The Effect of Climate Base State on the Remote Response to North Atlantic Freshwater Forcing: Comparison of Heinrich and 8.2 ka Events

Paleoclimate records suggest a hemispheric or larger climate response to events presumed to have been caused by freshwater perturbations in the North Atlantic (e.g., Heinrich events, the 8.2 ka event). It is still unclear how this response depends on the background climate state, however. This is important for understanding how remote regions could respond to a freshening of the North Atlantic in the future under a different climate state. To investigate this topic, we have completed two simulations using NCAR's Community Climate System Model, version 3. In these simulations, a freshwater flux of 1 Sverdrup was added to the North Atlantic between 50° and 70°N for two different climate states: the Last Glacial Maximum (21 ka) and Early Holocene (8.5 ka). The duration of the freshwater flux was 100 years, after which the integration was continued for several hundred years to examine recovery. There were several key differences between the two simulations. First, the Southern Hemisphere response is stronger in the LGM experiment than in the 8.5 ka experiment. This is despite the fact that temperature and precipitation changes in the Northern Hemisphere tend to be larger in the 8.5 ka experiment. Second, the climate of most regions recovers more quickly from the freshwater perturbation in the 8.5 ka experiment. One notable exception to this is tropical SSTs, which recover abruptly in both simulations as soon as the freshwater flux is turned off. We will compare these results with paleoclimate records from these two time intervals.