Western boundary currents (WBCs) play an essential role in regulating
global climate. In contrast to their widely examined horizontal motions,
less attention has been paid to vertical motions associated with WBCs.
Here, we examine the vertical motions associated with the major WBCs by
analyzing vertical velocity estimates from five ocean synthesis products
and one eddy-resolving ocean simulation. These data reveal robust and
intense subsurface upwelling in five major subtropical WBC systems.
These upwelling systems are parts of basin-scale zonal overturning
circulations and are likely driven by the meridional pressure gradients
along the western boundary. The intense subsurface upwelling associated
with WBCs and the basin-wide zonal overturning circulations are
potentially crucial for the transport of properties and materials in the
ocean interior but have long been neglected in the literature. This
study suggests an overlooked role of WBCs in the climate system and
showcases the usefulness of ocean vertical velocity estimates from
various data products.