The Role of Atlantic Ocean Heat Transport in Decade to Century Scale Climate Variability.

The global oceanic circulation is responsible for a large (2-3 PW) poleward transport of heat and is a fundamental part of the climate system. The Thermohaline Circulation (THC) plays a crucial role in this heat transport, and is recognised as being potentially unstable (Marotzke, 2000). We investigate the role of ocean heat transport anomalies in the climate of the Little Ice Age (LIA), using an atmospheric model coupled to a mixed layer (`slab') ocean of constant depth. The model requires the ocean heat flux convergence (OHFC) to be prescribed, and thus changes in this field can be imposed to study the coupled response to this forcing. We diagnose the relationship between the THC strength and OHFC in a 500 year control run of the Hadley Centre coupled model (HadCM3). This information is used to impose a realistic OHFC anomaly in the coupled, mixed layer model. Results will be presented from these studies demonstrating the potential sensitivity of the climate system to ocean heat transport anomalies associated with fluctuations in the THC. Furthermore, comparison of the simulated response with climatic reconstructions of the LIA will be presented to evaluate the potential role of a changed THC as a forcing factor for this large scale climatic deterioration.