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A multidecadal sea level rise and its hiatus in the tropical Atlantic margin off northwest Africa
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DOI：10.5194/os-22-2059-2026.png)
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Abstract
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Abstract. Satellite and reanalysis data sets are analyzed to explain sea level changes in the tropical North Atlantic margin off northwest Africa. The study domain sea level was rising as far back as 1986 and a pause in sea level rise (hiatus) began around 2010 and stopped in 2019. Characteristics of sea level anomaly and its drivers during a period of rise (1996–2004) and the hiatus period (2010–2018) are analyzed and compared. Results show that the most effective cause of domain-wide sea level rise during the period of rise is seawater expansion owing to changes in density structure (steric expansion); with almost equal contribution from temperature-driven (thermosteric) expansion and salinity-driven (halosteric) expansion. The cause of the domain-wide pause in sea level rise is a large thermosteric contraction that counteracted halosteric expansion and mass accumulation. Multidecadal sea level increase; defined here as the difference between the mean sea level during the period of rise and the hiatus period; is owing to steric expansion; vertical land motion; and mass accumulation; which contributed 56 %; 24 %; and 16 %; respectively. There are; however; regional differences in the patterns of multidecadal steric and mass adjustment. In the northern subdomain where ocean processes predominate mass-driven sea level variability; the steric adjustment is dominated by halosteric expansion; whereas in the southern subdomain where atmosphere-ocean processes predominate mass-driven sea level variability; the steric adjustment is dominated by thermosteric expansion. The accumulation of low-salinity water in the northern subdomain and precipitation in the southern subdomain appears to be associated with a mutual adjustment of vertical and horizontal velocity distribution inside the domain and west of it in the area of the Guinea Dome; a permanent upwelling region where isotherms are displaced upwards. The low-salinity water influx to the northern subdomain is linked to changes in the southward-flowing Canary Current. A probable hypothesis inferred from correlation and potential vorticity analysis is that the Canary Current source region was freshened by currents that supply water to the region via two pathways: an open ocean path that is consistent with the Azores Current; and a Western Europe coastal ocean path that is consistent with the Portugal Current and Portugal Coastal Current system. The results obtained highlight a multidecadal linkage between sea level anomalies in the eastern tropical North Atlantic margin and salinity anomalies elsewhere in the North Atlantic.
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