Publications

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2012
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.  2012.  Gas transport in firn: multiple-tracer characterisation and model intercomparison for NEEM, Northern Greenland. Atmospheric Chemistry and Physics. 12:4259-4277.   10.5194/acp-12-4259-2012   AbstractWebsite

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 1 sigma 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 (Delta age) at the firn-ice transition is calculated to be 182(-9)(+3) 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.

2006
Schaefer, H, Whiticar MJ, Brook EJ, Petrenko VV, Ferretti DF, Severinghaus JP.  2006.  Ice record of delta C-13 for atmospheric CH4 across the Younger Dryas-Preboreal transition. Science. 313:1109-1112.   10.1126/science.1126562   AbstractWebsite

We report atmospheric methane carbon isotope ratios (delta(CH4)-C-13) from the Western Greenland ice margin spanning the Younger Dryas - to - Preboreal (YD-PB) transition. Over the recorded similar to 800 years, delta(CH4)-C-13 was around - 46 per mil (parts per thousand); that is, similar to 1 parts per thousand higher than in the modern atmosphere and similar to 5.5 parts per thousand higher than would be expected from budgets without C-13-rich anthropogenic emissions. This requires higher natural C-13-rich emissions or stronger sink fractionation than conventionally assumed. Constant delta(CH4)-C-13 during the rise in methane concentration at the YD-PB transition is consistent with additional emissions from tropical wetlands, or aerobic plant CH4 production, or with a multisource scenario. A marine clathrate source is unlikely.