Formation of the Alboran oxygen minimum zone

Abstract

The enhanced oxygen minimum in the western Alboran Sea is the result of a chain of processes starting with nutrient injection into the inflowing Atlantic water at the Strait of Gibraltar. These nutrients originate in the outflowing Levantine Intermediate Water, outflowing Mediterranean deep water, and inflowing North Atlantic Central Water (from 200 m). They are injected into the inflowing Atlantic surface water by strong mixing at the eastern end of the Strait. They move with Atlantic surface waters along the Spanish coast, mix with nutrients upwelling in the northwestern Alboran Sea and stimulate phytoplankton productivity. The organic matter produced by this mechanism is transported both with the anticyclonically flowing waters of the Alboran gyre and with the waters that converge at the center of the gyre. Sedimentation in this convergence zone helps to deliver this organic matter to the Levantine Intermediate. Water where bacteria metabolize it to CO2 at the expense of the existing oxygen. This mechanism develops the most intense oxygen minimum zone in the Mediterranean Sea.