GEOPHYSICAL MONOGRAPH SERIES, VOL. 173, PP. 335-349, 2007
Antarctic stratification, atmospheric water vapor, and Heinrich Events: A hypothesis for Late Pleistocene deglaciations
We have previously argued that the Antarctic and subarctic North Pacific are stratified during ice ages, causing to a large
degree the observed low CO2 levels of ice age atmospheres by sequestering respired CO2 in the ocean abyss. Here, we suggest a mechanism for the major deglaciations of the late Pleistocene. The mechanism begins
with freshwater discharge to the North Atlantic, as evidenced by a Heinrich event, that shuts down North Atlantic overturning.
Because of a global requirement for deep ocean ventilation, the North Atlantic shutdown drives overturning in the Antarctic,
which, in turn, releases CO2 to the atmosphere and reduces Antarctic sea ice extent. The resulting increase in atmospheric CO2 and decrease in albedo then drive global warming and deglaciation. As a control on the timing of deglaciations, we look to
the sensitivity of atmospheric freshwater transport to low latitude temperature, which is a natural antagonist to Antarctic
stratification under cold climates. While Antarctic stratification is proposed to develop early in a glacial period, continued
cooling through the glacial period may reduce the poleward atmospheric freshwater transport and thus may prepare the Antarctic
halocline for collapse. Deglaciations may coincide with obliquity maxima because a reduced low-to-high latitude insolation
gradient decreases the net poleward freshwater transport and perhaps also because increased polar insolation can warm the
deep ocean and shift the westerly winds poleward, all of which should work to weaken Antarctic stratification. Precession
minima may encourage Antarctic destratification by biasing tropical water vapor transport toward the northern hemisphere.
Finally, obliquity and precession may work together to encourage the circum-North Atlantic freshwater discharge event that
initiates the deglacial sequence.
Citation: Sigman, D. M.,