WHERE DOES THE TRIGGER FOR ABRUPT CLIMATE CHANGE RESIDE, IN THE OCEAN OR IN THE TROPICS?

Any explanation for the abrupt changes which punctuated the last glacial period must identify: 1) the climate systems alternate states, 2) the trigger which allows the system to jump from one of these states to another, 3) the flywheel which locks the system into a single state for many centuries and 4) a means to transmit the impetus for change across the entire planet on a time scale of a few decades. Reorganizations of the ocean's thermohaline circulation can meet the first three of these requirements but to date, not the fourth. The more recently proposed tropical trigger meets the fourth but not the first three. While theory and models are essential to our thinking, the distinction between these two schools of thought must ultimately be based on the geologic record in ice, sediment and moraines. Key evidence comes from 1) the relationship between the timing of the Agassiz flood and of the Heinrich armadas relative to the far-field Younger Dryas and Heinrich impacts and 2) the existence of precursory events.