Climate response to freshwater perturbations in Northern or Southern Hemispheres at the last glacial inception, the last glacial maximum and the present-day

Abstract. Freshwater inputs in North Atlantic due to huge surge of icebergs coming from ice sheets might be responsible for drastic regional and global abrupt climatic transitions. To quantify the sensitivity of climate system to these freshwater inputs, we use a model of intermediate complexity coupled to ice-sheet models for both Northern and Southern Hemispheres. We mimic the Dansgaard-Oeschger and Heinrich Events by forcing the model with appropriate freshwater perturbations. The originality of this study is to investigate with such a global model, the response of the coupled system to freshwater discharges for three different climate contexts, the Last Glacial Maximum (LGM), the Last Glacial Inception (LGI) and the present-day (PD) climates.

We first show that in all climate contexts, the North Atlantic circulation is more sensitive to freshwater flux when ice sheets are present. Secondly, the "seesaw" mechanism occurs mostly for the North Atlantic freshwater perturbation whereas it remains very weak for the Southern Ocean freshwater release. Moreover, this seesaw is generally enhanced when ice sheets are interactive. The most striking result is that the freshwater perturbation amplifies the inception of the North American ice sheet at LGI the sea-level drop associated is significantly increased and in a much better agreement with data.