Global Change Biology (1999) 5, 201–212 Crop water availability in early agriculture: evidence from carbon isotope discrimination of seeds from a tenth millennium BP site on the Euphrates J. L. ARAUS,* A. FEBRERO,* M. CATALA,† M. MOLIST,‡ J. VOLTAS§ and I. ROMAGOSA§ *Unitat de Fisiologia Vegetal, Universitat de Barcelona, Spain, †Facultat de Humanitats. Universitat Pompeu Fabra. Spain, ‡Departament d’Antropologia Social i Prehistoria, Universitat Autonoma de Barcelona, Spain §Area de Conreus Extensius, Centre R + D UdL – IRTA, Lleida, Spain Abstract The analysis of carbon isotope discrimination (∆) in crop plant remains from archaeological sites may help to assess water availability for early agriculture. This study presents the analysis of ∆ in seeds of naked wheat (Triticum aestivum/durum), lentil (Lens orientalis/ culinaris), and flax (Linum sp.) found at the archaeological site of Tell Halula in the valley of the Middle Euphrates (Syria). This Neolithic site is the oldest in this region of the Fertile Crescent where the cultivation of domesticated plants has been reported, with seed remains ranging from 9550 to 8465 BP . Most of the seeds analysed showed ∆ values greater than 16 ‰, reaching 20 ‰ for some samples of flax. For wheat, ∆ values were much higher than those reported in present-day (1996) durum wheat crops cultivated under rainfed conditions in north-west Syria under environments with somewhat higher rainfall than Tell Halula. Similarly, grains of present-day (1997) barley cultivated in the archaeological site also showed lower values than those found in archaeological kernels. An empirical relationship between ∆ of mature kernels and total precipitation (plus irrigation where applicable) from heading to maturity (r 2 ⍧ 0.82, n ⍧ 11) was established for durum wheat, currently cultivated in different environments of the Mediterranean basin. The resulting relationship was applied to the data on ∆ of wheat fossil kernels from Tell Halula to estimate the accumulated water inputs during the time (about 6 weeks) the kernels were produced. Calculated water inputs for wheat during early agriculture were (over 110 mm) at least 5 times higher than current-day rainfall accumulated in Tell Halula during the same phenological period. These results strongly suggest that early agriculture wheat was cultivated at Tell Halula under much wetter conditions than are currently to be found in the area. The presence of flax and its very high ∆ values also support this conclusion. Whether such humid conditions during cultivation were due to moister conditions pre- vailing at this time, by planting in alluvial areas or by irrigation works is discussed. Keywords: early agriculture, flax, lentil, stable carbon isotope discrimination, water regime, wheat Abbreviations: ∆, stable carbon isotope discrimination; δ 13 C, ratio of 13 C/ 12 C relative to PeeDee belemnite standard; p i /p a , ratio of intercellular to atmospheric partial pressure of CO 2 ; BP , before present; L-N, Late Neolithic; M- and L-PPNB, Middle and Late Pre-Pottery Neolithic B (PPNB). Received 11 November 1997; revised version received and accepted 9 February 1998 Introduction The environmental conditions prevailing when agricul- ture was first developed in the Old World, in the Fertile Crescent (Near East) during the early Holocene, are Correspondence: J.L. Araus, e-mail josel@porthos.bio.ub.es, fax +34/ 34112842 © 1999 Blackwell Science Ltd. 201 somewhat obscure. Although recent data on climatic conditions are more precise chronologically (Baruch & Bottema 1991; Moore & Hillman 1992) and can explain the environmental setting during the transition from hunter/gathering to farming communities, such data are indirect and not conclusive (Hillman 1996). Present palaeoclimatological and archaeological findings suggest