Climate Instabilities during the last deglaciation
The end of the Last Ice Age, the “Last Termination”, is characterized by several rapid shifts between unusually cold (stadial) and warm (interstadial) periods. Contrasting the continuous increase in radiative forcing, these climate instabilities are (hypothetically) linked to large variations in the strength of the Atlantic Overturning Circulation (AMOC) in response to salinity disturbances by fresh water fluxes from melting ice sheets. The drivers and mechanisms behind these rapid shifts and different regional climatic feedbacks, and their global impacts via teleconnections, are however not well known. As part of our project “Climate instabilities during the last interstadial period” funded by the Swedish Research Council (VR 2015-04418), we perform high resolution (0.9°x1.25°, ~100 km) global climate simulations for several different (inter-)stadial periods during the late deglaciation (~16.000 to ~10.000 years before present). Our main focus is on climatic changes during the warm seasons of the different oscillations. These are characterized by different combinations of cold/warm ocean states under low/high radiative forcing. Specifically, we want to study to which extent changes in summer temperatures (and hydroclimate) and/or changes in seasonality dominate the signals reconstructed by various proxy data. In addition to a direct model-proxy comparison, we will use our climate model output to run a numerical lake model. This enables us to account for potentially diverging responses of lake water temperatures, which may be reflected by lake proxy data, relative to ambient air temperatures simulated by the climate model. For our climate simulations, we use the NCAR Community Earth System Model version 1 (CESM 1.0.5). In addition to changes in orbital and greenhouse gas forcing, horizontal boundary conditions are adjusted to incorporate realistic changes in the paleo-topography of continental ice sheets, glacio-isostatic land uplift and exposed land masses due to lower sea-level stands.