Characterization of light absorption by chromophoric dissolved organic matter (CDOM) in the upper layer of the Red Sea
Calleja, Maria Ll.
Moran, Xose Anxelu G.
Tiwari, Surya Prakash
KAUST DepartmentRed Sea Research Center (RSRC)
Biological and Environmental Sciences and Engineering (BESE) Division
Marine Science Program
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AbstractThe absorption coefficient of chromophoric dissolved organic matter (CDOM) is a major variable used in developing robust bio‐optical models and understanding biogeochemical processes. Over the last decade, the optical properties of CDOM in the open sea have been intensely studied. However, their variations in clear water are poorly documented, particularly in the Red Sea, owing to the absence of in situ measurements. We performed several cruises in the Red Sea to investigate the spatial distribution of the absorption coefficient of CDOM. The spectral absorption coefficients were determined from 400nm to 740nm using a WETLabs ac-s hyper-spectral spectrophotometer. In general, we found a latitudinal gradient in the CDOM absorption coefficient at 443nm (aCDOM(443)) from south to north that is likely influenced by the exchange of water through the strait of Bab-el-Mandeb and the thermohaline circulation of the Red Sea. However, high aCDOM(443) values were observed in the northern Red Sea due to the existence of a sub-mesoscale feature that may induce an increase in phytoplankton production and lead to CDOM production. The aCDOM(443) covaried with the chlorophyll a concentration ([Chl a],) despite a high scatter. Furthermore, the aCDOM(443) for a given [Chl a] concentration was higher than those predicted by global ocean bio-optical models. This study advances our understanding of CDOM concentration in the Red Sea and may help improve the accuracy of the algorithms used to obtain CDOM absorption from ocean color.
CitationKheireddine M, Ouhssain M, Calleja ML, Morán XAG, Sarma YV., et al. (2018) Characterization of light absorption by chromophoric dissolved organic matter (CDOM) in the upper layer of the Red Sea. Deep Sea Research Part I: Oceanographic Research Papers. Available: http://dx.doi.org/10.1016/j.dsr.2018.02.001.
SponsorsThe authors express their gratitude to the scientists, officers and crews of the research vessel Thuwal and the Coastal and Marine Resources Core Lab for logistical support and assistance onboard during the fieldwork. V. Vellucci, E. Organelli and E. Boss are cordially thanked for their advice and valuable discussions of the results presented here. We also thank David Antoine and Annick Bricaud for providing CDOM absorption data collected in the Mediterranean Sea (BOUSSOLE project, “BOUée pour l’acquiSition d’une Série Optique à Long termE project”) and in the Pacific Ocean (BIOSOPE cruise, “Biogeochemistry and Optics South Pacific Experiment”), respectively. Robert Brewin and six anonymous reviewers are warmly thanked for their constructive comments on a previous version of the manuscript. Most of the figures presented here were drawn using Ocean Data View software (Schlitzer, R., Ocean Data View, http://odv.awi.de, 2012). This study is funded by the King Abdullah University of Science and Technology (KAUST), Kingdom of Saudi Arabia. The data presented in this study are available from the authors upon request (email@example.com). The data are archived at the Red Sea database (RSDB) (https://lthdatalib.kaust.edu.sa/rsdbUI/).