Other data sources - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 199

Figure 6.8. Estimated variation of sea level from coral terraces (Lambeck et al., 2002; Lam-
beck, 2004).
that, according to the Imbrie model for ice volume based on the integration of
solar intensity, the ice volume would have had an intermediate peak at around
137,000 ybp and would have minimized about 120,000 ybp . Thus, the astronomical
theory seems to point to a high water mark at around 120,000 ybp and a signifi-
cant lowering of sea level about 17,000 years prior to that date. However, data
reported by a number of investigators (e.g., Henderson and Slowey, 2000)
indicated that the high water mark may have been reached by 130,000 ybp and sea
level began rising at around 140,000 ybp when solar intensity was low. This led
M&M to conclude that there is a ''causality problem'' with the astronomical
theory in which the timing of solar variations does not match the timing of
climate changes. However, Thompson and Goldstein (2005) revised the process
for dating coral terraces that corrects ages for the bias imposed by previous
workers who assumed closed-system behavior for Th isotopes. This shifted the
ages to more recent times as shown in Figure 6.9 . With this change, the peak sea
level is reached around 128 kybp , but sea level nevertheless began rising at around
135 kybp when the astronomical theory would have predicted a low sea level.
As Henderson (2005) commented, substantial swings in sea level appear to
have occurred not all of which can be explained by orbital changes. He said:
''Perhaps most surprising is that 185,000 years ago—at a time when orbital
parameters and climate proxies indicate cold conditions—sea level was only
about 20m below its present level. This event challenges our understanding of
the conditions required for ice growth. Between 130,000 and 90,000 years ago,
the record provides clear evidence for sea level change at higher frequency than
can be explained by orbital changes.''