Millennial‐scale northwest African droughts related to Heinrich events and Dansgaard‐Oeschger cycles: Evidence in marine sediments from offshore Senegal

Abstract

[1] We present a suite of new high-resolution records (0-135 ka) representing pulses of aeolian, fluvial, and biogenic sedimentation along the Senegalese continental margin. A multiproxy approach based on rock magnetic, element, and color data was applied on three cores enclosing the present-day northern limit of the ITCZ. A strong episodic aeolian contribution driven by stronger winds and dry conditions and characterized by high hematite and goethite input was revealed north of 13°N. These millennial-scale dust fluxes are synchronous with North Atlantic Heinrich stadials. Fluvial clay input driven by the West African monsoon predominates at 12°N and varies at Dansgaard-Oeschger time scales while marine productivity is strongly enhanced during the African humid periods and marine isotope stage 5. From latitudinal signal variations, we deduce that the last glacial ITCZ summer position was located between core positions at 12°26 0 and 13°40 0 N. Furthermore, this work also shows that submillennial periods of aridity over northwest Africa occurred more frequently and farther south than previously thought.

Hydrological variations of the intermediate water masses of the western Mediterranean Sea during the past 20 ka inferred from neodymium isotopic composition in foraminifera and cold-water corals

“…The last glacial period was associated with an aridification of North Africa (Sarnthein et al, 1981;Hooghiemstra et al, 1987;Moreno et al, 2002;Wienberg et al, 2010) and higher fluxes of Saharan dust to the NE tropical Atlantic (Itambi et al, 2009) and the western Mediterranean Sea characterized by unradiogenic εNd values (between −11 ± 0.4 and −14 ± 0.4; see synthesis in Scheuvens et al, 2013). Bout-Roumazeilles et al (2013) documented a dominant role of eolian supply in the SiculoTunisian Strait during the last 20 ka, with the exception of a significant riverine contribution (from the Nile River) and a strong reduction of eolian input during the sapropel S1 event.…”

“…This led to a rapid sea-level rise of about 20 m in less than 500 years and large freshwater discharges in the Atlantic Ocean due to the melting of continental ice sheets (Deschamps et al, 2012), resulting in an enhanced Atlantic inflow across the Strait of Gibraltar. Synchronously, cosmogenic dating of Alpine glacier retreat throughout the western Mediterranean hinterland suggests maximum retreat rates (Ivy-Ochs et al, 2007;Kelly et al, 2006). Overall, these events are responsible for freshening Mediterranean waters and reduced surface water density and, hence, weakened ventilation of intermediate (Toucanne et al, 2012) and deep-water masses Sierro et al, 2005).…”

Characterizing magnetic mineral assemblages of surface sediments from major Asian dust sources and implications for the Chinese loess magnetism

“…To better decipher the dust signal preserved in sedimentary archives, it is necessary not only to understand the magnetic properties of terrestrial and marine sediments in depositional sinks to obtain high-resolution records of dust flux from key source regions, but there is also a need to study the magnetic properties of dust material from different sources to their depositional sinks. Previous studies have focused on dust signals recorded by terrestrial and marine sediments, e.g., from the Chinese Loess Plateau (CLP) , the Red Sea (Rohling et al 2008;Roberts et al 2011), the Indian Ocean (Bloemendal and deMenocal 1989), the North Pacific Ocean (Doh et al 1988;Yamazaki and Ioka 1997;Bailey et al 2011), and the North Atlantic Ocean (Bloemendal and deMenocal 1989;Itambi et al 2009Itambi et al , 2010a. Recently, a few studies have been conducted on surface sediments from dust source regions, e.g., the Asian interior (Maher et al 2009;Zan et al 2015) and North Africa (Lyons et al 2010(Lyons et al , 2012Oldfield et al 2014).…”

Source-to-sink magnetic properties of NE Saharan dust in Eastern Mediterranean marine sediments: review and paleoenvironmental implications

“…The areas that have provided the most outstanding records of eolian dust deposition based on magnetic properties are the equatorial Atlantic Ocean (Bloemendal et al, 1993;deMenocal, 1995;Maher and Dennis, 2001;Itambi et al, 2009;Just et al, 2012), the N Pacific Ocean (Doh et al, 1988;Yamazaki and Ioka, 1997;Yamazaki, 2009Yamazaki, , 2012Bailey et al, 2011), the eastern Mediterranean Sea (Dinarès-Turell et al, 2003;Larrasoaña et al, 2003a;Köhler et al, 2008;Liu et al, 2012b), the Arabian Sea (Bloemendal and deMenocal, 1989;deMenocal et al, 1991;Bloemendal et al, 1993;deMenocal, 1995;Hounslow and Maher, 1999), and the Red Sea Roberts et al, 2011) (for a review see Maher, 2011). Given the often discontinuous nature of the continental sedimentary record, these marine magnetic records of eolian dust deposition provide valuable sources of information on past climate variability in continental regions (Liu et al, 2012a).…”