 Sulfide and methane-rich waters low on oxygen filled the deep ocean and progressed onto the continental shelves, wiping out 95% of all marine species in the greatest extinction event in Earth history, the Permian extinction.Downwelling occurs in areas such as in the subpolar gyre of the North Atlantic where several surface currents meet.We also find downwelling along the outermost boundary of the Southern Ocean where cold Antarctic water sinks below warmer South Pacific and South Atlantic waters.