Sigman studies the cycles of biologically important elements and their interaction with changing environmental conditions through the course of Earth history. His current research activities include the development of stable isotope methods by which to track the marine nitrogen cycle, today and in the past, and the construction of simple geochemical models for paleoceanographic and Earth history studies.
Much of his work to date has focused on the oscillation between ice ages and interglacial periods that has dominated Earth’s climate for the last two million years. These cyclic climatic changes provide an important test case for the interaction between physical and biological processes in setting environmental conditions on Earth. Of particular interest are the causes and effects of past changes in atmospheric concentration of carbon dioxide.