Ocean sediment data - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 176

Figure 5.1. Fit of a portion of the d 18 O curve to the ice model of Lisiecki and Raymo (2005).
physical model, but it is not immediately obvious where it lies between these
extremes.
Of course, it would be extremely desirable to develop a chronology that does
not depend on orbital tuning. As Huybers and Wunsch (2004) (H&W) said:
''Inference concerning past climate change relies heavily upon the
assignment of ages to measurements and events recorded in marine and ice cores
as well as to a variety of isolated markers in the geological record. Sedimentation
and snow accumulation are analogous to strip-chart recorders, marking the past
climate state in a large variety of physical variables. These records tend to be
noisy and blurred by bioturbation [the displacement and mixing of sediment
particles] and a variety of diffusive-like processes. The major diculty however,
is that these strip-chart recorders run at irregular rates, stop completely, or even
rewind and erase previous sections. If depth is taken as a simple proxy for time,
irregularities in sedimentation stretch and squeeze the apparent timescale, and so
distort the signals being sought. To the degree that the changes in rates are
proportional to the signals themselves, one has a challenging signal demodula-
tion problem. It is not an exaggeration to say that understanding and removing
these age-depth (or age model) errors is one of the most important of all
problems facing the paleoclimate community. Timing accuracy is crucial to
understanding the nature of climate variability and the underlying cause and
effect.''
H&W attempted to understand the nature of some of these age model errors,
and then apply that insight to construct a time scale for marine sediment cores
spanning the last 780,000 years. They pointed out: ''To avoid circular reasoning,
an age model devoid of orbital assumptions is needed.'' A number of previous
studies utilized mean sediment accumulation rates for multiple stratigraphies,