In search of in-situ radiocarbon in Law Dome ice and firn

Smith, A. M.; Levchenko, V.A.; Etheridge, D. M.; Lowe, David C.; Hua, Quan; Trudinger, Cathy M.; Zoppi, Ugo; Elcheikh, Alan

doi:10.1016/s0168-583x(00)00280-9

Cited by 37 publications

(34 citation statements)

References 32 publications

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“…This number is consistent with previous work 1, 23 and provides the age for which measurements of CH 4 concentration in DSS ice best overlap the measured CH 4 at DE08 and DE08--2 ice, and the age which is most consistent with the measured Δ 14 C--CO 2 bomb pulse 44 .…”

Section: Firn Modellingsupporting

confidence: 90%

Low atmospheric CO2 levels during the Little Ice Age due to cooling-induced terrestrial uptake

et al. 2016

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Section: Firn Modellingsupporting

confidence: 90%

Low atmospheric CO2 levels during the Little Ice Age due to cooling-induced terrestrial uptake

et al. 2016

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“…Much of that which may diffuse to open firn air will be lost through exchange with the open atmosphere. This is consistent with the work of Smith et al [2000], who found no evidence for additional contributions to 14 CO 2 in the bomb peak measured in firn air from Law Dome.…”

Section: Field and Laboratory Methodssupporting

confidence: 93%

CO₂ isotopes as tracers of firn air diffusion and age in an Arctic ice cap with summer melting, Devon Island, Canada

et al. 2007

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[1] Firn air and ice have been sampled and analyzed for trace gases (CO 2 , N 2 O, CH 4 , and CO) and isotopes ( 14 C, 13 C, and 18 O of CO 2 ; 3 H of ice) at 3 m intervals from the surface to the depth of closure at 60 m on the Devon Island Ice Cap, a low-elevation permanent glacier in the Canadian Arctic Islands, to investigate firn diffusion and the effects of summer melting. The 14 CO 2 profile from the permeable firn includes the 1963 thermonuclear peak at a depth of 53.9 ± 1.5 m. The twofold increase and rapid decay that characterize the recent atmospheric history for 14 CO 2 provide a robust atmospheric scenario that is used with a firn air diffusion model to inversely construct the firn diffusivity profile. The results show a permeable but essentially nondiffusive zone from 50 to 60 m depth. A firn-ice age profile was produced from density measurements, and accumulation rates were calibrated with the depth of the 1963 thermonuclear 3 H peak. The average ages for CO 2 in the sampled firn air profile were determined by a new method based on the rate of 18 O exchange between CO 2 and the ice matrix. Calibrated with the 1963 peak for thermonuclear 14 CO 2 , a 21.2-year reaction halftime is calculated for exchange taking place at the firn temperature of À22.8°C on Devon. This gives an average age of 54.9 (+6.0/À12.0) years for firn air at 60 m depth in 140-year-old ice. Thus CO 2 has a mean age 85 years younger than associated ice at the point of occlusion. The measured d18 O CO 2 in firn air provides no indication of alteration by summer melting, which is attributed to a high degree of convective and diffusive flushing of the upper firn as shown by diffusion modeling. This suggests that ice sheets with summer melt layers can reliably preserve atmospheric trace gas signals.

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“…It is neither very cold, nor is it warm enough to have melting episodes. The accumulation rate is comparable to Summit Greenland (∼ 25 cm yr −1 ) and Law Dome (∼ 16 cm yr −1 at DSSW20K) (Smith et al, 2000), higher than South Pole and Vostok (< 10 cm yr −1 ), but significantly lower than other Law Dome sites (65 cm yr −1 at DSS and 1.19 m yr −1 at DE08) (Etheridge et al, 1996).…”

Section: Air Movement In Firnmentioning

confidence: 70%

Controls on the movement and composition of firn air at the West Antarctic Ice Sheet Divide

et al. 2011

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Abstract. We sampled interstitial air from the perennial snowpack (firn) at a site near the West Antarctic Ice Sheet Divide (WAIS-D) and analyzed the air samples for a wide variety of gas species and their isotopes. We find limited convective influence (1.4-5.2 m, depending on detection method) in the shallow firn, gravitational enrichment of heavy species throughout the diffusive column in general agreement with theoretical expectations, a ∼ 10 m thick lock-in zone beginning at ∼ 67 m, and a total firn thickness consistent with predictions of Kaspers et al. (2004). Our modeling work shows that the air has an age spread (spectral width) of 4.8 yr for CO 2 at the firn-ice transition. We also find that advection of firn air due to the 22 cm yr −1 ice-equivalent accumulation rate has a minor impact on firn air composition, causing changes that are comparable to other modeling uncertainties and intrinsic sample variability. Furthermore, estimates of age (the gas age/ice age difference) at WAIS-D appear to be largely unaffected by bubble closure above the lock-in zone. Within the lock-in zone, small gas species and their isotopes show evidence of size-dependent fractionation due to permeation through the ice lattice with a size threshold of 0.36 nm, as at other sites. We also see an unequivocal and unprecedented signal of oxygen isotope fractionation within the lock-in zone, which we interpret as the mass-dependent expression of a size-dependent fractionation process.

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In search of in-situ radiocarbon in Law Dome ice and firn

Cited by 37 publications

References 32 publications

Low atmospheric CO2 levels during the Little Ice Age due to cooling-induced terrestrial uptake

Low atmospheric CO2 levels during the Little Ice Age due to cooling-induced terrestrial uptake

CO₂ isotopes as tracers of firn air diffusion and age in an Arctic ice cap with summer melting, Devon Island, Canada

Controls on the movement and composition of firn air at the West Antarctic Ice Sheet Divide

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In search of in-situ radiocarbon in Law Dome ice and firn

Cited by 37 publications

References 32 publications

Low atmospheric CO2 levels during the Little Ice Age due to cooling-induced terrestrial uptake

Low atmospheric CO2 levels during the Little Ice Age due to cooling-induced terrestrial uptake

CO2 isotopes as tracers of firn air diffusion and age in an Arctic ice cap with summer melting, Devon Island, Canada

Controls on the movement and composition of firn air at the West Antarctic Ice Sheet Divide

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CO₂ isotopes as tracers of firn air diffusion and age in an Arctic ice cap with summer melting, Devon Island, Canada