Browsing by Author "Rosen, JL"

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    Corrigendum to "Gas transport in firn: multiple-tracer characterisation and model intercomparison for NEEM, Northern Greenland'' published in Atmos. Chem. Phys., 12, 4259–-4277, 2012
    (Copernicus Publications, 2014-04-09) Buizert, C; Martinerie, P; Petrenko, VV; Severinghaus, JP; Trudinger, CM; Witrant, E; Rosen, JL; Orsi, AJ; Rubino, M; Etheridge, DM; Steele, LP; Hogan, C; Laube, JC; Sturges, WT; Levchenko, VA; Smith, AM; Levin, I; Conway, TJ; Dlugokencky, EJ; Lang, PM; Kawamura, K; Jenk, TM; White, JWC; Sowers, T; Schwander, J; Blunier, T
    It was kindly pointed out to us by M. Battle that Eq. (2) on p. 4263 contains a typo, and should instead be [X]corr(z) = [X]meas(z) ΔMδgrav(z)/1000 + 1 , (2) where [X]corr ([X]meas) is the gravity-corrected (measured) mixing ratio of gas species X, 1M = MX − Mair is the molar mass difference between gas X and air, and grav(z) is the gravitational fractionation per unit mass difference at depth z. All calculations in the study were done correctly, following Eq. (2) as given here. Furthermore, the present-day 1age value for NEEM is incorrect in the original manuscript, and underestimates Δage by 6 years. The correct value is 188+3 −9 yr. In our original, incorrect calculation we used the ice age in years before 2000 CE (b2k), while we should have used the ice age relative to the surface ice age. In the updated 1age calculation we use the ice age found by annual layer counting of the shallow NEEM 2011 S1 core (Sigl et al., 2013). The NEEM chronology published in Rasmussen et al. (2013) uses the correct, updated Δage estimate. Both errors addressed in this corrigendum affect neither the discussion nor the main conclusions of the original publication. © Author(s) 2014.
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    Gas transport in firn: multiple-tracer characterisation and model intercomparison for NEEM, Northern Greenland
    (Copernicus Publications, 2012-05-14) Buizert, C; Martinerie, P; Petrenko, VV; Severinghaus, JP; Trudinger, CM; Witrant, E; Rosen, JL; Orsi, AJ; Rubino, M; Etheridge, DM; Steele, LP; Hogan, C; Laube, JC; Sturges, WT; Levchenko, VA; Smith, AM; Levin, I; Conway, TJ; Dlugokencky, EJ; Lang, PM; Kawamura, K; Jenk, TM; White, JWC; Sowers, T; Schwander, J; Blunier, T
    Air was sampled from the porous firn layer at the NEEM site in Northern Greenland. We use an ensemble of ten reference tracers of known atmospheric history to characterise the transport properties of the site. By analysing uncertainties in both data and the reference gas atmospheric histories, we can objectively assign weights to each of the gases used for the depth-diffusivity reconstruction. We define an objective root mean square criterion that is minimised in the model tuning procedure. Each tracer constrains the firn profile differently through its unique atmospheric history and free air diffusivity, making our multiple-tracer characterisation method a clear improvement over the commonly used single-tracer tuning. Six firn air transport models are tuned to the NEEM site; all models successfully reproduce the data within a 1σ Gaussian distribution. A comparison between two replicate boreholes drilled 64 m apart shows differences in measured mixing ratio profiles that exceed the experimental error. We find evidence that diffusivity does not vanish completely in the lock-in zone, as is commonly assumed. The ice age- gas age difference (Δage) at the firn-ice transition is calculated to be 182+3−9 yr. We further present the first intercomparison study of firn air models, where we introduce diagnostic scenarios designed to probe specific aspects of the model physics. Our results show that there are major differences in the way the models handle advective transport. Furthermore, diffusive fractionation of isotopes in the firn is poorly constrained by the models, which has consequences for attempts to reconstruct the isotopic composition of trace gases back in time using firn air and ice core records. © Author(s) 2012.