The astronomical theory and data compared - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 286

Figure 10.7. Comparison of inverse solar input to 65 N ( Figure 9.11 ) with the slope of HW04
over the past 800,000 years. Note that the solar curve is plotted inversely so that higher solar
intensities lie lower on the vertical scale (adapted from Roe, 2006).

without the assumptions of orbital tuning remains an important, unsolved
problem.'' While tuning was used to generate the chronology of SPECMAP, the
agreement between dV

=

dt and solar intensity in Figure 10.6 is nevertheless

impressive.
Roe (2006) also carried out a similar analysis for the ocean sediment record
developed by Huybers and Wunsch (2004), which did not utilize orbital tuning.
In this case, however, comparison of dV dt with the solar curve is not as good.

Figure 10.7 shows the result of comparing the HW04 sediment curve with the
solar curve and the slopes of the HW04 sediment curve with the solar curve.
At first glance, there seems to be fair agreement between the slopes of the
HW04 curve and the solar intensity curve. However, when one increases the size
of the graphs, diculties appear.
Figure 10.8 highlights six specific time periods where further discussion is
appropriate (these are not the only ones). Between about 730 and 700 kybp , solar
intensity went through two oscillations. The first had an upturn in solar intensity
at around 720 kybp producing a sharp drop in dV

=

dt. The second had an upturn
at around 700 kybp producing almost no change in dV

=

dt. It might be supposed
that the first downturn reduced the ice sheet to the point that further increases in
solar intensity would have little effect, but there is nothing unique about the
upturn at 720 kybp . Between about 620 and 590 kybp , solar intensity underwent
wild gyrations while the ice volume hardly changed. The small sawtooth features
in the V curve then translate into larger gyrations in dV

=

= dt. Are those small saw-