James L. Bischoff, over his career of 40 years, has specialized in several fields; the geochemistry of marine and lacustrinee sediments, seafloor geothermal systems, hydrothermal ore deposits, climate change, and chronology of human evolution.
U.C. Berkeley 1962 - 1966 Geochemistry Ph.D. 1966
Occidental College 1958 - 1962 Geology A.B. 1962
PRESENT STATUS: Geochemist emeritus, U.S. Geological Survey (since 2002)
1974-2002 Geochemist, Pacific Branch of Marine Geology, U.S. Geological Survey
1968-1974 Associate Professor, University of Southern California
1966-1968 Postdoctoral Fellow, Woods Hole Oceanographic Institution
Jim Bischoff’s dissertation research, at UC Berkeley, studied the kinetics of the aragonite-calcite transition. At Woods Hole Oceanographic Institution and later at the University of Southern California, he made contributions in carbonate diagenesis, lunar geochemistry, pore-water chemistry, the Red Sea Geothermal system, and the plate tectonics of the Gulf of California. His studies of the metalliferous sediments of the Atlantis II Deep brine pool in the Red Sea established the relevance of these modern deposits as an analog to ancient ore deposits, a key to the understanding of massive sulfide deposits on land. Another study while at Woods Hole was the “temperature of squeezing effect,” related to reversible chemical changes that occur when deep sediment cores are warmed while being hoisted through the water column. This small experimental study, which showed that core must be returned to in situ temperatures before squeezing, is now the basis for all pore fluid diagenetic studies.
In 1974, Jim established a marine chemistry program at the U.S. Geological Survey (USGS). He managed the U.S.G.S participation in the DOMES program (Deep Ocean Mining Environmental Study), coordinating an interdisciplinary team of scientists to complete studies of sediments and the water column related to manganese nodule accumulations in the equatorial Pacific. A significant result of this work was the discovery that the silicate fraction of manganese nodules is almost entirely composed of phillipsite, which is coupled to iron and manganese oxidation during nodule growth.
During the early- and mid-seventies, Jim organized several oceanographic expeditions to the SE Pacific to find evidence of chemical changes in the sediment pore-fluids that might resolve the long-standing problems of the magnesium and hydrogen-ion budget of the global geochemical cycle. On these expeditions, a vast field of very pure metal-rich muds was discovered near the East Pacific Rise (EPR). Studies of these deposits led to the conclusion that they were hydrothermal and had formed from seawater that was convecting into the oceanic crust and leaching heavy metals from the rocks at high temperature. Jim then conducted laboratory experiments to test this hypothesis by reacting seawater and basalt at high temperatures. The result was that not only were the metals abundantly extracted, but intense magnesium-depletion produced distinctly acidic seawater. The acidity provided the missing source of hydrogen-ion in the geochemical cycle. Significant changes of other dissolved components were also observed and the process of seawater-basalt interaction became widely recognized as a major new part of the geochemical cycle.
Jim and Robert Rosenbauer then built a laboratory for the study of seawater-rock interaction. During these years their studies brought to light the specific reactions that produced the acidity and metal transport. The co-existence of dissolved sulfide with abundant heavy metals in seawater-basalt experiments led to the prediction of massive sulfide deposits at seafloor discharge sites of the heated seawater. Stimulated in part by the results of these experiments, various institutes launched expeditions to test these ideas. In 1979, four years after publication of these first experimental results, the famous black smokers and massive sulfides were discovered at 21°N EPR by an expedition using the research submersible Alvin. The compositions of seafloor vent fluids are very similar to the fluids produced in the experiments..
During recent years, Jim has continued experimental work on fluid-rock interaction and on the role of phase-separation of hydrothermal fluids. There are now abundant chemical and physical measurements indicating that some of the seafloor systems are boiling at depth below the seafloor. Jim undertook a study of the system NaCl-H2O as an analog to hydrothermal seawater. In collaboration with K.S. Pitzer of UC Berkeley. The results are directly applicable to the seafloor systems, but also have broad application to hydrothermal processes in general, and provide a crucial experimental basis for theoretical modeling of ionic solutions that is being used extensively by physical chemists. Discoveries resulting from these phase-separation studies include direct observation of significant metal transport in the vapor phase, extreme and unexpected acidity produced during phase-separation in the CaCl2-H2O system, and the realization that nearly all seafloor vents result from a mixture of previously phase-separated fluids and circulating, normal chlorinity seawater.
In parallel with his marine studies, Jim has pursued studies of paleoclimate and human evolution by U-series isotopes. He has developed techniques for dating evaporites, carbonates, bone and tooth enamel. Applying the techniques to sediments from a deep core from Searles Dry Lake, California, a chronology was constructed for the lake for the interval from 35,000 to 300,000 years ago. The results demonstrated that the lake was full during the last interglacial, in contrast to expectations from the marine climatic cycles. His study of rock shelters in northern Spain showed that the Neanderthals had been abruptly replaced by modern humans at 40,000 years ago.
Jim was the first American to participate on a Soviet oceanographic expedition (1972), and was twice a Special Guest of the Soviet Academy of Sciences, lecturing in Russian at numerous institutes throughout the Soviet Union. In turn he has hosted Soviet post-doctoral fellows in his laboratory. Jim was awarded the Goldschmidt Medal of the Geochemical Society in 1999. He is a Professeur Associe Honoraire of the Museum d'Histoire Naturelle, Paris. He was an invited Distinguished Researcher at the Instituto de Geología, Barcelona, Spain, where he gave lectures in Spanish and assisted Spanish colleagues in establishing a U-series dating laboratory.