Which type of boundary currents are characterized as shallow and broad, with poorly defined boundaries?

The type of boundary currents that are characterized as shallow and broad, with poorly defined boundaries, are indeed the eastern boundary currents. These currents flow along the eastern edges of ocean basins and tend to be slower and wider compared to their western counterparts. Due to their broad nature, they frequently lack sharp differentiation from the surrounding waters. This contrasts with western boundary currents, which are typically narrow, fast, and flow along the western edges of ocean basins, often exhibiting a more defined structure.

Eastern boundary currents generally result from the wind patterns in the subtropics and are influenced by the Ekman transport effect, where surface waters diverge, allowing cooler, nutrient-rich waters from the depths to rise. This process leads to a rich ecological environment, making these areas often crucial for marine productivity.

Equatorial currents, while also broad, are primarily located along the equator and behave differently due to the influence of the Coriolis effect. Southern boundary currents refer to currents found in the Southern Ocean and have regional characteristics distinct from eastern boundary currents.