A simple metabolic model of glacial-interglacial energy supply to the upper ocean

Abstract

We use a simple two-state two-box ocean to simulate the CO2 signal during the last four glacial-interglacial transitions in the earth system. The model is inspired by the similarity in spatial organization and temporal transition patterns between the earth and other complex systems, such as mammals. The comparison identifies the earth's metabolic rate with net autotrophic primary production in the upper ocean, sustained through new inorganic carbon and nutrients advected from the deep ocean and organic matter remineralized within the upper ocean. We view the glacial-interglacial transition as a switch of the upper ocean from a basal to an enhanced metabolic state, with energy supply initially relying on the remineralization of the local organic sources and the eventual steady state resulting from the increased advective supply of inorganic deep sources. During the interglacial-glacial transition the opposite occurs, with an initial excess of advective supply and primary production that allows the replenishment of the upper-ocean organic storages. We set the relative change in energy supply from the CO2 signal and use genetic algorithms to explore the sensitivity of the model output to both the basal recirculation rate and the intensity-timing of the maximum recirculation rate. The model is capable of reproducing quite well the long-term oscillations, as shown by correlations with observations typically about 0.8. The dominant time scale for each cycle ranges between about 40 and 45 kyr, close to the 41 kyr average obliquity astronomical period, and the deep-ocean recirculation rate increases between one and two orders of magnitude from glacial to interglacial periods