Toward a mechanistic understanding of glacial-interglacial cycles in atmospheric CO2

The concentration of CO2 in Earth’s atmosphere has oscillated over the last million years, with periods of lower CO2 associated with colder, glacial climates and vice versa. While the precise causes of these “glacial-interglacial cycles” remain unclear, the ocean, with its vast capacity to store carbon, has generally been considered to play a controlling role, with many different mechanisms – from changes in the Atlantic meridional overturning circulation to an enhanced biological pump due to iron fertilization – having been proposed. However, the precise cause of this variation still remains an open question, as coupled ocean circulation-biogeochemical models have generally not been able to simulate the full, observed change in atmospheric CO2. The primary aim of this project is to apply a computationally efficient coupled ocean circulation-biogeochemical-sediment model to mechanistically understand the cause of these variations. The model simulates a variety of isotopic tracers that can be directly compared with geochemical measurements. Furthermore, the ability to say, only
 change the sea ice distribution while keeping all other parameters fixed is a unique and powerful feature of the model, making it possible, for the first time, to quantitatively tease apart the role of different physical and biogeochemical factors believed to be responsible for glacial-interglacial CO2 variations.