Coastal to deep-marine geomorphic classification: a standardised framework and review of terms to support globally consistent mapping

Marine and coastal geomorphology is inherently interdisciplinary, involving the interpretation of landforms shaped by overlapping hydrodynamic, sedimentary, tectonic, and biogenic processes across diverse physiographic settings. As the United Nations Decade of Ocean Science drives the collection of information to address ocean challenges, geomorphic data is becoming an increasingly critical baseline resource to support evidence-based decision-making. Standardised, inter-jurisdictional geomorphic frameworks enable consistent terminology across scales. Though marine sub-discipline lexicons are generally well established, seabed geomorphology mapping encompasses terminological nuances that can hinder analysts working across disciplinary boundaries. To address these challenges, the International Seabed Geomorphology Mapping Working Group (ISGM) developed a comprehensive classification framework using an Ocean Best Practice process that incorporates science-community input. This two-part approach separates morphological mapping (Part 1) from geomorphic interpretation (Part 2), constraining the uncertainty inherent to stratigraphic interpretation to a second step. In Part 1, 40 bathymetric shapes are defined using standardised Morphology Feature terms. In Part 2, a hierarchical framework and glossary of 400 terms across 11 overlapping classes assigns geomorphic interpretation. The framework supports classification from Setting/Process through basic geomorphic units (BGU), types (BGU-T) and sub-types (BGU-sT), allowing users to tailor classification to available data quality and application needs. Implementation is supported by open-access, machine-readable digital vocabularies, which standardise established terms without redefining them, and GIS tools. Applied examples demonstrate utility across global datasets. By integrating existing terminology into a standardised hierarchy, the ISGM approach provides the first cross-class geomorphic framework capable of supporting consistent terminology from global to local scales.