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Paleoclimatic changes in the northern coast of Senegal are investigated on a peat core of 350 cm long spanning the past 3500 yrs extracted from the site of Mboro (15.07 degrees N, 16.53 degrees W). This deposit corresponds with a local stage, the Tafolian (4000 BP to 2000 BP) whose paleoclimatic trends, essentially defined by sedimentological methods, were previously considered to be dominated by drought. The delta 13C profile obtained from 70 successive peat samples shows climate oscillations between wet and dry periods. A wet period appears around 3200 BP. A shorter but equally wet one occurs around 1000 BP. These two humid phases are separated by a rather arid period that occurs around 2000 BP as shown by an exceptional rise in delta 13C values. This dry phase as well as a second one evidenced around 800 BP coincided with increases of dull-quartz abundance; originating from wind-reworking of surrounding dune sand. After 850 BP, the carbon isotope record suggests a progressive return to more humid conditions. Our carbon isotope trends shed new light on past monsoon rainfall oscillations over Sahelian areas during the Tafolian. (C) 2010 Elsevier B.V. All rights reserved.