The US Joint Global Ocean Flux Study US JGOFS seeks to understand the processes governing the production and fate of biogenic material in the sea well enough to predict their influences on, and responses to global scale perturbations. This will be done by identifying and quantifying the physical, chemical and biological processes controlling biogeochemical cycling in the ocean, and their interaction with the global atmosphere. The implicit assumption of this strategy for achieving a predictive capability is that the processes and interactions quantified today respond linearly to global scale perturbations and that knowledge of the present biogeochemical system dynamics will, therefore, allow us to predict response to global perturbations with accuracy. This is a fundamental assumption and is the keystone of the JGOFS strategy for predictive capability. The scientific justification for this assumption has never been stated and the object of this work is to verify this assumption.