A distal 140 kyr sediment record of Nile discharge and East African monsoon variability

Abstract

Abstract. Clay mineral assemblages in a sediment core from the distal Nile discharge plume off Israel have been used to reconstruct the late Quaternary Nile sediment discharge into the eastern Mediterranean Sea (EMS). The record spans the last ca. 140 kyr. Smectite abundances indicate the influence of the Blue Nile and the Atbara River that have their headwaters in the volcanic rocks of the Ethiopian Highlands. Kaolinite abundances indicate the influence of wadis, which contribute periodically to the suspension load of the Nile.Due to the geographical position, the climate and the sedimentary framework of the EMS is controlled by two climate systems. The long-term climate regime was governed by the African monsoon that caused major African humid periods (AHPs) with enhanced sediment discharge at 132 to < 126 (AHP 5), 116 to 99 (AHP4), and 89 to 77 ka (AHP3). They lasted much longer than the formation of the related sapropel layers S5 (> 2 kyr), S4 (3.5 kyr), and S3 (5 kyr). During the last glacial period (Marine Isotope Stages (MISs) 4-2), the long-term changes in the monsoonal system were superimposed by millennial-scale changes in an intensified midlatitude glacial system. This climate regime caused short but pronounced drought periods in the Nile catchment, which are linked to Heinrich events and alternate with more humid interstadials.The clay mineral record further implies that feedback mechanisms between vegetation cover and sediment discharge of the Nile are detectable but of minor importance for the sedimentary record in the southeastern Mediterranean Sea during the investigated African humid periods.

Methane Hydrate Stability and Potential Resource in the Levant Basin, Southeastern Mediterranean Sea

“…Both the Nile deep sea fan and margin sedimentary wedge prograded over the evaporites layer since the Pliocene, reaching at present thicknesses of~0.5 and~1.5 km respectively (e.g., [43]). Estimated quaternary sedimentation rates in the Levant Basin range between~2.2 cm/ka on its northeastern margin, southeast of Cyprus, to~6 to~20 cm/ka in its southeastern part [51][52][53]. Organic-rich sapropel units deposited recurrently in the EMS since the Miocene [54,55].…”

Humans as Agents in the Termination of the African Humid Period

“…In a large-scale analysis, sediment runoff in the Nile River progressively increases from the early termination phase of the AHP (ca. 8000 years BP), which is inferred to be the result of intensified use of land associated with farming and animal pastoralism (Ehrmann et al, 2016). More localized studies demonstrate the mechanisms by which large-scale changes could have been induced.…”

End-member modelling as a tool for climate reconstruction—An Eastern Mediterranean case study

“…Data of the grain size, clay mineral, geochemical and isotopic compositions have been widely used to reconstruct the provenance and transport processes for the Eastern Mediterranean Sea sediments. This information can be further used to decipher the archived climatic signals [ 4 – 10 ].…”

“…The strongest AHPs are further characterised by the deposition of sapropel layers in the Eastern Mediterranean Sea. It should be noted that the AHPs lasted longer than the sapropels which represent the culmination of the AHPs [ 9 , 10 ]. Favourable environmental conditions in North Africa during the AHPs provided migration pathways for anatomically modern humans and supported their movement out of Africa and into the Mediterranean region [ 25 , 26 ].…”