NSF Award
2333334
In order to combat the expected impacts of climate change, active removal of carbon dioxide from the atmosphere is needed in addition to emissions reductions. There is a growing consensus that at least some of society’s needs for carbon dioxide removal (CDR) will have to come from the ocean. Iron fertilization of natural phytoplankton populations is among the more promising means for ocean-based CDR, yet key questions remain, including: How effective is it? How long will the carbon be sequestered? How can we measure it? What are the intended and unintended consequences to marine ecosystems? Past ocean iron fertilization experiments have provided important information about short-term responses, but most studies were not long or large enough to measure an increase in carbon flux to the deep sea. To address the questions needed to design larger and longer field trials, this project will use ocean models to run Observing System Simulation Experiments (OSSEs) in three key regions of the ocean that are seen as likely targets for iron fertilization: the Southern Ocean, the Equatorial Pacific, and the Subarctic Pacific. Broader impacts include benefits to society via improved understanding of key physical and biological processes relevant to earth’s climate, and support of students in the research. This project is being jointly supported by the National Oceanic and Atmospheric Administration, through the National Oceanographic Partnership Program.<br/><br/>The OSSEs will be based on two state-of-the-art global ocean biogeochemical models with eddying (0.1-0.125°) resolution: the NCAR Community Earth System Model with the Marine Biogeochemistry Library (CESM-MARBL) and the GFDL Modular Ocean Model 6 with the Carbon, Ocean Biogeochemistry and Lower Trophics model (MOM6-COBALT). High resolution nested Regional Ocean Modeling System (ROMS) models will be embedded within both global models to provide realistic representation of the energetic eddies and fronts characteristic of the three regions of interest. This “ensemble” of two parent models will allow the team to assess the sensitivity of the results to the underlying biogeochemical formulation. Far-field effects of the limited-area iron fertilization experiments will be assessed with analogous limited-area fertilization experiments in the global models. Additional runs of the global models with fertilization over large areas of the target HNLC regions will address the efficacy of iron enrichment at scale, facilitating OSSEs for a global observing network. These global ocean-only simulations run for as long as practical (30 years). To address the long-term efficacy and effects of regional iron fertilization at the scale of gigatons of carbon per year, fully coupled earth system models (ESM4 at GFDL and CESM2 at NCAR) will be run for 100 years at coarse resolution.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
