A review typically has a comprehensive review of the literature, this manuscript lists 10 references. With a thorough review of the existing literature the author would have been aware that Arctic rivers are supersaturated with CO₂ most of the year, representing a source of CO₂ to the atmosphere and not a sink. The supersaturation in the rivers comes from the respiration of organic carbon mobilized from the watershed vegetation and soil.

General Comment:

This manuscript presents a compelling and perspective on the role of abiotic carbon sequestration through river runoff as a potential contributor to the "missing sink" in the global carbon cycle. The author offers a quantitative estimate of CO₂ dissolved in cold river waters flowing into the Arctic Ocean, arguing for its inclusion in global carbon budget assessments.

However, the current version suffers from serious shortcomings in both novelty and scientific rigor. The review of existing literature is notably insufficient. For instance, riverine carbon transport and its climatic implications have been extensively examined in previous studies, such as Ito (2019, Earth Syst. Dynam., doi:10.5194/esd-10-685-2019), which provides a comprehensive modeling framework, and Li et al. (2025, Environ. Rev., doi:10.1139/er-2024-0078), which offers a detailed review of recent advances in this domain.

Compared to these prior works, the present manuscript appears underdeveloped. It lacks a robust theoretical foundation and fails to engage meaningfully with the existing body of knowledge. The argumentation remains superficial, and critical processes—such as biogeochemical transformations at river-ocean interfaces—are not adequately addressed. There is also a lack of mechanistic explanation to support the central claims.

In its current form, the manuscript does not meet the standards required for publication. I cannot recommend acceptance at this stage. Substantial revisions are necessary, including a thorough review of the relevant literature and a deeper theoretical discussion to justify the scientific importance of the work. Only after these major improvements can the manuscript be reconsidered for publication.