CO₂ and O₂/N₂ variations in and just below the bubble–clathrate transformation zone of Antarctic ice cores

Dieter Lüthi (1, 2) , Bernhard Bereiter (1, 2) , Bernhard Stauffer (1, 2) , Renato Winkler (1, 2) , Jakob Schwander (1, 2) , Philippe Kindler (1, 2) , Markus Leuenberger (1, 2) , Sepp Kipfstuhl (3) , Emilie Capron (4, 5) , Amaelle Landais (4, 5) , Hubertus Fischer (1, 2) , Thomas Stocker (1, 2)

1 CEP - Climate and Environmental Physics [Bern]
2 OCCR - Oeschger Centre for Climate Change Research
3 AWI - Alfred Wegener Institute for Polar and Marine Research
4 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
5 GLACCIOS - Glaces et Continents, Climats et Isotopes Stables

CO$_2$ measurements on the EPICA (European Project for Ice Coring in Antarctica) DML ice core in depth levels just below the bubble ice–clathrate ice transformation zone (1230–2240 m depth) were performed. In the youngest part (1230–1600 m), they reveal variations of up to 25 ppmv around the mean atmospheric concentration within centimetres, corresponding to a snow deposition interval of a few years. Similar results are found at corresponding depth regions of the Dome C and the Talos Dome ice cores. Since we can exclude all hitherto known processes altering the concentration of CO$_2$ in ice cores, we present a hypothesis about spatial fractionation of air components related to episodically increasing clathrate formation followed by diffusion processes from bubbles to clathrates. This hypothesis is supported by optical line-scan observations and by O$_2$/N$_2$ measurements at the same depth where strong CO$_2$ variations are detected. Below the clathrate formation zone, this small-scale fractionation process is slowly smoothed out, most likely by diffusion, regaining the initial mean atmospheric concentration. Although this process compromises the representativeness of a single CO$_2$ measurement on small ice samples in the clathrate formation zone of an ice core, it does not affect the mean atmospheric CO$_2$ concentration if CO$_2$ values are averaged over a sufficiently long depth scale (> 10 cm in case of the EPICA DML ice core).

Domaines: Océan, Atmosphère; Interfaces continentales, environnement

Dieter Lüthi, Bernhard Bereiter, Bernhard Stauffer, Renato Winkler, Jakob Schwander, et al.. CO₂ and O₂/N₂ variations in and just below the bubble–clathrate transformation zone of Antarctic ice cores. Earth and Planetary Science Letters, 2010, 297 (1-2), pp.226-233. ⟨10.1016/j.epsl.2010.06.023⟩. ⟨hal-03200967⟩