[1] The influence of the large-scale ocean circulation on Sahel rainfall is elusive because of the shortness of the observational record. We reconstructed the history of eolian and fluvial sedimentation on the continental slope off Senegal during the past 57,000 years. Our data show that abrupt onsets of arid conditions in the West African Sahel were linked to cold North Atlantic sea surface temperatures during times of reduced meridional overturning circulation associated with Heinrich Stadials. Climate modeling suggests that this drying is induced by a southward shift of the West African monsoon trough in conjunction with an intensification and southward expansion of the midtropospheric African Easterly Jet.

No abstract

No abstract

A mid- to late-Holocene paleohydrological reconstruction from the northeast Atlantic is proposed through the study of a high-resolution sedimentary record from the northern continental shelf of the Bay of Biscay (BoB). Three foraminiferal species dominate the assemblages with Rosalina globularis showing an overall decrease in absolute and relative abundances from ~7 to 0.4 cal. ka BP, whereas the opposite trend is observed for Cibicides refulgens and Lobatula. These long-term patterns are interpreted as a response to the overall cooling trend and/or the progressive deepening of the water column because of the relative sea-level (RSL) rise. Foraminiferal δ18O and grain-size analyses show a significant shift around 3.5–2.5 cal. ka BP toward a heavier isotopic signature and finer sediments. We mainly link this change to enhanced contribution of continental freshwaters and fine sediments after the near-stabilization of the RSL rise. By reducing coastal accommodation spaces, this led to a better channelization of river outflows and probably to the formation of the modern winter thermohaline front. Superimposed on these long-term patterns, our data highlight strong millennial-scale variability (1250-year peak). Such cyclicity is consistent with several records tracing changes in rainfall and storminess regimes in northern Europe, and the dynamics of the subpolar gyre (SPG). We suggest a millennial time-scale control of a NAO-like (North Atlantic Oscillation) climatic process modulating continental humidity (and the associated river discharges) and SPG dynamics through wind stress. Spectral analyses reveal an additional 500-year frequency peak implying a possible solar forcing.

High-resolution climatic records of the late Holocene along the north-west African continental margin are scarce. Here we combine sediment grain size, elemental distribution and mineral assemblage data to trace dust and riverine sources at a shallowmarine sediment depocentre in the vicinity of the Senegal River mouth. The aim is to understand how these terrigenous components reflect climate variability during the late Holocene. Major element contents were measured and mineral identification was performed on three sub-fractions of our sediment core: (i) fluvial material < 2 mm, (ii) aeolian material of 18-63 mm and (iii) a sub-fraction of dual-origin material of 2-18 mm. Results show that more than 80% of the total Al and Fe terrigenous bulk content is present in the fluviogenic fraction. In contrast, Ti, K and Si cannot be considered as proxies for one specific source off Senegal. The Al/Ca ratio, recording the continental river runoff, reveals two dry periods from 3010 to 2750 cal a BP and from 1900 to 1000 cal a BP, and two main humid periods from 2750 to 1900 cal a BP and from 1000 to 700 cal a BP. The match between (i) intervals of low river runoff inferred by low Al/Ca values, (ii) reduced river discharge inferred by integrated palynological data from offshore Senegal and (iii) periods of enhanced dune reactivation in Mali confirms this interpretation.