Influence of carbonic anhydrase activity in terrestrial vegetation on the 18O content of atmospheric CO2.
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The oxygen-18 (18O) content of atmospheric carbon dioxide (CO2) is an important indicator of CO2 uptake on land. It has generally been assumed that during photosynthesis, oxygen in CO2 reaches isotopic equilibrium with oxygen in 18O-enriched water in leaves. We show, however, large differences in the activity of carbonic anhydrase (which catalyzes CO2 hydration and 18O exchange in leaves) among major plant groups that cause variations in the extent of 18O equilibrium (theta(eq)). A clear distinction in theta(eq) between C3 trees and shrubs, and C4 grasses makes atmospheric C18OO a potentially sensitive indicator to changes in C3 and C4 productivity. We estimate a global mean theta(eq) value of approximately 0.8, which reasonably reconciles inconsistencies between 18O budgets of atmospheric O2 (Dole effect) and CO2. (+info)
Ancient geodynamics and global-scale hydrology on Mars.
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Loading of the lithosphere of Mars by the Tharsis rise explains much of the global shape and long-wavelength gravity field of the planet, including a ring of negative gravity anomalies and a topographic trough around Tharsis, as well as gravity anomaly and topographic highs centered in Arabia Terra and extending northward toward Utopia. The Tharsis-induced trough and antipodal high were largely in place by the end of the Noachian Epoch and exerted control on the location and orientation of valley networks. The release of carbon dioxide and water accompanying the emplacement of approximately 3 x 10(8) cubic kilometers of Tharsis magmas may have sustained a warmer climate than at present, enabling the formation of ancient valley networks and fluvial landscape denudation in and adjacent to the large-scale trough. (+info)
Rising CO2 levels and the fecundity of forest trees.
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We determined the reproductive response of 19-year-old loblolly pine (Pinus taeda) to 4 years of carbon dioxide (CO2) enrichment (ambient concentration plus 200 microliters per liter) in an intact forest. After 3 years of CO2 fumigation, trees were twice as likely to be reproductively mature and produced three times as many cones and seeds as trees at ambient CO2 concentration. A disproportionate carbon allocation to reproduction under CO2 enrichment results in trees reaching maturity sooner and at a smaller size. This reproductive response to future increases in atmospheric CO2 concentration is expected to change loblolly dispersal and recruitment patterns. (+info)
On strategies for reducing greenhouse gas emissions.
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Equity is of fundamental concern in the quest for international cooperation to stabilize greenhouse gas concentrations by the reduction of emissions. By modeling the carbon cycle, we estimate the global CO(2) emissions that would be required to stabilize the atmospheric concentration of CO(2) at levels ranging from 450 to 1,000 ppm. These are compared, on both an absolute and a per-capita basis, to scenarios for emissions from the developed and developing worlds generated by socio-economic models under the assumption that actions to mitigate greenhouse gas emissions are not taken. Need and equity have provided strong arguments for developing countries to request that the developed world takes the lead in controlling its emissions, while permitting the developing countries in the meantime to use primarily fossil fuels for their development. Even with major and early control of CO(2) emissions by the developed world, limiting concentration to 450 ppm implies that the developing world also would need to control its emissions within decades, given that we expect developing world emissions would otherwise double over this time. Scenarios leading to CO(2) concentrations of 550 ppm exhibit a reduction of the developed world's per-capita emission by about 50% over the next 50 years. Even for the higher stabilization levels considered, the developing world would not be able to use fossil fuels for their development in the manner that the developed world has used them. (+info)
Climate response to orbital forcing across the Oligocene-Miocene boundary.
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Spectral analyses of an uninterrupted 5.5-million-year (My)-long chronology of late Oligocene-early Miocene climate and ocean carbon chemistry from two deep-sea cores recovered in the western equatorial Atlantic reveal variance concentrated at all Milankovitch frequencies. Exceptional spectral power in climate is recorded at the 406-thousand-year (ky) period eccentricity band over a 3.4-million-year period [20 to 23.4 My ago (Ma)] as well as in the 125- and 95-ky bands over a 1.3-million-year period (21.7 to 23.0 Ma) of suspected low greenhouse gas levels. Moreover, a major transient glaciation at the epoch boundary ( approximately 23 Ma), Mi-1, corresponds with a rare orbital congruence involving obliquity and eccentricity. The anomaly, which consists of low-amplitude variance in obliquity (a node) and a minimum in eccentricity, results in an extended period ( approximately 200 ky) of low seasonality orbits favorable to ice-sheet expansion on Antarctica. (+info)
Mass spectrometry in the U.S. space program: past, present, and future.
