| Abstract: |
We have analysed human and animal collagen samples from three geographically and temporally distinct cemeteries at the Dakhleh Oasis, Egypt. All sites display strikingly high average values of d15N: Kellis 1 (Late PtolemaicEarly Roman period) 18·0
Kellis 2 (Romano-Christian period) 18·0, and ein Tirghi (Roman period) 17·0. Rainfall at Dakhleh is essentially zero. The d15N values for humans and animals lie on the respective quasi-linear relationship between rainfall and d15N found by Heaton et al. (1986). Data from Dakhleh and other sites suggest that a single linear trend describes the rainfall-d15N relationship in a wide range of sites. This correlation is believed to be due to a combination of two eVects: excretion of excess 15N-depleted urea in order to increase osmolality of urine (Ambrose & DeNiro, 1986a, b) and 15N-enrichment in arid-region plants, as a result of 15N-enrichment in soils. Higher d15N values in human consumers were acquired through consumption of animal-derived protein. High d15N in desert soils may be caused by volatilization of isotopically light ammonia formed during bacterial activity, an eVect which increases near to the soil surface.
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