Climatic records of the late Holocene from sediment core GeoB9504-3 off Senegal

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 shallow-marine 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 µm, (ii) aeolian material of 18-63 µm and (iii) a sub-fraction of dual-origin material of 2-18 µm. 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.非洲西北大陆边缘晚全新世的高分辨率气候记录较为匮乏。本研究结合沉积物粒度、元素分布与矿物组合数据，对塞内加尔河口附近浅海沉积中心的粉尘与河流物源进行溯源，旨在厘清这些陆源组分如何响应晚全新世的气候波动。研究人员对沉积物岩心的三个粒级分样开展了主量元素含量测试与矿物鉴定：(i) 粒径<2 μm的河流成因组分，(ii) 粒径18~63 μm的风成组分，以及(iii) 粒径2~18 μm的双成因组分。结果显示，总陆源体相中80%以上的铝（Al）与铁（Fe）赋存于河流成因组分中。与之相反，钛（Ti）、钾（K）与硅（Si）无法作为塞内加尔近海单一物源的代用指标。记录大陆河流径流的铝钙比（Al/Ca）揭示了两段干旱期：3010~2750校准距今年（cal a BP）与1900~1000校准距今年，以及两段主要湿润期：2750~1900校准距今年与1000~700校准距今年。(i) 由低Al/Ca值推断的河流径流低值时段、(ii) 基于塞内加尔近海综合孢粉数据得到的河流径流量减少时段，以及(iii) 马里沙丘活化增强时段三者的吻合性，验证了本研究的解释结论。