Oxygen concentration: pycnocline (750 m) and deep layer (3000 m)

Focusing on the water depth of 750m, the oxygen concentration in the mid-latitude region of the eastern Atlantic Ocean (Africa continent's Atlantic coast) is lower than the average oxygen concentration in the surrounding Atlantic Ocean. A clear oxygen minimum layer appears at a depth of 750m in this area. This is thought to be due to the sedimentation of organic matter produced in the surface layer in situ (mid-latitude North Atlantic) and the consumption of oxygen in the pycnocline.

　On the other hand, in the subtropical zone south of the Japanese archipelago in the northwestern Pacific Ocean (around 30 degrees north latitude), oxygen concentrations are higher than in the surrounding Pacific Ocean. (A pale yellow area in the Pacific Ocean near the Japanese archipelago is spreading to the east. Look carefully to find it.) This is because the surface water in the area to the north (seas off the coast of Tohoku) sinks due to cooling in winter and it spreads into the middle layer, including depths of 750 m. Because it is close to the subduction area of ​​middle-layer water, a high oxygen concentration is maintained in middle-layer water. This middle-layer water spreads throughout the subtropics, but if a long period of time passes after subduction, the oxygen concentration will decrease due to the decomposition of organic matter. As a result, oxygen concentrations are not elevated in the middle layer throughout the subtropical North Pacific, but only near the Japanese archipelago.

水深 water depth

　Focusing on deep water (3000 m), the oxygen concentration is arranged in order from highest to lowest: North Atlantic → South Atlantic → South Pacific → North Pacific, which is the same as the flow order of the deep circulation. It can be seen that in the deep layer, dissolved organic carbon contained in deep water is decomposed and the oxygen concentration continues to decrease.