A reassessment of lake and wetland feedbacks on the North African英文版.pdf

GEOPHYSICAL RESEARCH LETTERS, VOL. 39, L07701, doi:10.1029/2012GL050992, 2012 A reassessment of lake and wetland feedbacks on the North African Holocene climate G. Krinner,1 A.-M. Lézine,2 P. Braconnot,2 P. Sepulchre,2 G. Ramstein,2 C. Grenier,2 and I. Gouttevin1,3 Received 24 January 2012; revised 2 March 2012; accepted 2 March 2012; published 3 April 2012. [1] Large parts of the Sahara were vegetated during the early stronger if the prescribed background bare soil albedo in a to mid Holocene. Several positive feedbacks, most notably climate model is lower. This is clearly in line with the analysis related to vegetation, have been shown to have favored the by Charney [1975] who suggested that an increased surface northward migration of the desert boundary. During this albedo suppresses atmospheric ascendance and, thus, leads to period, numerous lakes and wetlands existed in the Sahara reduced precipitation rates. This effect is illustrated in more region and might have acted as a local moisture source. recent work by Knorr and Schnitzler [2006] and Vamborg et al. However, earlier model studies of the effects of open water [2011] who show that the orbitally triggered mid-Holocene surfaces on the mid-Holocene North African climate Sahel precipitation increase can be amplified in a climate model suggested that these were weak and did not contribute if a soil albedo scheme is used that takes into account simulated significantly to this northward migration of the North or prescribed vegetation cover and litter. African climate zones. Using a state-of-the-art climate [4] Concerning open water surfaces, Coe and Bonan [1997] model, we suggest that the effect of open-water surfaces on showed that