We use a simple zonally averaged coupled atmosphere, ocean, land ice,
sea ice, and ocean biochemistry box model to demonstrate a novel mechanism
for self-sustained 100 kyr glacial-interglacial cycles. The mechanism
accounts for the main observed glacial cycle characteristics such
as the 100-kyr timescale, the asymmetric sawtooth shape, the teleconnection
between the hemispheres and the glacial-interglacial CO2
variations. The glacial-interglacial oscillations in our model result
from a combination of the temperature-precipitation and temperature-albedo
feedbacks. However, both the timescale and the asymmetric sawtooth
structure are determined in our model by a novel sea ice feedback
in which the sea ice grows and melts within a few decades and acts
as a switch of the climate system, switching it between growing and
retreating land ice modes.

We also propose a mechanism for the mid-Pleistocene transition from
41 kyr to 100 kyr glacial oscillations. The same mechanism is shown
to also explain the asymmetry between the long glaciation and short
deglaciation phases during the 100 kyr oscillations of the past 1
myr. It is shown that these features arise naturally as a result of
the gradual cooling of the deep ocean during the Pleistocene. The
deep ocean cooling results in a change of the relation between atmospheric
temperature and the rates of accumulation and ablation of land glaciers.
This change, in turn, leads to the activation of the sea ice switch
glacial cycle mechanism and therefore to the initiation of the 100
kyr oscillations. The asymmetry of the 100 kyr oscillation (gradual
glaciation, rapid deglaciations) occurs because the mean value of
the glacier ablation is not far from the maximum rate of snow accumulation
on the glaciers during warm periods. This proximity of mean ablation
and maximum accumulation rates is shown to also be a consequence of
the mid-Pleistocene gradual deep ocean cooling.

More information is available at http://rainbow.ldeo.columbia.edu/~hezi
E-mail: hezi@ldeo.columbia.edu