ATMOSPHERE-SURFACE INTERACTIONS ON MARS - DELTA-O-17 MEASUREMENTS OF CARBONATE FROM ALH-84001

Oxygen isotope measurements of carbonate from martian meteorite ALH 84 001 (delta(18)O = 18.3 +/- 0.4 per mil, delta(17)O = 10.3 +/- 0.2 per mil, and Delta(17)O = 0.8 +/- 0.05 per mil) are fractionated with resp ect to those of silicate minerals. These measurements support the exis tence of two oxygen isotope reservoirs (the atmosphere and the silicat e planet) on Mars at the time of carbonate growth. The cause of the at mospheric oxygen isotope anomaly may be exchange between CO2 and O(D-1 ) produced by the photodecomposition of ozone. Atmospheric oxygen isot ope compositions may be transferred to carbonate minerals by CO2-H2O e xchange and mineral growth. A sink of O-17-depleted oxygen, as require d by mass balance, may exist in the planetary regolith.