Coupled CO2 and O2-driven compromises to marine life in summer along the Chilean sector of the Humboldt Current System

[摘要] Carbon dioxide and coupled CO₂ and O₂-driven compromises to marinelife were examined along the Chilean sector of the Humboldt Current System,a particularly vulnerable hypoxic and upwelling area, applying theRespiration index (RI = log₁₀ pO₂pCO₂) and thepH-dependent aragonite saturation (Ω) to delineate the water masseswhere aerobic and calcifying organisms are stressed. As expected, there wasa strong negative relationship between oxygen concentration and pH orpCO₂ in the studied area, with the subsurface hypoxic EquatorialSubsurface Waters extending from 100 m to about 300 m depth and supportingelevated pCO₂ values. The lowest RI values, associated to aerobicstress, were found at about 200 m depth and decreased towards the Equator.Increased pCO₂ in the hypoxic water layer reduced the RI values by asmuch as 0.59 RI units, with the thickness of the upper water layer thatpresents conditions suitable for aerobic life (RI>0.7) declining by halfbetween 42° S and 28° S. The intermediate waters hardly reached thosestations closer to the equator so that the increased pCO₂ lowered pH andthe saturation of aragonite. A significant fraction of the water columnalong the Chilean sector of the Humboldt Current System suffers fromCO₂–driven compromises to biota, including waters corrosive tocalcifying organisms, stress to aerobic organisms or both. The habitat freeof CO₂-driven stresses was restricted to the upper mixed layer and tosmall water parcels at about 1000 m depth. Overall pCO₂ acts as a hingeconnecting respiratory and calcification challenges expected to increase inthe future, resulting in a spread of the challenges to aerobic organisms.

[学科分类] 地球化学与岩石