Noise-Induced Transitions in a Simplified Model of the Thermohaline Circulation

Abstract

A simplified box ocean model for the North Atlantic is used to study the influence of multiplicative short-term climate variability on the stability and long-term dynamics of the North Atlantic thermohaline circulation. A timescale separation between fast temperature and slow salinity fluctuations is used to decouple the dynamical equations resulting in a multiplicative stochastic differential equation for salinity. As a result the qualitative behavior and the stability of the thermohaline circulation become a function of the noise level. This can be understood in terms of the concept of noise-induced transitions. Furthermore, the role of nonvanishing noise autocorrelation times on the dynamics of the thermohaline circulation is investigated. Red noise temperature forcing generates new equilibria, which do not have a deterministic counterpart. This study suggests that noise-induced transitions might have climate relevance.