Geothermal heating and its influence on the meridional overturning circulation

The effect of geothermal heating on the meridional overturning circulation is examined using an idealized, coarse-resolution ocean general circulation model. This heating is parameterized as a spatially uniform heat flux of 50 mW m^-2 through the (flat) ocean floor, in contrast with previous studies that have considered regional circulation changes caused by an isolated hot spot or a series of plumes along the Mid-Atlantic Ridge. In our model results the equilibrated response is largely advective: a deep perturbation of the meridional overturning cell on the order of several sverdrups is produced, connecting with an upper level circulation at high latitudes, allowing the additional heat to be released to the atmosphere. Rising motion in the perturbation deep cell is concentrated near the equator. The upward penetration of this cell is limited by the thermocline, analogous to the role of the stratosphere in limiting the upward penetration of convective plumes in the atmosphere. The magnitude of the advective response is inversely proportional to the deep stratification; with a weaker background meridional overturning circulation and a less stratified abyss the overturning maximum of the perturbation deep cell is increased. This advective response also cools the low-latitude thermocline. The qualitative behavior is similar in both a single-hemisphere and a double-hemisphere configuration. In summary, the anomalous circulation driven by geothermal fluxes is more substantial than previously thought. We are able to understand the structure and strength of the response in the idealized geometry and further extend these ideas to explain the results of Adcroft et al. [2001], where the impact of geothermal heating was examined using a global configuration.