Final answer:
Ocean currents occur on both the surface, driven by wind, and at depth, driven by thermohaline processes due to temperature and salinity differences, leading to varying densities and creating circulation.
Step-by-step explanation:
Ocean currents can be found both on the surface and deep in the ocean. Surface currents are driven mainly by wind, while the deep ocean currents are thermohaline driven due to differences between temperature and salinity (salt concentration). The very cold water sinks due to increased density. The cold water is replaced by warmer, less dense water, creating circulation that results in ocean currents.
The diverse ocean ecosystems, which include the shallow ocean, deep ocean water, and deep ocean surfaces, are critical for the health of our planet. The Coriolis effect also influences these patterns of water movement, distributing heat more evenly over the surface of the planet. Furthermore, the exchange of water at zones like the Subtropical Convergence leads to upwelling and high levels of productivity, which are essential for a variety of marine organisms, from phytoplankton to krill.