analyses of datable ice cores from Antarctica (Fig. 16.10) and Greenland, the
atmospheric CO 2 level was repeatedly close to 185 ppmv at the glacial maxima at
350, 260, 140, and 25 kyr BP (i.e. thousands of years before 1950, somewhat
approximately determined). With the break-ups of glaciation, atmospheric CO 2
rebounded to the pre-industrial level of 270 ppmv, actually and briefly (a few
thousand years) to 290 ppmv in the three earlier interglacials. The declines in
atmospheric CO 2 during the four major glaciations did not have exactly the same
patterns. They occurred in pulses that paralleled the accumulation of ice as
represented by the increase in deuterium and ^18 O 2 in glacial water (see below). Return
of CO 2 at the major glacial terminations is fast, covering the whole 100 ppmv range in
∼5 kyr. That fits both a slow, or pulsed with gaps, reduction by ocean uptake during
growth of glaciation, mostly by biological pumping, and rapid return by onset of
ventilation of the deep sea at the end of the glaciation.
Fig. 16.10 Analytical time-series for constituents of a deep ice core from Vostok
station, East Antarctica, and other sources. (a) Temperature variation at Vostok, based
primarily on deuterium variation, a proxy for air temperature near the deposition site.
(b) Global volume of ice on land estimated from δ^18 O in marine core carbonate. (c)
CO 2 and (d) methane in air from Vostok ice. (e) Sodium and (f) dust in Vostok ice.
Sodium is a proxy for marine storm activity. Dust may be a proxy for iron transport to
the Antarctic and thus to the surrounding ocean.
(After Petit et al. 1999.)