Orbitally-induced changes of the Atlantic and Indian monsoons over the past 20,000 years: New insights based on the comparison of continental and marine records

International audienceVariations of Atlantic and Indian monsoon systems since the last glacial period are investigated by comparing eolian fluxes from two marine cores (ODP site 658 off western Africa and core 74KL off the Arabian peninsula) with 2147 hydrological records (lacustrine, palustrine, spring and fluvial, arid) gathered over a large continental area extending between 10 and 30oN across Africa, Arabia and western India. We show that the hydrological response to the Holocene humid phase in the northern tropics strongly differs from a region to another. The humid period is significantly shorter in the Arabian peninsula and the horn of Africa compared to northern Africa even though its maximum is contemporaneous (11,000-7,000 cal yr BP). Western India displays a specific hydrological signal characterized by the importance of well-developed fluvial systems from the Himalayas and the paucity of lakes compared to the other regions. In western India, the humid peak is shifted toward the mid Holocene (8,000-6,000 cal yr BP). Both marine records show a peak between ~ 11,000 and 7,000 cal yr BP for the Holocene humid period, in good accordance with African-Arabian records. However, while continental hydrological data suggest that the onset and termination of this humid period might have been relatively progressive, the marine windborne records indicate abrupt transitions, somewhat out-of-phase with continental evidence (e.g. abrupt decrease of aeolian proxies as early as ~ 15,000 cal yr BP). Discrepancies between marine and continental likely result from the fact that aeolian fluxes at a given marine location do not simply record monsoon-related changes of humidity over the adjacent continental sources but could be affected also by changes of the source area (e.g., emersion of the Arabo-Persian gulf associated to the glacial, low sea-level stand), and changes in wind intensity and/or direction