In oligotrophic waters, dissolved organic carbon (DOC) is mostly produced in the surface layers by phytoplankton and remineralized by heterotrophic prokaryotes throughout the water column. DOC surface excess is subducted and exported to deeper layers where a semi-labile fraction is further processed contributing to oxygen consumption. How this cycling of DOC occurs in the Red Sea, one of the warmest oligotrophic marine basins, is virtually unknown. We examined DOC vertical and seasonal variability in a mesopelagic station (ca. 700 m depth) of the central Red Sea performing monthly profile samplings over a two-year period. Together with DOC vertical and seasonal distribution we evaluated the interaction with heterotrophic prokaryotes and contribution to oxygen respiration. DOC values ranged from 41.4 to 95.4 µmol C L-1, with concentrations in the epipelagic (70.0 ± 7.5 µmol C L-1) 40% higher on average than in the mesopelagic (50.7 ± 4.1 µmol C L-1). Subduction of seasonally accumulated semi-labile DOC was estimated to be responsible for ∼20% of the oxygen consumption mostly occurring at the low epipelagic-upper mesopelagic boundary layer. Variability in mesopelagic waters was higher than expected (ca. 20 µmol C L-1) evidencing a more active realm than previously thought, with consequences for carbon sequestration.
|Original language||English (US)|
|State||Published - Mar 18 2019|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: We gratefully acknowledge the crew of the workboat R.V. KAUST Explorer and all the personnel from the coastal and marine resources core lab (CMORE) for their diligent fieldwork assistance. M. Viegas, L. Silva and S. Ivetic (KAUST) aided with fieldwork and sample collection. This research was supported by King Abdullah University for Science and Technology through the baseline funding provided to X.A.G. Morán.