Dansgaard-Oeschger Oscillations: A Hydrodynamic Theory

On the basis of the oxygen isotopic proxy for atmospheric temperature which has been measured in the GRIP and GISP2 deep ice-cores from Summit, Greenland, it is well known that climate in the North Atlantic sector of the planet was highly variable throughout the period of time conventionally referred to as Oxygen Isotope Stage (OIS) 3. This variability consists of millennium time-scale oscillations clustered in packets in which each successive oscillation has a somewhat smaller amplitude than the last. The time scale of individual packets is approximately 10 kyr. A hydrodynamic theory of the basic Dansgaard-Oeschger oscillation has been developed which comprises the millennium time-scale variability based upon a reduced model of the thermohaline circulation (THC). In the present paper the most recent results delivered by this hydrodynamic model are compared with those provided by a much simpler dynamical systems model based upon the assumption that the low-frequency time dependence of the THC may be described by interactions between the time evolving uniform salinities ascribed to each of three interacting boxes. The simple model is shown to agree remarkably well with the predictions of its more complicated hydrodynamic counterpart insofar as its qualitative behavior is concerned.