We focus on identifying the complex set of processes that regulate photosynthetic organic carbon production in marine surface waters and Earth surface oxygen concentrations. During photosynthesis in marine surface waters, organisms use CO2, water, and energy from the sun to produce organic carbon and oxygen. Prolonged intervals of enhanced photosynthetic productivity in the ocean, coupled with increased organic carbon burial in marine sediments, lead to the net addition of oxygen to the ocean-atmosphere system and the drawdown of atmospheric CO2. These processes have immense significance for the oceans and atmosphere; oxygen is critical for the evolution and diversification of multicellular life and CO2 is a greenhouse gas whose concentration is strongly tied to Earth surface temperatures and climate.
More specifically, my research addresses biogeochemical cycling, the exchange of elements among the atmosphere, biosphere, hydrosphere and solid Earth and includes both biotic and abiotic processes. I focus on the couplings and feedbacks that link the biogeochemical cycles of carbon, sulfur, phosphorus, nitrogen, iron, and oxygen. In the broadest sense, my research is driven by three questions:
When did oxygen concentrations in the coupled ocean-atmosphere system rise to near modern values, and how and why have these levels varied through the past one billion years?
How do variations in oxygen levels in the past relate to extreme climate change (e.g., glaciation) and the evolution and diversification of macroscopic organisms?
How have past changes in ocean chemistry affected the way in which the Earth system operates to regulate the global carbon and oxygen cycles?