Abyssal ocean circulation driven by geothermal fluxes

Abstract

Geothermal heating is increasingly recognised as an important factor a ecting ocean circulation, with modelling studies suggesting that this heat source could lead to rst-order changes in the formation rate of Antarctic Bottom Water, as well as a signi cant warming e ect in the abyssal ocean. Where it has been represented in numerical models, however, the geothermal heat ux into the ocean is generally treated as an entirely conductive ux, despite an estimated one third of the global geothermal ux being introduced to the ocean via hydrothermal sources. In this project I use analytical and computational modelling methods to explore how the geothermal heat ux a ects the deep ocean in both its forms, conductive and hydrothermal. There is a focus on the Panama Basin in the eastern equatorial Paci c, as the bathymetry and prevalence of geothermal heating in the region make it an appropriate area to study. The main di erence between the two geothermal mechanisms is the addition of a volume ux through the seabed for the hydrothermal heating. The circulations caused by such a volume ux through the seabed - initially ignoring the attending heat uxes - are the focus of the rst section of this thesis. It can be seen that these ows have the potential to drive abyssal circulations signi cantly di erent from those resulting from heating the bottom water. The second section of the project takes a close look at how the partitioning of a heat ux between conductive and hydrothermal sources a ects the circulation and hydrography in an idealised domain. In the rst study of its kind, a hydrothermal input is added to the bottom boundary of a primitive equation model and simulations are completed to look at how the circulation changes as the proportion of the heat ux entering the ocean in this way increases. It is found that vertical transport of heat from the abyss is increased when hydrothermal uxes are present. In the nal section, a 3-dimensional regional model of the Panama Basin is used to simulate the e ects of geothermal heating on circulation in a semi-enclosed ocean basin. Of particular interest is the change to the ow through the deepest channels which connect the basin to the greater Paci c Ocean, where the heat transport is doubled. The simulations indicate that geothermal heating of the basin is a signi cant driver of its overturning circulation.