1. Upwelling Currents play a huge role in marine productivity, through a process called upwelling. Sea life is concentrated in the sunlit waters near the surface, but most organic matter is far below, in deep waters and on the sea floor. When currents upwell, or flow up to the surface from beneath, they sweep vital nutrients back to where they're needed most.

2. Downwelling Downwelling, or the sinking of surface water
Downwelling Downwelling, or the sinking of surface water. Downwelling takes oxygen-rich surface water and to the deep sea. Without this renewal, the dissolved oxygen in bottom sediments and waters would quickly be used up by the decay of organic matter. Anaerobic bacteria would take over decomposition, leading to a build up of hydrogen sulfide. Few benthic animals would survive such toxic conditions.In the most extreme cases, a lack of downwelling may lead to mass extinctions.