A theory of abrupt climate changes: their genesis and anatomy
- Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY10964, USA
Abstract. We integrate our previous ice-sheet and climate models to examine abrupt climate changes pertaining to Heinrich event (HE), Dansgaard-Oeschger (DO) cycle as well as last deglaciation punctuated by Younger Dryas (YD). Since they are all accompanied by ice-rafted debris, we posit their common origin in the calving of ice sheet due to thermal switch at its bed. Such thermal switch would generate step-like freshwater flux and together with decadal ocean response, they would endow abruptness to these millennial climate signals, which need not involve ocean mode change, as commonly assumed. We distinguish thermal switches due to geothermal heat and surface melt, which would calve inland/marginal ice to drive HE/DO-cycle, respectively. As such, the glacial DO-cycle hinges on post-HE warmth that enables the ablation whereas the Holocene DO-cycle is self-sustaining. The ocean response to freshwater flux entails millennial adjustment to maximum entropy production (MEP), a process termed “MEP adjustment”. As its direct consequence, the termination of HE is accompanied by sudden warming followed by gradual cooling to exhibit saw-toothed H-cycle, and the cooling moreover would anchor DO-cycles to form the hierarchical Bond cycle. The meltwater produced during deglaciation, if rerouted to Hudson Bay, may augment the calving-induced freshwater flux to cause YD, the latter thus involves happenstance and did not materialize during penultimate deglaciation. By incorporating calving origin of the freshwater flux and MEP adjustment of the ocean, the theory has provided an integral account of these abrupt climate changes.
Viewed (geographical distribution)