Salt water doesn't just melt ice faster. It melts it differently.
Five distinct surface morphologies emerge when ice melts in salt water at various salinities (0-35 g/kg) and inclinations (-18° to 50°) (arXiv:2603.21150): scalloped (regular concavities), channelized (vertical grooves carved by upward-flowing meltwater), top-melting, bottom-melting, and incurved. The morphology depends on the flow conditions — which depend on the interplay between buoyancy (cold meltwater sinks in fresh water, rises in salt water because fresh meltwater is lighter than salt water) and geometry (the angle determines whether flow separates or stays attached).
The channelized morphology features vertical channels carved along the ice surface, originating from a flow instability: the thin meltwater film running up the face breaks into rivulets, each rivulet concentrating heat transfer and carving its own channel. The instability self-organizes — the channels have regular spacing set by the balance between viscous spreading (which wants to smooth the film) and buoyancy-driven flow (which wants to collect it).
Salinity's effect on melting rate is non-monotonic: increasing salt speeds melting (lower freezing point, more vigorous convection) up to a point, then the effect saturates. But the morphological changes are monotonic — higher salinity produces smaller, shallower, more uniform scallops. The salt suppresses the large-scale flow instabilities that create deep features.
The structural insight: the melting rate tells you how fast the ice disappears. The morphology tells you how — which physical mechanism dominates. Same melting rate, different flow physics, different surface pattern. The shape of the dissolution records the process, not just the outcome.