Monsoon related variations in Zaire (Congo) sediment load and influence of fluvial silicate supply on marine productivity in the east equatorial Atlantic during the last 200,000 years

Abstract

Abstract. Two sediment cores from the Zaire Fan and the Angola Margin have been investigated for their composition of terrigenous and biogenic constituents, respectively. For the late Quaternary, kaolinite/feldspar ratios and variations of terrigenous element ratios of Zr, Ti, K, Rb, and Al reveal that the composition of Zaire River sediment load has fluctuated in tune with precessional variations of boreal summer insolation. In particular, the correspondence of high kaolinite/ feldspar and Al/K ratios with low-latitude insolation maxima strongly corroborates the assumption that west African monsoonal precipitation and chemical weathering was enhanced during periods of increased central African heating. The most striking feauture observed is that opal accumulation has been 2 to 10 times higher in Zaire Fan sediments than outside in continental margin sediments off Angola, although biogenic Ba and Corg fluctuations from both areas indicate that changes of total paleoproductivity were of the same magnitude in the Zaire River plume and off Angola. From this we infer that the contribution of biogenic opal production to total paleoproductivity has been significantly higher within the Zaire River plume than in the oceanic upwelling regime farther to the south off Angola over the last 200,000 years. The pattern of opal accumulation rates with respect to that of marine organic carbon implies that enhanced opal production off the Zaire River to a great extent was the result of additional fluvial supply of dissolved silica during humid climates characterized by more intense chemical weathering on the continent, while total paleoproductivity created by oceanic upwelling was high in periods of increased zonal trade wind intensity at precessional insolation minima and during cold, more arid glacial climate conditions. We presume that paleoproductivity off the Zaire was controlled by the following two sources of nutrients: (1) marine nutrients including nitrate and phosphate as well as the uptake of Ba on particulate Corg caused by upwelling, and (2) silica, mainly delivered by the Zaire River dissolved silicate. Hence our results underline the importance of dissolved silicate in large rivers for marine silicate cycling in the tropical to subtropical Atlantic at a millenial timescale.

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

“…Al contents in marine sediments generally can be assigned to the fine-grained aluminosilicate detrital fraction (Calvert, 1976). K is associated with potassium feldspar (K[AlSi 3 O 8 ]) (Schneider et al, 1997;Martinez et al, 1999), although illite ((K,H 3 O)Al 2 [(OH) 2 Si 3 AlO 10 ]) has also been considered to be the primary source of K (Yarincik et al, 2000). Fe can be contained in variable amounts in the aluminosilicate detrital fraction (Caquineau et al, 1998) as well as different iron oxides like goethite and hematite (Balsam et al, 1995).…”

“…Potassium and its main mineralogical carrier illite are frequently used to infer the supply of terrigenous material to marine sediments (e.g., Fütterer, 1983;Sirocko et al, 2000;Yarincik et al, 2000), for climatic (arid/humid) changes of the source region (Schneider et al, 1997;Kuhlmann et al, 2004) and for identification of source regions of aeolian dust (Delany et al, 1967;Caquineau et al, 1998;Goudie and Middleton, 2001;Caquineau et al, 2002;Stuut et al, 2005). In the investigated area near the coast of NW Africa river discharge has to be considered as a transport process of terrigenous material as described before.…”

Late Oligocene obliquity-paced contourite sedimentation in the Wilkes Land margin of East Antarctica: implications for paleoceanographic and ice sheet configurations

“…Table 3) implies that they are settled in different minerals and processes. The Zr/Rb ratio has been applied as a sediment grain-size proxy in marine records (Schneider, et al, 1997;Dypvik and Harris 2001;Croudace et al, 2006;Campagne et al, 2015). Zr/Al has been interpreted as an indicator for the accumulation of heavy minerals due to bottom currents (Bahr et al, 2014).…”

Gas hydrate decomposition recorded by authigenic barite at pockmark sites of the northern Congo Fan

“…Today, sedimentation on the northern Congo Fan comprises suspended material originating from the Congo River, as well as high organic matter input resulting from a mixture of high, river-induced marine productivity (Schneider et al 1997) and terrestrial matter of various sources (Holtvoeth et al 2001(Holtvoeth et al , 2003. Sedimentation rates determined by Schneider et al (1997) for deposits of the Congo Fan vary between 3 and 17 cm 1,000 years -1 for the last 200,000 years.…”

“…Sedimentation rates determined by Schneider et al (1997) for deposits of the Congo Fan vary between 3 and 17 cm 1,000 years -1 for the last 200,000 years. For the hemipelagic sediments of the northern Congo Fan at ODP site 1075, sedimentation rates determined by Wefer et al (1998) are typically in the order of 10 cm 1,000 years -1 .…”