Dynamical models for marine biogeochemical cycles


Ongoing, related work concerns how physical oceanography influences biogeochemical cycles in general and organic carbon preservation in particular. I am especially interested in ocean anoxic events, as they likely caused drastic carbon- and nitrogen-cycle perturbations. However, the question remains: what triggered ocean anoxia?

By developing dynamical ocean box models, I (in collaboration with Felix Elling) have recently identified a positive feedback loop whereby ocean circulation slowdown favors growth of large phytoplankton that host nitrogen-fixing symbionts. These organisms rapidly sink to the deep ocean and are respired, further promoting oxygen depletion. Looking forward, this approach will critically inform future microbial and geochemical models by providing direct evidence of ecosystem responses to circulation changes. This new conceptual framework will address the fundamental relationships between ocean circulation, microbial metabolisms, and geochemical cycles.


What controls Phanerozoic pyrite isotope signatures?


The isotope composition of sedimentary pyrite has changed drastically throughout the Phanerozoic eon. While it is generally accepted that this record is rich with environmental information, there is currently no consensus explanation for why pyrite isotopes have evolved this way.

To address this question, I am currently building a non-dimensional kinetic model that assesses how sedimentological processes generate signals that are preserved in the rock record. My model extracts the natural variables controlling each signal. Properly interpreting the pyrite record is crucial for reconstructing and understanding long-term fluctuations in Earth's oxygen budget. Challenging the paradigm that pyrite isotopes directly quantify marine sulfate concentrations and reduction rates, my model explains this record by decreasing organic matter reactivity and delivery to sediments. I interpret this as a progressive increase in aerobic respiration due to the rise of bioturbation.