a series of large-scale, spatially
resolved composition maps of active region (AR) 11389. The composition maps
show how FIP bias evolves within the decaying AR from 2012 January 4-6.
Globally, FIP bias decreases throughout the AR. We analyzed areas of
significant plasma composition changes within the decaying AR and found that
small-scale evolution in the photospheric magnetic field is closely linked to
the FIP bias evolution observed in the corona. During the AR's decay phase,
small bipoles emerging within supergranular cells reconnect with the
pre-existing AR field, creating a pathway along which photospheric and coronal
plasmas can mix. The mixing time scales are shorter than those of plasma
enrichment processes. Eruptive activity also results in shifting the FIP bias
closer to photospheric in the affected areas. Finally, the FIP bias still
remains dominantly coronal only in a part of the AR's high-flux density core.
We conclude that in the decay phase of an AR's lifetime, the FIP bias is
becoming increasingly modulated by episodes of small-scale flux emergence, i.e.
decreasing the AR's overall FIP bias. Our results show that magnetic field
evolution plays an important role in compositional changes during AR
development, revealing a more complex relationship than expected from previous
well-known Skylab results showing that FIP bias increases almost linearly with
age in young ARs (Widing & Feldman, 2001, ApJ, 555, 426)