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

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. Plain Language Summary In this study, we explore for the first time the seasonal cycle of the main ocean currents existing at the eastern side of the North Atlantic Subtropical Gyre using data from four cruises that took place in each season in 2015. The Canary Current (CC) is the southward flow that connects the Azores Current with the North Equatorial Current. The 2015 estimations show that CC shifts westward from winter to fall. In addition, it also changes transport seasonally being the weakest in spring and summer, and the strongest in fall. The Lanzarote Passage (LP) is the geographical area between Lanzarote and Africa, it is considered to be the eastern end of the North Atlantic Subtropical Gyre. Through the LP the flow is mainly southward except in fall when the flow reverses. A composite seasonal cycle arises from combining all the available observations with the outputs of this study. The LP seasonal amplitude and cycle match the ones of the Atlantic Meridional Overturning Circulation (AMOC) measured by the RAPID-MOCHA data array. These results indicate that this seasonal cycle of the AMOC is driven by the dynamics of the eastern boundary currents.