The Seasonal Cycle of the Eastern Boundary Currents of the North Atlantic Subtropical Gyre

Abstract

For the first time, four dedicated hydrographic cruises—one in each season—took place in 2015 around the Canary Islands to determine the seasonality of the flows at the eastern boundary of the North Atlantic Subtropical Gyre. The Canary Current (CC) is the eastern boundary current of the North Atlantic Subtropical Gyre and links the Azores Current with the North Equatorial Current. The 2015 estimations show that the CC has a seasonal behavior in its path and strength, flowing on its easternmost position in winter (3.4 ± 0.3 Sv), through the Canary Islands in spring (2.1 ± 0.7 Sv) and summer (2.0 ± 0.6 Sv) and on its westernmost position in fall (3.2 ± 0.4 Sv). At the Lanzarote Passage (LP), the dominant flow is southward except in fall, where a northward transport is observed at the surface (1.1 ± 0.3 Sv) and intermediate (1.3 ± 0.2 Sv) layers. Combining all the available transport estimations, a historical composite observational seasonal cycle is constructed which fits the 2015 seasonal cycle. Hence, a solid seasonal cycle is constructed supported by all the available observations in the area. The LP seasonal cycle and its seasonal amplitude match the seasonal cycle and amplitude of the Atlantic Meridional Overturning Circulation (AMOC) measured by the RAPID-MOCHA data array. These results indicate that the seasonal cycle of the AMOC of the RAPID-MOCHA data array is driven by the dynamics of the eastern boundary current system.