Reconstruction of the Holocene hydro-ecological and environmental change
of the Nile Delta: insights from organic geochemical records in MZ-1
The Holocene hydro-ecological and environmental change of the Nile Delta
remains a knowledge gap. The study aimed to approach this objective by
using multi-proxies of organic carbon (OC) in a well-dated MZ-1 core in
Manzala lagoon off the Nile Delta. The data defined five distinctive
stages at decadal-centennial scale. Stage I (ca. 8.2-7.7 ka) was
characterized by remarkedly high reconstructed pH and low mean annual
air temperature (the 8.2-ka cold event). The obviously low TOC and C/N,
but higher short-chain n-alkanes indicated more marine OC deposition.
This was followed by highly fluctuated organic geochemical proxies at
Stage Ⅱ (ca. 7.7-5.8 ka) indicating episodic but significant terrestrial
OC input delivered by Nile floods during the African Humid Period (AHP).
Subsequent increase in short- and medium-chain n-alkanes suggested
macrophytes prevailing in the lagoon during Stage Ⅲ (ca. 5.8-5.4 ka)
with cooling-drying climate transitioned from the AHP. Stage Ⅳ (ca.
5.4-1.2 ka) witnessed decreased short-chain n-alkanes of marine origin
and increased long-chain n-alkanes of terrestrial origin when the Nile
climate entered into the mega-trend of aridification. Abnormal pulses of
terrestrial OC with high TOC likely reflected the modified landscape due
to early human occupation around the area. The highly fluctuated
charcoal fluxes since ca. 6 ka implied such clearing-firing-aided land
exploitation activity. The lagoon eco-setting was further affected by
intensified anthropogenic-OC input after the latest millennium. Our
study highlighted the land-ocean interactions on modulating the
paleo-lagoonal ecology of the Nile Delta, which should be incorporated
into healthy management in the Nile Delta.