10 Thermodynamics of the Ocean Circulation: A Global Perspective on the Ocean System and Living Systems

Abstract

In this chapter, we investigate thermodynamics in ag lobal-scale open ocean circulation and discuss the physical properties of " living systems " , that is, individual organisms, by analogy to the behavior of the ocean system. Despite the fact that the ocean system has long been examined from ad ynamic pointo fv iew, its thermodynamic aspects remain to be explored. We showaq uantitative method that expresses the rate of entropyp roduction in an open dissipatives ystem that exchanges heat and matter with its surrounding system. This methodi sa pplied to an ocean circulation model, and the rate of entropyp roduction is examined in relation to the dynamic behavior of the system. Multiple steady states can exist under the same set of boundary conditions, and the state can be shifted by applying perturbations at the surface boundary.T he perturbations tend to shift the system to as tate of higher entropyp roduction, except when ap erturbation destroys the initial circulation completely. This result supports the hypothesis that an onlinear dynamic system tends to move to as tate with higher entropyp roduction by pro-ducing an activec irculationi nt he system when triggered by perturbations. When suchas ystem is subject to random perturbations for ac ertain periodo ft ime,t he most probable state to result willb et he one with the maximum entropyp roduc-tion. The entropyp roduced in as teady-state dissipatives ystem is discharged into the surrounding system through boundary fluxes of heat and matter, therebyc on-tributing to the entropyinthe surrounding system. Finally,ananalogy is suggested between the ocean system and al ivings ystem, in whichah ighly organized circu-latorys tructure of fluids has evolved from al ess organized primeval one, thereby producing entropyi nt he surrounding system at an increased rate. 10.1 Introduction The world'soceans can be seen as an open dissipativesystem connected with its surroundings by the exchange fluxes of heat and freshwater. The surround-ing system consists of the other components of the Earth system, specifically the atmosphere, the cryosphere, and the land surface, and ultimately space. Because of the curvatureo ft he Earth'ss urface andt he inclination of itsr o-tation axisr elativet ot he Sun, the ocean receives an et gain of heat from solarr adiation in thee quatorial regions, and high evaporation rates lead to the removalo ff reshwater from the ocean surface, resulting in an apparent