Our Current Research
The Sigman group studies the cycles of biologically important elements and their interaction with changing environmental conditions through the course of Earth history. Current research activities include the development and application 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 studies. Our work in the modern environment focuses on isotopic measurements of dissolved nitrogen forms in natural waters, which can provide an integrative view of biogeochemical and physical processes that are highly variable in time and space. Much of our Earth history work is on the oscillation between ice ages and interglacial periods which has dominated Earth's climate for the last two million years. These cyclic climatic changes provide an important test case for the interaction between inorganic and biological processes in setting environmental conditions on Earth. Ongoing work is building the case that biogeochemical changes in the polar ocean are responsible for the large swings in atmospheric carbon dioxide concentration between ice ages and interglacial periods, amplifying glacial cycles and converting ice ages into global phenomena.