The Oligocene to the Quaternary: climate and biology - Climate Change: Biological and Human Aspects - page 137

Ocean ic conv eyor be lt

Cold, deeper
salty current

Warm, less salty
current at surface

AsimpliiedrepresentationoftheBroeckerconveyor(reproducedfromCowie,1998).

Fig. 4.7

of this work is that it demonstrated the importance of the deep ocean as an increased
reservoir of carbon dioxide during cold glacials 5 .
However, were that life was this simple (if indeed the above is 'simple'). While the
above, teased from the complexities, is a fair generalisation of the global situation,
researchers gleaning evidence elsewhere in the field may receive a more muddled
picture. Whereas there is the aforementioned ocean temperature evidence, there is
other evidence suggesting that terrestrial temperatures at mid latitudes within glacials
differ between hemispheres to the ocean time lag suggested above. Local insolation
at mid latitudes of the southern hemisphere is almost completely out of phase with
that of high northern latitudes. Mid-latitude long-term terrestrial records going back
one or more complete glacial-interglacial cycles are rare but one such exists in
the form of a 10 m-deep peat bog in Okarito Pakihi in southern New Zealand that
was outside the limits of the ice during the LGM (see Figure 4.8). Palaeovegetation
analysis of bog peat cores has provided an indication of climate change going back
two glacial-interglacial cycles. This revealed an earlier onset and longer duration of
the LGM. The explanation for this is likely to relate to the Milankovitch-driven levels
of insolation at that latitude (Vandergoes et al., 2005).

5

See also a very readable 2009 review article by Jeffrey Severinghaus on the work of Barker et al. (2009).
For a comprehensive review of ocean circulation changes and glacial and interglacial timing see also
Sigman et al. (2010).