A Dynamical Systems Model of the Dansgaard–Oeschger Oscillation and the Origin of the Bond Cycle

Abstract

A low-dimensional dynamical systems model of the North Atlantic thermohaline circulation has been developed in order to better understand the mechanism underlying the so-called Dansgaard?Oeschger oscillation that is so clearly evident during the late glacial period (oxygen isotope stage 3) of the most recent ice-age cycle. The reduced system is designed to describe the evolution of the salinity distribution in this region that has previously been analyzed using both two- and three-dimensional models of the deep ocean circulation. The drastically simplified model described herein is shown to accurately represent the essence of the Dansgaard?Oeschger oscillation as this was previously revealed through detailed analyses performed with a model in which the deep circulation was described using a set of linked interacting two-dimensional (latitude?depth) basins. The authors? analyses with the reduced dynamical system reinforce their previous contention that the Dansgaard?Oeschger oscillation is driven by low?midlatitude salt accumulation and controlled by high-latitude freshening, as suggested in previous investigations performed with the more complex model. The dependence of the response of the reduced dynamical systems model to time-dependent external forcing is also investigated. These analyses demonstrate that the mechanism underlying the Dansgaard?Oeschger oscillation that is supported by the model is rather stable against relatively short timescale perturbations, but that the oscillation is effectively modulated by relatively long timescale perturbations such as those that Greenland ice-core data suggest to have existed on the timescale of successive Heinrich events. The dynamical systems model is thereby shown to provide a viable explanation of the Bond cycle that consists of packets of Dansgaard?Oeschger oscillations.