Éditeur(s) : HAL CCSD Elsevier
Résumé : Iron content of the bulk marine sediment from the Chilean continental margin has been used to infer millenial-scale climate changes in southeast Pacific [Lamy, F., Klump, J., Hebbeln, D., Wefer, G., 2000. Rapid climate change in northern Chile over the last 80 ka recorded in a marine sediment core. Terra Nova 12: 8–13]. Changes of iron contents have been related to a varying contribution of Andean (Fe-rich) versus Coastal Range (Fe-poor) source rocks ultimately controlled by continental rainfall changes. However, variations observed could also be produced by changes in the proportions of two components in the sediment — a detrital component with low and constant Fe content and an authigenic phase (Fe oxide, pyrite, apatite, etc.) with high Fe content. A sequential extraction has been used to partition the total iron content in the sediment of core GeoB 7101 at the continental margin of Chile. The extraction steps included five fractions: exchangeable, bound to carbonates, bound to Fe–Mn oxides, bound to organic matter, and residual. Iron appeared to be mainly present in the residual fraction, i.e. in the detrital component. Our study indicates that total Fe or Fe/Al may be used to infer millenial-scales climate changes in the southeastern Pacific.
ISSN: 0025-3227

hal-00407253
https://hal.archives-ouvertes.fr/hal-00407253
DOI : 10.1016/j.margeo.2007.03.006

Éditeur(s) : Copernicus Gesellschaft Mbh
Résumé : Relict dune fields that are found as far south as 14 N in the modern-day African Sahel are testament to equatorward expansions of the Sahara desert during the Late Pleistocene. However, the discontinuous nature of dune records means that abrupt millennial-timescale climate events are not always resolved. High-resolution marine core studies have identified Heinrich stadials as the dustiest periods of the last glacial in West Africa although the spatial evolution of dust export on millennial timescales has so far not been investigated. We use the major-element composition of four high-resolution marine sediment cores to reconstruct the spatial extent of Saharan-dust versus river-sediment input to the continental margin from West Africa over the last 60 ka. This allows us to map the position of the sediment composition corresponding to the Sahara Sahel boundary. Our records indicate that the Sahara Sahel boundary reached its most southerly position (13 N) during Heinrich stadials and hence suggest that these were the periods when the sand dunes formed at 14 N on the continent. Heinrich stadials are associated with cold North Atlantic sea surface temperatures which appear to have triggered abrupt increases of aridity and wind strength in the Sahel. Our study illustrates the influence of the Atlantic meridional overturning circulation on the position of the Sahara Sahel boundary and on global atmospheric dust loading.
Climate Of The Past (1814-9324) (Copernicus Gesellschaft Mbh), 2013 , Vol. 9 , N. 3 , P. 1181-1191

Droits : Author(s) 2013. CC Attribution 3.0 License. Access Climate of
http://archimer.ifremer.fr/doc/00181/29240/27635.pdf
DOI:10.5194/cp-9-1181-2013
http://archimer.ifremer.fr/doc/00181/29240/