Gravitational Separation of Gases and Isotopes in Polar Ice Caps

Craig, H.; Horibe, Yoshio; Sowers, Todd

doi:10.1126/science.242.4886.1675

Cited by 223 publications

(177 citation statements)

References 8 publications

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“…Here, we consider 3 mesospheric processes that have been previously studied in other contexts: Gravitational separation of upper atmospheric air, UV photolysis of O 2 , and UV photolysis of CO 2 . Gravitational separation can concentrate heavy isotopologues of CO 2 into the lower mesosphere (37), but the isotopic enrichments we calculate, based on the expression reported by Craig et al (38), are insufficient to generate significant ⌬ 47 changes (see SI). Alternatively, isotope effects in the photolysis of O 2 by short-wavelength UV radiation in the upper mesosphere might lead to unusually enriched CO 2 .…”

Section: Effects Of Mesospheric and Heterogeneous Chemistrymentioning

confidence: 97%

Large and unexpected enrichment in stratospheric ¹⁶ O ¹³ C ¹⁸ O and its meridional variation

Yeung¹,

Affek

Hoag³

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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The stratospheric CO 2 oxygen isotope budget is thought to be governed primarily by the O( 1 D)+CO 2 isotope exchange reaction. However, there is increasing evidence that other important physical processes may be occurring that standard isotopic tools have been unable to identify. Measuring the distribution of the exceedingly rare CO 2 isotopologue 16 O 13 C 18 O, in concert with 18 O and 17 O abundances, provides sensitivities to these additional processes and, thus, is a valuable test of current models. We identify a large and unexpected meridional variation in stratospheric 16 O 13 C 18 O, observed as proportions in the polar vortex that are higher than in any naturally derived CO 2 sample to date. We show, through photochemical experiments, that lower 16 O 13 C 18 O proportions observed in the midlatitudes are determined primarily by the O( 1 D)+CO 2 isotope exchange reaction, which promotes a stochastic isotopologue distribution. In contrast, higher 16 O 13 C 18 O proportions in the polar vortex show correlations with long-lived stratospheric tracer and bulk isotope abundances opposite to those observed at midlatitudes and, thus, opposite to those easily explained by O( 1 D)+CO 2 . We believe the most plausible explanation for this meridional variation is either an unrecognized isotopic fractionation associated with the mesospheric photochemistry of CO 2 or temperature-dependent isotopic exchange on polar stratospheric clouds. Unraveling the ultimate source of stratospheric 16 O 13 C 18 O enrichments may impose additional isotopic constraints on biosphere–atmosphere carbon exchange, biosphere productivity, and their respective responses to climate change.

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Section: Effects Of Mesospheric and Heterogeneous Chemistrymentioning

confidence: 97%

Large and unexpected enrichment in stratospheric ¹⁶ O ¹³ C ¹⁸ O and its meridional variation

Yeung¹,

Affek

Hoag³

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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“…[49] Gravitational enrichment of heavier species in air in the firn open porosity [Craig et al, 1988;Schwander, 1989] causes the CO 2 concentration and ı 13 C measured in firn and ice to be higher (more positive) than the original atmospheric values, and needs to be taken into account to correct the measured values to produce an atmospheric record.…”

Section: Corrections For Gravitational and Diffusion Fractionation 2mentioning

confidence: 99%

A revised 1000 year atmospheric δ¹³C‐CO₂ record from Law Dome and South Pole, Antarctica

et al. 2013

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[1] We present new measurements of ı 13 C of CO 2 extracted from a high-resolution ice core from Law Dome (East Antarctica), together with firn measurements performed at Law Dome and South Pole, covering the last 150 years. Our analysis is motivated by the need to better understand the role and feedback of the carbon (C) cycle in climate change, by advances in measurement methods, and by apparent anomalies when comparing ice core and firn air ı 13 C records from Law Dome and South Pole. We demonstrate improved consistency between Law Dome ice, South Pole firn, and the Cape Grim (Tasmania) atmospheric ı 13 C data, providing evidence that our new record reliably extends direct atmospheric measurements back in time. We also show a revised version of early ı 13 C measurements covering the last 1000 years, with a mean preindustrial level of -6.50 . Finally, we use a Kalman Filter Double Deconvolution to infer net natural CO 2 fluxes between atmosphere, ocean, and land, which cause small ı 13 C deviations from the predominant anthropogenically induced ı 13 C decrease. The main features found from the previous ı 13 C record are confirmed, including the ocean as the dominant cause for the 1940 A.D. CO 2 leveling. Our new record provides a solid basis for future investigation of the causes of decadal to centennial variations of the preindustrial atmospheric CO 2 concentration. Those causes are of potential significance for predicting future CO 2 levels and when attempting atmospheric verification of recent and future global carbon emission mitigation measures through Coupled Climate Carbon Cycle Models.

