Significance of the sedimentary Al:Ti ratio as an indicator for variations in the circulation patterns of the equatorial North Atlantic

Abstract

This paper presents results of geochemical investigations conducted on three gravity cores recovered along an E-W transect (3°-5°N) in the equatorial Atlantic. Considering the high terrigenous content of the sediments (approximately 12-74 wt%), Al and Ti concentrations are predominantly associated with the input of lithogenous phases. The terrigenous fraction of western equatorial Atlantic sediments is more influenced by material derived from the Amazon River than by deposition of African dust particles. As a possible route of transport, the North Equatorial Countercurrent is considered. Fluctuations in Al/Ti records generally reflect changes in the low-latitude insolation cycle (19-23 kyr) and thus indicate a close coupling to variations of the trade-wind systems and continental climate changes. However, characteristics of the terrigenous signals in the eastern and western equatorial Atlantic differ significantly. While the precessional signal in the Al/Ti record and low latitude portion in the δ18O record are in phase in the eastern equatorial Atlantic, variations in the terrigenous fraction westward of the Mid-Atlantic Ridge precede the marine signal by 2-3 kyr, which we ascribe to a shift between trade-wind systems of the Northern and Southern Hemispheres.