African monsoon enhancement during the penultimate glacial period (MIS 6.5 ∼ 170 ka) and its atmospheric impact

Abstract

[1] A reconstruction of northwest African summer monsoon strength during the cold marine isotopic stage (MIS) 6 indicates a link to the seasonal migration of the Intertropical Convergence Zone (ITCZ). Highresolution studies of eolian dust supply and sea surface temperature recorded in marine core MD03-2705, on the Mauritanian margin, provide a better understanding about the penultimate glacial history of northwestern African aridity/humidity and upwelling coastal activity. Today, site MD03-2705 experiences increased upwelling and dust flux during the winter months, when the ITCZ is in a southerly position. Analyses of foraminifera isotopic composition suggest that during MIS 6.5 (180-168 ka) the average position of the ITCZ migrated north, marked by an increase in the strength of the summer monsoon, which decreased eolian dust transport and the coastal upwelling activity. The northward migration is in phase with a specific orbital combination of a low precessional index with a high obliquity signal. High-resolution analysis of stable isotopes (d 18 O and d 13 C) and microscale resolution geochemical (Ti/Al and quartz grain counts) determinations reveal that the transition between monsoonal humid (MIS 6.5) and dry (MIS 6.4) conditions has occurred in less than 1.3 ka. Such rapid changes suggest a nonlinear link between the African monsoonal rainfall system and environmental changes over the continent. This study provides new insights about the influence of vegetation and oceanic temperature feedbacks on the onset of African summer monsoon and demonstrates that, during the penultimate glacial period, changes in tropical dynamics had regional and global impacts.

Twenty Years of XRF Core Scanning Marine Sediments: What Do Geochemical Proxies Tell Us?

“…In one study used to infer weathering intensity (Sluijs et al 2008). Si/Al considered a proxy for changes in aluminosilicate composition by Tisserand et al (2009) Applications and literature …”

“…Use: Ti/Al used as proxy for aeolian dust flux/wind strength, hence hinterland aridity (Itambi et al 2009;Jullien et al 2007;Tisserand et al 2009 …”

Reconstrucción paleoceanográfica de los últimos 32 ka en el Atlántico Nororiental y Mediterráneo Occidental a partir del desarrollo de técnicas geoquímicas en asociaciones de cocolitofóros

“…La evolución estacional de la productividad superficial muestra unos regímenes bien diferenciados para cada estación: el régimen de eclosión de invierno (noviembre a marzo) con temperaturas superficiales (SST) ≤ 17 ºC , el régimen de no eclosión de verano (mayo a septiembre) que presenta SST ≥ 19,5 ºC y las dos fases de transición de abril-mayo y octubre-noviembre, cuando comienza a estratificarse y desestratificarse la columna de agua en respuesta a la acción de los vientos (Garcia-Gorriz y Carr, 2001). En tiempo geológico, las variaciones en los máximos de insolación han provocado cambios en los gradientes térmicos interhemisféricos, que a su vez, se han asociado con desplazamientos meridionales de la ZCIT durante periodos más fríos (Broccoli et al, 2006;Tisserand et al, 2009) .…”

“…In past climates, variations in maximum of insolation caused different interhemispheric temperature gradients and produced southward migrations of the ITCZ during colder periods (Broccoli et al, 2006;Tisserand et al, 2009). The ITCZ displacement exerts a strong influence on both the atmospheric and oceanic systems conditioning the strength and position of the trade winds and, therefore, the intensity and persistence of the upwelling off NW Africa.…”

“…In parallel, Jullien et al (2007) and Mulitza et al (2008), identify a series of low-latitude "dusty" and arid events and suggest synchronicity between them and the classic high-latitude Heinrich events. This, being a remote response to a large-scale atmospheric and hydrological reorganization that could be amplified by a tropical phenomenon like the monsoon and would foster a subsequent shift in the mean position of the Intertropical Convergence Zone (Broccoli et al, 2006;deMenocal et al, 2000;Ivanochko et al, 2005;Tisserand et al, 2009).…”