How does downwelling occur in subtropical ocean regions?

In subtropical ocean regions, downwelling occurs primarily due to wind-driven Ekman transport, which creates zones of surface water convergence.12

As wind blows across the ocean surface, the Coriolis force causes the surface layer to move at an angle—to the right of the wind direction in the Northern Hemisphere and to the left in the Southern Hemisphere. In subtropical anticyclonic systems, this transport drives surface waters toward the center of the gyre. Because these surface waters are less dense than the deeper water, they accumulate and are forced downward into the deeper ocean.123

This process creates a "hill" in sea level and results in the formation of deep lenses of warm, saline water, such as the North Atlantic Central Water found in the Sargasso Sea. Because this downwelling removes nutrients from the surface layer, these subtropical regions are typically characterized as being poor in marine life.132