Daniel Stolper was born and raised in Pasadena, California. He earned an A. B. degree from Harvard, was Fulbright Scholar for a year at the University of Southern Denmark, and did his Ph. D. at Caltech. After a postdoc at Princeton, Daniel moved to the University of California, where he is Assistant Professor at the time of writing.
Daniel is a geochemist whose research has 3 broad themes. The first is the isotope geochemistry of methane. Daniel did pioneering work using a reimagined isotope ratio mass spectrometer conceived and developed by his Ph. D. advisor, John Eiler. This instrument enabled the user to determine the abundance of methane isotopologues with 2 heavy atoms, 13CH3D or 12CH2D2. The property of merit is the clumped isotope anomaly, the departure in the abundance of an isotopologue with 2 heavy atoms from its stochastic abundance. Daniel and his collaborators used experiments and theory to determine the temperature dependence of the clumped isotope anomalies in methane. They then showed that many methane sources had a clumped isotope composition at isotopic equilibrium, given their temperature of formation or alteration. They also showed that kinetics induced disequilibrium in biogenic methane sources, especially when methane production was rapid. They developed a concept for classifying methane according to its C and H isotope composition, its clumped isotope composition, and the abundance of methane relative to that of other light hydrocarbons. They also explored the application of clumped isotopes to studies of methane geochemistry in particular deposits.
The second theme of Daniel’s research is an investigation of clumped isotope diagenesis in carbonates. With colleagues, Daniel made models of diagenetic changes to clumped isotope abundances, and challenged the models’ simulations with data. Daniel had the deep insight that apparently large changes observed when calcites were first heated could be attributed to isotope exchanges with neighboring calcite molecules. He and his colleagues worked out the roles of diagenesis in the presence and absence of water. They also showed that one could reconstruct environmental information with diagenetic models of calcite recrystallization in deep-sea sediments.
The third theme of Daniel’s research is centered around O2, in both geological and biogeochemical contexts. Daniel reasoned that he could use the oxidation state of ocean crust, accessed via ophiolites and island arc volcanics, to determine the oxidation state of the deep ocean. The connection comes from the fact that ocean crust is altered by reaction with seawater. Seawater-basalt exchange then imprints the ocean crust, and eventually arc volcanics, with the oxidation state of the deep ocean. This approach then gave a time of about 400–500 Ma for elevating the deep ocean O2 concentration. Since gases in the deep ocean mix with air over a timescale of ∼ 1 kyr, the history of deep ocean oxygenation may be similar for the surface ocean and atmosphere. Daniel has also worked on the more recent history of atmospheric O2. He repurposed a large database of O2 concentration in ice core trapped gases to determine changes over the past 800 kyr. This work showed that the O2 concentration is decreasing at a rate of about 1200 ppm/Myr (out of 210,000 ppm O2 in air). The imbalance is very small, pointing to the role of strong feedbacks in the carbon cycle that remain to be identified. On the biogeochemical side, Daniel characterized oxygen isotope fractionation associated with respiration with exceptional depth. He showed that the fractionation patterns he observed implied a 2-step process for O2 consumption at cytochrome oxidase: a reversible step in which O2 is bound, followed by a kinetic step in which O2 is reduced. He also showed that O2 isotope fractionation at cold temperatures was much smaller than heretofore estimated. This observation accounts for weak O2 isotope fractionation associated with O2 consumption in the deep ocean, solving a mystery going back nearly 50 years.
Daniel is a brilliant scholar who takes great joy in the doing of science. He is a wonderful colleague: interactive, stimulating, and deeply knowledgeable about a very broad range of topics. He is hardworking and efficient. He is generous intellectually and personally. Daniel will contribute to the community of earth scientists, and provide leadership in the research, for many years to come.