Thermohaline Circulation

Abstract

In coastal waters several thermodynamic processes combine to generate horizontal gradients of density, due to differences in temperature or salinity, or both. During early spring, solar radiation heats up nearshore shallow waters rapidly and generates a warm wedge of water at the shores separated from the deeper waters by an inclined density interface (Figure 7.1) known as the ‘spring thermocline’.* As was discussed in Section 1.3, horizontal density gradients imply the presence of horizontal pressure gradients, which may then drive fluid moths. When the density gradients cause the motion in this manner (and are not themselves a consequence of the internal adjustment of fluid masses to geostrophic equilibrium in e.g., a wind-driven current) the resulting circulation is described as ‘thermohaline’.