Remineralization and preservation of the Organic Matter (OM) in the Peruvian Oxygen Minimum Zone

The intense surface production in the Eastern Boundary Upwelling Systems (EBUS), linked to the low subsurface ventilation, leads to the formation of the Oxygen Minimum Zone (OMZ). The degradation of Organic Matter (OM) by respiration or remineralization impacts climate (ocean carbon sequestration; greenhouse gases emission (e.g. N2O, CO2)) and ecosystems (nitrogen loss; toxic gas (e.g. H2S) production). Due to the O2 stress, OM fate is an OMZ key-issue. On one hand, the low O2 concentration would imply OM preservation, enhancing the export to the sediments. On the other hand, the intense bacteria activity would imply OM recycling. The Peruvian EBUS, one of the most productive systems with the shallowest oxycline, is the perfect case study to investigate both hypotheses. In order to study the particles fluxes and its variability, sediment traps in the oxycline (35 m) and OMZ core (150 m) were deployed on an instrumented moored line off Lima (12°S) in 2013-2014, as part of the AMOP project (Activities of research dedicated to the Minimum of Oxygen in the eastern Pacific).The particles proportion which reaches the deep trap allows to define mathematically a vertical transfer function, suggesting predominant remineralization and preservation configurations. Concerning OM quality, carbon and nitrogen fluxes are proportional to the matter fluxes, contrary to phosphorus and biogenic silica fluxes. The different configurations derived from the transfer function analysis in terms of both OM quantity and quality can mainly be linked to oxygenation conditions, with a potential remineralization predominance associated with O2 concentration at the oxycline higher than a threshold of ~5 µmol/kg. Oxygenation events are alternately associated with a specific influence of SubTropical Water, more or less oxygenated (Surface (STSW) or Under (STUW), respectively).