Do Oceanic Hypoxic Regions Act as Barriers for Sinking Particles? A Case Study in the Eastern Tropical North Atlantic

• Published in: Global Biogeochemical Cycles
• Main Authors: Rasse, R, Dall'Olmo, G
• Format: Article in Journal/Newspaper
• Language: English
• Published: AGU100 2019
• Subjects: North Atlantic
• Online Access: http://plymsea.ac.uk/id/eprint/8881/; http://plymsea.ac.uk/id/eprint/8881/1/Rasse_DallOlmo_2019.pdf; https://doi.org/10.1029/2019GB006305

In oxygen minimum zones (OMZs), the attenuation rates of particulate organic carbon (POC) fluxes of large particles are known to be reduced, thus increasing the efficiency with which the biological carbonpump(BCP)transferscarbontotheabyss.TheBCPefficiencyisexpectedtofurtherincreaseifOMZs expand. However, little is known about how the POC fluxes of small particles—a significant component of the BCP—are attenuated inside OMZs. In this study, data collected by two BGC‐Argo floats deployed in the hypoxic OMZ of the eastern tropical North Atlantic were used to estimate net instantaneous fluxes of POCviasmallparticleduring3years.Thisinformationwasanalyzedtogetherwithmeteorologicaldataand published POC fluxes of large particles and allowed us to conclude that (1) major pulses of surface‐derived small particles toward the OMZ interior coincided with seasonal changes in wind stress and precipitation; (2) a permanent layer of small particles, presumably linked to microbial communities, was found in the upper section of the OMZ which might play a key role attenuating POC fluxes; and (3) fluxes of large particles were attenuated less efficiently inside this poorly oxygenated region than above it, while attenuation of small‐particle fluxes were equivalent or significantly higher inside the OMZ. These results highlight that more information about the processes controlling the fluxes of small and large particles in hypoxic OMZs is needed to better understand the impact of hypoxic OMZs on the BCP efficiency.