HEAT-FLOW FROM THE EARTHS INTERIOR - ANALYSIS OF THE GLOBAL DATA SET

We present a new estimate of the Earth's heat loss based on a new glob al compilation of heat flow measurements comprising 24,774 observation s at 20,201 sites. On a 5-degrees x 5-degrees grid, the observations c over 62% of the Earth's surface. Empirical estimators, referenced to g eological map units and derived from the observations, enable heat flo w to be estimated in areas without measurements. Corrections for the e ffects of hydrothermal circulation in the oceanic crust compensate for the advected heat undetected in measurements of the conductive heat f lux. The mean heat flows of continents and oceans are 65 and 101 mW m- 2, respectively, which when areally weighted yield a global mean of 87 mW m-2 and a global heat loss of 44.2 x 10(12) W, an increase of some 4-8% over earlier estimates. More than half of the Earth's heat loss comes from Cenozoic oceanic lithosphere. A spherical harmonic analysis of the global heat flow field reveals strong sectoral components and lesser zonal strength. The spectrum principally reflects the geographi c distribution of the ocean ridge system. The rate at which the heat f low spectrum loses strength with increasing harmonic degree is similar to the decline in spectral strength exhibited by the Earth's topograp hy. The spectra of the gravitational and magnetic fields fall off much more steeply, consistent with field sources in the lower mantle and c ore, respectively. Families of continental and oceanic conductive geot herms indicate the range of temperatures existing in the lithosphere u nder various surface heat flow conditions. The heat flow field is very well correlated with the seismic shear wave velocity distribution nea r the top of the upper mantle.