Nested Coherence Transitions in Arctic Sea Ice Dynamics (Paper 4, V1)

The preceding papers in this series identified a non-monotonic coherence transition in large- scale geophysical observables, biological growth dynamics, and deep-ocean temperature fields, raising the question of whether the same organizational signature appears in the cryosphere. Here we analyze Arctic sea ice extent using a null-first, dimensionless framework designed to isolate internal coordination rather than external forcing or absolute variability. Using daily regional sea ice extent from the NSIDC Sea Ice Index v4.0, we examine coherence between subregional dynamics as a function of seasonal depth, defined relative to each annual melt–freeze cycle. After removing climatological seasonality and rescaling time, we find a robust rise–peak–collapse structure in inter-regional coherence. The observed transition exceeds the 95th percentile of time-shuffled null models and disappears under spatial aggregation, indicating that it reflects internal organization rather than stochastic fluctuation or common forcing. Sea ice provides a particularly stringent test of cross-scale structure due to its strong sea- sonal driver, geometric constraints, and slow collective dynamics. The appearance of the same coherence transition in this domain extends the evidence for a scale-invariant organizational sig- nature to the cryosphere. Together with the earlier results, this finding supports the view that complex systems may enter larger constraint domains through transient increases in internal coordination, followed by a breakdown when integration capacity is exceeded.