NW African hydrology and vegetation during the Last Glacial cycle reflected in plant-wax-specific hydrogen and carbon isotopes

We present a hydrologic reconstruction of the Sahara-Sahel transition, covering the complete Last Glacial cycle (130 ka), based on a combination of plant-wax-specific hydrogen (delta D) and carbon isotopes (PC). The delta D and delta C-13 signatures of long-chain n-alkanes from ODP Site 659 off NW Africa reveal a significant anti-correlation. Complementary to published pollen data, we infer that this plant-wax signal reflects sensitive responses of the vegetation cover to precipitation changes in the Sahel region, as well as varying contributions from biomes north of the Sahara (C-3 domain) by North-East Trade Winds (NETW). During arid phases, especially the northern parts of the Sahel likely experienced crucial water stress, which resulted in a pronounced contraction of the vegetation cover, thus reducing the amount of C-4 plant waxes from the region. The increase in NETW strength during dry periods further promoted a more pronounced C-3-plant-wax signal derived from the North African C-3 plant domain. During humid periods, the C-4-dominated Sahelian environments spread northward into the Saharan realm, in association with lower NETW inputs of C-3 plant waxes. Arid humid cycles deduced from plant-wax delta D are in accordance with concomitant changes in weathering intensity reflected in varying major element distributions. Environmental shifts are generally linked to periods with large fluctuations in Northern Hemisphere summer insolation. During Marine Isotope Stages 2 and 3, when insolation variability was low, coupling of the hydrologic regime to alkenone-based estimates of NE Atlantic sea-surface temperatures becomes apparent. (C) 2013 Elsevier Ltd. All rights reserved.