CO2-climate relationship as deduced from the Vostok ice core: a re-examination based on new measurements and on a re-evaluation of the air dating

Abstract

Interpretation of the past CO2 variations recorded in polar ice during the large climatic transitions requires an accurate determination of the air‐ice age difference. For the Vostok core, the age differences resulting from different assumptions on the firn densification process are compared and a new procedure is proposed to date the air trapped in this core. The penultimate deglaciation is studied on the basis of this new air dating and new CO2 measurements. These measurements and results obtained on other ice cores indicate that at the beginning of the deglaciations, the CO2 increase is either in phase or lags by less than about 1000 years with respect to the Antarctic temperature, while it clearly lags the temperature at the onset of the last glaciation.

Pore morphology of polar firn around closure revealed by X-ray tomography

“…Deeper in the firn, in the diffusive zone, molecular diffusion dominates and gravitational fractionation also occurs. The lock-in depth (LID) is defined as the depth at which gravitational fractionation stops (Battle et al, 1996). In the deepest firn zone named the lock-in zone (LIZ), the transport of gases in open pores becomes limited and eventually stops because pores close and entrap air.…”

“…Ancient atmospheric air is embedded in polar ice caps, making them a major source of data for reconstructing past climates (Barnola et al, 1991;Battle et al, 1996). For example, the EPICA community traced climate variability back to 800 kyr before present (Augustin et al, 2004) from ice cores drilled at Dome Concordia (also named Dome C).…”

Ice Core Records of Atmospheric CO 2 Around the Last Three Glacial Terminations

“…1, our data and previously published CO 2 concentration records (1,6,9,11,15,16) are compared with Antarctic isotope (temperature) ice core records (13,(17)(18)(19). Note that the CO 2 concentrations represent essentially a global signal.…”

“…The internal temporal resolution of ice core air samples is restricted by the age distribution of the bubbles caused by the enclosure process (10). This age spread is about 300 years for Vostok (11) and 140 years for the TD ice core (9) at present but about three times higher for glacial conditions (11). The depth-ice age scale used for terminations II and III in the Vostok core is a recently expanded version of the extended glaciological time scale (12).…”

“…The ice age-air age difference (⌬age) was calculated with a climatological firn densification model (11) and varies between about 2000 and 6000 years for warm and cold periods, respectively. The accuracy of the model is better than 100 years for recent periods but on the order of 1000 years for glacial conditions (11), which has to be kept in mind when interpreting the phase shift between ice and gas records of the ice core archive. In the case of termination I, recently published age scales derived by synchronization of CH 4 variations in central Greenland and Antarctic ice cores (13,14) were used.…”