Abstract
Understanding deltaic resilience in the face of Holocene climate change and human impacts is an important challenge for the earth sciences in characterizing the full range of present and future wetland responses to global warming. Here, we report an 8000-year mass balance record from the Nile Delta to reconstruct when and how this sedimentary basin has responded to past hydrological shifts. In a global Holocene context, the long-term decrease in Nile Delta accretion rates is consistent with insolation-driven changes in the ‘monsoon pacemaker’, attested throughout the mid-latitude tropics. Following the early to mid-Holocene growth of the Nile’s deltaic plain, sediment losses and pronounced erosion are first recorded after ~4000 years ago, the corollaries of falling sediment supply and an intensification of anthropogenic impacts from the Pharaonic period onwards. Against the backcloth of the Saharan ‘depeopling’, reduced river flow underpinned by a weakening of monsoonal precipitation appears to have been particularly conducive to the expansion of human activities on the delta by exposing productive floodplain lands for occupation and irrigation agriculture. The reconstruction suggests that the Nile Delta has a particularly long history of vulnerability to extreme events (e.g. floods and storms) and sea-level rise, although the present sediment-starved system does not have a direct Holocene analogue. This study highlights the importance of the world’s deltas as sensitive archives to investigate Holocene geosystem responses to climate change, risks and hazards, and societal interaction.
Highlights
A key challenge concerning continental rivers is to better understand past, present and future river fluxes in the face of climate shifts, land-use alterations, river catchment modifications and their impact upon base-level geosystems [1,2,3]
Various literature sources [23,24,34,35] and our present ongoing research [36,37,38] were used to compile a database of Holocene radiocarbon dates and stratigraphies from the Nile Delta area
This record is comparable in amplitude and direction to other regional palaeoclimate archives [25,26,27] and demonstrates that Nile Delta sedimentation has primarily been controlled by Holocene shifts in fluvial discharge, modulated by low-latitude summer insolation and the position of the eastern African Rain Belt [28]
Summary
A key challenge concerning continental rivers is to better understand past, present and future river fluxes in the face of climate shifts, land-use alterations, river catchment modifications and their impact upon base-level geosystems [1,2,3] Within this context, delta fronts are sensitive recorders of global change because their sedimentary basins have sequestered rich environmental information at the terminus of the source-to-sink sediment conveyor [4,5,6]. Whilst human activities have increased fluvial sediment supply, the net amount of sediment reaching the ocean has decreased by ~10% through infrastructure projects such as dams and reservoirs [6,19] These changes in sediment flux have led to significant coastal retreat, in deltaic areas, and underscore the importance of understanding source-to-sink sediment conveyors at a variety of spatial and temporal scales [20]. In a key study of 33 of the world’s most important deltas, Syvitski et al.[14]. found that
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