A Heuristic Model of Dansgaard - Oeschger Cycles : Description , 1 Results , and Sensitivity Studies : Part I

6 We present a simple column model for studying the D-O cycles of the last glacial period, 7 based on the Nordic Ice Machine hypothesis presented by Dokken, et al (manuscript in 8 preparation). The model is comprised of ocean boxes stacked below a one-layer sea ice model 9 with an energy-balance atmosphere. Parameterizations are included for offshore polyñya 10 activity and sea ice export from the column. The resulting heuristic model was found to 11 cycle between stadial and interstadial states at times scales similar to those seen in the 12 proxy observational data, with the presence or absence of perennial sea ice in the Nordic 13 Seas being the defining characteristic for each of these states. The modelled oscillations 14 were found to be robust to parameter changes, including those related to the ocean heat flux 15 convergence (OHFC) into the column. Including natural variability in the OHFC increased 16 the robustness of the modelled oscillations. We conclude by discussing the implications of 17 such a hypothesis for the state of the Nordic Seas today, its state during the Last Glacial 18 Maximum, and other hypotheses that invoke large-scale changes in the Atlantic Meridional 19 Overturning Circulation for explaining millennial scale variability in the climate system. An 20 extensive time scale analysis will be presented in Part II. 21