Water column characteristics in the Clarion Clipperton Fracture Zone, north-eastern tropical Pacific Ocean
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Four exploration license areas for manganese nodules (German, Inter Ocean Metal, Belgian, and French) and one Area of Particular Environmental Interest, located within Clarion-Clipperton Fracture Zone (north-eastern tropical Pacific Ocean) were investigated in terms of CTD, nutrients and chlorophyll data during the SONNE 239 cruise carried out in March-April 2015. Chlorophyll measured either in the surface layer (concentrations within 0.05-0.15 mg·m-3) or subsurface chlorophyll maximum layer (concentrations within 0.23-0.45 mg·m-3) showed a quite low primary productivity, strongly influenced by the thermocline position. The shallow thermocline (75-90 m depth) observed in the southern edge of the studied area (≈11°N) led to a shallow and moderate subsurface chlorophyll maximum layer (50-60 m depth and concentrations within 0.4-0.45 mg·m-3). Northwards, at ≈18°N, the thermocline dropped down to 120 m depth, resulting in a deeper (110 m depth) and weaker subsurface chlorophyll maximum (concentration of 0.23 mg·m-3). The oxygen minimum layer, characteristic to the eastern Pacific Ocean, showed a spatial variability in the studied area in terms of the depth of occurrence and thickness. Thus, shallower (80-90 m depth) and thicker (thickness within 1000-1050 m) oxygen minimum zones were observed in the southernmost license areas as compared to the northernmost area (280 m depth and thickness of 750 m).