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Recent years have witnessed significant progress on the miniaturization of mass spectrometers for a variety of field applications. This article describes the development and application of mass spectrometry (MS) instrumentation to support of goals of the U.S. space program. Its main focus is on the two most common space-related applications of MS: studying the composition of planetary atmospheres and monitoring air quality on manned space missions. Both sets of applications present special requirements in terms of analytical performance (sensitivity, selectivity, speed, etc.), logistical considerations (space, weight, and power requirements), and deployment in perhaps the harshest of all possible environments (space). The MS instruments deployed on the Pioneer Venus and Mars Viking Lander missions are reviewed for the purposes of illustrating the unique features of the sample introduction systems, mass analyzers, and vacuum systems, and for presenting their specifications which are impressive even by today's standards. The various approaches for monitoring volatile organic compounds (VOCs) in cabin atmospheres are also reviewed. In the past, ground-based GC/MS instruments have been used to identify and quantify VOCs in archival samples collected during the Mercury, Apollo, Skylab, Space Shuttle, and Mir missions. Some of the data from the more recent missions are provided to illustrate the composition data obtained and to underscore the need for instrumentation to perform such monitoring in situ. Lastly, the development of two emerging technologies, Direct Sampling Ion Trap Mass Spectrometry (DSITMS) and GC/Ion Mobility Spectrometry (GC/IMS), will be discussed to illustrate their potential utility for future missions. (+info)
The high oxygen atmosphere toward the end-Cretaceous; a possible contributing factor to the K/T boundary extinctions and to the emergence of C(4) species.
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Angiosperm plants were grown under either the present day 21 kPa O(2) atmosphere or 28 kPa, as estimated for the end-Cretaceous (100-65 MyBP). CO(2) was held at different levels, within the 24-60 Pa range, as also estimated for the same period. In C(3) Xanthium strumarium and Atriplex prostrata, leaf area and net photosynthesis per unit leaf area, were reduced by the high O(2), while the whole-plant respiration/photosynthesis ratio increased. The high O(2) effects were strongest under 24 Pa, but still significant under 60 Pa CO(2). Growth was reduced by high O(2) in these C(3) species, but not in Flaveria sp., whether C(3), C(4), or intermediary grown under light intensities <350 micromol m(-2) s(-1) PPF. Photosynthesis of C(3) Flaveria sp. was reduced by high O(2), but only at light intensities >350 micromol m(-2) s(-1) PPF. It is concluded that the high O(2) atmosphere at the end-Cretaceous would have reduced growth of at least some of the vegetation, thus adversely affecting dependent fauna. The weakened biota would have been predisposed to the consequences of volcanism and the K/T boundary bolide impact. Conversely, photosynthesis and growth of C(4) Zea mays and Atriplex halimus were little affected by high, 28 kPa, O(2). This suggests an environmental driver for the evolution of C(4) physiology. (+info)
Paleobotanical evidence for near present-day levels of atmospheric Co2 during part of the tertiary.
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Understanding the link between the greenhouse gas carbon dioxide (CO(2)) and Earth's temperature underpins much of paleoclimatology and our predictions of future global warming. Here, we use the inverse relationship between leaf stomatal indices and the partial pressure of CO(2) in modern Ginkgo biloba and Metasequoia glyptostroboides to develop a CO(2) reconstruction based on fossil Ginkgo and Metasequoia cuticles for the middle Paleocene to early Eocene and middle Miocene. Our reconstruction indicates that CO(2) remained between 300 and 450 parts per million by volume for these intervals with the exception of a single high estimate near the Paleocene/Eocene boundary. These results suggest that factors in addition to CO(2) are required to explain these past intervals of global warmth. (+info)