Abstract
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Optically stimulated luminescence (OSL) measurements were made on individual, sand-sized grains of
quartz from Middle Palaeolithic deposits at two cave sites (El Harhoura 2 and El Mnasra) on the Atlantic
coast of Morocco. We were able to calculate OSL ages for 32 of the 33 samples collected from the Middle
Palaeolithic deposits, including the earliest and latest Aterian levels at both sites. These ages reveal
periods of occupation between about 110 and 95 ka (thousands of years ago), and at w75 ka. A late
Middle Palaeolithic occupation of El Harhoura 2 is also recorded at w55 ka. Our single-grain OSL
chronologies largely support previous age estimates from El Mnasra and other sites along the Atlantic
coast of Morocco, but are generally more precise, reproducible and stratigraphically more coherent (i.e.,
fewer age reversals). We compare the single-grain ages for El Harhoura 2 and El Mnasra with those
obtained from single- and multi-grain OSL dating of Middle Palaeolithic deposits in the nearby sites of
Contrebandiers and Dar es-Soltan 1 and 2, and with records of past regional environments preserved in
sediment cores collected from off the coast of northwest Africa. A conspicuous feature of the new
chronologies is the close correspondence between the three identified episodes of human occupation
and periods of wetter climate and expanded grassland habitat. Owing to the precision of the single-grain
OSL ages, we are able to discern gaps in occupation during Marine Isotope Stages 5 and 4, which may
represent drier periods with reduced vegetation cover. We propose that these climatic conditions can be
correlated with events in the North Atlantic Ocean that exert a major control on abrupt, millennial-scale
fluctuations between wet and dry periods in northwest and central North Africa.