Comment on "Climate-Driven Ecosystem Succession in the Sahara: The Past 6000 Years"
Victor Brovkin1* and
Martin Claussen1,2
1 Max Planck Institute for Meteorology, Bundesstraße 55, 20146 Hamburg, Germany.
2 Meteorological Institute, University of Hamburg, Bundesstraße 55, 20146 Hamburg, Germany.
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Fig. 1. Simulated difference between mid-Holocene and present-day vegetation cover, revealing changes mainly in the Western part of the Sahara, the focus of earlier hypotheses of abrupt ecosystem change in the Sahara. Gray shading indicates changes from mid-Holocene vegetated state to present-day desert (4); the green shaded area has more than 30% reduction in vegetation cover during the Holocene (3). A strong positive biogeophysical feedback between vegetation cover and precipitation in the Western Sahara found in (3, 4) may result in an abrupt shift from wet to dry regime. The blue shaded area indicates the area of abrupt vegetation changes attributed to a nonlinear response of vegetation to precipitation from simulation by Liu et al. (14). The stars indicate the position of Lake Yoa (19.03°N, 20.31°E) and Ocean Drilling Program site 658C (20.45°N, 18.35°W). The record from Lake Yoa does not seem to show evidence of abrupt ecosystem transitions (2), whereas the marine sediment core reveals an abrupt change in dust transport from the continent (13). Yellow circles indicate sites with mid-Holocene steppes or xerophytic shrubs from the BIOME-6000 database (10).
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