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“…Measuring the paleoatmospheric 40 Ar/ 38 Ar ratio in ice core samples is complicated by gravitational fractionation in the firn (8,9), the snowpack overlying the zone of ice where air is trapped in isolated bubbles. At Vostok and Dome C, the firn layer is Ϸ100 m thick, and gravitational fractionation enriches heavy isotopes relative to light isotopes by Ϸ0.5 ‰/mass unit.…”

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confidence: 99%

The contemporary degassing rate of ⁴⁰ Ar from the solid Earth

Bender

Barnett

Dreyfus

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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Knowledge of the outgassing history of radiogenic 40 Ar, derived over geologic time from the radioactive decay of 40 K, contributes to our understanding of the geodynamic history of the planet and the origin of volatiles on Earth's surface. The 40 Ar inventory of the atmosphere equals total 40 Ar outgassing during Earth history. Here, we report the current rate of 40 Ar outgassing, accessed by measuring the Ar isotope composition of trapped gases in samples of the Vostok and Dome C deep ice cores dating back to almost 800 ka. The modern outgassing rate (1.1 ؎ 0.1 ؋ 10 8 mol/yr) is in the range of values expected by summing outgassing from the continental crust and the upper mantle, as estimated from simple calculations and models. The measured outgassing rate is also of interest because it allows dating of air trapped in ancient ice core samples of unknown age, although uncertainties are large (؎180 kyr for a single sample or ؎11% of the calculated age, whichever is greater).geochronology ͉ ice cores ͉ geodynamics ͉ noble gases T he elemental abundance and isotopic composition of noble gases in the atmosphere inform us about Earth's composition, the history of the ocean and atmosphere, and the present and past geodynamics of the planet. The atmospheric abundance of 40 Ar reflects the balance between production by radioactive decay of 40 K in the crust, upper mantle, and lower mantle, and outgassing to the atmosphere. It is well recognized that the atmospheric inventory comprises approximately half of the total 40 Ar produced by potassium decay over Earth history, assuming the canonical value of 240 ppm for the K content of the bulk silicate Earth (1). The most parsimonious explanation for the remainder is that there is a large reservoir containing undegassed Ar, which is presumably the lower mantle (1). However, extensive seismic evidence has shown that oceanic plates subduct into the lower mantle while plumes rise from the core-mantle boundary to produce volcanism at the surface (e.g., refs. 2 and 3). Because of such observations, it is problematic to maintain that the lower mantle is undegassed. A number of recent papers have attempted to explain the limited atmospheric 40 Ar inventory in the face of whole mantle convection. As one example, Davies (4) and Lassiter (5) have proposed that the bulk silicate Earth K concentration is Ϸ150 ppm rather than 240.In this article, we present and explore another constraint on the planetary 40 Ar balance: the contemporary degassing rate of 40 Ar. We determine this rate by measuring the paleoatmospheric 40 Ar/ 38 Ar ratio of fossil air from ice core samples. Critical to this effort are the Vostok and especially EPICA Dome C cores (6), which allow us to access air as old as Ϸ779 ka. We compare the observed outgassing rate with the contributions to this term from outgassing of the continental crust and various degassing modes of the upper mantle. It is possible to account for the present rate of 40 Ar increase with our estimates of degassing rates by the continental crust and...

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Gravitational Separation of Gases and Isotopes in Polar Ice Caps

Cited by 223 publications

References 8 publications

Large and unexpected enrichment in stratospheric ¹⁶ O ¹³ C ¹⁸ O and its meridional variation

Large and unexpected enrichment in stratospheric ¹⁶ O ¹³ C ¹⁸ O and its meridional variation

A revised 1000 year atmospheric δ¹³C‐CO₂ record from Law Dome and South Pole, Antarctica

The contemporary degassing rate of ⁴⁰ Ar from the solid Earth

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Gravitational Separation of Gases and Isotopes in Polar Ice Caps

Cited by 223 publications

References 8 publications

Large and unexpected enrichment in stratospheric 16 O 13 C 18 O and its meridional variation

Large and unexpected enrichment in stratospheric 16 O 13 C 18 O and its meridional variation

A revised 1000 year atmospheric δ13C‐CO2 record from Law Dome and South Pole, Antarctica

The contemporary degassing rate of 40 Ar from the solid Earth

Contact Info

Product

Resources

About

Large and unexpected enrichment in stratospheric ¹⁶ O ¹³ C ¹⁸ O and its meridional variation

Large and unexpected enrichment in stratospheric ¹⁶ O ¹³ C ¹⁸ O and its meridional variation

A revised 1000 year atmospheric δ¹³C‐CO₂ record from Law Dome and South Pole, Antarctica

The contemporary degassing rate of ⁴⁰ Ar from the solid Earth