The mean oceanic residence time (MORT) concept - a rationalisation

Abstract

Abstract The properties of a well-stirred ocean at steady state are considered and are used to define the scope of the mean oceanic residence time (MORT) concept. Simple relationships are established between the electronegativities of the elements and their mean oceanic residence times ( t Y ) on the assumption that sea-water composition is controlled by general adsorption/desorption reactions at the surface of oxygen-dominated mineral lattices. The elements are divided into three categories (depleted, pre-equilibrated and enriched) according to their behaviour on transfer from river water to seawater. The nature of the elements in each category and their t Y values are discussed. On the assumption that the transfer kinetics are first order, the rate of removal of material during the approach to steady state following a step change in input is used to calculate the residence time distribution function EY(t). The solutions for equations showing the response of the oceanic reactor to square pulse, sinusoidal and exponential changes in the input are given in a dimensionless (reduced) form which makes them generally applicable. The MORT concept as developed here enables the steady state composition of the oceans and the sensitivity of that composition to fluctuations in the input to be calculated to within an order of magnitude from the electronegativities of the elements and the rate of input of material.