Evidence of Increased Deep Ocean Warming From a Sea Level Budget Approach

Abstract Assessments of the global mean sea level (GMSL) budget over the satellite altimetry era (since the early 1990s) have concluded that the GMSL budget is closed within data uncertainties until 2016. However, studies have shown that since then, the sea level budget based on Argo data down to 2,000 m for the thermosteric contribution is no longer closed. Using an ocean reanalysis with no altimetry data assimilation, we show that accounting for deep ocean thermosteric contribution (below 2,000 m, not sampled by Argo) allows the GMSL budget to be almost closed since 2016. The deep ocean contribution over 2005–2022 is estimated to be 0.4 ± 0.15 mm/yr, that is, about 10% of the observed GMSL rise over that period. This represents a substantial increase of the deep ocean contribution to sea level rise, previously estimated on the order of 0.1 mm/yr only over 1980–2010. This finding reveals that deep ocean warming is gaining importance and that ocean heat uptake has now reached several regions below 2,000 m depth, notably the Northwestern Atlantic Ocean and Southern Ocean.