Multidecadal sea level rise hiatus in the tropical Atlantic margin off northwest Africa

Abstract. Satellite and reanalysis data sets are used to find and explain the drivers of a multidecadal sea level rise hiatus in the tropical North Atlantic margin off northwest Africa. The study domain sea level was rising as far back as 1986, and the hiatus began around 2010 and stopped in 2019. Mean sea level anomaly during a rising period (1996–2004) was compared to the hiatus period (2010–2018). Results show that domain-wide seawater expansion owing to shifts in density structure (steric shifts) contributed 74 % of the multidecadal sea level shift and increase in mass contributed 22 %. There are, however, regional differences in the steric and mass shift patterns. In the northern subdomain, the steric shift is dominated by salinity-driven (halosteric) expansion, whereas in the southern subdomain the steric shift is dominated by temperature-driven (thermosteric) expansion. Stronger anticyclonic circulation shift in the Guinea Dome, a permanent upwelling region where isotherms are displaced upwards, and the necessary adjustment of horizontal flow toward this anticyclonic sink, enable accumulation of low-salinity water in the northern subdomain and precipitation in the southern subdomain. The low-salinity water influx to the northern subdomain is linked to a shift in the southward-flowing Canary Current. This current was freshened by subpolar North Atlantic waters that reached the northwest African coast via two pathways: an open ocean path that is consistent with the Azores current, and a Western Europe coastal ocean path. These results highlight a multidecadal linkage between subpolar salinity anomalies and tropical sea level anomalies in the North Atlantic, with a transit period of about 5.5 years.