Deoxygenation dynamics on the western Nile deep-sea fan during sapropel S1 from seasonal to millennial timescales

Abstract. Ocean deoxygenation is a rising threat to marine ecosystems and food resources under present climate warming conditions. Organic-rich sapropel layers deposited in the Mediterranean Sea provide natural laboratory study processes that have controlled changes seawater oxygen levels recent geological past. Our based on three sediment cores spanning last 10 000 years located bathymetric transect offshore from western distributaries of Nile delta. These are partly continuously laminated sections recording S1, which indicative bottom-water anoxia above deep-sea fan. We used combination microfacies analyses inorganic organic geochemical measurements reconstruct oxygenation conditions at seasonal millennial timescales. Millimetre-thick laminations composed detrital, biogenic chemogenic sublayers reflecting successions sedimentation. Dark reflect deposition summer floods two types light correspond autumn plankton blooms authigenic carbonates formed water column during spring–early summer, respectively. The isotopic signature suggests permanent anoxic euxinic bottom waters resulting high anaerobic remineralization matter highlights their potential chemistry times when benthic fauna was absent. Ratios major elements combined with biomarkers terrestrial redox-sensitive compounds allow terrigenous input, primary productivity past dynamics timescales be tracked. Rapid fluctuations upper 700 m depth occurred fan between 6.5 ka BP, while deeper recorded more stable Synchronous after BP show runoff-driven eutrophication played central role rapid south-eastern Levantine Basin. findings further supported by other regional records reveal time-transgressive state driven period long-term deep-water stagnation.