Anthropogenic perturbation of carbon fluxes from land to ocean has significantly altered the natural carbon cycle. A synthesis of published research shows that human activities have increased the flux of carbon to inland waters by up to 1.0 Pg C yr⁻¹ since pre-industrial times, mainly due to enhanced carbon export from soils. Most of this additional carbon is either emitted back to the atmosphere as CO₂ or sequestered in sediments, leaving only a small perturbation of -0.1 Pg C yr⁻¹ to the open ocean. Terrestrial ecosystems currently store -0.9 Pg C yr⁻¹, which aligns with forest inventory results but differs from previous estimates that ignored lateral carbon fluxes. The study emphasizes the need to include carbon fluxes along the land–ocean aquatic continuum in global CO₂ budgets. Human activities over the past two centuries have significantly modified the exchange of carbon and nutrients between land, atmosphere, freshwater bodies, coastal zones, and the open ocean. Land-use changes, soil erosion, liming, fertilizer and pesticide application, sewage-water production, damming of water courses, water withdrawal, and human-induced climatic change have altered the delivery of these elements through the aquatic continuum, impacting global biogeochemical cycles. The importance of the aquatic continuum in terms of lateral carbon fluxes has been known for over two decades, but the magnitude of its anthropogenic perturbation has only recently become apparent. The lateral transport of carbon from land to sea has long been considered a natural loop in the global carbon cycle unaffected by anthropogenic perturbations. However, this flux is currently neglected in assessments of the anthropogenic CO₂ budget, such as those by the IPCC or the Global Carbon Project. Quantifying lateral carbon fluxes and their implications for CO₂ exchange with the atmosphere is crucial for understanding the mechanisms driving the natural carbon cycle along the aquatic continuum and for closing the carbon budget of anthropogenic perturbations. Data on the carbon cycle in the aquatic continuum from land to ocean are sparse, with insufficient water sampling, poorly constrained hydrology, and surface area extent of various ecosystems, and few direct pCO₂ and other carbon-relevant measurements. Global box models have been used to explore the magnitude of these fluxes and their anthropogenic perturbations, but the processes remain highly parameterized. The current generation of three-dimensional Earth system models includes the coupling between the carbon cycle and the physical climate system but ignores lateral flows of carbon (and nutrients) altogether. Major challenges in studying carbon in the aquatic continuum include disentangling anthropogenic perturbations from natural transfers, identifying the drivers of ongoing changes, and forecasting their future evolution. The term 'boundless carbon cycle' refers to the present-day lateral and vertical carbon fluxes to and from inland waters. This concept is extended to all components of the global carbon cycle connected by the land–ocean aquatic continuum. The study provides new separate estimates for the present day and theAnthropogenic perturbation of carbon fluxes from land to ocean has significantly altered the natural carbon cycle. A synthesis of published research shows that human activities have increased the flux of carbon to inland waters by up to 1.0 Pg C yr⁻¹ since pre-industrial times, mainly due to enhanced carbon export from soils. Most of this additional carbon is either emitted back to the atmosphere as CO₂ or sequestered in sediments, leaving only a small perturbation of -0.1 Pg C yr⁻¹ to the open ocean. Terrestrial ecosystems currently store -0.9 Pg C yr⁻¹, which aligns with forest inventory results but differs from previous estimates that ignored lateral carbon fluxes. The study emphasizes the need to include carbon fluxes along the land–ocean aquatic continuum in global CO₂ budgets. Human activities over the past two centuries have significantly modified the exchange of carbon and nutrients between land, atmosphere, freshwater bodies, coastal zones, and the open ocean. Land-use changes, soil erosion, liming, fertilizer and pesticide application, sewage-water production, damming of water courses, water withdrawal, and human-induced climatic change have altered the delivery of these elements through the aquatic continuum, impacting global biogeochemical cycles. The importance of the aquatic continuum in terms of lateral carbon fluxes has been known for over two decades, but the magnitude of its anthropogenic perturbation has only recently become apparent. The lateral transport of carbon from land to sea has long been considered a natural loop in the global carbon cycle unaffected by anthropogenic perturbations. However, this flux is currently neglected in assessments of the anthropogenic CO₂ budget, such as those by the IPCC or the Global Carbon Project. Quantifying lateral carbon fluxes and their implications for CO₂ exchange with the atmosphere is crucial for understanding the mechanisms driving the natural carbon cycle along the aquatic continuum and for closing the carbon budget of anthropogenic perturbations. Data on the carbon cycle in the aquatic continuum from land to ocean are sparse, with insufficient water sampling, poorly constrained hydrology, and surface area extent of various ecosystems, and few direct pCO₂ and other carbon-relevant measurements. Global box models have been used to explore the magnitude of these fluxes and their anthropogenic perturbations, but the processes remain highly parameterized. The current generation of three-dimensional Earth system models includes the coupling between the carbon cycle and the physical climate system but ignores lateral flows of carbon (and nutrients) altogether. Major challenges in studying carbon in the aquatic continuum include disentangling anthropogenic perturbations from natural transfers, identifying the drivers of ongoing changes, and forecasting their future evolution. The term 'boundless carbon cycle' refers to the present-day lateral and vertical carbon fluxes to and from inland waters. This concept is extended to all components of the global carbon cycle connected by the land–ocean aquatic continuum. The study provides new separate estimates for the present day and the