A central challenge in Earth system science is determining whether anthropogenic warming simply amplifies existing variability or fundamentally reorganizes how different components of the Earth system regulate fluctuations. The ocean has absorbed increasing amounts of anthropogenic CO₂, leading to rising surface-ocean pCO₂ and potentially altering its temporal variability. While open-ocean carbon variability has received increasing attention, temporal changes in coastal-ocean pCO₂ variability remain poorly constrained, limiting assessments of coastal carbon uptake, acidification risk, and future biogeochemical extremes.

Here we investigate whether coastal and open-ocean carbon variability respond coherently or diverge under sustained anthropogenic forcing. Using nine independent observation-based pCO₂ products and 19 CMIP6 Earth system models, we identify a pronounced amplification of interannual pCO₂ variability in coastal regions relative to the open ocean. This amplification is pervasive across global continental margins and strengthens over time under continued forcing. Interannual variability in coastal regions not only exceeds offshore variability but also amplifies nearly twice as fast, resulting in a progressive widening of the coastal–open-ocean variance gap.

This divergence reflects a fundamental contrast in the mechanisms regulating carbon variability. Enhanced variability in pCO₂-relevant dissolved tracers strengthens non-thermal control of pCO₂ variability in coastal waters, whereas weaker tracer variability and stronger thermal–nonthermal compensation dampen variability growth offshore. Consequently, anthropogenic warming is not merely amplifying ocean carbon variability, but is progressively reorganizing the regulatory architecture governing variability across oceanic regimes.

Importantly, this structural divergence is not confined to pCO₂. Consistent and statistically robust amplification patterns are detected in dissolved inorganic carbon (DIC), alkalinity, and salinity, indicating that warming is reshaping the variability of multiple coupled tracers rather than altering a single carbon-cycle metric. Although amplification magnitudes differ among tracers, the direction and coastal–open-ocean contrast remain consistent across datasets and models.

Together, these findings reveal that anthropogenic forcing is reshaping the spatial architecture of ocean carbon variability, generating increasing heterogeneity between continental margins and the open ocean. Because coastal systems play a disproportionate role in air–sea CO₂ exchange and biogeochemical exposure, this divergence has important implications for carbon-cycle predictability, acidification risk, and future biogeochemical extremes.