Oceanic Climate Variability at Millennial Time-Scales: Models of Climate Connections

One of the most exciting questions in palaeoclimatology is the study of the complex interactions between the different components of the climate system in order to understand how climate changes occur at Milankovitch as well as at millennial and centennial time-scales. The primary objective of this paper is to place the PEP III transect palaeo-data within a global climate context in relation to oceanic climate variability during the last glacial. To take ocean-continent interactions into account is essential to develop our understanding of past climate change.

Recently, several studies have brought to light the role of the tropical/subtropical areas in climate changes. Continental and oceanic low-latitude records have documented the high frequency climate variability during the last glacial period. The inferred continental climate conditions in the sub-tropics might provide evidence for the contribution of atmospheric processes associated with rapid climate variability.

Another key question concerns the forcing mechanisms for rapid climate change. One of the most discussed hypotheses relies on ice sheet-ocean-atmosphere interactions driving millennial scale climate variations during the last glacial period (Alley et al. 1999; Ganopolski and Rahmstorf 2001). As already mentioned, ocean-atmosphere coupling is very sensitive to the freshwater flux into the North Atlantic. Modelling of the cryosphere shows that the internal dynamics of the northern hemisphere ice-sheets during periods of ice-building could lead to major reorganisation of the global climate (MacAyeal 1993). Likewise internal oscillations of the ocean-atmosphere system should also be considered as a potential candidate for climate forcing (Winton 1993; Paul and Schulz 2002). On the other hand, studies on rapid climate variability during the Younger Dryas and the Holocene point to an external forcing by revealing a possible connection between solar activity and global climate (Renssen et al. 2000; this volume; Bond et al. 2001). However, knowledge about the importance of the different potential triggers is poor, as climate components have different responses in space and time (and most probably during glacial and interglacial periods).

Therefore, in this paper we concentrate on the interactions between the different climate sub-systems.Areviewof rapid climate variability during the last glacial period mostly based on marine sediment records with a focus on recent studies based on sub-tropical records is attempted. By compiling these high quality data, we discuss what can be learned about millennial climate changes and connections.