Late Quaternary Climate Changes in Central Africa as Inferred from Terrigenous Input to the Niger Fan

Abstract

Time series of terrigenous source elements (Al, K, Ti, Zr) from core GeoB4901-8 recovered from the deep-sea fan of the Niger River record variations in riverine sediment discharge over the past 245,000 yr. Although the flux rates of all the elements depend on physical erosion, which is mainly controlled by the extent of vegetation coverage in central Africa, element/Al ratios reflect conditions for chemical weathering in the river basin. Maximum sediment input to the ocean occurs during cold and arid periods, when precipitation intensity and associated freshwater runoff are reduced. High carbonate contents during the same periods indicate that the sediment supply has a positive effect on river-induced marine productivity. In general, variations in the terrestrial signals contain a strong precessional component in tune with changes in low-latitude solar radiation. However, the terrestrial signal lags the insolation signal by several thousand years. K/Al, Ti/Al, and Zr/Al records reveal that African monsoonal precipitation depends on high-latitude forcing. We attribute the shift between insolation cycle and river discharge to the frequently reported nonlinear response of African climate to primary orbital configurations, which may be caused by a complex interaction of the secondary control parameters, such as surface albedo and/or thermohaline circulation.

A new look at old carbon in active margin sediments

“…Terrigenous fl ood deposits are collectively identifi ed by elevations in TOC/TN, K/Ti, and Si/Ti ratios in sediments, light-colored bands in visible and positive X-ray photographs, historical records, and previous stratigraphic investigations ( Leithold and Hope, 1999;Yarincik et al, 2000;Zabel et al, 2001), and are thus delineated by these criteria in Figure 1. Due to the uncertainty in the age model, it is not surprising that the dates for these events given by the chronol ogy for GGC5 do not exactly match those assigned in other studies (Leithold and Blair, 2001;Leithold et al, 2005;Sommerfi eld et al, 2002), although they do generally agree within several years.…”

Geochemical distribution patterns as indicators for productivity and terrigenous input off NW Africa

“…Ba, Al, Fe, K and Ti, the key elements of our study, were measured together with various major and minor elements by inductively coupled plasma optical emission spectrometry ICP-OES (Perkin Elmer, Optima 3300 R) with a cross-flow nebulizer (Perkin Elmer). For further information on analytical procedures refer to Zabel et al (2001). Marine sediment reference standard MAG-1 (U.S. Geological Survey) was repeatedly digested.…”

“…Therefore samples sets from these different groups were comprised (visualized by ellipses) and the correlation coefficient (R 2 ) for the group ''rest'' is included. Bozzano et al, 2002;Guieu et al, 2002), for climatic reconstructions Yarincik et al, 2000;Zabel et al, 2001;Kuhlmann, 2004) and for identification of source regions of aeolian dust (Coude-Gaussen et al, 1987;Bergametti et al, 1989;Balsam et al, 1995;Chiapello et al, 1997;Stuut et al, 2005).…”

Geochemical characterisation of northern Norwegian fjord surface sediments: A baseline for further paleo-environmental investigations

“…We focus our discussion mainly on the elements of Al, Si, Hf, Fe, Ti, and Zr because most of these elements are frequently used as indicators of terrestrial sediment supply in sediment core studies (e.g. Bertrand et al, 2012;Brendryen et al, 2015;Faust et al, 2014a;Wehrmann et al, 2014;Zabel et al, 2001). Moreover, to avoid dilution and grain size effects, we discuss the spatial distribution of these elements in the fjords as Al-based ratios (Bertrand et al, 2012;Faust et al, 2014b;Loring, 1990).…”

“…Govin et al, 2012;Lamy et al, 2001;White and Blum, 1995). However, a detailed knowledge of the controlling transport mechanisms of the particle supply is required to explore the relationship between terrigenous input and changes in environmental conditions (Zabel et al, 2001). Sediment characteristics, accumulation and distribution vary with climate, seafloor topography, basin geometry, size of the drainage area, oceanographic regime, and distance to river outlets (e.g.…”