Imbrie, J., A. Berger, E. A. Boyle, S. C. Clemens, A. Duffy, W. R. Howard,
G. Kukla, J. Kutzbach, D. G. Martinson, A. McIntyre, A. C. Mix, B. Molfino,
J. J. Morley, L. C. Peterson, N. G. Pisias, W. L. Prell, M. E. Raymo, N.
J. Shackleton, and J. R. Toggweiler, 1993: On the structure and origin
of major glaciation cycles 2. The 100,000-year cycle. Paleoceanography,
8(6), 699-735.
Abstract: Climate over the past million years has been dominated
by glaciation cycles with periods near 23,000, 41,000, and 100,000 years.
In a linear version of the Milankovitch theory, the two shorter cycles
can be explained as responses to insolation cycles driven by precession
and obliquity. But the 100,000-year radiation cycle (arising from eccentricity
variation) is much too small in amplitude and too late in phase to produce
the corresponding climate cycle by direct forcing. We present phase observations
showing that the geographic progression of local responses over the 100,000-year
cycle is similar to the progression in the other two cycles, implying that
a similar set of internal climatic mechanisms operates in all three. But
the phase sequence in the 100,000-year cycle requires a source of climatic
inertia having a time constant (~15,000 years) much larger than the other
cycles (~5,000 years). Our conceptual model identifies massive northern
hemisphere ice sheets as this larger inertial source. When these ice sheets,
forced by precession and obliquity, exceed a critical size, they cease
responding as linear Milankovitch slaves and drive atmospheric and oceanic
responses that mimic the externally forced responses. In our model, the
coupled system acts as a nonlinear amplifier that is particularly sensitive
to eccentricity-driven modulations in the 23,000-year sea level cycle.
During an interval when sea level is forced upward from a major low stand
by a Milankovitch response acting either alone or in combination with an
internally driven, higher-frequency process, ice sheets grounded on continental
shelves become unstable, mass wasting accelerates, and the resulting deglaciation
sets the phase of one wave in the train of 100,000-year oscillations.
Whether a glacier or ice sheet influences the climate depends very much
on the scale....The interesting aspect is that an effect on the local climate
can still make an ice mass grow larger and larger, thereby gradually increasing
its radius of influence.