We report data on the martian meteorite Northwest Africa (NWA) 7034, which shares some petrologic and geochemical characteristics with known martian meteorites of the SNC (i.e., shergottite, nakhlite, and chassignite) group, but also has some unique characteristics that would exclude it from that group. NWA 7034 is a geochemically enriched crustal rock compositionally similar to basalts and average martian crust measured by recent Rover and Orbiter missions. It formed 2.089 ± 0.081 billion years ago, during the early Amazonian epoch in Mars' geologic history. NWA 7034 has an order of magnitude more indigenous water than most SNC meteorites, with up to 6000 parts per million extraterrestrial H(2)O released during stepped heating. It also has bulk oxygen isotope values of Δ(17)O = 0.58 ± 0.05 per mil and a heat-released water oxygen isotope average value of Δ(17)O = 0.330 ± 0.011 per mil, suggesting the existence of multiple oxygen reservoirs on Mars.

Previous Δ(17)O measurements of sulfate that rely on pyrolysis in a quartz cup have been affected by oxygen exchange. These previous results can be corrected using a simple linear equation (Δ(17)O(gold) = Δ(17)O(quartz) * 1.14 + 0.06). Future pyrolysis of silver sulfate should be conducted in gold capsules or corrected to data obtained from gold capsules to avoid obtaining oxygen isotope exchange-affected data.

Significance The highest S-isotope anomaly is observed in a nonvolcanic period, and the magnitude of anomaly is similar to the largest volcanic eruptions of the 20th century. S-quadruple isotope data provided the first evidence of how super El Niño Southern Oscillation (ENSO) events (1997–1998) have affected the transport and transformation of aerosols to the stratosphere; thus, record of paleo-ENSO events of this magnitude can be traced with the S-isotopic anomaly. High-resolution and high-precision S-isotopic fingerprinting also revealed that the tropospheric sulfate produced during fossil-fuel and biomass burning contributes to the stratospheric sulfate aerosol layer, a contribution previously unrecognized. The distribution of sulfur anomalies mimics the Archean isotope record, which is used to track the origin and evolution of oxygen on earth.

Executive Summary Return of samples from the surface of Mars has been a goal of the international Mars science community for many years. Affirmation by NASA and ESA of the importance of Mars exploration led the agencies to establish the international MSR Objectives and Samples Team (iMOST). The purpose of the team is to re‐evaluate and update the sample‐related science and engineering objectives of a Mars Sample Return (MSR) campaign. The iMOST team has also undertaken to define the measurements and the types of samples that can best address the objectives. Seven objectives have been defined for MSR, traceable through two decades of previously published international priorities. The first two objectives are further divided into sub‐objectives. Within the main part of the report, the importance to science and/or engineering of each objective is described, critical measurements that would address the objectives are specified, and the kinds of samples that would be most likely to carry key information are identified. These seven objectives provide a framework for demonstrating how the first set of returned Martian samples would impact future Martian science and exploration. They also have implications for how analogous investigations might be conducted for samples returned by future missions from other solar system bodies, especially those that may harbor biologically relevant or sensitive material, such as Ocean Worlds (Europa, Enceladus, Titan) and others. Summary of Objectives and Sub‐Objectives for MSR Identified by iMOST This objective is divided into five sub‐objectives that would apply at different landing sites. 1.1 Characterize the essential stratigraphic, sedimentologic, and facies variations of a sequence of Martian sedimentary rocks. 1.2 Understand an ancient Martian hydrothermal system through study of its mineralization products and morphological expression. 1.3 Understand the rocks and minerals representative of a deep subsurface groundwater environment. 1.4 Understand water/rock/atmosphere interactions at the Martian surface and how they have changed with time. 1.5 Determine the petrogenesis of Martian igneous rocks in time and space. This objective has three sub‐objectives: 2.1 Assess and characterize carbon, including possible organic and pre‐biotic chemistry. 2.2 Assay for the presence of biosignatures of past life at sites that hosted habitable environments and could have preserved any biosignatures. 2.3 Assess the possibility that any life forms detected are alive, or were recently alive. Summary of iMOST Findings Several specific findings were identified during the iMOST study. While they are not explicit recommendations, we suggest that they should serve as guidelines for future decision making regarding planning of potential future MSR missions. The samples to be collected by the Mars 2020 (M‐2020) rover will be of sufficient size and quality to address and solve a wide variety of scientific questions. Samples, by definition, are a statistical representation of a larger entity...

