North Atlantic sea level budget revisited

Based on satellite altimetry, GRACE space gravimetry and ARGO-based steric data down to 2000m, recent studies have shown that the North Atlantic sea level budget of the past two decades is not closed, with strong regional residuals in the mid-latitudes. It was proposed that this results from salinity errors reported since 2015/2016 in some Argo float measurements. In this study,  we revisit the North Atlantic sea level budget using altimetry, GRACE, different Argo products and ocean reanalyses. The reanalyses are used to estimate the manometric contribution for further comparisons with GRACE data, as well as for estimating the deep ocean contribution to the sea level budget, not yet sampled by Argo. We first find that using the CIGAR ocean reanalysis-based manometric component instead of GRACE reduces the residuals of the sea level budget in the North Atlantic (ie, altimetry-based sea level minus sum of components). We also find that accounting for the deep ocean (below 2000m) thermal expansion (from the CIGAR reanalysis) allows for the quasi closure of the North Atlantic sea level budget. The North Atlantic halosteric component in the upper 2000 m displays a small decrease since the early 2010s, significantly larger after 2016. The 2010–2016 halosteric decrease may reflect a real salinity increase in the region, but salinity measurement errors may have impacted the halosteric component after that date. The main result of this study is that deep ocean warming plays a non-negligible role in the North Atlantic and has to be accounted for in the sea level budget assessment.