Challenges of the Milankovitch Hypothesis at Termination II

Carson Rittel

 

The Milankovitch hypothesis states that changes in the earth’s orbit directly causes ice ages. This hypothesis has proved controversial based on the timing of termination II. Several proxy records (Fig. 1 and 2) indicate that termination II occurred earlier than the hypothesis allows. Coral data from Bahamas, Hawaii, Barbados, and other proxy sources (Devils Hole and Vostok ice core) present challenges to the Milankovitch hypothesis and the SPECMAP. This data suggests that other factors can take precedence over orbital forcing of the ice ages. While the Milankovitch hypothesis can generally be considered as the pacemaker of the ice ages, alternate mechanisms need to be investigated.

 

Figure 1:

Source: Nature, 2000



Timing comparison of the Bahamas coral, Vostok ice core, Devils Hole cave deposit, Barbados coral, Milankovitch insolation values, and ENSO events.



Vertical line indicates the midpoint of deglaciation at 135.2±2.5 ka.
Figure 2:

Source: Nature, 2002



Timing comparison of Milankovitch insolation values, sea level from Barbados coral, SPECMAP (thick line), Devils Hole (thin line), and the Vostok record.





Dotted line half way point for insolation rise between 140 and 130 ka. Solid lines represent points of maximum insolation.

 

 

 

SOURCES:

Journals:

Gallup, C.D., Cheng, H., Taylor, F.W., and Edwards, R.L., (2002). Direct Determination of the Timing of Sea Level Change During Termination II, Science, vol. 295, p. 310-313.

Gildor, H., Tziperman, E., (2000). Sea ice as the glacial cyclers’ climate switch: Role of seasonal and orbital forcing, Paleoceanography, vol. 15, no. 15, p. 605-615.

Henderson, G.M., and Slowey, N.C., (2000). Evidence from U-Th dating against Northern Hemisphere forcing of the penultimate deglaciation, Nature, vol. 404, p. 61-66.


Books:

Bradley, Raymond S., (1999). Paleoclimatology – Reconstructing Climates of the Quaternary, Harcourt Academic Press.

Lowe, J.J. and Walker, M.J.C., (1998). Reconstructing Quaternary Environments, 2nd edition, Longman, London.