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SJSU METR 112 - Satellite Measurements

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source rocks of this material (0.25 and 0.12,respectively). The recycling rate inferred fromthe F(t) constraint is too small to explain thediscrepancy between the observed and inferredSm/Nd ratios in each reservoir. Therefore, Ndisotopic evolution of the upper mantle is con-trolled not only by recycling of continentalcrust but also by exchange of material with adifferent reservoir (21) with a low147Sm/144Ndratio, which could be material segregated fromsubducted lithospheric plates (22) or a deeplayer left behind by early terrestrial differentia-tion (23).These constraints from the40Ar budget ofthe observable reservoirs depend on the veryincompatible behavior of K and Ar and there-fore are robust. Only if Ar were substantiallymore compatible than K would the conclu-sions be clearly inadequate. The solubility ofAr in olivine melt actually may decreasedramatically beyond 4 to 5 GPa (24 ). Partialmelting possibly extended at 150 to 200 kmin the past because the mantle was hotter,especially under the MORs. So far, however,the compatible behavior of40Ar during melt-ing remains to be demonstrated and the con-straints on the rate of continental growth andmantle degassing given by the40Ar and Kbudget remain.References and Notes1. D. K. Rea and L. J. Ruff, Earth Planet. Sci. Lett. 140,1(1996); T. Plank and C. H. Langmuir, Chem. Geol. 145,325 (1998) and references therein.2. R. von Huene and D. W. Scholl, Rev. Geophys. 29, 279(1991).3. A. Reymer and G. Schubert, Tectonics 3, 63 (1984).4. G. Schubert and D. Sandwell, Earth Planet. Sci. Lett.92, 234 (1989).5. D. DePaolo, Geophys. Res. Lett. 10, 705 (1983).6. F. Albare`de, Tectonophysics 161, 299 (1989).7. C. J. Alle`gre, A. W. Hofmann, R. K. O’Nions, Geophys.Res. Lett. 23, 3555 (1996).8. D. W. Schwartzman, Geochim. Cosmochim. Acta 37,2479 (1973).9. H. Craig, W. B. Clarke, W. A. Beg, Earth Planet. Sci.Lett. 26, 125 (1975); E. R. Oxburgh, R. K. O’Nions, R. I.Hill, Nature 324, 632 (1986); P. Jean Baptiste et al.,Earth Planet. Sci. Lett. 106, 17 (1991); A. Jambon,Rev. Mineral. 30, 379 (1994).10. A. W. Hofmann, Earth Planet. Sci. Lett. 90, 297(1988); H. Hiyagon and M. Ozima, Geochim. Cosmo-chim. Acta 50, 2945 (1986); R. A. Brooker, J. A.Wartho, M. R. Carroll, S. P. Kelley, Chem. Geol. 147,185 (1998).11. H.-C. Nataf and Y. Ricard, Phys. Earth Planet. Int. 95,101 (1996); W. D. Mooney, G. Laske, T. G. Master, J.Geophys. Res. 103, 727 (1998).12. K. Turekian, Geochim. Cosmochim. Acta 17,37(1959).13. R. L. Rudnick and D. M. Fountain, Rev. Geophys. 33,267 (1995).14. K. H. Weaver and J. Tarney, Nature 310, 575 (1984);D. M. Shaw, J. J. Cramer, M. D. Higgins, M. G. Truscott,in The Nature of the Lower Continental Crust,J.B.Dawson, Ed. (Geological Society of London, London,1986), pp. 257–282.15. K. H. Wedepohl, Mineral. Mag. 58, 959 (1994).16. S. R. Taylor and S. M. McLennan, The ContinentalCrust: Its Composition and Evolution (Blackwell, Cam-bridge, 1985).17. J. G. Sclater, C. Jaupart, D. Galson, Rev. Geophys. 18,269 (1980).18. The radioactive production rate ␭R40Kmantleassum-ing a K content of the mantle of 240 parts per millionas in [W. F. McDonough and S. Sun, Chem. Geol. 120,223 (1995)].19. C. J. Alle`gre, T. Staudacher, P. Sarda, Earth Planet. Sci.Lett. 81, 127 (1986/1987).20. P. Burnard, D. Graham, G. Turner, Science 276, 568(1997); P. Sarda, M. Moreira, T. Staudacher, Science283, 666 (1999).21. It has been argued that comparison of the Th/Uratio of MOR basalts with that inferred from theirvalues of208Pb/204Pb and230Th/232Th [S. J. G.Galer and R. K. O’Nions, Nature 316, 778 (1985)]indicates chemical buffering of the upper mantleby the lower mantle, but this model dependedentirely on the assumption of complete removal ofPb, U, and Th at the subduction zone by orogenicvolcanism. Similarly, the possibility that the uppermantle and the deep mantle were exchanging ma-terial through the 660-km discontinuity was alsoconsidered [P. J. Patchett and C. Chauvel, Geophys.Res. Lett. 11, 151 (1984)] as an alternative toDePaolo’s interpretation of Nd and Hf isotopicsecular evolution, but this lower mantle was thenconsidered to be of primitive composition, whichmodern mantle tomography makes untenable[R. D. van der Hilst, S. Widiyantoro, E. R. Engdahl,Nature 386, 578 (1997)].22. U. R. Christensen and A. W. Hofmann, J. Geophys.Res. 99, 19867 (1994); T. Elliott, A. Zindler, B. Bour-don, Earth Planet. Sci. Lett. 169, 129 (1999); N.Coltice and Y. Ricard, Earth Planet. Sci. Lett. 174, 125(1999).23. L. H. Kellogg, B. H. Hager, R. D. van der Hilst, Science283, 1881 (1999).24. E. Chamorro-Pe´rez, P. Gillet, A. Jambon, J. Badro, P.McMillan, Nature 393, 352 (1998).25. We thank A. Jambon for his comments on this work.6 January 2000; accepted 20 March 2000Satellite Measurements of SeaSurface Temperature ThroughCloudsFrank J. Wentz,1Chelle Gentemann,1Deborah Smith,1Dudley Chelton2Measurements of sea surface temperature (SST) can be made by satellitemicrowave radiometry in all weather conditions except rain. Microwaves pen-etrate clouds with little attenuation, giving an uninterrupted view of the oceansurface. This is a distinct advantage over infrared measurements of SST, whichare obstructed by clouds. Comparisons with ocean buoys show a root meansquare difference of about 0.6°C, which is partly due to the satellite-buoyspatial-temporal sampling mismatch and the difference between the ocean skintemperature and bulk temperature. Microwave SST retrievals provide insightsin a number of areas, including tropical instability waves, marine boundary layerdynamics, and the prediction of hurricane intensity.The surface temperature of the world’soceans plays a fundamental role in the ex-change of energy, momentum, and moisturebetween the ocean and the atmosphere. It is acentral determinant of air-sea interactions andclimate variability. The recurring El Nin˜o–LaNin˜a cycle, which has a profound effect onthe world’s weather and climate, is a dramaticmanifestation of the coupling of SST to at-mospheric circulation (1, 2). The surface tem-perature field also influences the developmentand evolution of tropical storms and hurricanes(3, 4) and is correlated with nutrient concentra-tion and primary productivity (5).Satellite measurements of SST began inthe 1970s, using infrared radiometers flyingaboard the National Oceanic and Atmospher-ic Administration’s geostationary and polarorbiting platforms (6 ). Satellite infrared SSTmeasurements have resulted in major


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