This proposal seeks to improve the representation of the marine cycling of key elements in the oceans in the Energy Exascale Earth System Model (E3SM), including carbon, nitrogen, phosphorus, and iron, among others. The cycling of these elements interact in the oceans, strongly impacted by biological processes. Aspects of the carbon cycling can impact Earth's climate by modifying the air-sea exchange of carbon dioxide, or by changing ocean emissions of methane, both are greenhouse gases (GHG) that influence climate. Phytoplankton take up these elements to form organic matter as they carry out photosynthesis and growth. Recent ocean observations have demonstrated that the relative amounts of these nutrients in the phytoplankton varies, as phytoplankton adapt to environmental conditions. Accounting for the dynamic adjustment of this plankton cellular elemental stoichiometry is critical for predicting ocean ecosystem and biogeochemical response to climate change.
In this project the team will implement fully variable, dynamic stoichiometry for the phytoplankton, accounting for variability in the cellular quotas, often referenced to cellular carbon as ratios (e.g., N/C, P/C, Fe/C, Si/C). The team will implement variable N/C stoichiometry, and they will implement and validate phytoplankton group-specific minimum and maximum C/N/P/Fe ratios, that vary as a function of ambient nutrient concentrations. This extends their previous implementations of variable P/C and Fe/C stoichiometry, making the E3SM ocean ecosystem fully representative of the observed stoichiometry of the plankton and dissolved organic pools.
Methane is an abundant GHG in Earth’s atmosphere, representing 1/6 of total GHG forcing in 2015. This work will represent the marine biogeochemical cycling of methane with the addition of a methane tracer in the E3SM MPAS-O ocean model, with sources from the sediments, and the newly discovered source from degradation of the dissolved organic phosphorus (DOP). Glaciers flowing from the Greenland and Antarctic ice sheets into the oceans bring fresh water, but also nutrients, like iron, that can affect phytoplankton productivity. The team will study how increasing glacial inputs with climate warming will modify both ocean circulation and biogeochemistry with the E3SM. All the developments proposed are key aspects of marine biogeochemistry for the study of future climate-biogeochemistry interactions and feedbacks.