On the thermodynamics of the oceanic general circulation: entropy increase rate of an open dissipative system and its surroundings

Abstract

The role of thermodynamics in the oceanic general circulation is investigated. The ocean isregarded as an open dissipative system that exchanges heat and salt with the surroundingsystem. A new quantitative method is presented to express the rate of entropy increase for alarge-scale open system and its surroundings by the transports of heat and matter. This methodis based on Clausius’s definition of thermodynamic entropy, and is independent of explicitexpressions of small-scale dissipation processes. This method is applied to an oceanic generalcirculation model, and the entropy increase rate is calculated during the spin-up period of themodel. It is found that, in a steady-state, the entropy increase rate of the ocean system is zero, whereas that of the surroundings shows positive values, for both heat and salt transports. Thezero entropy increase rate of the ocean system represents the fact that the system is in a steadystate, while the positive entropy increase rate in the surroundings is caused by irreversibletransports of heat and salt through the steady-state circulation. The calculated entropy increaserate in the surroundings is 1.9×1011WK-1, and is primarily due to the heat transport. It issuggested that the existence of a steady-state dissipative system on the Earth, from a livingsystem to the oceanic circulation, has a certain contribution to the entropy increase in itsnonequilibrium surroundings.