Nile River sediment fluctuations over the past 7000 yr and their key role in sapropel development

Abstract

The provenance pattern of Nile River sediments can be used as a proxy for paleoclimatic changes in East Africa. The 87 Sr/ 86 Sr ratios are particularly appropriate for such provenance investigations, because the White Nile drains predominantly crystalline basement rocks, whereas the Blue Nile and Atbara flow off the Ethiopian Highlands, which consist of Tertiary volcanic rocks. A high-resolution profile of 87 Sr/ 86 Sr and Ti/Al ratios from a well-dated core in the Nile Delta shows a close correspondence with known changes in Nile flow over the past 7000 yr. At times of higher river flow there was markedly decreased input of Blue Nile-derived and total sediment. This change was caused by northward movement of the Inter Tropical Convergence Zone, resulting in increased vegetative cover in the Ethiopian Highlands due to higher rainfall and a longer wet season. This inverse relationship between Nile River flow and sediment flux may have had important implications in the development of agricultural technology in ancient Egypt. The marked minimum in 87 Sr/ 86 Sr at 4200-4500 yr B.P. is coincident with the end of the Old Kingdom in Egypt and provides independent evidence that demise of the Old Kingdom might have been associated with an extended period of catastrophic low floods. During the Quaternary and late Neogene, there was periodic deposition of organic-rich sediments (sapropels) in the eastern Mediterranean that represent important indicators of major environmental change. Evidence from the Ti/Al ratio suggests that the pattern of erosion and sediment supply from the Nile catchment observed in this study also occurred throughout much of the Neogene and Quaternary. The reduced inputs of Blue Nile sediment during times of sapropel formation contributed to the increased primary productivity by reducing the amount of phosphate removed on particles and to the observed change to N limitation in the eastern Mediterranean, which are important characteristics of sapropel deposition.

Lakeside View: Sociocultural Responses to Changing Water Levels of Lake Turkana, Kenya

“…Estimated northernmost positions of the ITCZ during the AHP and present day adapted from Junginger et al (2014). a Gulf of Aden sediment core (Tierney and deMenocal 2013), b Indian Ocean sediment core (Bard et al 1997), c Paleolake Suguta (Garcin et al 2009;Junginger et al 2014), d Lake Chew Bahir (Foerster et al 2012), e Lake Ashenge (Marshall et al 2009), f Lake Tilo (Lamb et al 2000), g Lakes Ziway and Shala (Gillespie et al 1983), h Lake Tana (Costa et al 2014;Marshall et al 2011), i Lake Abbe (Gasse and Van Campo 1994), j Blue Nile sediment sources (Krom et al 2002) and k Lake Hayq (Lamb et al 2007) (image in full color online) and a permanent lowstand at Lake Abbe (a.k.a. Abhé; Fig.…”

“…High sedimentation rates and low flows in the Blue Nile ( Fig. 1(j)) are documented from 5,650 to 4,750 and 2,050 to 1,000 years BP (Krom et al 2002). An analysis of oxygen and carbon isotopes in carbonates and diatom assemblages from a sediment core from Lake Hayq ( Fig.…”

The Effects of Holocene Landscape Changes on the Formation of the Archaeological Record in the Fayum Basin, Egypt

“…Well dated records for the dynamics of the River Nile in Northern Sudan and the Nile Delta now exist (e.g., Krom et al, 2002;Kuper & Kröpelin, 2006;Williams et al, 2010;Macklin et al, 2013), however correlation of these data with the data reported here remains problematic since we do not have direct dates on the sediments in which our data were observed. In the past, sediments indicative of past lake levels were correlated with archaeological materials and regional to global palaeoenvironmental records but as we suggest in this paper, these associations were not correctly interpreted due to the types of absolute dates that were obtained (i.e., from archaeological not lacustrine deposits).…”

Evolution du climat et du régime alimentaire pendant l’Egypte ancienne

“…Ces considérations ont motivé plusieurs études miné-ralogiques, chimiques et géochimiques portant sur la contribution relative des deux sources (équatoriale et éthiopienne) au cours du temps. Foucault & Stanley (1989) Sr dans les sédiments du Nil (Box et al, 2011 ;Krom et al, 2002 ;Revel et al, 2010 ;Stanley et al, 2003). L'analyse isotopique du strontium a permis de retracer l'évolution de la quantité de précipitations en Éthiopie entre 6000 et 1500 BP (Krom et al, 2002 ;Stanley et al, 2003).…”

“…Foucault & Stanley (1989) Sr dans les sédiments du Nil (Box et al, 2011 ;Krom et al, 2002 ;Revel et al, 2010 ;Stanley et al, 2003). L'analyse isotopique du strontium a permis de retracer l'évolution de la quantité de précipitations en Éthiopie entre 6000 et 1500 BP (Krom et al, 2002 ;Stanley et al, 2003). Elle présente cependant plusieurs limites : d'une part, l'intégration du signal par le couvert forestier implique un décalage temporel entre l'augmentation des précipitations et la réduction de la charge sédimentaire ; d'autre part, le (Iacumin et al, 1996).…”