Ice core data - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 161

Figure 4.22. Variation of d 14 C and CO 2 concentration during the past 40,000 years (Marchitto
et al., 2007).
the last glacial termination.'' Some of their results are shown in Figure 4.23 . They
particularly noted that the deep Pacific temperature as measured by benthic
species in ocean sediments, and the South Pacific SST (around 45 S off the coast
of Chile) both revealed a remarkable 2 C temperature rise while the tropical SST
remained at glacial levels during the period from about 19 to 17 kybp . As Stott et
al. (2007) pointed out, if atmospheric CO 2 was the main driver of deglacial tem-
perature changes, the ensuing rise in temperature should be global and work from
the top down; deep-sea temperatures would ''reflect this with an appropriate
lagged relation that would account for the response time between CO 2 forcing and
the turnover time of deep waters.'' The fact that deep-sea and South Pacific
surface temperatures rose prior to tropical sea surface temperatures suggests
that CO 2 was not a cause of this warming. Stott et al. (2007) suggested that the
explanation for the early warming in the Southern Hemisphere could involve
increasing springtime solar insolation during the austral spring that influenced the
retreat of sea ice. They hypothesized that these forcings promoted enhanced
ventilation of the deep sea and the subsequent rise in atmospheric CO 2 . However,
their curve for ''averaged mean longitude spring insolation (21 August to 20
November) at 65 S'' seems strange to this writer. In fact, their insolation curve
lies almost exactly on the peak solar curve for 65 N (or equivalently, the duration
of summer at 65 S) and it is not clear how they arrived at this curve. The yearly
variation of insolation for early spring at 65 S would be as shown in Figure 4.24 .
From 20 to 15 kybp , the insolation actually decreased whereas, according to the
model of Stott et al. (2007), it was increasing.
Timmermann et al. (2009) carried out climate model simulations of the last
21,000 years in an effort to identify the driving forces for deglaciation in the
Southern Hemisphere after the LGM. They concluded: