The fate of the organic matter (OM) produced by marine life controls the major biogeochemical cycles of the Earth's system. The OM produced through photosynthesis is either preserved, exported towards sediments or degraded through remineralisation in the water column. The productive eastern boundary upwelling systems (EBUSs) associated with oxygen minimum zones (OMZs) would be expected to foster OM preservation due to low O₂ conditions. But their intense and diverse microbial activity should enhance OM degradation. To investigate this contradiction, sediment traps were deployed near the oxycline and in the OMZ core on an instrumented moored line off Peru. Data provided high-temporal-resolution O₂ series characterising two seasonal steady states at the upper trap: suboxic ([O₂] < 25µmolkg−1) and hypoxic–oxic (15 < [O₂] < 160µmolkg−1) in austral summer and winte...

The oxygen minimum zone (OMZ) of Peru is recognized as a source of CO₂ to the atmosphere due to upwelling that brings water with high concentrations of dissolved inorganic carbon (DIC) to the surface. However, the influence of OMZ dynamics on the carbonate system remains poorly understood given a lack of direct observations. This study examines the influence of a coastal Eastern South Pacific OMZ on carbonate system dynamics based on a multidisciplinary cruise that took place in 2014. During the cruise, onboard DIC and pH measurements were used to estimate pCO₂ and to calculate the calcium carbonate saturation state ( Ω aragonite and calcite). South of Chimbote (9ºS), water stratification decreased and both the oxycline and carbocline moved from 150m depth to 20–50m below the surface. The aragonite saturation depth was observed to be close to 50m. However, values <1.2 were detect...