Significant Impact of Non‐Tidal Oceanic and Atmospheric Mass Variations on Regional Ocean Mass Budgets: A Comparative Analysis Across 19 Representative Regions

Abstract Accurate quantification of regional ocean mass changes is crucial for coastal communities to formulate effective management strategies. The regional ocean mass budget comprises the barystatic component driven by terrestrial water and ice mass changes, and ocean mass redistribution resulting from non‐tidal oceanic and atmospheric (Nt‐OcnAtm), the latter being zero in the global mean. This study investigates the influence of the Nt‐OcnAtm component on the ocean mass budget across 19 critical marginal seas spanning the period from 2005 to 2015, utilizing an improved ocean mass budget equation. Our analyses suggest that 14 regions close the ocean mass budget within 1‐sigma uncertainty, while five regions close within 1.65‐sigma uncertainty. Then, the findings indicate that the Nt‐OcnAtm component significantly impacts regional ocean mass budgets on both spatial and temporal scales, and its importance is equivalent to that of barystatic. In regions with pronounced seasonal fluctuations (e.g., the Southeast Asian Coast and the Red Sea), ocean mass variations are predominantly controlled by Nt‐OcnAtm. Additionally, the Nt‐OcnAtm component is responsible for anomalous changes in regional ocean mass, such as the significant positive mass anomalies observed in the Mediterranean Sea during 2010–2011. Furthermore, the Nt‐OcnAtm component accounts for more than 50% of the total trend budget in five regions. Wind‐driven Nt‐OcnAtm component is also identified as a major source of interannual variability in regional ocean mass. These findings underscore the importance of the Nt‐OcnAtm component in regional ocean mass budgets and highlight the necessity of quantifying it separately when conducting attribution analyses.