Contributions of sea ice dynamic and thermodynamic processes to the late-summer sea ice volume (SIV) changes in 2007, 2012, and 2016 are investigated using a new dynamically-consistent ocean-sea ice synthesis product. The synthesis and satellite observations indicate that summer sea ice in the Pacific sector is sensitive to atmospheric and oceanic forcing and is reducing significantly since 2007. For 2012, reduced ice thickness in April preconditions the late-summer ice loss. Ice-ocean heat exchange and ice advection support further ice loss, resulting in unprecedented ice loss. Sea ice advected to the Eurasian Basin and the central Arctic survives until late summer in 2007 and 2016, increasing local SIV. Enhanced basal melting is visible in regions with strong contributions from dynamic processes.