Increased anthropogenic-induced aerosol concentrations over the Himalayas and Tibetan Plateau have affected regional climate, accelerated snow/glacier melting, and influenced water supply and quality in Asia. Although sulfate is a predominant chemical component in aerosols and the hydrosphere, the contributions from different sources remain contentious. Here, we report multiple sulfur isotope composition of sedimentary sulfates from a remote freshwater alpine lake near Mount Everest to reconstruct a two-century record of the atmospheric sulfur cycle. The sulfur isotopic anomaly is utilized as a probe for sulfur source apportionment and chemical transformation history. The nineteenth-century record displays a distinct sulfur isotopic signature compared with the twentieth-century record when sulfate concentrations increased. Along with other elemental measurements, the isotopic proxy suggests that the increased trend of sulfate is mainly attributed to enhancements of dust-associated sulfate aerosols and climate-induced weathering/erosion, which overprinted sulfur isotopic anomalies originating from other sources (e.g., sulfates produced in the stratosphere by photolytic oxidation processes and/or emitted from combustion) as observed in most modern tropospheric aerosols. The changes in sulfur cycling reported in this study have implications for better quantification of radiative forcing and snow/glacier melting at this climatically sensitive region and potentially other temperate glacial hydrological systems. Additionally, the unique ΔS-δS pattern in the nineteenth century, a period with extensive global biomass burning, is similar to the Paleoarchean (3.6-3.2 Ga) barite record, potentially providing a deeper insight into sulfur photochemical/thermal reactions and possible volcanic influences on the Earth's earliest sulfur cycle.

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The ability of sulfate aerosols to reflect solar radiation and simultaneously act as cloud condensation nuclei renders them central players in the global climate system. The oxidation of S(IV) compounds and their transport as stable S(VI) in the Earth's system are intricately linked to planetary scale processes, and precise characterization of the overall process requires a detailed understanding of the linkage between climate dynamics and the chemistry leading to the product sulfate. This paper reports a high-resolution, 22-y (1980-2002) record of the oxygen-triple isotopic composition of sulfate (SO 4 ) aerosols retrieved from a snow pit at the South Pole. Observed variation in the O-isotopic anomaly of SO 4 aerosol is linked to the ozone variation in the tropical upper troposphere/ lower stratosphere via the Ozone El-Niño Southern Oscillations (ENSO) Index (OEI). Higher Δ 17 O values (3.3‰, 4.5‰, and 4.2‰) were observed during the three largest ENSO events of the past 2 decades. Volcanic events inject significant quantities of SO 4 aerosol into the stratosphere, which are known to affect ENSO strength by modulating stratospheric ozone levels (OEI = 6 and Δ 17 O = 3.3‰, OEI = 11 and Δ 17 O = 4.5‰) and normal oxidative pathways. Our high-resolution data indicated that Δ 17 O of sulfate aerosols can record extreme phases of naturally occurring climate cycles, such as ENSOs, which couple variations in the ozone levels in the atmosphere and the hydrosphere via temperature driven changes in relative humidity levels. A longer term, higher resolution oxygen-triple isotope analysis of sulfate aerosols from ice cores, encompassing more ENSO periods, is required to reconstruct paleo-ENSO events and paleotropical ozone variations.

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 Δ 17 O, δ 18 O, and δ 13 C 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 18 O that formed sometime after the primary aqueous event at 3.9 Ga. The phases showed excess 17 O (0.7‰) that captured the atmosphere-regolith chemical reservoir transfer, as well as CO 2 , O 3 , and H 2 O 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 13 C compared with the modern atmosphere.Martian meteorite | oxygen isotope anomaly | aqueous interaction | carbon isotope | photochemistry G eological evidence suggests that early Mars was sufficiently warm for liquid water to flow on the surface for at least brief periods, if not longer (1). Identifying the nature and duration of warmer conditions on the Martian surface is one of the key pieces of information for understanding atmosphere-hydrosphere-geosphere interactions, the evolution of the atmosphere, and potential past habitability. A better understanding of the evolution of the Martian atmosphere and, in particular, the behavior of its primary component, CO 2 , provides a means for characterizing the nature of the ancient Martian environment. The amount of CO 2 present in the atmosphere should provide critical insight into the characteristics of the Martian climate, with a denser atmosphere being more likely to be able to support prolonged warmer temperatures (2, 3).The Martian meteorite ALH 84001 is a critical source for understanding the history of the Martian atmosphere, as it is the oldest known rock (crystallographic age ∼4.09 ± 0.03 Ga) (4), and its carbonate fractions (<1% wt/wt) are considered to have preserved the carbon isotope signature of the ancient atmosphere ∼3.9 Ga ago (5). These carbonates are chemically (Mg-, Ca-, and FeMn rich) and isotopically (δ 13 C VPDB = 27-64, where VPDB stands for Vienna Pee Dee Belemnite, and δ 18 O SMOW = −10-27‰, where SMOW stands for Standard Mean Ocean Water) heterogeneous on micrometer scales; carbon and oxygen isotopes show a covariant relationship that is correlated with Mg content of the mineral (6-8). The exact process responsible for their formation is not clear, although low-temperature aqueous precipitation, biogenic production, evaporation, and high-temperature reactions are all candidate processes (9-13). Decoding the fingerprints of various oxygen-carry...