Ice core data - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 147

The EPICA Community compared data covering 125,000 years from three
Antarctic sites with NGRIP data from Greenland. The results are similar to those
shown in Figures 4.15 and 4.16 . As in the case of Figures 4.15 and 4.16 , the
occasional sharp rises in Greenland data also appear to be preceded by slower
more gradual increases in Antarctica (EPICA, 2006).

4.3.2 Interpretation in terms of ocean circulation

It has been proposed that there is a correlation between temperature patterns in
Antarctica and Greenland due to a connection between them via heat transport
via ocean currents known as the bipolar seesaw (see, e.g., Barker and Knorr, 2007;
Toggweiler and Lea, 2010). While a number of papers mention the bipolar seesaw
hypothesis, the descriptions of this hypothesis seem to be variable. It appears to
involve a slow buildup of heat in the Antarctic that stimulates the flow of heat
toward Greenland via thermohaline circulation and, when some nonlinear
threshold is exceeded, the NH undergoes a rather sudden and decisive heating. As
this process proceeds, heat is drawn away from Antarctica and it starts to cool.
This reduces the flow of heat to the NH. In addition, meltwater in the Greenland
area interferes with North Atlantic Deep Water (NADW) formation, reducing
thermohaline circulation. Thus, the NH begins to cool. Meanwhile, circulation
away from Antarctica is impeded so it begins to slowly warm again.
However, Wunsch (2003) provided a dissenting view. He pointed out that
when one attempts to synchronize two time series (in this case temperature varia-
tions in Greenland and Antarctica), visual comparison of features could be very
misleading. The association of a feature on one time series with a corresponding
feature on a second time series can be a very subjective process, which he demon-
strated with examples. If the innate errors in chronology in Figures 4.15 and 4.16
are comparable with the time scale over which relationships between north and
south are sought, claims that there is time phasing between north and south
records must be subject to considerable doubt. Thus, pinpointing the time phasing
of features in the Greenland and Antarctica isotope time series may not be as
accurate as has been claimed. Furthermore, Wunsch claimed that sudden changes
in Greenland are not necessarily correlated with changes in Antarctica, and may
have been generated by changes in winds. He claimed there is no evidence of a
bipolar seesaw. However, Figures 4.15 and 4.16 are fairly convincing to this writer
and, unless some improper procedure was used in assessing these chronologies, it
is dicult to dispute the apparent relationship between north and south.
A Comment on Wunsch's paper was published about a year later (Huber et
al., 2004). This Comment claimed that abrupt shifts in atmospheric methane con-
centration are observed to occur at the same time (within 30 yr) as changes in
Antarctic and Greenland temperature. New data on the nitrogen and argon
isotopic composition of gases trapped in Greenland ice cores show that all of the
abrupt d 18 O shifts studied thus far were accompanied by gas isotope anomalies.
This suggests that the large temperature changes were global in nature and were