Since the Last Interglacial (~122 ka), global ice sheets have undergone significant mass loss, profoundly reshaping the spatial pattern of global relative sea level (RSL) through glacial isostatic adjustment (GIA). However, existing long-term GIA simulations largely rely on traditional spherical-harmonic expansion or finite-difference frameworks, making it difficult to reconcile global far-field responses with nearshore high-resolution demands within a unified model. This study extends the Sea-Level module of the Ice-sheet and Sea-level System Model (ISSM) to long-term simulations since 122 ka. Driven by the ICE-6G_C ice-sheet reconstruction, we employ an unstructured variable-resolution triangular mesh (150 km near coastlines to 600 km in the open ocean) and viscoelastic Earth response theory to quantitatively resolve the synergistic effects of ice-sheet mass change and GIA processes on global RSL.
Simulation results indicate that the global ocean area-weighted mean RSL change is approximately –6 m. Spatially, the Antarctic near-field exhibits an average RSL rise of +14.60 m due to the combined effects of ice-sheet loading and crustal viscoelastic rebound; mid-to-low latitude far-field oceans experience an average RSL fall of approximately –6 m driven by mantle material migration. The global RSL change ranges from –23.88 m to +120.01 m, with a maximum vertical displacement of 130.63 m. These results quantitatively characterize the GIA-dominated spatial pattern of global RSL and are broadly comparable in magnitude to Last Interglacial coral-reef proxy records.
This study not only expands the application boundary of ISSM in long-term paleoclimate sea-level reconstruction, but also establishes a unified simulation framework that can be validated against paleo-sea-level constraints and further extended to regional high-resolution future projections, providing new numerical evidence for understanding ice-sheet–solid Earth–sea-level interactions.

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