Ocean Temperature-Induced Change in Lithospheric Thermal Structure: A Mechanism for Long-Term Eustatic Sea Level Change

Abstract

Eustatic sea level change can be produced by a change in ocean bottom water temperature through an alteration of the upper thermal boundary condition of oceanic lithosphere. The consequent evolution of lithospheric thermal structure can cause thermal expansion or contraction of the lithosphere. If continental lithosphere remains unaffected by the change in ocean temperatures, "eustatic" sea level will change as measured in the continental frame of reference. A two-dimensional finite difference model has been formulated and shows that if ocean bottom water temperature were to change rapidly by 14°C, as it may have during the Tertiary, sea level would change by 8 m in 8 m.y., and 17 m in 40 m.y. This result is in agreement with the one-dimensional error function solution for a heating or cooling halfspace. However, the changes in lateral heat flow between ocean water and the continental slope, and between oceanic and continental lithosphere, can produce epeirogenic motions of the continental margins (and thus may represent a climatic control on epeirogenic processes). Thus, the affected margins should not be used as a reference frame against which to measure the magnitude of sea level change produced by this mechanism. While this mechanism of water temperature-induced change in lithospheric thermal structure produces effects with magnitudes which are less than those resulting from changes in the average age of ocean floor and operates on timescales longer than those of ice volume changes, the effects of the mechanism are relatively simple to calculate and should be included when consideration is made of eustatic sea level changes in the past.