Ocean Floor Heatflow

Our Earth's evolution has been greatly determined by the history of heat transfer from the deep interior through the crust and to the land surface and seabed by means of the fundamental process of plate tectonics, thermal conduction through the rigid lithospheric mantle, convection in the deeper ductile mantle and by hotspot volcanism. Heatflow is determined by measuring the temperature increase with depth to determine the thermal gradient. The outward heatflow is is the product of the thermal gradient and the measured conductivity of the substate. In the case of the ocean floor, the gradient is obtained by inserting electrical thermometers attached to a long pipe driven downward by a heavy weight. The conductivity is measured on the sediments recovered from inside the pipe.

Ocean floor measured heatflow spans the range of 0-250 milliwatts per square meter (mW/m²) and the thermal gradient varies from 10 to 80 degrees Celcius per kilometer (°C/km).

Ocean floor heatflow is highest near the crest (axis) of the mid-ocean ridges where the ocean crust is youngest, the lithoshere beneath is thin and the interior mantle is its warmest. The lithosphere cools as it ages during its transport away from the ridge axis by seafloor spreading. Average heatflow is greater than 100 mW/m² for ocean floor younger than 10 million years. However, the variability in measured heatflow is quite large for young seafloor, because a significant amount of heat escapes from our planet's interor not by conduction through the crust and sediment cover, but via springs of heated seawater called hydrothermal vents.

Heatflow decreases away from the axis of the mid-ocean ridges in proportion to the square root of the age of the crust. The seafloor deepens in the same relationship. These observations support a half-space model in which the lithosphere behaves as a cooling boundary layer where heat only escapes through the top of the layer.

Left Top: The varience in heatflow (maximum and minumum values in average 2 my bins provide the envelop) for the north Pacific and northwestern Atlantic Oceans.
Left Bottom: Ocean floor depth (also averaged in 2my bins) in relationship to the ocean floor age.
Right: Predicted versus observed (measured) heatflow through the ocean floor as a function of the ocean floor age.
(all from Stein, 1995)

Hydrothermal circulation distorts this simplist pattern of convective heatflow and may account for more than 30% of the total heat loss. Of the predicted global heat flux of 32 x 10¹²W for the entire ocean floor, some 11 ±4 x10¹²W of the heat flux may be due to hydrothermal vents, spring and seeps, even in regions older than 10 million years. In fact the "sealing age" for hydrothermal fluid escape (i.e., the age when the measured heat flux is equivalent to the calculated heat flux) does not occur until the ocean floor reaches 60 to 70 my in age. Within the uncertainities of tabulating large datsets with sizable variance, there is no apparent difference for the "sealing age" between the different oceans and basins. The cause of the eventual "sealing" is not well understood, but may be the result of a sufficiently thick sediment cover with enough compacttion to eliminate pore-water permeability. It has been estimated that "sealing" may be accomplished when the sediment blanket exceeds 200 m in thickness.

Published articles of interest:

  • Gallagher, K., Ramsdale, M., Lonergan, L. & Morrow, D. The role of thermal conductivity measurements in modelling thermal histories in sedimentary basins. Mar. Petrol. Geol. 14, 201–214 (1997).
  • Langseth, M.G, Le Pichon, X., Ewing, M. Crustal Structure of the Mid-Ocean Ridges, 5, Heat Flow through the Atlantic Ocean Floor and Convection Currents. Journal of Geophysical Research, Vol. 71, p.5321 (1966)
  • Langseth, M. G., M. A. Hobart, and K. Horai (1980), Heat Flow in the Bering Sea, J. Geophys. Res., 85(B7), 3740–3750,
  • Langseth, M.G., Grim, P.J., Ewing, M. Heat-Flow Measurements in the East Pacific Ocean. Journal Of Geophysical Research, Vol. 70, NO. 2, PP. 367-380, 1965 doi:10.1029/JZ070i002p00367
  • Langseth, 1965. M.G. Langseth , Techniques of measuring heat flow through the ocean floor. In: W.H.K. Lee, Editor, Terrestrial heat flow, Am. Geophys. Union, Washington, D.C. (1965), p. 58.
  • Lee, W. H. K. On the global variations of terrestrial heat-flow, Physics of The Earth and Planetary Interiors Volume 2, Issue 5, December 1969, Pages 332-341
  • Lister, C. R. B. Heat Flow and Hydrothermal Circulation. Annual Review of Earth and Planetary Sciences, Vol. 8, p.95
  • Louden, K. E., Sibuet, J.-C. & Foucher, J.-P. Variations in heat flow across the Goban Spur and Galicia Bank continental margins. J. Geophys. Res. 96, 16131–16150 (1991).
  • Louden, K. E., Sibuet, J.-C. & Harmegnies, F. Variations in heatflow across the ocean-continent transition in the Iberian abyssal plain. Earth Planet. Sci. Lett. 151, 233–254 (1997)
  • Oxburgh, E. R. INature, Volume 223, Issue 5213, pp. 1354-1355 (1969) Increased Estimate for Heat Flow at Oceanic Ridges
  • Stein, C. A. (1995) Heat Flow of the Earth, Global earth physics: a handbook of physical constants. T. J Ahrens editor, AGU Refrence Shelf 1, pp 144-158
  • Von Herzen and Uyeda, 1963R.P. Von Herzen and S. Uyeda, Heat flow through the eastern Pacific Ocean floor, J. Geophys. Res. 68 (1963), pp. 4219–4250.
  • Data Citations:
  • Louden, K. E., Marine heat flow data listing, Appendix B. in Handbook of seafloor heatflow, edited by J. A. Wright and K. E. Louden pp. 325-485. CRC Press, Inc. Boca Raton, FLorida, 1989.
  • Louden, K. E. and J. A Wright. Marine heat flow data: A new compilation of observations and a brief review of its analysis: in Handbook of seafloor heatflow, edited by J. A. Wright and K. E. Louden pp. 3-67. CRC Press, Inc. Boca Raton, FLorida, 1989.
  • Marcus G. Langseth and Dallas Abbott, personal communications of compiled datasets

  • Some Links:
    Understanding the thermal evolution of deep-water continental margins