What is the primary factor that causes the formation of eddies in boundary currents?

The formation of eddies in boundary currents is primarily attributed to sharp boundaries. These sharp boundaries occur where there is a significant transition in water properties, such as when warm and cold water masses meet, or where ocean currents encounter coastlines, underwater topography, or other currents. When the flow of water is constrained by these features, it can lead to instabilities, causing the current to break away from the main flow and form rotating masses of water known as eddies.

This process is influenced heavily by the dynamics of fluid flow, where the interaction of the boundary current with geographical features creates conditions conducive to swirling motion. The distinct change in the flow direction at these boundaries introduces turbulence and rotational patterns, which manifest as eddies. Understanding this interaction is crucial for comprehending ocean circulation, mixing processes, and the distribution of heat and nutrients in the ocean.

While temperature gradients, wind patterns, and depth differences certainly influence ocean dynamics, they do not play as direct a role in the immediate generation and formation of eddies as the sharp boundaries do.