Palaeoenvironmental reconstruction of the southeast Red Sea based on XRF core scanning data and complementary environmental proxies
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Date
2025-07-09
Authors
Παράσχου, Φραντζέσκα
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Abstract
In an era of intensifying climate disruption, the southern Red Sea offers a rare sedimentary archive for decoding how marginal marine systems respond to the interplay of hydrological extremes, sea-level rise, and ocean-atmosphere feedbacks. Situated between the arid Saharan and Arabian deserts this region is uniquely positioned to record threshold-driven environmental shifts. This dissertation presents a comprehensive, multiproxy reconstruction of Red Sea palaeoenvironmental evolution by integrating high-resolution sediment records from both the open continental shelf and the bathymetrically isolated Farasan Deep. Together, these complementary archives illuminate how sea-level change, hydroclimate variability, and ocean-atmosphere feedbacks drove radical shifts in sedimentation, redox conditions, and ecological structure from the late Pleistocene through the Holocene.
In the first study, a high-resolution reconstruction of sedimentation dynamics from the southern Red Sea shelf reveals a marked reorganization of depositional regimes in response to glacial-interglacial transitions. The sediment core, capturing the interval from ca. 30 to 0.8 ka, shows a clear transition from a detrital-dominated regime (30–14.6 ka) to a marine-dominated phase (14.6–0.8 ka), corresponding with the termination of Heinrich Event 1 and the onset of Meltwater Pulse 1a. This transition reflects both the regional hydroclimatic shift from arid to pluvial conditions and the geomorphological reconfiguration due to rapid sea-level rise and shelf flooding. Detrital grain-size distributions and mineralogical data indicate reduced aridity and potentially weakened aeolian transport coinciding with Greenland Interstadial 1. Enhanced delivery of fluvially sourced fine material and terrestrial n-alkanes from ~16 to 8 ka is attributed to intensified wadi runoff and vegetative expansion during the African Humid Period. Concurrently, a surge in marine productivity—driven by re-established exchange with the Gulf of Aden and improved ventilation—highlights the interplay between basin connectivity and nutrient cycling. From ~5 ka onward, the gradual increase in detrital input is interpreted as a signal of Holocene aridification and the retreat of humid climatic conditions.
Complementing this open-shelf perspective, the second study focuses on the Farasan Deep, a bathymetrically isolated depression on the carbonate shelf of the southwestern Red Sea. This site captures the transformation of a marginal palaeolake into a stratified marine basin during the Holocene. Multiproxy analyses, including inorganic geochemistry (XRF-CS, LOI), sedimentology, micropaleontology, and lipid biomarkers (GDGTs), reveal a tripartite evolution of the basin's hydrography and ecology. In the early Holocene (11.8–8.7 ka), the Farasan Deep remained largely disconnected from open marine circulation, marked by extreme stratification, persistent anoxia, and microbial-dominated communities. This phase is characterized by laminated organic-rich sediment, elevated GDGT-0/crenarchaeol ratios, and the preferential synthesis of brGMGTs and 6-methyl brGDGTs, signaling suppressed ventilation and an ecologically unique microbial assemblage. A transitional phase (8.7–6.7 ka) is defined by episodic marine incursions and fluctuating redox conditions, evidenced by transient foraminiferal assemblages and shifts in redox-sensitive elemental concentrations. From ~6.7 ka onwards, a fully marine yet strongly anoxic environment became established, with stable enrichment in calcium, iron, and sulfur and a benthic ecosystem increasingly dominated by infaunal taxa tolerant of low-oxygen conditions.
Together, the two records provide a detailed reconstruction of late Pleistocene to Holocene environmental dynamics in the southern Red Sea. They underscore the spatial heterogeneity of sedimentary and ecological responses to climate forcing, governed by local basin morphology, connectivity to oceanic circulation, and the balance between aeolian and fluvial inputs. Moreover, they highlight the importance of sea-level rise not only in shaping geomorphology but also in modulating biogeochemical conditions and microbial ecology in marginal marine settings. The integrated multiproxy approach employed here enables a high-resolution temporal perspective on the cascading effects of climatic and oceanographic reorganization, from terrestrial runoff and sediment transport to redox stratification and microbial shifts. These findings contribute to a growing understanding of how tropical marginal basins responded to orbitally forced hydroclimate variability, abrupt climate events, and postglacial marine transgressions. Importantly, the redox-sensitive carbon cycling processes, sediment delivery mechanisms, and stratified water column dynamics reconstructed for the southern Red Sea during the last deglaciation and Holocene provide valuable analogues for predicting future responses of similar coastal systems under anthropogenically forced climate change and accelerating sea-level rise.
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Keywords
Organic biomarkers, Palaeoclimatology, Palaeoenvironment, Sedimentology, Geoarchaeology, Pleistocene, Geochemistry, Foraminifera