Organic carbon export and loss rates in the Red Sea

The export and fate of organic carbon in the mesopelagic zone are still poorly understood and quantified due to lack of observations. We exploited data from a BGC-Argo float that was deployed in the Red Sea to study how a warm and hypoxic environment can affect the fate of the organic carbon in the ocean’s interior. We observed that only 10% of the particulate organic carbon (POC) exported survived at depth due to remineralization processes in the upper mesopelagic zone. We also found that POC exported was rapidly degraded in a first stage and slowly in a second one, which may be dependent on the palatability of the organic matter. We observed that AOU-based loss rates (a proxy of the remineralization of total organic matter) were significantly higher than the POC-based loss rates, likely because changes in AOU are mainly attributed to changes in dissolved organic carbon. Finally, we showed that POC- and AOU-based loss rates could be expressed as a function of temperature and oxygen concentration. These findings advance our understanding of the biological carbon pump and mesopelagic ecosystem.

Citation

Kheireddine, M., Dall’Olmo, G., Ouhssain, M., Krokos, G., Claustre, H., Schmechtig, C., … Jones, B. H. (2020). Organic carbon export and loss rates in the Red Sea. Global Biogeochemical Cycles. doi:10.1029/2020gb006650

Sponsors

The authors express their gratitude to the scientists, officers and crews of the research vessel Thuwal for logistical support and assistance onboard during the deployment of the BGC-Argo float. U. Langner is cordially thanked for plotting the map of the Red Sea, L. Legendre and L. Prieur, Peter Brewer and Edward Peltzer for their advices and discussions on the results presented here and for reading the manuscript. This study is funded by the King Abdullah University of Science and Technology (KAUST), Kingdom of Saudi Arabia. The collection of the data was funded by a European Research Council Advanced grant (remOcean, agreement no. 246577) while final writing was funded by a European Research Council Advanced grant (REFINE, agreement no. 834177). The data presented here are freely available by the International Argo Program and the national programs that contribute to it (http://argo.jcommops.org).