WHY DOES INTIMATE MATTER?
The period 30,000 to 10,000 years ago spans the Last Glacial Maximum and the transition to the present warm period (the ‘Holocene’). This period was characterized throughout the North Atlantic region by a sequence of abrupt climate changes that included rapid warming at 14,700 GRIP ice-core years ago (the start of the “Bølling” Interstadial, or GI-1 in the Greenland ice-core isotope stratigraphy) and the well-known period of severe cooling referred to as the Younger Dryas Stadial (GS-1) dated to between 12,800 and 11,500 GRIP ice-core years ago (Lowe et al., 2001).
It has been assumed that a North Atlantic ‘template’ of climate change would provide a useful model for interpreting the climate history of other parts of the world, and that the vigour of the thermohaline circulation (THC) in the North Atlantic provided the mechanism driving globally-synchronous, abrupt climatic change (Broecker, 2003).
Direct comparisons of Antarctic and Greenland ice-core records have led some to conclude that climate changes during this period were indeed globally synchronous (Steig et al., 1998). This view is challenged by other data, however, suggesting that warmer episodes in the north coincided with cooling periods in the south (Blunier and Brook, 2001) or that climatic changes in the south led those in the northern hemisphere (Morgan et al., 2002). The former view has led to the idea of a ‘bipolar seesaw’ of opposing climate tendencies between the two hemispheres (Broecker, 1998) potentially initiated by Antarctic melting (Weaver at al., 2003).
Figure: Comparison of datasets spanning 20,000 to 10,000 years ago. GRIP δ18O (Brook and Blunier, 2001) with isotope stratigraphy (Lowe et al., 2001); Cariaco Basin grey-scale (Hughen et al., 1996); Coleoptera central Britain maximum temperature (Coope et al., 1998); Taylor Dome (Steig et al., 1998); Law Dome (Morgan et al., 2003); Byrd (Brook and Blunier, 2001) δ18O. All Antarctic records are on the GRIP chronology.
The only way to rigorously test the hypothesis of synchronous climate change is to generate detailed palaeoclimatic records from different parts of the world that are independently and securely dated, and which provide an adequate temporal resolution of the key events in question (Lynch-Stieglitz, 2004). There is a significant dearth of sites from the Australasian region, despite the key role this region plays on world climate.
It is essential we have a better understanding of the global earth-ocean-atmosphere system. By reconstructing highly precise and accurate climatic changes in the Australian region and testing the degree to which changes were synchronous (or not) with the North Atlantic region, the mechanisms by which climate signals are propagated globally can be identified. These results are critical for improving our ability to predict future climate change in the Australian region.
Home/Meetings/Links