Harmon Craig
USA
1998 Balzan Prize for Geochemistry
A pioneer in earth sciences, Harmon Craig has used the varied tools of isotope geochemistry to solve problems of fundamental scientific importance and immediate relevance in the atmosphere, hydrosphere and solid earth.
Harmon Craig (1926-2003) contributed significantly and fundamentally to solving a broad range of geochemical problems which bear directly on our
understanding of the earth upon which we live, its origins and its response to anthropogenic changes.
He is singularly innovative in the use of isotopes in every area of geochemistry from meteorite studies through earth mantle processes influencing oceanography, atmospheric sciences, hydrology and glaciology.
As the father of the field of carbon isotope geochemistry he was the first to characterise the distribution of stable carbon isotopes in nature and also to quantify the atmospheric lifetime of carbon dioxide with respect to exchange with the sea, a parameter which is of crucial importance to all modern modelling of the effects of anthropogenic carbon dioxide on climate.
He was one of the pioneers of the systematic classification of meteorites according to their chemical composition and the co-originator of the Urey-Craig meteorite classifications, As one of the founders of stable isotope studies of water in the meteoric cycle he established fundamental relationships between temperature and stable isotopic composition which today form the basis for the study of paleoclimatology using stable isotopes in polar ice cores.
In marine geochemistry Harmon Craig was one of the initiators of the GEOSECS program, the first combined study of chemical tracers and hydrography in the word’s major oceans, which today provides an important benchmark for the study of global change and anthropogenic impacts on the oceans, In this area of research he did original work on the geochemical cycling of carbon, oxygen, and nutrients in the deep sea, on the scavenging of heavy metals therein, and on geochemical techniques to determine primary production rates in open ocean surface waters. Furthermore, he was a co-discoverer of the deep sea helium-3 isotope anomaly at seafloor spreading centres, but also at volcanic hot spots, rift zones and subduction volcanism.
In atmospheric geochemistry he was one of the first to study the composition of atmospheric gases frapped in glacier ice, and to determine that methane has roughly doubled due to anthropogenic activities. He has also made major contributions to the study of atmospheric nitrous oxide, the natural modulator of the earth’s ozone layer.
A common theme in his work is the combination of imagination, a strong commitment to field work and laboratory measurements of the highest standard, and a formidable thoroughness in the interpretation of the resulting data. Over the years, he has mentored a remarkable group of graduate and postdoctoral students who have become distinguished scientific leaders at a number of institutions around the world.


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