How can subsurface magnetic reconnection change the elemental composition in the solar corona?

In September 2017, AR 12673 was a remarkably complex active region with unprecedented levels of transverse field strength, high shear, fast sunspot motions and produced the largest flares of solar cycle 24. It also showed anomalous (Inverse FIP or IFIP) coronal elemental composition above certain observed with Hinode/EIS. We suggest that the magnetic evolution of this AR in the sub-photospheric layers led to its unusual complexity, including the formation of a large-scale U-loop, which was the centre of major activity for several days. We provide the first observational evidence from sunspot motions that sub-surface magnetic reconnection took place in this active region (AR) at the U-loop. Anomalous, IFIP, coronal composition, which evolved in the midst of the FIP-composition dominated AR corona, was observed above the sunspot umbrae linked to the reconnecting flux tubes. IFIP was observed when those umbrae were crossed by are ribbons. Subsurface reconnection leads to the generation of magnetosonic waves, which can create a downward ponderomotive force at the chromospheric level where these waves are reflected back. The locations of the IFIP plasma is interpreted in the context of the Laming FIP/IFIP model (Laming, LRSP, 2015). We suggest that flare evaporation reveals the plasma composition, which is depleted in low-FIP elements as a result of the waves coming from below (in contrast of the FIP effect where waves are coming from above).