Response of tropical African and East Atlantic climates to orbital forcing over the last 1.7 Ma

Abstract

Records of organic matter accumulation, organic carbon isotopic composition and iron content covering the last 1.7 Ma are presented for the Congo Fan Ocean Drilling Program (ODP) Site 1075, and are compared with their counterparts from ODP Site 663 in the equatorial upwelling region. They are discussed with regard to variations in African precipitation and Congo River discharge and in the context of changes in trade-wind-driven marine productivity for the tropical Atlantic at periodicities typical of Milankovitch forcing. On the Congo Fan, elevated total organic carbon mass accumulation rates (TOC MAR) and Fe intensities occur predominantly during interglacial periods when the African monsoon was most intense. Band-pass filtering applied to TOC MAR shows distinct precessional variations, indicating that the African climate was largely controlled by low-latitude insolation changes. Only for the last 0.6 Ma, an interval of enhanced glacial-interglacial climate changes, is the precessional TOC MAR signal superimposed by a strong 100 ka oscillation. In contrast, variations in terrestrial iron input to the Congo Fan indicate pronounced 100 ka variance already well before global glacial-interglacial cycles increased in amplitude between 0.9 and 0.6 Ma. Obliquity cycles in the Fe signal are strongly expressed for the last 0.9 Ma. The highest amplitudes in the precessional variance of fluvial Fe input occur when amplitudes in the 100 ka oscillation were at intermediate levels and reveal a 800 ka cycle in phase shift with respect to precessional forcing. Together with a pronounced 800 ka signal in the 100 ka amplitude variations during the last 1.7 Ma, the Congo Fan iron record therefore suggests that eccentricity modulation of the low-latitude insolation directly influenced the equatorial African monsoon system and probably the weathering conditions on land. It further suggests that low-latitude precessional forcing and monsoonal response in the tropics might have played an important role for 100 ka cycles in global climate well before huge continental ice sheets existed.

Synthesising bushmeat research effort in West and Central Africa: A new regional database

“…2) together with 2 other minor BHPs related to aminopentol (IIIa and IIIb; Table S1), up to 115 metres below sea floor (mbsf) and an estimated age of ca. 1.2 Ma based on the age model of Jahn et al (2005). We did not find any C-3 methylated hopanoids in this study (see also Handley et al, 2010).…”

“…The collected sediments are bioturbated monotonous greenish-grey clays. The age model for ODP 1075 was adopted from Jahn et al (2005) with the age assignment of marine isotope stages and sub-stages according to Lisiecki and Raymo (2005).…”

“…Within the uncertainties of accuracy of the age model (Jahn et al, 2005) there appears to be a relationship between aminopentol concentrations and marine isotope stages (MIS), which are defined by shifts in global ocean oxygen isotopic composition (Lisiecki and Raymo, 2005): concentrations are generally higher during interglacial stages (Fig. 2).…”

A record of aerobic methane oxidation in tropical Africa over the last 2.5 Ma

“…Sediments from ODP 1075 and neighboring cores (e.g. ODP 1077) have been closely correlated with climatic signaling (Jahn et al, 2005) and large scale shifts in terrestrial vegetation relating to humidityaridity cycles (Dupont et al, 2000;Schefuß et al, 2003;2004). ODP 1075 is approximately 200 m.b.s.f.…”

Astronomical Control of the Hydroclimate During the Past 1.2 Million Years

“…L) Log-ratio of silica to aluminium as a proxy of sediment opal content (ODP Site 658, subtropical North Atlantic [48]. M) Organic carbon isotope record (δ¹³C org ) of marine sediments including equivalently mixed material of terrestrial and marine photosynthesis, ODP Site 1077, Angola Basin [67]. N) Ti/Al ratio, ODP Sites 967 and 968, eastern Mediterranean [17].…”