期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：2
页码：336-341
DOI：10.1073/pnas.1315615112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceMartian meteorite ALH 84001 serves as a witness plate to the history of the Martian climate [~]4 Ga ago. This study describes ion microprobe {delta}18O analyses coupled with {delta}13C, {delta}18O, and {Delta}17O analyses from stepped acid dissolution of the meteorite that identifies a new carbonate phase with distinct isotope compositions. These new measurements of the oxygen isotope composition of carbonates within this meteorite reveal several episodes of aqueous activity that were strongly influenced by atmospheric chemistry. When paired with carbon isotope measurements, these data suggest that the ancient atmosphere of Mars was significantly depleted in 13C compared to the present day. This implies substantial enrichment in the {delta}13C of the atmosphere since the Noachian which may have occurred through extensive atmospheric loss. Carbonate minerals provide critical information for defining atmosphere-hydrosphere interactions. Carbonate minerals in the Martian meteorite ALH 84001 have been dated to [~]3.9 Ga, and both C and O-triple isotopes can be used to decipher the planet's climate history. Here we report {Delta}17O, {delta}18O, and {delta}13C data of ALH 84001 of at least two varieties of carbonates, using a stepped acid dissolution technique paired with ion microprobe analyses to specifically target carbonates from distinct formation events and constrain the Martian atmosphere-hydrosphere-geosphere interactions and surficial aqueous alterations. These results indicate the presence of a Ca-rich carbonate phase enriched in 18O that formed sometime after the primary aqueous event at 3.9 Ga. The phases showed excess 17O (0.7{per thousand}) that captured the atmosphere-regolith chemical reservoir transfer, as well as CO2, O3, and H2O isotopic interactions at the time of formation of each specific carbonate. The carbon isotopes preserved in the Ca-rich carbonate phase indicate that the Noachian atmosphere of Mars was substantially depleted in 13C compared with the modern atmosphere.
