In the recent discussion and comments on this topic among colleagues from the U.S. and U.S.S.R. which were published in EOS (April 24,1979), several points centered on the purported equality of heat flow between ocean basins and continents and the heat flow variation with age in the oceans. Although the equality has been a major tenet since the first marine heat flow data were obtained and was supported with a statistical analysis of over 2,500 measurements only a decade ago [Von Herzen and Lee, 1969], recent field evidence and model development have substantially changed this conclusion.
The hypothesis that a substantial fraction of heat is lost by hydrothermal circulation in oceanic crustal rocks, particularly on young sea floor, first put forward by Lister , has received increased support in detailed studies of marine heat flow [Williams et al., 1974; Davis and Lister, 1977; Anderson etal, 1977]. Combined with quantitative estimates of heat loss based on plate tectonics models [McKenzie, 1967; Sclater andFrancheteau, 1970; Parsons and Sclater, 1977], it has been shown that hydrothermal effects account for a large fraction of the total sea floor heat loss up to several tens m.y. in age. Taking account of this hydrothermal loss, Williams and Von Herzen  calculated that the mean heat loss per unit area of oceans is about 2.2 H FU (heat flow units; 1HFU = 10−6/μcal cm−2 sec−1), about 50% greater than that for continents. This difference has been recently corroborated using a somewhat different approach by Langseth and Anderson .